# Pure horse power DC vs AC



## Ioku (Sep 27, 2007)

I know its hard to really find the max house power of an electric motor but I'm wondering what is generally more powerful an AC motor or a DC. This cite here http://www.electricvehiclesusa.com/category_s/67.htm states this "The WarP 13" diameter series wound DC Motor is a high performance motor used in some racing Electric Vehicles and could be used in very large vehicle. We have heard of uses of this motor, developing over 2,000 hp!" Over 2000 hp so what would that mean for the warp 11, 1000 hp. And how about the AC motors found here http://www.metricmind.com/index1.htm, some for them look very powerful but it seems hard to compare them to the DC motors. So if I'm just looking for high power what do you think would be better AC or DC.


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## lazzer408 (May 18, 2008)

You can't beat a series wound DC motor for pure low-rpm torque. On the other hand, AC motors can run at very high rpm and geared down to make torque. There's pros and cons for either. The DC motor is usually cheaper and easier to control. The AC motor has a much more complex controller adding to the cost. DC motors have brushes and a commutator to wear out. The AC does not. I think DC motors even sound better. =)
If one style of motor had any serious advantage over another we wouldn't have a choice. An example of this would be PM motors. It's not very cost effective to make a 13" PM motor for use in an EV. That's why we have series wound and AC motors. AC motors are begining to gain popularity as the "technology" comes down in price. Their already replacing series wound motors in golfcarts.
If I could afford it I'd be using AC. I think it has more advantages. Higher voltage being one of them. I can't fit 20+ lead acid batteries on a motorcycle chassis or afford lions so I'm using a series wound.


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## major (Apr 4, 2008)

Ioku said:


> This cite here http://www.electricvehiclesusa.com/category_s/67.htm states this "The WarP 13" diameter series wound DC Motor is a high performance motor used in some racing Electric Vehicles and could be used in very large vehicle. We have heard of uses of this motor, developing over 2,000 hp!"
> <snip>
> So if I'm just looking for high power what do you think would be better AC or DC.


Hey Ioku,

Don't believe everything you read. 2000 hp. NOT!!!!! And in an EV context? What do you think a 2 megawatt battery would weigh? 2000 hp? I don't think even railway locomotive traction motors will hit that, and they are 5 to 10 times the motor.

"just looking for high power" you say, AC or DC? Well, you can always go bigger for more power. So let's compare on size or mass. Call it power density. The high power dense motors are AC. This is primarily due to the fact that AC motors can operate at much higher speed. Some of the development has impressive hp/lb at 50 to 60,000 RPM. Even those used in the Prius are AC at 12,000 RPM and have great power density.

But at some point you have to get real and look at the hp/$. Then the line becomes fuzzy, AC vs DC. And a lot depends on you application constraints.

Regards,

major


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## mattW (Sep 14, 2007)

The other major advantage of AC motors is that a lot of them are liquid cooled which would be the major limiting factor for serious hp. The more amps you throw in a motor the hotter it will get, but an AC is more efficient so you don't need to dissipate as much and is liquid cooled so it can dissipate more. Also the higher voltages mean its easy to get the amps to the motor... I cast my vote for AC, though the current records for both MC and car are with series DC so I could be wrong or that could be a cost thing.


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## lazzer408 (May 18, 2008)

Most of the DCs I see at the track are air cooled. If AC was naturally _more_ efficient, why would it need to be water cooled? If it was more efficient it would run _cooler_ for the same output as a DC. More voltage to the motor means _less_ current draw for the same output. In an AC motor, the source of the repelling magnetic fields, for both the armature and stator, is provided by only the stator windings. In DC both fields have their own windings. That could account for a stronger field? Motor theory isn't my cup of tea. Someone else would have to chime in on that thought.
On the other hand, radio controlled cars and planes are switching to the brushless motors and they are FAST.


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## Wirecutter (Jul 26, 2007)

major said:


> Don't believe everything you read. 2000 hp. NOT!!!!! And in an EV context? What do you think a 2 megawatt battery would weigh? 2000 hp? I don't think even railway locomotive traction motors will hit that, and they are 5 to 10 times the motor.


    Thanks for that, major. Great laugh. I've seen that number before, too, but when you put it that way, it really does sound ridiculous. 

A coworker once ran the numbers on an EV with 200+ mile range and a 5 minute (or similarly very short) recharge time. Using conservative estimates for vehicle weight, it turned out that it took an incredible amount of power draw to acheive the stated recharge time, simply by virtue of replacing enough energy to move a car 200 miles in such a short time. (edit: Tesla -> 53kWh battery. To replace that 53kWh (or 3.18 megawatt-minutes) of energy in 5 minutes takes a 636kW draw, assuming everything's 100% efficient, which it's not. My house has 200A service, which at 220v works out to 44kW.)

It reminds me of the stereo maker back in the '70s that rated their stuff in "Maximum Music Power" and gave insane numbers for wattage. They got this number by putting the amplifier on a perfect power supply, driving a half cycle spike through it, then claiming that this instantaneous power was the fabled "MMP". 

 

-Mark


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## Dennis (Feb 25, 2008)

> Most of the DCs I see at the track are air cooled. *If AC was naturally more efficient, why would it need to be water cooled?* If it was more efficient it would run _cooler_ for the same output as a DC. More voltage to the motor means _less_ current draw for the same output. In an AC motor, the source of the repelling magnetic fields, for both the armature and stator, is provided by only the stator windings. In DC both fields have their own windings. That could account for a stronger field? Motor theory isn't my cup of tea. Someone else would have to chime in on that thought.
> 
> On the other hand, radio controlled cars and planes are switching to the brushless motors and they are FAST.



While an AC motor is more efficient it will over heat just like any electric motor would if you demand it's peak horsepower for too long and therefore the insulation will start to breakdown. AC motors have whats called service factor rating which means they can be overloaded above their continuous horsepower rating for short durations. Usually the service factor is between 1.15 to 1.25 for air cooled AC motors. Now if it was water cooled then the AC motor can be under severe loading and not overheat since the water will keep the stator windings cool.


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## xrotaryguy (Jul 26, 2007)

Also, the AC motors that are water cooled were generally designed to be EV motors. In fact, no one actually designs a DC motor from the ground up to be an EV motor. Most large electric motors do duty as hydraulic pumps, elevator motors, industrial air compressor motors, CNC machine motors, etc. These applications don't demand much of the motor and so the motor doesn't need a very capable cooling system. A motorist will place much more demand on his motor than a than a lift equipment operator, so the motor needs to be designed in a more rugged fashion from day one. 

AC motors can run at higher voltage because they have no commutator to arc or melt. This means that AC motors can run lower amperage to get an equivalent amount of power. That's why AC motors are more efficient. 

Can you guess that I like AC motors better?

Most drag cars use lead acid batteries. Is that because lead is better?


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## lazzer408 (May 18, 2008)

Why do so many industrial vehicles use dc motors? You'd think an industrial vehicle would want power, longevity, and low maintenance. Yet they chose dc. My guess would be cost. That doesn't make much sense because AC motors cost less to manufacture.


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## saab96 (Mar 19, 2008)

lazzer408 said:


> Why do so many industrial vehicles use dc motors? You'd think an industrial vehicle would want power, longevity, and low maintenance. Yet they chose dc. My guess would be cost. That doesn't make much sense because AC motors cost less to manufacture.


AC controllers cost more.


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## Dennis (Feb 25, 2008)

> Also, the AC motors that are water cooled were generally designed to be EV motors. In fact, no one actually designs a DC motor from the ground up to be an EV motor. Most large electric motors do duty as hydraulic pumps, elevator motors, industrial air compressor motors, CNC machine motors, etc. These applications don't demand much of the motor and so the motor doesn't need a very capable cooling system. A motorist will place much more demand on his motor than a than a lift equipment operator, so the motor needs to be designed in a more rugged fashion from day one.


AC motors are put under much more strain than a car would be. Examples are AC motors used to lift large crushed rocks up a steep inclined conveyor into a silo, drilling, train propulsion, shredders, rock crushers, ultra high viscosity mixers, mills, and mining truck propulsion. Non of these motors though are water cooled, but are large and heavy. With water cooling you can stick with a small motor and peak horespower the living daylights out of it compared to one being air cooled. So weight reduction is possible.


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## Dunkard (Jun 1, 2008)

With industrial equipment size and weight are not usually such an important consideration, nor is efficiency for long range, but cost is certainly very important.


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## J_R_S (Feb 23, 2009)

Every time I read a comparison discussion between DC and AC motors it seems that there is something missing. The logic usually goes like this:

A series wound DC motor is tops for pure low-rpm torque and a DC motor is usually cheaper and easier to control. AC motors can run at much higher rpm and be geared down to make torque, are more expensive and complex to control. The higher rpm factor always seems to win out and push people towards AC motors. But, wait, follow the logic: If a high-rpm AC motor can be geared down to make torque, then doesn't that mean that a lower-rpm DC motor can be geared up to make more rpm?

If so, doesn't that put the DC motor back on top again? Particularly when you consider that if you're going to have storage batteries on board then you must store that energy in DC form and then waste 10% to 20% of it converting it to alternating current for your AC motor to use. An on-board generator/alternator creates electricity as DC, which then must also be converted to AC as well. But with a DC motor, both sources of electrical "fuel" can go straight to the motor with no conversion.

I can't help but think that the current enthusiasm people have with high-rpm AC motors might not be leading us down the same garden path that Edison did when he convinced the public that Tesla was wrong about DC current being the way to go. At least Edison was right that you need AC to transmit power over long distances -- but that's not an issue with EVs.


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## Dunkard (Jun 1, 2008)

I agree with your opinion about DC EV motors, except you've got Tesla and Edison confused with each other.

Edison was the guy who promoted DC for everything because he owned the patents on it - in spite of the fact that he knew as well as anyone that AC was better for certain things. Edison promoted a DC town-distribution system that was very dangerous, and stupid by todays thinking. Edison also promoted the use of the electric chair as a method of execution - but only when using AC power - as a false tactic to spread lies about the "dangers" of AC power. Edison was smart, but was also a nasty skunk.

Tesla was the guy who promoted AC, invented AC motors, got screwed out of a truck load of money while he was an employee of Edison, then died broke because he had given up his per horsepower royalty on the sale of AC motors by Westinghouse, to save Westinghouse's butt when they were in trouble. Later when Tesla was broke, Westinghouse never returned any favors.

But on the real point, I am starting to reconsider my thoughts about DC for electric cars because I've recently seen some nice DC motors with better efficiency than I would have thought possible a couple of years ago. Upwards of 88 to 90 percent.


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## CroDriver (Jan 8, 2009)

Dunkard said:


> I agree with your opinion about DC EV motors, except you've got Tesla and Edison confused with each other.
> 
> Edison was the guy who promoted DC for everything because he owned the patents on it - in spite of the fact that he knew as well as anyone that AC was better for certain things. Edison promoted a DC town-distribution system that was very dangerous, and stupid by todays thinking. Edison also promoted the use of the electric chair as a method of execution - but only when using AC power - as a false tactic to spread lies about the "dangers" of AC power. Edison was smart, but was also a nasty skunk.
> 
> ...


...and he was from Croatia. Just like me


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## Bowser330 (Jun 15, 2008)

A DC motor purposefully refurbished for High Voltage EV use could compete very well with an AC system....and for a fraction of the price...

240V Interpoled DC motor with 800A for 5 seconds would have 257hp...of course you have to take back emf into the picture, but the point is, 257 hp is nearly as much as the tesla has....

and for the price of the tesla drivetrain (approx 25,000$) you could get 2 high voltage DC systems and have plenty of left over cash to invest in some lithiums...

So even with back-emf you would have 300-400hp with a dual dc setup...


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## etischer (Jun 16, 2008)

An AC motor has constant torque up to base speed, and is constant horsepower from base speed to max speed. 

This is a huge advantage. I think if you look at the area under the hp*rpm curve, the AC motor will be doing more work.


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## Wirecutter (Jul 26, 2007)

Bowser330 said:


> 257 hp is nearly as much as the tesla has....


 Actually, it's quite a bit more. The Tesla is closer to 200 HP.



Bowser330 said:


> and for the price of the tesla drivetrain (approx 25,000$) you could get 2 high voltage DC systems


Uh, how do you figure this price? I'm thinking it's much more. The base vehicle (Lotus Elise) runs $60,000 well optioned, and a Tesla is what, $110,000? Anyway, I tried to run the numbers with the AC-150 drivetrain, the 6831 lithium ion 18650 cells, and wild guesses for the modifications to the base vehicle. The only way I could imagine that Tesla Motors could make money on the car was with volume purchasing discounts.

I suppose it's a moot point, since AC Propulsion won't sell its drive system to anyone who doesn't know the Secret Handshake...

-M


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## Zer0 (May 9, 2008)

He said price of the *Tesla Drivetrain*. The Drivetrain itself includes only the motor and the controller, really, and it's a well known fact that the AC-150 from AC Propulsion is $25k.

That's not counting the batteries.. which have been estimated to be in the $20k range.

No-one really knows how much the glider (car without batteries and Drivetrain) costs. You can't use the Elise as your ruler because 
a) the price you quote includes a combustion engine drivetrain
b) the Tesla is designed with a similar architecture, but is, in fact, NOT an elise. they only share a handful of interchangeable parts, which means that price includes almost no Tesla parts. It would be a joke to buy an elise to turn it into a Tesla. It's like buying a Camaro to turn it into a Corvette.

He was simply quoting a price for the drivetrain, nothing more.


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## Bowser330 (Jun 15, 2008)

Zer0 is correct I only meant the drivetrain and thats because just as you said, Wirecutter, I thought they used the AC-150 for 25K$...

However...after looking at this... it says 248hp....so....maybe its an upgraded version? 

http://www.teslamotors.com/performance/perf_specs.php

Also I thought I read an interview with Tesla where they said that half the cost is the battery pack, 50K$...i believe it too...but maybe Im wrong and youre right..20K$...seems too cheap for a 200+ mile pack though! doesn't it?

and for sure a lot of cost comes from the carbon fiber body and custom design R&D cost...they're trying to get their investment back!!! haha...makes sense...


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## rds130 (Feb 23, 2009)

Zer0 said:


> He said price of the *Tesla Drivetrain*. The Drivetrain itself includes only the motor and the controller, really, and it's a well known fact that the AC-150 from AC Propulsion is $25k.
> 
> That's not counting the batteries.. which have been estimated to be in the $20k range.
> 
> ...


A replacement battery pack for the Tesla is about $30,000.
The estimated cost to build a Roadster is/was--according to Edmunds--something like $140,000. The original cost to build a prototype was roughly $350,000 (Popular Mechanics). A full CF front end for an Elise should cost in the area of $8,000 and that's only a wet lay-up method. I'm pretty sure the Roadster uses a dry-carbon method which would double that front end to about $14,000-16,000 (a dry carbon hood for an R35 GT-R averages about $5,000...you're paying for the lay-up method and the "luxury/high-end" premium). Multiply that by what you'd estimate the rest of the body to cost and...you get the point.

In the given context, $109,000 base price (2008 model) is a bargain compared to what they could charge to break even and/or make a profit. Really makes me stop whining about not wanting to pay so much for an aftermarket drivetrain. Lol.

These AC motors really have my attention, though.


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## Wirecutter (Jul 26, 2007)

Zer0 said:


> He said price of the *Tesla Drivetrain*. The Drivetrain itself includes only the motor and the controller, really, and it's a well known fact that the AC-150 from AC Propulsion is $25k.


You're right - my mistake.

The rest in another thread so not to hijack this one.

-Mark


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## DavidDymaxion (Dec 1, 2008)

I'll 2nd that! DC is not hopeless, you can get back that lost area under the curve via sepex or some other tricks. Good luck finding a high powered sepex controller, though. The NEDRA guys compensate by high voltages and twin motors.



etischer said:


> An AC motor has constant torque up to base speed, and is constant horsepower from base speed to max speed.
> 
> This is a huge advantage. I think if you look at the area under the hp*rpm curve, the AC motor will be doing more work.


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## etischer (Jun 16, 2008)

The process is called field weakening, this allows the motor to spin faster speed at lower torque given the same voltage. You would just have to energize the field at a lower voltage. Just don't accidently shut off the field, or the motor will try to run away, basically trying to achieve infinite rpms. Seems like you could just use a curtis controller, and a cheap pwm to control the field wiring? generally the field wiring is much lower current than the armature wiring, so the controller controlling the field could be much cheaper. 




DavidDymaxion said:


> I'll 2nd that! DC is not hopeless, you can get back that lost area under the curve via sepex or some other tricks. Good luck finding a high powered sepex controller, though. The NEDRA guys compensate by high voltages and twin motors.


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## Efiero (Feb 7, 2009)

Ok I dont know to much so dont kill me but if you take 2 or more DC motors and run them in series isnt this making things more efficiant due to if you put out 500 amps each motor see it but you need to go up on the voltage due to they only see a fraction of the total and your total HP & torque go up with out using more amps . this cures the rpm limits and voltage limits of the motors . can AC motors be run in series


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## Bowser330 (Jun 15, 2008)

Efiero said:


> Ok I dont know to much so dont kill me but if you take 2 or more DC motors and run them in series isnt this making things more efficiant due to if you put out 500 amps each motor see it but you need to go up on the voltage due to they only see a fraction of the total and your total HP & torque go up with out using more amps . this cures the rpm limits and voltage limits of the motors . can AC motors be run in series


I have asked the same question about series AC motors and some people have done it...although they've used pulleys and a belt...Ive never seen AC siamese style...although the Brusa motors do have a pancake motor which is "stackable" so, that would imply they can be attached that way...


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## Efiero (Feb 7, 2009)

Ok now for anothere ? i know some will think it is dumb but i dont know much about electricity why cant a tranformer be put in line and catch the back RMF and make power back to the batteries or would this just eat power ?


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## Dalardan (Jul 4, 2008)

I do think Synkromotive has a kart powered by 2 car alternators running as motors, but I just can't get a hand on the statement were they say so. 

I'm planning (I do admit that right now, I'm going really really slowly...) to put in parallel several of those synchronous motors and time them so I could drive them all with 1 tri-phase power source and 1 DC field source. But for right now, I've not yet built my drive for even 1 motor so don't count on me yet .

Maybe you should ask Synkromotive about what they did, but I do think that you can as a no-brainer serialize ou parallelize 2 asynchronous (induction) motors and use the same controller to drive the 2. That is just how far I understand the game...

Dalardan


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## major (Apr 4, 2008)

Efiero said:


> can AC motors be run in series


Theoretically, maybe it is possible. But for all practical purposes, no, you need a controller (inverter) for each AC motor. It might be possible to run AC motors in parallel from a single inverter, if the shafts were solidly coupled, or if you didn't need torque control.

I can't imagine why one would want to run AC motors if series. You typically have a hard time getting high enough voltage to the motor as it is.

Regards,

major


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## Frank (Dec 6, 2008)

I understand motors to be mechanical transformers: if you have a controller/battery system that can deliver thousands of amps to a motor, it will try to convert it to mechanical power. It might melt in the process, but it will try...

That's why the Zilla controller is so popular with the racers. They carry enough battery and the controller can deliver the current. It can do series/parallel switching if you run dual motors. It's well built, water-cooled and price is probably on par with an AC controller (depending on the size.) DC motors are tweaked to withstand higher mechanical forces but the major limitation remains the ability to transfer current via brushes. I think no brushes and built-in regen ability are the largest advantages an AC motor offer.


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## Efiero (Feb 7, 2009)

it seems that as far as HP its a tie it seems that it is just a matter of what you like and efficiency AC has a slight edge motor for motor but you need an inverter to change the DC to AC so i think that makes thing equal


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## Bowser330 (Jun 15, 2008)

I am still unclear as to why Kostov motors arent more popular...is it due to price...availability...? 

Due to the interpoles...The Kostovs can handle up to 336V and 1000A bursts as proved by John Wayland's "White Zombie" EV...

Running at 300V and 500A = 150kw = 200HP

(Note: A controller is due out that will be able to handle 500A cont.)

With 300V the 500A should be available in a higher rpm band than a lower voltage system and the kostov motor can handle 250 cont. so thats 100HP continuously available...

Even with a single motor/controller setup it would make for a quick EV and with a dual motor setup (one for each axle, awd) this would make for a seriously quick EV...

Back to the main question....why arent these motors more popular??


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## DavidDymaxion (Dec 1, 2008)

There's a thread about Kostovs here: http://www.diyelectriccar.com/forums/showthread.php/kaylor-monster-motor-27350.html

Randy Holmquist of Canadian EV would rewind them, put in new bearings, put in new brushes, and band them -- presumably these were weak points in the stock motor. The EVDL had posts about a couple failures. The above thread has a link to Kostov that shows a new motor with a higher voltage limit -- maybe it is tougher? I've heard the brushes are smaller than Advanced DC, that would make them less tolerant of high currents. On the flip side, like you said, Wayland leaned hard on his, and there were some anecdotal reports them seemed to be more efficient than other DC motors, presumably due to the interpoles.



Bowser330 said:


> I am still unclear as to why Kostov motors arent more popular...is it due to price...availability...?
> 
> Due to the interpoles...The Kostovs can handle up to 336V and 1000A bursts as proved by John Wayland's "White Zombie" EV...
> 
> ...


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## Bowser330 (Jun 15, 2008)

DavidDymaxion said:


> There's a thread about Kostovs here: http://www.diyelectriccar.com/forums/showthread.php/kaylor-monster-motor-27350.html
> 
> Randy Holmquist of Canadian EV would rewind them, put in new bearings, put in new brushes, and band them -- presumably these were weak points in the stock motor. The EVDL had posts about a couple failures. The above thread has a link to Kostov that shows a new motor with a higher voltage limit -- maybe it is tougher? I've heard the brushes are smaller than Advanced DC, that would make them less tolerant of high currents. On the flip side, like you said, Wayland leaned hard on his, and there were some anecdotal reports them seemed to be more efficient than other DC motors, presumably due to the interpoles.


I know about the thread as I've been the most recent poster for awhile now...I was brining this up in the performance section in hopes of attaining a more specific opinion as it relates to the power output/performance factor...

It is stated in his blog that John Wayland did the same thing as Randy to "build up" the kostov to handle the higher inputs...

It must be the lack of availability and experience working with them that keeps them out of the DIY'ers hands...With all the DIY'ers working with the ADC and now many with the Warp, there really isnt any motivation to use another motor if you arent planning on using more than 156V...


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## DavidDymaxion (Dec 1, 2008)

Whoops, didn't occur to me to check you were in that thread already!

I have a Kostov -- but it's not in the car yet, but hopefully will be soon. I plan to use it hard, I'll report how I do.

As John's blog and posts have said, he ran his at 1200+ Amps for 30 to 40 seconds at very low rpm (skidding his line-locked front wheels, instead of doing the high rpm burnout he originally intended) before it blew. As I recall he also had modified the brushes for better cooling, among other mods.

He was running a 336 Volt pack. John and Berube are the only folks I know that have run a pack that high on a single DC motor (John with the Kostov, and Berube with the GE). The Kostov for sure has interpoles, I believe the GE does, too. NEDRA lore is you shouldn't run an Advanced DC motor above about 160 Volts.

BTW, Berube might have a GE or 2 for sale -- he has shown them to be great motors.



Bowser330 said:


> I know about the thread as I've been the most recent poster for awhile now...I was bringing this up in the performance section in hopes of attaining a more specific opinion as it relates to the power output/performance factor...
> 
> It is stated in his blog that John Wayland did the same thing as Randy to "build up" the kostov to handle the higher inputs...
> 
> It must be the lack of availability and experience working with them that keeps them out of the DIY'ers hands...With all the DIY'ers working with the ADC and now many with the Warp, there really isnt any motivation to use another motor if you arent planning on using more than 156V...


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## Bowser330 (Jun 15, 2008)

DavidDymaxion said:


> Whoops, didn't occur to me to check you were in that thread already!
> 
> I have a Kostov -- but it's not in the car yet, but hopefully will be soon. I plan to use it hard, I'll report how I do.
> 
> As John's blog and posts have said, he ran his at 1200+ Amps for 30 to 40 seconds at very low rpm (pushing his skidding his front wheels, instead of doing the high rpm burnout he originally intended) before it blew. As I recall he also had modified the brushes for better cooling, among other mods.....


Please do report what your results all, that would be useful data for future kotovers like me...

I think John W. really showed what the motor could take...and from what It looks like is that it can handle a lot when properly built/setup.

Thanks!


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## Dennis (Feb 25, 2008)

Interpoles prevent armature reaction _(magnetic field distortion of the field poles cause by the armature magnetic field causing "early back EMF" before brush contact)_ from occurring or what you see as sparking so naturally it makes sense that these motors can handle lots of current since the magentic field distortion of the field poles is compensated for by the interpoles which carry the same current as the armature circuit but is wound to have a magnetic field that is opposing to the armature magnetic field which casues the armature field to be in the correct orientation relative to the field poles. Usually though interpoles are only used in quite large DC motors. I suppose the >=11" diameter ones have them.


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## engineer_Bill (Jun 24, 2008)

etischer said:


> The process is called field weakening, this allows the motor to spin faster speed at lower torque given the same voltage. You would just have to energize the field at a lower voltage. Just don't accidently shut off the field, or the motor will try to run away, basically trying to achieve infinite rpms. Seems like you could just use a curtis controller, and a cheap pwm to control the field wiring? generally the field wiring is much lower current than the armature wiring, so the controller controlling the field could be much cheaper.


Actually switching off the field will cause the motor to not turn at all as the field will have no current = no field. However with NO backemf you will draw infinite current, or pack voltage / .1 - .01 ohms(armature resistance) = 144V = 1440 - 14400amps.


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## IamIan (Mar 29, 2009)

I think it is best determined on a case by case basis ....

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I think the question of AC vs DC is too open to to many variables ... like many things ... it will depend on the specifics.

For instance some people correctly say the DC power of the batteries inverted to AC has losses ... but how much loss ? ... depends on the batteries and the controller / inverter ... I know there are DC to AC inverters out there that can do ~98% efficiencies ... but I admit I don't know of any AC motor inverters that are built for that level of efficiency ... $/W seems more important that the % efficiency ratings.

As it has been said ... a transmission can be used for a DC motor to get RPMs ... or for a AC motor to get torque ... but that doesn't mean all transmissions are equally good at doing either... depending on the specifics used ... one way might be better / cheaper / etc... than the other.

The burshes of a brushed DC motor are a disadvantage ... but their are brushless DC motors.

DC motors and AC motors can both be used for power output ... and for regenerative braking ... but that doesn't mean every motor is equally capable ... the specific design of the motor can lead to better performance in one mode of operation than the other.

I will say this ... as technology develops it also changes the variables more ... at one time the control electronics for a AC motor were large and uber expensive ... not only are they smaller and cheaper today ... they do more... but that isn't to say DC motors and DC power electronics have been sitting on their hands either.

Once you define sertain things you need your EV to do... accelerate 0 to 60 in x seconds ... have x range ... etc..etc... then the best approach is to objectively look at both options in detail ... maybe for your application DC is better ... or mayber AC is better ... maybe that will change in 6 months of 6 years... maybe some of that is that you already have the knowledge an skill to work with one but not so much the other ... no matter what the reason is... I think it is best decided on a case by case basis.

-----------------

Eventaully it will becomes a question of economies of scale ... which ever type is used significantly more for a significantly longer period of time ... will gain significantly more funding toward improvements ... which will result in one option becoming massively dominate while the alternative option might continue to improve ... the rate of improvement and funding for research will slow as significantly as the dominate one increased.

Same thing happened with my we have gasoilne powered cars today... 

Now if the mass market choosen option has a fundamental limiting factor that the alternative does not share ... there is the potential that eventually the tide will turn again... which is what we are seeing with EVs ... the fundamental limits of a gasoline vehicle have caused even with the significantly larger amounts of funding that the improvements have begun to tapper off... while the EV side has continued to grow as electronics and batteries have grown.


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## Dennis (Feb 25, 2008)

> Actually switching off the field will cause the motor to not turn at all as the field will have no current = no field. However with NO backemf you will draw infinite current, or pack voltage / .1 - .01 ohms(armature resistance) = 144V = 1440 - 14400amps.



Wrong, you never seen a shunt wound motor in a run away condition when field power is disconnected. The poles have some residual magnetism left in them. Removal of the field will cause the armature to spin to destruction. Trust me I have seen this happen first hand and it isn't pretty.


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## timpaniboy (Apr 22, 2009)

lazzer408 said:


> Most of the DCs I see at the track are air cooled. If AC was naturally _more_ efficient, why would it need to be water cooled? If it was more efficient it would run _cooler_ for the same output as a DC. More voltage to the motor means _less_ current draw for the same output. In an AC motor, the source of the repelling magnetic fields, for both the armature and stator, is provided by only the stator windings. In DC both fields have their own windings. That could account for a stronger field? Motor theory isn't my cup of tea. Someone else would have to chime in on that thought.
> On the other hand, radio controlled cars and planes are switching to the brushless motors and they are FAST.


Definitions:
Stator: Stationary winding in any motor ie the ones attached to the case
Rotor: the rotating portion of the motor ie the part in the middle
These terms refer to physical construction of the motor. The Armature is on the rotor for an DC motor and in the Stator for an AC motor. In an AC induction or squirrel cage motor(which is what you are referring to) the motive force to cause the rotor to rotate is caused by the stator which induces a current which causes a magnetic flux in the rotor to "lock" onto the rotating stator magnetic flux causing it to rotate. There is no field in an ac motor, in a ac generator yes, but not in a ac motor.
The DC motor has the armature on the rotor, so the main magnetic flux that is causing the rotor to rotate is generated on the rotor. The major reason why AC motors are more efficient is because they have less rotating mass to spin for the same output. Also the higher voltages of AC motors cause less heat losses due to P=r*I^2 where P is the power loss due to resistance of wires and windings, r is the resistance of the wires+windings and I is the current passed. So if we raise voltage and lower current(look up ohm's law if you don't understand) the power loss due to heating of wires is reduced. Specifically 3 phase AC motors are more efficient(which this is what people are referring to when they say "AC motors are more efficient" even if they don't realize it) because they are essentially the equivelent of 3 single phase motors in one motor, so you have 3 times the output, with only 1.3 times the size/weight. 

Brushless DC motors are small ac motors, with electronics taking place of the brushes and commutator, so ac motors with an electronic controller ie what everyone who builds a AC EV has.


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## Dennis (Feb 25, 2008)

> The DC motor has the armature on the rotor, so the main magnetic flux that is causing the rotor to rotate is generated on the rotor. The major reason why AC motors are more efficient is because they have less rotating mass to spin for the same output. Also the higher voltages of AC motors cause less heat losses due to P=r*I^2 where P is the power loss due to resistance of wires and windings, r is the resistance of the wires+windings and I is the current passed. So if we raise voltage and lower current(look up ohm's law if you don't understand) the power loss due to heating of wires is reduced.


These points are not the main reason why 3-phase AC induction motors are more efficient. They are more efficient because they do not need brushes to provide power to the rotating member as what is needed for DC motors. So there are no contact resistance losses or losses due to carbon brush's resistance. Induction wins hands down for efficiency versus sliding brushes against copper segments.




> Specifically 3 phase AC motors are more efficient(which this is what people are referring to when they say "AC motors are more efficient" even if they don't realize it) because they are essentially the equivelent of 3 single phase motors in one motor, so you have 3 times the output, with only 1.3 times the size/weight.


In actuality, a single phase motor is a 2-phase motor due to the reactive components whether it be capacitive or inductive depending on the motor design which is needed to set up a rotating magnetic field for rotation. Three phase motors are fed 120 degree separated AC sine waves that results in the sum of the three magnetic vectors producing a rotating magnetic field that induces a current into the rotor bars of the rotor causing a magnetic field to be set up in the rotor that tends to be attracted to the rotating magnetic field of the stator. If the rotor ever turns synchronously with the stator magnetic field, the rotor will cease to turn because no current will be induced due to no magnetic field lines being "cut" through. Thus, AC induction motors always have slip.


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## tomofreno (Mar 3, 2009)

One thing I don't see in discussions of AC vs DC is data. The old torque-speed curves from ADC for their 8" and 9" DC motors give efficiencies in the mid to high 80s for the voltages used in the charts. The DC controllers seem to have efficiencies in the mid 90s, giving overall efficiency of motor/controller around 80%. Azure Dyamics gives efficiencies in the low to high 80s for their AC24 motor/DMOC445 controller, and high 70's to mid 80s for their AC24LS/DMOC445 controller. The latter would seem to be about the same efficiency as a DC motor/controller.


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## CroDriver (Jan 8, 2009)

tomofreno said:


> One thing I don't see in discussions of AC vs DC is data. The old torque-speed curves from ADC for their 8" and 9" DC motors give efficiencies in the mid to high 80s for the voltages used in the charts. The DC controllers seem to have efficiencies in the mid 90s, giving overall efficiency of motor/controller around 80%. Azure Dyamics gives efficiencies in the low to high 80s for their AC24 motor/DMOC445 controller, and high 70's to mid 80s for their AC24LS/DMOC445 controller. The latter would seem to be about the same efficiency as a DC motor/controller.


Here is what an DC motor manufacturer sent me:



> At 168V/265A efficiency is 85-86%.​ It rises slightly to 87% at 168/350A and then falls to 80% at 168V/550A (550A is 60kW).​ From here on it decreases rapidly to probably around 65% at 168V/1000A.​ I believe that 168V is representative for 156V too.​


Minus the controller efficiency 

The most AC systems I saw were about 95%.

My opinion is that the price of high performance AC systems is way to high for what they offer. The controllers are the major problem.


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## engineer_Bill (Jun 24, 2008)

Dennis said:


> Wrong, you never seen a shunt wound motor in a run away condition when field power is disconnected. The poles have some residual magnetism left in them. Removal of the field will cause the armature to spin to destruction. Trust me I have seen this happen first hand and it isn't pretty.


I stand corrected: My assumption was current switched on armature with no field. Of course if the armature is already spinning you will have an induced field magnetism, or if the field is already on you will have a collapsing field with the results you mentioned.


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## engineer_Bill (Jun 24, 2008)

The torque curve for AC motors is flatter than DC. That and the higher RPM gives them an advantage for ev's. Right now the limiting factor is price, but I expect ecomony of scale to bring that down. Nedra guys mostly go with DC because higher power is MUCH cheaper and easier than High power AC. When you need full torque at startup a series DC motor is great because it will keep drawing current until it overcomes the load up to limiting or breakdown. An AC motor has a much flatter torque curve. The efficiency curves of ALL modern motor types is soo high we are splitting hairs to compare one to another. Better is to look at what torque curve you want and pick the motor appropriatly. I went with SEP-EX even though I am not as familiar with that motor type because of the ease of regen. The cost is the loss of the ramped torque curve of the series motor, (SPE-EX has a flat torque curve kinda like AC). AC motors are water cooled because they where specificaly designed and built for EV, and water cooling is easier in an AC motor, (no brushes), current is runthrough stator. If someone wanted to, a water cooled DC motor would be possible with rotary unions. Mose us are using Dc motors from the forklift world, (or motors based on those designs), the intermittent usage makes water cooling uneeded. In fact with the battery range most of us have it is still not needed. Long run I expect DC motors to always be used in specific applications where low cost or sheer raw power is needed, but like the rest of the world eventually AC will be used for most vehicles. It is already taking over the forklift world, soon used AC forklifts will be available for EV hobbyist's.


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## Alchemist (Apr 16, 2009)

So, compare BLDC motors to AC motors please? 

On a smaller scale I've seen RC cars now upgrading from the standad brushed DC motors to brushless DC motors. I've read how power-to-weight ratios is vastly improved having more power inside a smaller package is obviously advantagious for performance. Also, the fact that there aren't any brushes to be concerned about thus allowing a much longer motor lifespan.

Are there Brushless DC motors available for EV use or I should ask "specifically made for EV use"?

Thanks!

Ernie


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## major (Apr 4, 2008)

Alchemist said:


> Are there Brushless DC motors available for EV use or I should ask "specifically made for EV use"?
> 
> Thanks!
> 
> Ernie


Here ya go, Ernie,

http://www.uqm.com/ 

Regards,

major


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## JRP3 (Mar 7, 2008)

Yeah, if you want to spend $30,000 or so


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## major (Apr 4, 2008)

Oh, cost is an issue?


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## Alchemist (Apr 16, 2009)

""Here ya go, Ernie,

http://www.uqm.com/ ""



Thank you Major Sir!!!

Appreciate it.

Over-N-Out

Ernie


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## JRP3 (Mar 7, 2008)

Don't get too excited, not only do they overcharge for the UQM motor but they also won't sell to the general public.


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## DieselTwitch (May 19, 2009)

Sense this topic has moved away from the main topic in to the typical AC vs DC fight. I thought i would quote from the MM website as to the advantages of AC. Personally I have been working around AC motors and VFD's for some time now. I figure with a DC motor all your getting is a valve between the motor and the battery like a carb, the AC system is more EFI, change the program and you change the way the entire system runs. But really it all depends on the drive, the budget, the car, and just simply what you want to do! 

So here is what i copied from the MM website. I have never met the author but I tend to agree with him 100%

Reason 1 - of course natural regenerative braking without extra hardware. Deceleration during regen can be the same as acceleration during drive - the system is symmetrical in this respect - you can supply into the battery as much current as you can take out of it. It should be mentioned that few DC systems with special controller and (usually) SepEx DC motor also offer regen (at extra complexity and cost).

Reason 2 - favorable torque - RPM characteristics providing constant torque for wide range of RPM. This provides constant acceleration regardless of the speed (within certain limits), and often allows driving without shifting gears. To get fair comparison, a DC system can be set up to provide constant torque if the controller is programmable - it has to work at the current limit at stall and low RPM. This way constant torque can be achieved as well; however top rotor RPM speed of a typical DC motor remains about twice as low as for an AC motor requiring to shift gears in this case, thus loosing torque at the wheels. Normally vehicles using DC systems avoid need for shifting by starting on 3rd or even 4th gear so the RPM at freeway speeds remains manageable. This, however, aside requiring very large motor (to provide high starting torque at the wheels while on 3rd gear), greatly stresses transmission components normally not intended for such abuse, sometimes resulting in broken gear teeth, stripped splines, twisted shafts, damaged CV-joints etc. AC setups don't have these issues.

Reason 3 - no motor brushes. Sure, unless abused, the brushes can last very long time, and yet there are all these issues with brush advancing, seating, commutator arcing and self-destroying at high RPM etc. If electric reverse is used, the requirements for brush advance for forward and reverse rotation direction are contradictory. If you want to avoid these problems all together, consider AC motor.

Reason 4 - programmability. Strictly speaking, this is not the property of AC system in oppose to a DC one, a DC controller can be made programmable and be as sophisticated as any AC one. But great majority of the DC controllers are not programmable, especially with EV specific parameters. For featured on this site AC inverters a user has access to the software and able to set all the parameters to adapt not only the battery parameters but driving style. For example: Max battery voltage for regen and Min voltage for driving (for battery protection), max battery current for driving and regen separately, throttle response profile, off-throttle regen option, tachometer output, creeping current, power mode and economy mode limits, acceptable inverter and motor temperature, electric reverse, safe motor RPM range (separately for forward and reverse) and many more others. All programmable parameters can be displayed on a PC/laptop screen in real time in digital and analog graphic form as you drive, so you can optimize the settings while in the vehicle. Configurable graphs plotted and can be stored for later analysis and comparison. Try to find a DC controller offering this.

Reason 5 - safety. Well known fact that if a DC controller's power stage fails, entire pack voltage is applied to the motor and you better have good circuit breakers, fuses, kill switches and good reaction time if partial failure happens to be at the intersection while you are waiting your green. In contrast, power stages of AC inverter are used to *generate* power for the motor, not *regulate* it, so in case of a failure AC generation just stops and so AC motor just looses power.

Reason 6 - easier (smaller gauge, more flexible) battery wiring. This actually applies to a high voltage AC systems (typically using higher voltage and lower current than DC systems of the same power). Since resistive power losses equal I2R where I is current through a conductor and R is its resistance, the lower current, the lower losses. Note, the *battery* voltage U is not part of equation. (don't confuse voltage drop U *on the wire* which is part of equation with total system (battery pack) voltage U which is potential between supply wires). So with typically lower voltage and thus higher current systems you're forced to use heavy gauge wire - typically with crossection area ~100 mm2 (US gauge 2/0) or larger. Even fine stranded welding cable of that size is not very flexible if a short pieces needed for battery interconnects, not to mention need for heavy duty lugs, crimpers, etc. Now and then you hear the stories of melted battery posts, loose connections due to the lead creep etc. This is all due to high current draw: little resistance increase due to loosen connection will cause generating enough heat to cause the damage. And it is hard to keep connections tight because lead the battery posts usually made from, creeps ("cold flows") under pressure and no matter how well your connections tightened, they will loose over time. All the same applies to AC setup with the exception that loosen connection for low current system will not cause nearly as much trouble as for high current one because of flower voltage drop on loose connection and thus less heat generation. Yes, you do have more interconnections to make, but this is one time thing, while maintaining tight connections is ongoing maintenance. For the high voltage system (312V...336V) you can use thin ~30 mm2 wire (US gauge 4) which is far easier to handle, bend and route in tight places. The amount of connections is typically higher than for low voltage systems Of course, if a low voltage AC system is used, this advantage is lost.

Reason 7: Excellent thermal reserve characteristics. Technically, it is not AC vs. DC feature, but you will be hard pressed to find a water cooled DC motor. This also means no large fan which takes extra space, consumes extra energy and produces extra noise.

Reason 8: Naturally, electric reverse accomplished by adding only a small toggle switch on the dash. All it makes for an inverter is to swap sequence of 2 phases, so the rotor runs in opposite direction. A DC system requires reversing contactors, not to mention that the brush advance is far from optimal when DC motor runs in reverse. At low speeds, however, it is not that critical for a DC drive; nevertheless commutator and brush damage has been known issue while driving a DC motor in reverse while it's advanced for forward rotation. Please ask me or John Wayland how do we know.

Reason 9 - ease of installation. Despite common opinion, let's evaluate complexity of the system from the user stand point, as a black box. Complexity of an AC inverter or a good DC controller itself is not the concern, they are both very complex microprocessor based units. We evaluate difficulty of installation. Basically to wire a Siemens AC system you have to make 6 connections: 3 phases to the motor, 2 cables to the battery (through the external contactor box if short inverter is used), and plug encoder cable. The rest is low voltage wiring: +12V DC-DC output - to 12V wiring system in the car, enable and "start" wires from the ignition switch. Also, 3 wires to the throttle pot, 3 - to the direction switch, 2 - to optional start inhibit switch. All this wiring harness is pre-made and included. Since typical DC system doesn't have other controls (temp sensors input, power reduction indication, etc.), will stop here for the fair comparison sake.

Let take a typical setup for a DC system with series wound motor. Then: 2 cables from the battery to the main contactors. 3 jumper cables for reversing contactors. 2 cables from the main contactors to the controller. 2 cables from the controller to the motor. One cable to jump the field and armature of the motor. 2 wires to the DC-DC converter input. Low voltage side: 3 wires to ignition switch. 2 wires to the throttle pot. 2 wires to the precharge contactor coil. 2 wires to the reversing contactors coils. 2 wires to the power resistor precharging capacitors in the controller. 2 wires for start inhibit switch. One heavy wire to ground DC-DC converter neg. side, and one - to connect its output to the 12V system in the car. 2 wires from the motor temp switch to the light on the dash. Typically, no harness exist or included, you come up with your own.

There are other good reasons as well. For Siemens systems it is for instance motor-inverter matching parameters, i.e. motor's stator winding parameters and magnetic characteristics are stored in inverter's EEPROM to maximize performance and efficiency working with that particular motor. Usually in case of DC systems the motor manufacturer has no idea what the controller running it will be, and vice versa, so agreement and more-less precise match between the two is not possible. It is up to the user to puck components to match. We're not discussing relevance of mismatch (for a DC chopper it's not critical), we' re stating the fact that it does exist.

In general, a user should ask himself/herself if all the advantages of an AC system are relevant for the application, driving habits, personal preferences and some extra cost is justified


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## mm22176 (May 25, 2009)

But at some point you have to get real and look at the _hp_/$. Then the line becomes fuzzy, _AC vs DC_. And a lot depends on you application *...
________________________________________________________
search engine marketing
airsoft gun

*


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## Overlander23 (Jun 15, 2009)

Apologies if this has been said before. Isn't the real issue here, brushless or brushed? And in this respect, it's usually DC brushed vs AC or DC brushless, the latter category being more defined by controller implementation. Or is this semantics? Are you all referring to brushed when mentioning "DC" and brushless with "AC"?

The obvious performance benefits of a brushless design (AC or DC) is no brushes. This leads to higher and more consistent performance across a broader range of operation, and better longevity. The brushes can't skip on the commutator (since there aren't any brushes) so power isn't lost due to arcing from bouncing. Similarly, lack of brushes mean higher efficient RPM capability due to the same reason. The only things that really wear are bearings. As the motor heats up you don't get the same losses as a brushed system.

I'm only speaking from the RC plane world, but we all switched to brushless motors because of efficiency and lower cost. I mean, from a motor manufacturing standpoint (and demand being equal), wouldn't a brushless motor be cheaper to manufacture (controllers aside)?

And even in this age of microprocessor technology, I think the only thing keeping the cost of controllers high is relative demand. But brushless is pretty clearly the future.


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## Tesseract (Sep 27, 2008)

Overlander23 said:


> ... Are you all referring to brushed when mentioning "DC" and brushless with "AC"?


Yes.

More specifically, "DC Brushless" _implies_ that the motor does not use an induced field (i.e. - an induction motor), rather, either permanent magnets or a wound rotor (a common example of the latter: an alternator).



Overlander23 said:


> .... I mean, from a motor manufacturing standpoint (and demand being equal), wouldn't a brushless motor be cheaper to manufacture (controllers aside)?


Sure the *motor* is cheaper to manufacture, but how can you consider the motor without the controller? A brushless motor is truly useless without a controller; a brushed motor, however, can be operated with nothing more exotic than a bank of batteries and contactors.

Furthermore, while the brushless motor is more efficient, it's controller is always less efficient than similar power brushed DC controller. Net-net, the difference in overall efficiency between the two technologies is not particularly compelling when you consider the motor and controller together.




Overlander23 said:


> And even in this age of microprocessor technology, I think the only thing keeping the cost of controllers high is relative demand. But brushless is pretty clearly the future.


Hmmm... I _know_ that the cost of the 'microprocessor' has very little to do with the overall cost of the controller. Really, on a cost/kW basis even "super expensive" DC controllers like the Zilla Z2K are a *steal* compared to the equivalent size AC inverter. The $4600 Z2K will control 300kW (600kW peak); the best price I could find on a 300kW VFD was $17,000...

So while brushless may eventually dominate, for sheer performance on a budget it's still very hard to beat the series DC motor.


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## sunworksco (Sep 8, 2008)

DC brushless motors used by Novak in rc rock crawlers are basically ac motors with electronic sensoring speed controllers.The power graphs for dc brushless and ac motors are so similar that these dc brushless motors can be called ac motors.AC ev motors are the best economical way to go,light,powerful,easy contols/wiring and longevity.
It is comical to see builders here clamering around dc motors/controls.
They first find a much too heavy vehicle to convert, then find a massively heavy drivetrain to push it ,then install lead acid batteries to finally build the ultimate "Lead-Sled".Better to take your bank account and move slower on the ground-up build then wiilly-nilly throw the ev together and the find that it is too heavy,short ranged and high maintainence.


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## Tesseract (Sep 27, 2008)

sunworksco said:


> ...
> It is comical to see builders here clamering around dc motors/controls.
> ...


Lemme see if I got this straight... you think it is comical that people select series dc motors over BLDC motors and as proof you supply a picture of a BLDC used in a _toy???_ 

Well, I'll agree at least that something's comical here, for sure.


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## sunworksco (Sep 8, 2008)

This Novak motor is a truer ac motor than what you are talking about.


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## sunworksco (Sep 8, 2008)

I was commenting about dc brushed motors and yes why not consider using ac motors?


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## CroDriver (Jan 8, 2009)

Here are some BLDC motors that could be used for EV-s

http://pdf.directindustry.com/pdf/ph...49815-_29.html

Btw. What's the efficiency of the different systems?

AC 90%+

BLDC 90%+

DC 60-?

I think that my Kostovs will be below 60% on 350V and 1000 Amp 

Look at the graph from the manufacturer:




I extended the efficiency graph with the red line.


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## JRP3 (Mar 7, 2008)

sunworksco said:


> AC ev motors are the best economical way to go,light,powerful,easy contols/wiring and longevity.
> It is comical to see builders here clamering around dc motors/controls.
> They first find a much too heavy vehicle to convert, then find a massively heavy drivetrain to push it ,then install lead acid batteries to finally build the ultimate "Lead-Sled".Better to take your bank account and move slower on the ground-up build then wiilly-nilly throw the ev together and the find that it is too heavy,short ranged and high maintainence.


People have built hundreds of successful series DC lead acid conversions that perfectly fit their needs, and done so for much less time and money than a scratch built vehicle with an AC system. Personally I'm choosing a small vehicle with a small AC system, but if I wanted a more powerful AC system there aren't many choices unless I spend a lot of money, or take a chance on an unproven Chinese system. I'll let some others test those out for me for now


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## major (Apr 4, 2008)

CroDriver said:


> Btw. What's the efficiency of the different systems?
> 
> AC 90%+
> 
> ...


Hi Cro,

You're taking some rule of thumb and extrapolated numbers for a 350 kW input and trying to draw a valid comparison. I have to wonder if any system you can fit into your car will even do 350 kW. But to address your question, the AC systems (including BLDC) will likely be about 5, maybe 10 percent more efficient than the DC at heavy overloads. Of course this varies with the particular systems in question and the actual load condition.

Regards,

major


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## PhantomPholly (Aug 20, 2008)

I'm no expert but can read a spec sheet.

In motors, you look for lb/hp (or equivalent power/weight ratio).

At 133lbs for a 70hp max/28hp 1hr DC series wound motor, you are looking at almost 2lb/hp max rating / 4lb/hp continuous rating.

While it isn't in large scale production yet, Raser Technologies (www.rasertech.com) has developed and demonstrated a motor specifically for large EVs. The "Governator" has been driving around in their demo Hummer with that motor. At 246 lbs and 268 hp peak, it achieves better than 1:1 hp/lb at peak and better than .5hp/lb continuous (water cooled). That is getting closer to the better gasoline engines (non-racing variety). Others will follow, I'm sure.

I don't really know if this is the best out there, I'm just comparing it to the Warp 11 motors. I do know that the key is to forget about the hp of the motor and focus on the hp/weight ratio - you can always gang multiple motors together if you need a "big motor."


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## Tesseract (Sep 27, 2008)

PhantomPholly said:


> I'm no expert but can read a spec sheet.
> 
> In motors, you look for lb/hp (or equivalent power/weight ratio).
> 
> At 133lbs for a 70hp max/28hp 1hr DC series wound motor, you are looking at almost 2lb/hp max rating / 4lb/hp continuous rating....


Yes, but can you _translate_ the spec sheet into the real world? 

In testing our controller, we've routinely crammed 105kW (141hp) through a WarP 9 motor (143#). We could push the motor even more, so says major (and we plan on blaming him publicly if our motor zorches!).

Anyway, our dyno registered 118hp of actual mechanical output so coming from that angle the WarP 9 is clocking in a peak rating of around 1.21#/hp.

How 'bout them apples?


EDIT: one other thing... the average (ie - non-race-prepped) ICE doesn't have a very high continuous power output rating, either. Probably 30-50hp is what you can reasonably expect (this is more or less an "edumacated" WAG)


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## JRP3 (Mar 7, 2008)

If Rasertech follows the standard model they won't sell to the public and will be insanely high priced, so as far as we are concerned they might as well have invented warp drive.


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## Bowser330 (Jun 15, 2008)

JRP3 said:


> If Rasertech follows the standard model they won't sell to the public and will be insanely high priced, so as far as we are concerned they might as well have invented warp drive.


hahahahaha

+1


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## Bowser330 (Jun 15, 2008)

CroDriver said:


> Here are some BLDC motors that could be used for EV-s
> 
> http://pdf.directindustry.com/pdf/ph...49815-_29.html
> 
> ...


Most motors when they are operated at maximum power are not very efficient...


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## PhantomPholly (Aug 20, 2008)

Tesseract said:


> Yes, but can you _translate_ the spec sheet into the real world?


Nah, I leave that to the engineers!





> In testing our controller, we've routinely crammed 105kW (141hp) through a WarP 9 motor (143#). We could push the motor even more, so says major (and we plan on blaming him publicly if our motor zorches!).
> 
> Anyway, our dyno registered 118hp of actual mechanical output so coming from that angle the WarP 9 is clocking in a peak rating of around 1.21#/hp.
> 
> ...


Yah, I know less about auto engines than about aircraft engines, which routinely operate at 75-80% of rated hp. However, with them their hp/wt ratio is about 1hp/2lb, too.

I agree Raser will probably not sell to DIYers, at least not initially (if ever). Was only pointing it out because it shows what can be done. I am curious, though, why the controller (the smaller one - made for the smaller motor) supposedly "matched to the motor" is rated at twice the current of the motor - perhaps they are intending a two motor installation? Perhaps it, too, is designed for a hybrid setup where an ICE mated to a generator supplies power real-time to the electric motor.


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## 2cycle (Jul 2, 2009)

In my profession, 2 cycle engines, our engines can run at 80% power for as long as you keep feeding it gas and oil or until the piston rings wear out. Any 2 cycle engine produced in powersports vehicles have likely gone through multiple hour full throttle runs on the durability dynos and cannot show any wear or problems. 
When looking at hp/lb in ICE engines the 2 cycle is hands down the clear winner. High compression 2 cycle engines make 2.5 to 3 hp / lb naturally aspirated and 4 to 5 hp/lb with turbo charging. Consumer OEM engines produce 1 to 1.65 hp/lb.
I think with battery technology getting better and lighter motors being built the EV industry will soon be the leader in power/weight.


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## Tesseract (Sep 27, 2008)

2cycle said:


> In my profession, 2 cycle engines, our engines can run at 80% power for as long as you keep feeding it gas and oil or until the piston rings wear out. ...


That sounds pretty good, but are those AC or DC 2 cycle engines???


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## Qer (May 7, 2008)

DieselTwitch said:


> Reason 4 - programmability. Strictly speaking, this is not the property of AC system in oppose to a DC one, a DC controller can be made programmable and be as sophisticated as any AC one. But great majority of the DC controllers are not programmable, especially with EV specific parameters.


That's mainly because most DC-controllers that you find in an EV are budget controllers with very little functionality beyond throttle and pack in, motor out. If AC controllers came in cheap flavours as well, you'd probably not have all those fancy thingies on those as well since it'll cost time and money to develop them.

It's more of a market focus rather than technology issue and thus a moot point.



DieselTwitch said:


> Reason 5 - safety. Well known fact that if a DC controller's power stage fails, entire pack voltage is applied to the motor


I'm calling FUD on this one.

It is definitely true that if the controller fails you MIGHT get full pack voltage over the motor, but from our own experiences (we've blown a few controllers in our tests) and from what I've read in the forum the most common situation seems to be that you get a power spike and then something (fuse, bonding wires, cables, whatever) burns off and the motor stops. I have a nice graph of a power spike where the motor suddenly gets several times more current because the IGBT fails, but the spike only last a few ms, then it drops down to 0 Ampere. Fancy blue smoke is optional.

Now, what happens if an AC-controller breaks and you get full DC to the motor? Well, the motor will go into full breaking, so called DC injection breaking, which typically will mean a force that is stronger than regen and only affects two of your wheels (unless, of course, you're using 4WD) and you will probably lose control of your vehicle. If you don't believe me, drive on the highway and ask a good(?) friend to pull the parking brake when you don't expect it and see if you can keep the vehicle on the road...

But these are CATASTROPHIC faults! You might as well ask "Which car will handle better if one wheel falls off?" and the best answer is "Tighten those nuts so it doesn't happen!". Same thing here, buy quality stuff that's known to work and avoid those with a questionable reputation and you should be OK no matter what system you choose.



DieselTwitch said:


> Since typical DC system doesn't have other controls (temp sensors input, power reduction indication, etc.), will stop here for the fair comparison sake.


How convenient. Especially since, for example, tachometer is mandatory in an AC-setup but optional in a DC-setup...



DieselTwitch said:


> Let take a typical setup for a DC system with series wound motor. Then: 2 cables from the battery to the main contactors. 3 jumper cables for reversing contactors. 2 cables from the main contactors to the controller. 2 cables from the controller to the motor. One cable to jump the field and armature of the motor. 2 wires to the DC-DC converter input. Low voltage side: 3 wires to ignition switch. 2 wires to the throttle pot. 2 wires to the precharge contactor coil. 2 wires to the reversing contactors coils. 2 wires to the power resistor precharging capacitors in the controller. 2 wires for start inhibit switch. One heavy wire to ground DC-DC converter neg. side, and one - to connect its output to the 12V system in the car. 2 wires from the motor temp switch to the light on the dash. Typically, no harness exist or included, you come up with your own.


...and this is your (or MM's) idea of a "typical" DC-setup? As in what most people will use? For going to work and back (since that is, as far as I know, a typical usage)? And the DC/DC converter only exist (and is mandatory!) in DC-powered cars and never in AC-powered dittos? And, uh, don't AC-powered cars have head lights or a ar stereo?

To further bias the view, why not include the cables and contactors for series/parallel shift as well and, oh, I know, a separate battery pack so you REALLY can pull more than 1kA from the pack and make the 0-60 in pure Tesla style with tire smoke and all! More cables! More intimidating and cumbersome to set up in comparsion to the "Just connect a few cables and you're ready to take off" glorious AC-system!



DieselTwitch said:


> For Siemens systems it is for instance motor-inverter matching parameters, i.e. motor's stator winding parameters and magnetic characteristics are stored in inverter's EEPROM to maximize performance and efficiency working with that particular motor.


Right. Because in an AC-system the controller MUST have the motor parameters in EEPROM or similar to know how to control the motor.



DieselTwitch said:


> Usually in case of DC systems the motor manufacturer has no idea what the controller running it will be, and vice versa, so agreement and more-less precise match between the two is not possible.


Because it's a DC system and thus the controller doesn't have to know these things. It only converts raw DC from one voltage to another and let the motor shift polarity mechannically. In fact, the controller can't really optimize anything depending on motor type, it can only convert DC to ... uh .... another DC. Wow. Duh.



DieselTwitch said:


> In general, a user should ask himself/herself if all the advantages of an AC system are relevant for the application, driving habits, personal preferences and some extra cost is justified


Not to mention the authors intentions...

If it isn't obvious already, I'd like to mention that this essay is a liiiitle biased in it's views. Just making sure everyone's aware of that and that it's more focused to prove a point of view rather than weighting AC versus DC from a real life perspective. Just a tad biased, not much. Nope. Of course, a ship leaning this much towards one side would take in water and sink, but what the hell.

Seriously, the whole AC versus DC discussion feels like when I was a kid and most families either had SAAB or Volvo (I live in Sweden, back then those were Swedish car brands and most people bought Swedish cars). SAAB was FWD and Volvo was RWD and ALL us pre-school kids were experts on which system was the best. The FWD supporters of course focused on the advantages of FWD when the roads are covered with perfectly blank ice (which, typically, happens every fifth winter if even that) while the RWD supporters pressed on the fact that RWD is superior when you want to get loads of horse power into the street (which, of course, the average Volvo 240 didn't even had)!

In real life, most of our mums and dads had under powered cars, didn't drive faster than regulated and would probably lose control over the car way before it's technical limitations so it was strictly a very hypothetical discussion and with the exception for CroDriver and a few more guys, so is this! For most EV-owners the whole concept of motor, controller and battery is that you need one of each and preferably versions that match eachother well enough for the car to work.

So what is best? AC or DC? Chocolate or vanilla? Piano or guitar? Hailgun or Haubits?

In a Zen-influenced lack of dualistic thinking my answer is: Mu.

Get a system that fits your budget and gives you enough horse powers for you to like your car. Most of us will probably benefit more from putting most of the budget in better batteries than better motor/controller combo.

PS. http://en.wikipedia.org/wiki/Mu_(negative)


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## Bowser330 (Jun 15, 2008)

Qer said:


> That's mainly because most DC-controllers that you find in an EV are budget controllers with very little functionality beyond throttle and pack in, motor out. If AC controllers came in cheap flavours as well, you'd probably not have all those fancy thingies on those as well since it'll cost time and money to develop them.........


I am seriously unimpressed with the arguments from the AC camp...Thanks for taking the time to address their pointlessly repeated (oh and now even copied) comments Qer...

Personally, I think we should all focus on *DIY* EV, no matter what parts are used.

But i guess that wont happen till these AC guys get their heads out of the clouds and come back down to earth...


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## Overlander23 (Jun 15, 2009)

Can someone (Tesseract maybe) give a quick rundown on where the efficiencies are gained/lost between AC and DC controllers... and what the major cost items are? I realize that you *can* operate a DC brushed motor with merely a bank of batteries and contactors, but that's not exactly realistic for EV operation.

What are the biggest cost items on the controllers? I'm just trying to get an idea of why AC controllers are so much more expensive than DC.

Thanks...


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## Tesseract (Sep 27, 2008)

Overlander23 said:


> Can someone (Tesseract maybe) give a quick rundown on where the efficiencies are gained/lost between AC and DC controllers... and what the major cost items are?


The only major difference from an efficiency standpoint between a DC converter ("controller") and an AC inverter ("VFD") is that there are two switches in series in an inverter, thus, conduction _and_ switching losses are doubled right there.




Overlander23 said:


> I realize that you *can* operate a DC brushed motor with merely a bank of batteries and contactors, but that's not exactly realistic for EV operation.


Sure it is. Search on "rectactor" or "batpack". With 3V nominal LFP cells I imagine the control granularity would be quite good - nearly "stepless" - and 6V would probably be just fine. Of course, at some point you will spend more in contactors, crimp terminals and wire than you would for a "proper" semiconductor-based controller (what, in the 70's, would have been advertised as "Solid State"  ).




Overlander23 said:


> What are the biggest cost items on the controllers? I'm just trying to get an idea of why AC controllers are so much more expensive than DC.




Input capacitors (less capacitance and higher ESR is tolerable for an inverter - the only point in its favor)
Switches/Diodes - only one of each are needed in a converter; 6 of each are needed in an inverter
Gate Drivers - one is needed in a converter; 6 in an inverter
There are other differences in circuit and control algorithm complexity, of course, but except for NRE (one-time) costs these do not GREATLY affect the final price of the product.


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## Drew (Jul 26, 2009)

Something I'm interested in that I've never seen before is a dyno curve for a DC motor, all the AC motor suppliers seem to have them in a conventional format.

This is the one reason I'm thinking about going with AC over DC, because AC delivers peak power from a very low RPM compared to the rev limit, which means I can get away without a gearbox, which is a big bonus in terms of complexity and weight, as I'm designing an electric motorbike. Also, regenerative braking is extremely valuable as I want to simulate engine braking to make the bike a bit more stable under hard brakes.

If anyone does have a dyno curve for a DC motor or can debunk my current assumption that power from DC motors is proportional to RPM then it would be greatly appreciated.


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## tomofreno (Mar 3, 2009)

> AC delivers peak power from a very low RPM compared to the rev limit


I've seen this stated before, and am confused by it. AC induction motors typically have a so-called "flat torque-speed curve" meaning constant torque over a range of lower rpm, out to 3000 to 4500 typically. Motor shaft power is the product of torque and shaft radial velocity, so power increases linearly as rpm increases over this "flat" part of the torque-speed curve. Peak power is achieved at an rpm slightly greater than the max rpm for the "flat" part of the t-s curve and decreases beyond this as available torque decreases faster than rpm increases.

Because DC motor torque at lower rpm is usually limited by the max current the controller can supply, they also effectively have a flat t-s curve. So I don't see much difference in AC vs DC in this regard. Am I missing something?

Tom (an AC owner)


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## Drew (Jul 26, 2009)

Do you mean Torque to Speed by TS? If thats the case then that means that power is proportional to speed and you need a gearbox


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## etischer (Jun 16, 2008)

AC motors are generally constant torque up to base speed.
From base speed to max speed they are constant horsepower. 

So once the motor has reached base speed (3500-4000), there is no real reason to shift until you reach max speed (13krpm). 

A tach/encoder is not mandatory for AC motors, I don't have one =)

Torque in an AC motor is directly related to slip.
Slip is the difference between what speed the inverter is commanding, and what speed the motor is turning. 
The inverters commanded speed is related to frequency (virtually limitless)
So the AC motor can produce torque at very high speeds. 

Torque in a DC motor is based on slip too
Slip is the difference between commanded speed and actual motor speed.
Commanded speed is related to voltage, limited by battery voltage
So a DC motor can only produce as much torque as you have batteries. 

This is why most production EVs are AC powered. There is more area under the horsepower vs. rpm curve. 

AC motors are generally more efficient because the timing is computer controlled, no need to advance brushes. Think of it as a DC motor with VTECH and vacuum advance distributor =) What brush advance setting works at 100 rpm isn't what works best at 8000 rpm. DC brushless solves this problem by using an encoder for commutation, and the efficiency is on par with AC.


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## Drew (Jul 26, 2009)

etischer said:


> AC motors are generally constant torque up to base speed.
> From base speed to max speed they are constant horsepower.
> 
> So once the motor has reached base speed (3500-4000), there is no real reason to shift until you reach max speed (13krpm).
> ...


I realise that, but I haven't ever seen a DC motor torque curve, thats what I'm interested in.

Reason being that I can design a transmission system for a 300kg bike and rider combination using something like an Azure Dynamics AC24LS and match the power curve of the motor to the limit of traction of the bike and I'll get a 0-100 in the range of 4-5 seconds and a top speed of around 140-150kmh which is almost exactly what I'm after, but if a DC motor will do the same thing then there may be an opertunity to save money, weight and complexity.


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## Qer (May 7, 2008)

Drew said:


> I realise that, but I haven't ever seen a DC motor torque curve, thats what I'm interested in.


I googled some and even though I didn't find a graph, I found this:

http://www.micromotcontrols.com/htmls/Motor characteristics.html



> This type of motor speed varies automatically with the load, increasing as the load decreases. Use of series motor is generally limited to case where a heavy power demand is necessary to bring the machine up to speed, as in the case of certain elevator and hoist installations, for steelcars, etc.





> The coils in the series field are made of a few turns of large gauge wire, to facilitate large current flow. This provides high starting torque, approximately 2 ¼ times the rated load torque. Series motor armatures are usually lap wound. Lap windings are good for high current, low voltage applications because they have additional parallel paths for current flow.


So, how much torque can a series wound motor give? Depends on the motor, of course, but everything I've read about it (sorry, don't have an EV myself yet, but I've been reading up on the series wound since I needed that knowledge for the controller project) has told me the torque is proportional to the amps. If it's enough for you? Good question. 

That Azure system seems to give a little less than 70 ft. lbs. of start torque, that's what a WarP 9" gives at a little above 300 Amps. On the other hand, it's probably not healthy for a WarP 9" to go faster than 6000 RPM (if even that, nominal seems to be around 2000-3000 as far as I've understood) where the Azure can reach 12000 RPM (nominal around 4000). On the third hand, we've pushed the poor WarP 9" in the dyno to something north of 200 ft. lbs. but on the fourth hand the WarP 9" didn't like it (1000 Amps is a wee bit more than the WarP 9" is rated for) and if you keep it up for too long it'll blow.

http://www.youtube.com/watch?v=TsK1tc8iY7E

With a 2kA controller the torque will be brutal and hard to beat, but the life expectancy of the motor will drop like a stone and you'll probably have to replace the brushes quite often to avoid them blowing. On the other hand, both KillaCycle and White Zombie has managed numerous starts with motor currents close to 2kA but both teams has suffered blown motors a few times. And so on, and so on, etcetera, etcetera...

So, what's best? Apples or pears?

Your pick.


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## Tesseract (Sep 27, 2008)

Drew said:


> I realise that, but I haven't ever seen a DC motor torque curve, thats what I'm interested in....


This has been posted here numerous times:

http://www.go-ev.com/images/003_15_WarP_9_Graph.jpg


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## Drew (Jul 26, 2009)

Tesseract said:


> This has been posted here numerous times:
> 
> http://www.go-ev.com/images/003_15_WarP_9_Graph.jpg



I don't really understand what that means though, I would have thought that each line ties into its relative axis and te torque axis at the bottom, but thats not possible with the way that horse power is demonstrated on that graph, it appears proportional to torque, which implies constant RPM.

What I'm looking for is something like kW vs Rpm so that I can do tractive effort calcs...

ie here is an example of what I'm trying to do with the data, the motor power line is an approximation of an Azure Dynamics AC24LS and the tractive limit is calculated based on a motorcycle with the bike/rider combo weighing 250kg and having a tipping point of 1g










This also serves to illustrate what I was getting at with the AC motor thing, this indicates that if I gear for peak power at limit of traction I'll end up with a (2 minute limited) top speed of approx 150km/h due to wind drag and a separately derived 0-100 time of approx 4-5 seconds.

This is why I'm interested in the power vs RPM characteristics of DC motors, if they're similar to AC then I can do the same thing, but I need dyno chart type information to calculate gearing etc.

If you could tell me how to convert your linked graph into something similar to the above then I'd be most appreciative.


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## Tesseract (Sep 27, 2008)

Drew said:


> I don't really understand what that [graph] means though,...


That graph shows many things at the same time, but since you specifically stated:



Drew said:


> I haven't ever seen a DC motor torque curve, thats what I'm interested in.


we will first consider the plotted line labeled "Amps".

That line illustrates that torque (x-axis) is proportional to motor current (the y-axis labeled "amps").

The plotted line labeled "RPM" illustrates the shaft speed of the motor if volts are kept constant (in this case, 72V) while torque loading is increased (i.e. - "Amps"). Roughly speaking, if you double the motor volts you will double the shaft speed attainable for a given torque load (there are some other losses and, of course, limits that come into play).

A final example: at 250A and 72V the WarP 9 motor should be spinning at 2500 rpm and delivering approx. 43 ft-lb of torque.


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## Drew (Jul 26, 2009)

So that means that no data on that graph concerns RPM outside of the 2000-5000 range and the power falls off as RPM increase?


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## Tesseract (Sep 27, 2008)

Drew said:


> So that means that no data on that graph concerns RPM outside of the 2000-5000 range...


That would appear to be the case.



Drew said:


> ...and the power falls off as RPM increase?


That's not what the line labeled "HP" indicates...

Two things about series DC motors you seem to not be aware of: 

1. the stall torque of the series DC motor is limited only by it's internal resistance and the internal resistance of the WarP motors is very low indeed (down in the tens of milliohms range). They are quite capable of snapping their own shafts.

2. the no load RPM of the series DC motor is limited only by parasitic loads like bearing and commutator friction and windage. They will happily blow themselves to pieces if run unloaded with more than a few tens of volts across them.

The behavior of the motor at these two extremes is not terribly important to know (hp = 0 if either torque or rpm is 0). Furthermore, on the low RPM end of the plot the torque is practically limited by I^2R losses and, of course, the current limit of the controller. On the high RPM side it is practically limited by the parasitic drag of the drivetrain and the maximum battery voltage.

AC motors have torque and rpm limits, too, they just behave differently. The biggest difference is that the series DC motor will keep producing more torque if fed more current until it burns up or snaps a shaft whereas the AC induction motor has a definite limit to the amount of torque it can produce _regardless_ of how much current is forced through its stator windings.

This is why the series DC motor works so well in traction applications: you can extract tremendous amounts of torque from it at 0 RPM while the drop off in available torque (for a given battery voltage) as RPM increases is generally of no concern because last time I checked there are speed limits on most roads in the world


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## Drew (Jul 26, 2009)

Tesseract said:


> That would appear to be the case.
> 
> 
> 
> ...



Not so much on race tracks etc though 

So in theory at least the starting torque is practically limited by the amount of amps pumped into them? so in theory at least you just pick the mount of torque you want to plateau to by the amps your controller is capable of spitting out. Correct? And from there it would be limited by motor characteristics?

Also, I've seen info saying that the Netgain motors are rated to 192V or something like that? Is there similar data available for them then?


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## CroDriver (Jan 8, 2009)

Here is a mail I got from Kostov, I think that it could help here...



> If you look at the performance curve for a single 192V motor, you can read from it the point 68kW/425A/4200rpm/192V.​ Moving this to 350V will yield 124kW/425A/7700rpm/350V.​ Now double that to account for the 2 motors - 248kW/850A/7700rpm/350V for the dual motor.​ Torque is 248000W/(7700*0.10455)=308Nm.​ The point is very bad - rpm are too high.​ Even 1000A will not get you to the safety of <6000rpm.​ You will need 1200-1300A for that, where torque will also rise to 500-520Nm.​ Also have in mind that 350V is way out of specs - white zombi blew the Kostov at 260V/620A...​


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## tomofreno (Mar 3, 2009)

Yes, the DC motor power decreases at higher rpm due to the back emf of the rotor decreasing the input voltage to the motor, resulting in less current through the motor and less torque. 

Torque is a fairly linear function of current in a series DC motor. Motor output power is the product of torque and shaft radial velocity. You can calculate it from the motor torque-speed graph as: torque (lb-ft)*0.7376*rpm*2*pi/60 = power (Watt). The 0.7376 converts lb-ft to N-m, "pi" is 3.1416, and the 2*pi/60 converts rpm to radians/second radial shaft velocity. To convert Watt to HP divide by 747.5. The motor input power is just the product of the voltage (don't forget to subtract the "droop" voltage, usually 0.03 times the current) and current. The ratio of the output power to input power is the efficiency, so you can calculate these from the graph.

People say AC motors are constant power above "base speed" but you can see this isn't the case for the Azure Dynamics motors from the power curves on their website. It also isn't the case for the HPGC AC motors. Power decreases from a peak just beyond the end of the flat part of the torque speed curve. But power decreases fairly slowly, so I guess "constant" is an approximation.

Imo there isn't a great deal of difference in performance in similar size AC induction motors and DC series motors. Efficiency of the combined motor and controller (what counts) is very similar, typically mid-eighties at running rpm (worse at lower). You can get considerably more torque and power from the DC motor at lower rpm if you use a high current controller, but most people use a controller with max of about 500A so the torque at low rpm is limited by the current the controller can supply.

Tom


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## tomofreno (Mar 3, 2009)

Whoops, a bit dyslexic, that should have been 745.7 to convert Watt to HP.


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## Drew (Jul 26, 2009)

So effectively (if I'm understanding this correctly) the power vs RPM for a DC motor will always be an approximation of a triangle, with a constant torque until the back EMF(?) reduces voltage proportionally to RPM and you get a linear reduction in power?

I'd love it if somebody had just put their car on a dyno or similar.


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## Qer (May 7, 2008)

Drew said:


> So in theory at least the starting torque is practically limited by the amount of amps pumped into them? so in theory at least you just pick the mount of torque you want to plateau to by the amps your controller is capable of spitting out. Correct?


Yes. There's probably some non-linearity mixed in as well but I doubt it will make much of a practical difference.



Drew said:


> And from there it would be limited by motor characteristics?


Rather by material limits. The motor will happily comply until it melts, the shaft snaps or the brushes zorch.



Drew said:


> Also, I've seen info saying that the Netgain motors are rated to 192V or something like that?


They are, but I DOUBT you can push 1kA through a WarP at 192 Volt, probably not even close to that. It's possible a Kostov with interpoles can handle higher current at high Voltages better, but I would be very impressed if any brushed motor can handle 4 digit current at max Voltage.

On the other hand, cramming "only" 100 kW into the motor will take a serious battery pack that would be hard to fit in a car and you're planning an MC...



Drew said:


> Is there similar data available for them then?


As far as I know, nope. They only present graphs at 72 Volts as far as I've seen. Kostov, however, seems to plot their graphs at max Voltage, which is pretty nice:

http://kostov-motors.com/tractionmotors/kostovlineofevmotors/

Personally I'm pondering Kostov rather than WarP, but that's mainly because since I live in Europe they'll be easier for me to obtain. A WarP would probably be quite enough as well and several people have proven over and over that WarP's can generate serious power. The limiting factor doesn't seem to be the motor but the controllers and, especially, the batteries.

Maybe you should turn this the other way around? Start with looking at how much power you can bring and pick a motor after you have those numbers done?


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## Drew (Jul 26, 2009)

Qer said:


> Yes. There's probably some non-linearity mixed in as well but I doubt it will make much of a practical difference.
> 
> 
> 
> ...


I've done some back of the envelope calcs with the intent of producing a very high performance electric bike. I'm a mechanical engineer myself which should go some way to explaining my lack of understanding of electrickery but I'm hoping to design chassis elements from the ground up to suit a motor in the 150kW range for the prototype bike and I was hoping to have a friend build a pack from A123 batteries with a proprietary management system intended to make flexible pack construction much more accessible.

I was hoping to get something in the range of 6kWh of A123s into the bike, which should deliever a peak power in the range of 300kW with a continuos delivery of about 160kW and an intended charge time of about 20 mins on three phase 

One of the reasons that I'm so keen on the no transmission thing is because I'm hoping to be able to produce these things so that they require no maintenance that an operator can't carry out.

Unfortunately I have a very limited understanding of the electrical side of things myself, so I'll be depending very heavily on my friend, but it is nice to understand these things in some detail before going into them.


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## Qer (May 7, 2008)

Drew said:


> I was hoping to get something in the range of 6kWh of A123s into the bike, which should deliever a peak power in the range of 300kW with a continuos delivery of about 160kW and an intended charge time of about 20 mins on three phase


Hmm. You're talking about a discharge rate of 50C peak and 26C continuously. Quite frankly, I've never heard of any battery chemistry that can handle that amount of abuse. Admittedly, I'm no battery expert but as far as I know A123 are Lithium based and then I'd say that these numbers are quite unreasonably. You'll probably blow the pack more or less instantly.


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## Drew (Jul 26, 2009)

Qer said:


> Hmm. You're talking about a discharge rate of 50C peak and 26C continuously. Quite frankly, I've never heard of any battery chemistry that can handle that amount of abuse. Admittedly, I'm no battery expert but as far as I know A123 are Lithium based and then I'd say that these numbers are quite unreasonably. You'll probably blow the pack more or less instantly.


These are just what the A123 site product information states;

http://a123systems.textdriven.com/product/pdf/1/ANR26650M1A_Datasheet_APRIL_2009.pdf


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## Qer (May 7, 2008)

Drew said:


> These are just what the A123 site product information states;
> 
> http://a123systems.textdriven.com/product/pdf/1/ANR26650M1A_Datasheet_APRIL_2009.pdf


I'll be damned. Ok, as I stated I'm no battery expert. 

I knew that A123 were appreciated in racing situations for their specs, I just didn't realise they were THAT much better than "ordinary" Lithium batteries. Pretty brutal, indeed.


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## dimitri (May 16, 2008)

Drew,

pardon my ignorance, but at 26C-50C discharge your pack will be depleted in 1-2 min, which seems like the only purpose of the bike is the drag race? Am I correct? 

Are you planning to use this bike for any other purpose rather than drag race? If so, I don't see how 6kW pack with no transmission will be useful on regular roads.

Sorry if I misunderstood your intentions for the bike.


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## etischer (Jun 16, 2008)

Using the data from the rpm vs. torque graph, I changed it to torque vs. rpm. Here is what I got. 








http://etischer.com/awdev/motor/warp9.jpg



Tesseract said:


> This has been posted here numerous times:
> 
> http://www.go-ev.com/images/003_15_WarP_9_Graph.jpg


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## etischer (Jun 16, 2008)

here is a comparison of warp9, ac55, and siemens/ford motor. KW vs. Hp

here are links to the data used to generate the graph.
http://etischer.com/awdev/motor/003_15_WarP_9_Graph.jpg
http://etischer.com/awdev/motor/AC55_DMOC445ProductSheet.pdf
http://etischer.com/awdev/motor/Ford_Siemens.pdf 

Warp 9 hp data was based on torque*rpm/5252


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## Qer (May 7, 2008)

etischer said:


> Warp 9 hp data was based on torque*rpm/5252


Considering we've pulled over 100 kW out of a WarP 9", that looks a tad low. Is that based on the 72 Volt numbers? What if you base it on the data for Kostov 11" instead?


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## major (Apr 4, 2008)

Drew said:


> I'd love it if somebody had just put their car on a dyno or similar.


Mike was kind enough to post up his test.



> Here's links to the electrical data from the dyno run:
> http://home.gci.net/~saintbernard/Cr...Q4_06AUG08.pdf
> http://home.gci.net/~saintbernard/Cr...ue_06AUG08.pdf
> http://home.gci.net/~saintbernard/Cr...ut_06AUG08.pdf


From this thread: http://www.diyelectriccar.com/forum...pinto-16474p3.html?highlight=crazyhorse+pinto


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## etischer (Jun 16, 2008)

Well, I'm just comparing mfg spec to mfg spec, apples to apples. 

Pretty impressive numbers from the DC motor, but for a reliable daily driver I don't think one should plan on running 1500A current limit on a Warp9. 

Like I said before, DC motor torque is limited by battery voltage. The way he gets high end torque is by running 370 volts. 
From his graphs, it looks like it sags to 200v at peak current. I suppose this is normal for a dragster, but not feasible for a daily driver =)


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## etischer (Jun 16, 2008)

I based the numbers off the graph that was posted earlier.

http://www.go-ev.com/images/003_15_WarP_9_Graph.jpg


Their graph shows peak hp is 35hp

but peak torque shown on the graph is 75lbft @ 2100 rpm, this is only 30hp. I tried other points on the torque/rpm curve, but 30 was the highest I could find. 






Qer said:


> Considering we've pulled over 100 kW out of a WarP 9", that looks a tad low. Is that based on the 72 Volt numbers? What if you base it on the data for Kostov 11" instead?


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## tomofreno (Mar 3, 2009)

> I tried other points on the torque/rpm curve, but 30 was the highest I could find.


 Well yeah, because like you said the torque and power at higher rpm are limited by motor input voltage, and that graph is for 72V. Use the curves for the Advanced DC 9" motor. They are available for 75, 84. 96, 120, and 144 volt, and it is similar to the Warp9. You get much more torque and power at 144V. You can't get much current through the motor at higher rpm with 72V. The back emf is driving the motor input voltage down low.

Tom


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## Qer (May 7, 2008)

etischer said:


> Like I said before, DC motor torque is limited by battery voltage. The way he gets high end torque is by running 370 volts.
> From his graphs, it looks like it sags to 200v at peak current. I suppose this is normal for a dragster, but not feasible for a daily driver =)


He is using puny lead-acid batteries that are specified for high constant current but seriously I think they're junk. Look at these graphs:

http://www.diyelectriccar.com/forums/showthread.php/new-controller-prototype-29062p21.html

There's some graphs on that page and there's more later on. His graphs shows a drop of about 200 Volt at 1000 battery Amps, our pack doesn't even sag 50 Volt at 600 battery Amps. Battery pack voltage is "only" 180 Volt (don't remember the Ah-rating, but as far as I've understood they're pretty ordinary EV-batteries) and that makes it quite possible to get 1000 motor Amps and over 100 kW in our dyno. The pack voltage used to be 192 Volt, but one battery couldn't take the stress any longer...

So a daily driver can get 1000 Amps no problem, especially as start torque it's a piece of cake. We have a controller in a VW Beetle now. It's powered by pretty ordinary lead acid batteries (gel?) at 120 Volt nominal. Highest peak current registered: 980 Amps, the clutch can't quite handle it. After all, it's a Beetle.


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## etischer (Jun 16, 2008)

send me a link to a graph showing hp vs. rpm @ 144v and we can do a fair comparison, which is what we are trying to do in this thread. 




tomofreno said:


> Well yeah, because like you said the torque and power at higher rpm are limited by motor input voltage, and that graph is for 72V. Use the curves for the Advanced DC 9" motor. They are available for 75, 84. 96, 120, and 144 volt, and it is similar to the Warp9. You get much more torque and power at 144V. You can't get much current through the motor at higher rpm with 72V. The back emf is driving the motor input voltage down low.
> 
> Tom


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## Tesseract (Sep 27, 2008)

etischer said:


> send me a link to a graph showing hp vs. rpm @ 144v and we can do a fair comparison, which is what we are trying to do in this thread.


For like the thousandth time already: *Back EMF is proportional to RPM* and basically directly opposes the flow of current through the motor (this applies to AC motors, too, btw). The familiar NetGain graph shows the motor voltage being held constant at 72V and loading increased across a 5000 to 2000 rpm range.

The pathetic power output of the WarP 9 motor at 72V is why no one (well, except for gottdi) drives around with that size battery pack!!!

If you want to get serious power out of a motor at higher RPM you need a pack voltage appreciably higher than the BEMF opposing it. Simple as that. 

And like I mentioned above, AC motors are not immune to this, either. Everyone seems to realize that RPM is proportional to frequency, but for some reason forgets that so is voltage! You want to spin an AC motor at twice the RPM but with the same torque load (ie - 2x power) then you will need twice the voltage.

AC motors do not give you some magical way to cheat the laws of physics!


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## etischer (Jun 16, 2008)

I understand how a dc motor works. The point of the thread was to compare hp from a DC system and an AC system. The best way to do that is compare the hp vs. rpm graphs for each system. So let's compare a typical 312v AC system with typical 144v system with an equvialent battery pack (around 17kwh). Would also be interesting to compare a dc motor with seperate field and field weakening. 



Tesseract said:


> For like the thousandth time already: *Back EMF is proportional to RPM* and basically directly opposes the flow of current through the motor (this applies to AC motors, too, btw). The familiar NetGain graph shows the motor voltage being held constant at 72V and loading increased across a 5000 to 2000 rpm range.
> 
> The pathetic power output of the WarP 9 motor at 72V is why no one (well, except for gottdi) drives around with that size battery pack!!!
> 
> ...


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## major (Apr 4, 2008)

etischer said:


> I based the numbers off the graph that was posted earlier.
> 
> http://www.go-ev.com/images/003_15_WarP_9_Graph.jpg
> 
> ...


Hi etischer,

That graph just shows a portion of the complete motor performance characteristic. Up to 350 amps. It extends far to the right. It is only fair to say it has a peak of 35 hp if your application has a limit of 350 amps.



> but peak torque shown on the graph is 75lbft @ 2100 rpm, this is only 30hp. I tried other points on the torque/rpm curve, but 30 was the highest I could find


Yes, I have noticed that discrepancy and commented about before. I have seen quite a few poorly drawn DC motor curves lately.


Regards,

major


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## major (Apr 4, 2008)

etischer said:


> Torque in a DC motor is based on slip too
> Slip is the difference between commanded speed and actual motor speed.


Hi etischer,

I follow your thinking on this, but would put forth that it is really a torque command, not speed. And the actual speed of the motor is a consequence of the commanded torque and the load behavior, of course factoring in your power source limitations.

Likely two ways of arriving at the same place.



> Commanded speed is related to voltage, limited by battery voltage. So a DC motor can only produce as much torque as you have batteries.


Same for an AC motor, isn't it?



> This is why most production EVs are AC powered. There is more area under the horsepower vs. rpm curve.


I agree production EVs are and will be AC traction drives, but do not necessarily see this hp curve area as the reason. Simply put, the reason is product validation.

Regards,

major


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## etischer (Jun 16, 2008)

My basis for DC torque being based on commanded speed is this. 

Commanded speed is basically applied voltage to the motor.

Actual speed is basically back EMF.

Commanded speed - Actual speed = torque

At 5000 rpm lets say a motor is generating 100v of back EMF. Applying 100v will give you zero torque. To achieve the same torque you would get at zero speed, you would have to apply 200v, (100v worth of slip speed). I haven't tested this out, but seems to be the DC equivalent to AC motor theory. 




For AC motors, voltage has no direct relation to motor speed. Give me 100 volts DC and I can get my AC motor to spin to 12,000 rpm. (70vac @ 400hz) Granted, you would have 1/3rd the torque you would have at 300vdc, but the rpm is achievable, and torque would be something greater than zero.






major said:


> Hi etischer,
> 
> I follow your thinking on this, but would put forth that it is really a torque command, not speed. And the actual speed of the motor is a consequence of the commanded torque and the load behavior, of course factoring in your power source limitations.
> 
> ...


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## Bowser330 (Jun 15, 2008)

etischer said:


> here is a comparison of warp9, ac55, and siemens/ford motor. KW vs. Hp
> 
> here are links to the data used to generate the graph.
> http://etischer.com/awdev/motor/003_15_WarP_9_Graph.jpg
> ...


http://etischer.com/awdev/motor/AC55_DMOC445ProductSheet.pdf

Can someone help me understand why the data sheet says 250A peak but why the graphs (on subsequent pages) say 400A @ 312V...

72V Warp-9 vs. 312V AC-55....yah that makes so much sense

HAHAHAAHA


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## etischer (Jun 16, 2008)

Bowser330 said:


> http://etischer.com/awdev/motor/AC55_DMOC445ProductSheet.pdf
> 
> Can someone help me understand why the data sheet says 250A peak but why the graphs (on subsequent pages) say 400A @ 312V...
> 
> ...


It reads 250A RMS (dc battery current), which is 400A peak (3 phase ac motor current)

144v would make more sense in a comparison, but nobody has provided data for 144v. Both systems should be comparable in terms of peak torque. 250A @ 300V vs 550A @ 144V


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## tomofreno (Mar 3, 2009)

Click on the "144 Volt" link near the bottom of the page:

http://www.evmotors.com.au/products/fb1.html


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## Bowser330 (Jun 15, 2008)

tomofreno said:


> Click on the "144 Volt" link near the bottom of the page:
> 
> http://www.evmotors.com.au/products/fb1.html


http://kostov-motors.com/files/productattachments/817455860674b455566486badd21c31d_9-168V.pdf

Kostov-9" @ 168V

~58kw (~80HP) @ 500A @ 3500RPM

http://kostov-motors.com/files/productattachments/56556adf221d6b72d07f26795bfbc05a_9-144V.pdf

Kostov-9" @ 144V

~52kw (~70HP) @ 500A @ 3500RPM

Also, when did the 9" motor start being compared to the AC55? Seems the 9" more compares the the AC24 and the 11" compares better in size to the AC55...doesn't it?


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## Qer (May 7, 2008)

etischer said:


> At 5000 rpm lets say a motor is generating 100v of back EMF. Applying 100v will give you zero torque. To achieve the same torque you would get at zero speed, you would have to apply 200v, (100v worth of slip speed). I haven't tested this out, but seems to be the DC equivalent to AC motor theory.


I have graphs of it. Your theory is sound, but your numbers are completely shot. To get serious torque from a WarP 9" you only need a few Volts over the motor when RPM is 0. Here's a graph showing a car accelerating:











As you can see it takes less than 10 Volts to maintain about 300 Amps in a moving vehicle and almost 1000 Amps is reached with about 30 Volts over the motor while the car's accelerating hard.



etischer said:


> For AC motors, voltage has no direct relation to motor speed. Give me 100 volts DC and I can get my AC motor to spin to 12,000 rpm. (70vac @ 400hz) Granted, you would have 1/3rd the torque you would have at 300vdc, but the rpm is achievable, and torque would be something greater than zero.


This is still no different to a series wound motor. It has been repeated in this forum several times that a series wound motor can spin itself to death at pretty low voltage if it's unloaded and the only voltage that's considered pretty safe for testing a motor is 12 Volt. Apply more Volt and you get some torque too, but FULL torque (whatever that is for a WarP 9", I guess the limit is when the shaft snaps) will take some serious Voltage @ 6000 RPM, sure, exactly as it would with an AC-system.

Unfortunately the graph above doesn't include the tachometer so I can't tell you how many RPM's the motor was doing, but we're DEFINITELY NOT talking about "100v worth of slip speed"...


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## major (Apr 4, 2008)

etischer said:


> Commanded speed - Actual speed = torque


Actually it goes something like this.

Ia = (Va - Eg) / Ra

Where:

Ia = armature current

Va = voltage applied to the armature

Eg = generated voltage in the armature (which is proportional to RPM)

Ra = resistance of the armature

Of course the torque is proportional to Ia.



> At 5000 rpm lets say a motor is generating 100v of back EMF. Applying 100v will give you zero torque. To achieve the same torque you would get at zero speed, you would have to apply 200v, (100v worth of slip speed). I haven't tested this out, but seems to be the DC equivalent to AC motor theory.


I'd like to see you test that out with a nice inertial load attached to the motor 

Using the above equations and using a figure of 0.01 ohm for Ra, you'd see a 10,000 amp spike.



> For AC motors, voltage has no direct relation to motor speed. Give me 100 volts DC and I can get my AC motor to spin to 12,000 rpm. (70vac @ 400hz) Granted, you would have 1/3rd the torque you would have at 300vdc, but the rpm is achievable, and torque would be something greater than zero.


True, that the speed of the AC motor is governed by the frequency. But voltage is related to frequency. In your example, I suspect that your motor would have essentially no torque at 70Vac and 400 Hz. Nock your battery pack down to 100V and try it.

Your use of the term "slip" bothers me. Slip only applies to asynchronous machines and is the applied stator frequency minus the rotor frequency. DC commutator machines are synchronous machines by virtue of the commutator switching the armature at synchronous speed. 

Regards,

major


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## etischer (Jun 16, 2008)

Here is the result from the data you guys collected:













Here is the data points I used. Keep in mind the spreadsheet is in LbFt & Kw. 

http://etischer.com/awdev/compare/hp_data.jpg


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## Qer (May 7, 2008)

Fancy graph. But what are you trying to prove?


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## etischer (Jun 16, 2008)

I'm not trying to prove anything. It is simply a comparison of various AC and DC motors, which is what the original poster was asking for. I find it quite useful, especially for someone trying to decide which motor to buy. 

It also shows that the "peak horsepower" value can be decieving. 

Comparing the AC55 to Warp9 144v, they both have roughly the same peak power, but Warp9 has roughly 15 more kw across the rpm range. 

The Siemens motor so far looks like the best choice. 

I'd be interested to see what the Warp 13" does at 144v & 168v.





Qer said:


> Fancy graph. But what are you trying to prove?


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## Qer (May 7, 2008)

etischer said:


> Comparing the AC55 to Warp9 144v, they both have roughly the same peak power, but Warp9 has roughly 15 more kw across the rpm range.
> 
> The Siemens motor so far looks like the best choice.


That is conclusions you can't make on the data you've used because the output power and torque from an electric motor depends not only on the motor but very much on the controller as well (and, of course, the batteries, but that's a common problem no matter type of controller/motor).

If you make graphs of output power based on motor *and* controller combinations you might have a valid comparison, but just comparing random data without knowing how the data was collected or what controller (if any) was used makes it a pretty random comparison. For example, we've showed that we can get at least 100 kW out from a WarP 9" with our controller at about 90 Volt over the motor which means that the WarP 9" is capable of more than your graph shows and at lower pack voltage too. With a 2kA-controller the power should pretty much double and those nice graphs from the Crazyhorse Pinto shows that that's, indeed, the case.

Just to be clear, I'm not saing the Siemens motor is worthless or that it would be a bad choice, I am, however, saying that you're comparing apples with pears. Your comparison is based on arbitrary data and ignores too many variables to make it meaningful.


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## etischer (Jun 16, 2008)

Well, it may not be perfect, but it is a good start, and better than not having any data to compare.

The power I get out of my Siemens motor and home brew controller seems to be on par with the siemens supplied graph. I'm sure the Ballard and Siemens controllers are also well tuned to the motor.

I assume if the hp graph for a DC motor specifies 500A, it doesn't matter what controller was used, as long as it can supply 500A. 

I think my comparison is fair. I can put a DC motor running 2000A on my graph, but a motor that only runs 100 miles before needing a rebuild is hardly a fair comparison. Certainly not feasible for a daily driver, which I assume most people in this forum are interested in building. 

To make the battery a level playing field, lets assume a 17KwHr Lead Acid pack. (55Ah X 312V) and (120Ah x 144v)




Qer said:


> That is conclusions you can't make on the data you've used because the output power and torque from an electric motor depends not only on the motor but very much on the controller as well (and, of course, the batteries, but that's a common problem no matter type of controller/motor).
> 
> If you make graphs of output power based on motor *and* controller combinations you might have a valid comparison, but just comparing random data without knowing how the data was collected or what controller (if any) was used makes it a pretty random comparison. For example, we've showed that we can get at least 100 kW out from a WarP 9" with our controller at about 90 Volt over the motor which means that the WarP 9" is capable of more than your graph shows and at lower pack voltage too. With a 2kA-controller the power should pretty much double and those nice graphs from the Crazyhorse Pinto shows that that's, indeed, the case.
> 
> Just to be clear, I'm not saing the Siemens motor is worthless or that it would be a bad choice, I am, however, saying that you're comparing apples with pears. Your comparison is based on arbitrary data and ignores too many variables to make it meaningful.


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## major (Apr 4, 2008)

etischer said:


> Well, it may not be perfect, but it is a good start, and better than not having any data to compare.


Hi etischer,

Please add the motor I have attached to your graph.

Thanks,

major


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## etischer (Jun 16, 2008)

http://etischer.com/awdev/compare/compare2/hp_data.jpg


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## Qer (May 7, 2008)

etischer said:


> I think my comparison is fair. I can put a DC motor running 2000A on my graph, but a motor that only runs 100 miles before needing a rebuild is hardly a fair comparison.


That depends on your goal with your EV. If you want to commute with your EV with a minimum of maintenance your argument is valid (but then you probably don't need this kind of power as well), but if you want performance and is prepared to take more brush wear a high current burst now and then doesn't seem to harm the motor (at least not the one in the dyno).

That's why I still think you're comparing apples with pears. It's two different kinds of technology and you can't compare them just by a power curve. It's not that I think it's unfair as much as misleading, actually.


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## major (Apr 4, 2008)

major said:


> Please add the motor I have attached to your graph.


Thanks, etischer....


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## etischer (Jun 16, 2008)

Well, for the majority of EV converters, the goal is to eliminate their need for gas, and maintenance. 

Including a dyno chart for an unsustainable overload condition would be misleading. If a motor can withstand the abuse dished out for 1 year (under normal driving conditions) without servicing, I would feel justified including it's dyno chart in the comparison. 

Heck, let's go ahead and throw in a motor running 2000A. Send me a dyno chart and I'll throw it in for fun, I'll make it a dotted line though =) 

In what ways does a DC motor surpass an AC motor. What other parameters should we be comparing?



Qer said:


> That depends on your goal with your EV. If you want to commute with your EV with a minimum of maintenance your argument is valid (but then you probably don't need this kind of power as well), but if you want performance and is prepared to take more brush wear a high current burst now and then doesn't seem to harm the motor (at least not the one in the dyno).
> 
> That's why I still think you're comparing apples with pears. It's two different kinds of technology and you can't compare them just by a power curve. It's not that I think it's unfair as much as misleading, actually.


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## Qer (May 7, 2008)

etischer said:


> Well, for the majority of EV converters, the goal is to eliminate their need for gas, and maintenance.


For that any of the motors will probably be quite sufficient provided the car isn't extremely heavy.



etischer said:


> Including a dyno chart for an unsustainable overload condition would be misleading.


Well, if you keep the throttle floored for more than 15 seconds with 1kA and the police sees you, I bet you might have other problems to worry about than if the motor can handle it... 



etischer said:


> In what ways does a DC motor surpass an AC motor. What other parameters should we be comparing?


Not surpass. Apples, pears, you know. Same same but different.

For the average EV'er I think price should be part of the graph, for the power freak a torque curve would be very nice as well.


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## major (Apr 4, 2008)

etischer said:


> What other parameters should we be comparing?


Mass, price, availability.

Then you could get into efficiency, power ratings, warranty, durability, service life and all sorts of crap like that.

But it is what it is. Just a chart showing some interesting colored lines. I like it. Sure, some of the curves are short changed. No one should use this alone to make a motor selection or buy decision.

Regards,

major


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## etischer (Jun 16, 2008)

I think the most interesting thing from the graph was the AC-55 hp curve. AC motors are known for having sustained high rpm power, but the AC-55 looks like one of the worst in the group.


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## Bowser330 (Jun 15, 2008)

etischer said:


> I think the most interesting thing from the graph was the AC-55 hp curve. AC motors are known for having sustained high rpm power, but the AC-55 looks like one of the worst in the group.


I knew your screen name was familiar...you have that thread about making your own AC controller/inverter for the Siemens motor...

http://www.diyelectriccar.com/forums/showthread.php/home-built-ac-drive-ford-siemens-27893p15.html

So what kind of range are you getting out of your pack?


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## Tesseract (Sep 27, 2008)

etischer said:


> I think the most interesting thing from the graph was the AC-55 hp curve. AC motors are known for having sustained high rpm power, but the AC-55 looks like one of the worst in the group.


Is that the motor's fault? The inverter's? The battery pack's? Who knows for sure - not enough data.

This is an example of where, in contrast to your stated position earlier, incomplete data is actually _worse_ than no data at all, because one might conclude that the motor is crap (which it may very well be) when it could be the controller and/or battery pack limiting its power output.

Also, you just can't say AC motors are "better" than DC motors at delivering pure hp (title of the thread, remember - how long each motor lasts in a given application is irrelevant for this discussion). Each motor type has its own particular strengths and weaknesses, but when each is considered along with the necessary power conversion stage (inverter or converter, that is), there is not much difference in total power capability and efficiency. For example, everyone "knows" that AC induction motors are more efficient than series DC motors, but just because WarP motors, specifically, are nominally 85% efficienct doesn't mean that that's the *best* efficiency possible. If you are willing to sacrifice a lighter weight in either type of motor you can achieve nearly arbitrarily higher efficiency (though it is true that an AC induction motor will always be at least slightly more efficient than a similar size DC motor).

Correspondingly, the half-bridge inverter will always be less efficient than a buck converter. You can throw more silicon at both to lower the total inefficiency, but the inverter will always put two switches in series on any given phase leg.

Series DC motors generate torque in proportion to current right up until the point of destruction while AC induction motors stall at a certain torque (breakdown torque) regardless of how much current you force through each phase leg. Conversely, AC motors can deliver the same rated torque at as high an RPM as the rotor can withstand as long as the volts are proportional to the frequency (the DC motor's commutator will flashover, aka - zorch, at some point).

Apples and... um... _pears_ as Qer said


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## etischer (Jun 16, 2008)

Bowser330 said:


> I knew your screen name was familiar...you have that thread about making your own AC controller/inverter for the Siemens motor...
> 
> http://www.diyelectriccar.com/forums/showthread.php/home-built-ac-drive-ford-siemens-27893p15.html
> 
> So what kind of range are you getting out of your pack?


My typical commute is 21 miles, most of it is at 60mph, and I have a 6-8% grade to go up and over (sunol grade) which I maintain 60 mph on. My pack (25 batteries) starts at 328 and ends at 314-312 depending which direction I'm headed. 

So after 21 miles, I'm at 12.52v per battery
After 25 miles, I'm at 12.32v per battery (done this once)

That is the deepest Ive discharged. Having regen is really nice! It is about a 2 mile climb up the Sunol grade, and I can regen about 3 miles down the other side. At 200 amps (280 is max) I can maintain 63mph in 3rd gear up the 6% grade. I definitely feel like I have plenty of power.


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## Bowser330 (Jun 15, 2008)

I guess I was looking for an overall range estimate... I am not too good with understanding what it means to have voltage drop and what 200A going 63mph means...

so basically if you had 200AH batteries, if you are cruising at 63mph and it takes 200A to hold that speed (lets ignore the grade for now), you have a 63 mile range (@63MPH)

What AH batteries do you have?


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## etischer (Jun 16, 2008)

Range assuming 80% dod would be 35 miles.

At 60mph Im pulling 60A, about 320 whr/mile. 

Battery is 55Ah @ 312v


You will only get about 100Ah from a 200Ah battery due to Peukerts effect if you are pulling 200A




Bowser330 said:


> I guess I was looking for an overall range estimate... I am not too good with understanding what it means to have voltage drop and what 200A going 63mph means...
> 
> so basically if you had 200AH batteries, if you are cruising at 63mph and it takes 200A to hold that speed (lets ignore the grade for now), you have a 63 mile range (@63MPH)
> 
> What AH batteries do you have?


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## Bowser330 (Jun 15, 2008)

etischer said:


> Range assuming 80% dod would be 35 miles.
> 
> At 60mph Im pulling 60A, about 320 whr/mile.
> 
> ...


I see, thank you for the information.

Only 60A @ 60mph, thats pretty good...

I wonder If a similar voltage DC system could pull that off...hmm...??


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## Qer (May 7, 2008)

Bowser330 said:


> I wonder If a similar voltage DC system could pull that off...hmm...??


This is where all this goes totally confusing again. What you WANT to look at for range estimation is not Ampere or Ah, because what's propelling the car is kW. No matter motor, controller or even battery you will need a certain amount of kW and the amount of kW you need will depend on, for example, drag. So let's say you need 10 kW mechanical speed at the tires to maintain a certain speed and that every step in the chain (transmission, motor, controller) is 90% (I'm obviously just pulling numbers out of a hat here ) then you need 10/(.9*3) = a little less than 14 kW out of the pack. If you want to maintain this speed for 30 minutes you obviously have to be able to pull 7 kWh from the pack. Let's say we end up with 14 kWh after compensating for Peukert.

Now, P=U*I is the standard formula here and by multiplying both sides with time, you get P*t=U*I*t, ie the amount of Ah you need for a certain Wh and pack voltage. If you have a pack voltage of 300 Volt (which seems pretty normal for AC-systems) you get a little less than 50 Ah and if you have a pack voltage of 120 Volt (more normal for DC-systems) you get just about 120 Ah. So even if the low current or lesser Ah might look impressive from a DC-perspective, you must keep in mind that even if you need smaller, lighter, batteries you will end up with at least twice the amount and in the end you'll end up with roughly the same amount of kilos and volume of your pack.

In both cases you have the same amount of energy stored and in both cases you will pull more or less the same amount of energy from the batteries to maintain speed. What can vary the result is things like the shape of the car (much), tire friction (also much, for example too low pressure increases friction a lot), transmission (not a clue ), motor efficiency (AC is a bit better than DC here), controller efficiency (the opposite, DC is better here), batteries (here choosing Lithium will make a huge difference compared to lead-acid) and, of course, regenerative braking (although that depends on where and how you drive).

Ampere, or Ah, can't really be compared unless you compare two systems with the same pack voltage because then Wh and Ah will be proportionally the same since V is a constant.


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## Drew (Jul 26, 2009)

Qer said:


> This is where all this goes totally confusing again. What you WANT to look at for range estimation is not Ampere or Ah, because what's propelling the car is kW. No matter motor, controller or even battery you will need a certain amount of kW and the amount of kW you need will depend on, for example, drag. So let's say you need 10 kW mechanical speed at the tires to maintain a certain speed and that every step in the chain (transmission, motor, controller) is 90% (I'm obviously just pulling numbers out of a hat here ) then you need 10/(.9*3) = a little less than 14 kW out of the pack. If you want to maintain this speed for 30 minutes you obviously have to be able to pull 7 kWh from the pack. Let's say we end up with 14 kWh after compensating for Peukert.
> 
> Now, P=U*I is the standard formula here and by multiplying both sides with time, you get P*t=U*I*t, ie the amount of Ah you need for a certain Wh and pack voltage. If you have a pack voltage of 300 Volt (which seems pretty normal for AC-systems) you get a little less than 50 Ah and if you have a pack voltage of 120 Volt (more normal for DC-systems) you get just about 120 Ah. So even if the low current or lesser Ah might look impressive from a DC-perspective, you must keep in mind that even if you need smaller, lighter, batteries you will end up with at least twice the amount and in the end you'll end up with roughly the same amount of kilos and volume of your pack.
> 
> ...



This is interesting to me because this is a little more up my alley.

As far as power consumption at speed go you've got three factors, one is drag, the second is rolling resistance and the third is grade.

Drag is defined by 1/2 Rho V^3 x A x Cd

Rolling resistance is Crr x Vehicle Mass x Speed

and grade power is just a modification of MgH where you substitute the vertical component of the vehicles velocity to get additional power consumption; MgVSinA where A is the angle of the grade in degrees.

Of course this is all in SI units, so you'll have to sub in additional conversion factors if you want to use horse power, pounds whatever.


On the point of system efficiency, one of the reasons I was a fan of AC in the first place is because I wouldn't have to have a gearbox which would mean an additional 5-10% efficiency over a manual gearbox straight off.

Another important consideration is the use of front wheel drive gearboxes wherever possible, a front wheel drive uses only parallel shafts which means that the drive doesn't turn corners, whereas a front engine rear drive type layout costs you something in the order of 20-30% to turn the 90 degrees at the rear axle because of the hypoid drive in the diff.


----------



## Qer (May 7, 2008)

Drew said:


> Of course this is all in SI units, so you'll have to sub in additional conversion factors if you want to use horse power, pounds whatever.


I live in Europe, I like SI-units. They make much more sense. 



Drew said:


> On the point of system efficiency, one of the reasons I was a fan of AC in the first place is because I wouldn't have to have a gearbox which would mean an additional 5-10% efficiency over a manual gearbox straight off.


Um, as far as I've understood you'd still need SOME kind of gear box, wouldn't you? Either by getting a diff that's just right or adding a fixed gearing to get those 12000 rpm down to something more useful.

What's the usual RPM out from a normal gear box when you go at, say, 90 km/h (55 mph)?



Drew said:


> Another important consideration is the use of front wheel drive gearboxes wherever possible, a front wheel drive uses only parallel shafts which means that the drive doesn't turn corners, whereas a front engine rear drive type layout costs you something in the order of 20-30% to turn the 90 degrees at the rear axle because of the hypoid drive in the diff.


20-30%?? You're sure? That sounds like an awful lot to me.

No, not a mechanics, I just find it hard to believe losses at that magnitude just in the diff. Wouldn't that mean it'd be burning hot after a good, long drive on the highway?


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## Tesseract (Sep 27, 2008)

Drew said:


> ...whereas a front engine rear drive type layout costs you something in the order of 20-30% to turn the 90 degrees at the rear axle because of the hypoid drive in the diff.


This seemed obscenely high to me, so I did a little research. It seems hypoid gear differentials are 92-96% efficient (spiral bevel just a tad more but can handle less torque for a given size gearset). Here's one site that did a good job making it clear to me:

http://www.zakgear.com/Hypoid_worm.html


This did lead me to wonder one other thing, though... if the AC hypoid would be _even more efficient_ than the DC hypoid???


----------



## Drew (Jul 26, 2009)

Qer said:


> I live in Europe, I like SI-units. They make much more sense.
> 
> 
> 
> ...


I'm a big fan of SI units myself, I always remember doing basic tractive effort calcs the number of conversion factors that creep in on FPS making it a bit nonsensical, but that might just be me.

As I said in my original post, if you can integrate as many gearing components as possible and eliminate components in the gear train then you gain efficiency, I standard layout manual gearbox transfers drive off the main shaft to a layshaft and then back, direct driving only through 4th gear. You then transfer drive through to a differential gearset which represents another loss, if you can do this in two junps rather than the three then this represents a few percent improvement in total drive. You can only really do that if you can go with one ratio.

With my system I'm actually looking at a double reduction belt drive to reduce maintenance, this system will cost me a little bit in drive efficiency but I'll make it up by not having to touch the thing for a year at a time 

Based on my fairytale engine I am expecting two jumps of approx 2.55 to one giving me a two step system, as opposed to the previous manual example where the drive goes from input to layshaft, then layshaft to main shaft, then through the diff which is three jumps, all of higher ratio and therefore higher loss.



Tesseract said:


> This seemed obscenely high to me, so I did a little research. It seems hypoid gear differentials are 92-96% efficient (spiral bevel just a tad more but can handle less torque for a given size gearset). Here's one site that did a good job making it clear to me:
> 
> http://www.zakgear.com/Hypoid_worm.html
> 
> ...


The numbers in that article don't seem quite right to me. 

A standard gearbox assembly would achieve something like 96-98% effiency, a bevel drive is generally not that efficient because of the losses to bending moment in the two shafts which are only supported on one side.

Hypoid gears are especially susceptible to offset effects and the efficiency is hurt badly by the sliding friction component of the gear motion. To address your efficincy concerns a car cruising at highway speed might use 10kW, which means, most likely the differential is absorbing something like 5kW which it can easily disipate into underbody airflow via the cooling fins on the diff housing. When used more intensively the differential would tend to absorb a lot more power, which leads to diff failure and in high duty cars the installation of differential oil coolers or larger than required differentials.

On top of that, in the example they've used they've increased the crown wheel diameter and reduced the hypoid offset, which would tend to reduce losses further due to lower total transmitted thrust load.

Car manufacturers generally use spiral bevel gears for diffs these days except in rear wheel drive cars, this is because the pinion offset allows the driveshaft to be lower in the car relative to the diff center which increases underbody space, at a mild fuel ecconomy cost.

To use a real life example from Australia there are many available dyno charts for commadores which have a flywheel output of approx 150kW from '96 to '08 (for v6) and a rear wheel output of approx 100kW. This should be easily searchable for you if you want to confirm it. The manual gearbox will absorb the aforementioned 2-4% and the diff soaks up the rest.


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## major (Apr 4, 2008)

Drew said:


> A standard gearbox assembly would achieve something like 96-98% effiency,


Hey Drew,

Got myself into an argument with a friend about gear efficiency. Not saying which side I'm taking, but can you provide a good link or two supporting your statement? And possibly give your opinion or reference concerning say a 2 to 1 planetary vs helical spur mesh? 

I guess it is relative to this thread because many of the AC systems run much faster and require an extra gear.

Thanks,

major


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## Drew (Jul 26, 2009)

Unfortunately most of what i've just posted comes from memory.

I'll have to get somebody to help me dig out some of my reference books tomorrow as I'm somewhat immobile after breaking my leg recently in a motorbike accident.

As for planetary vs helical gear sets, I'm not sure about the efficiency side of things as I haven't had a lot to do with planetary gear systems, but i would have assumed that because there are more gears in the system that there would be greater losses. That being said the main benefits of planetary gear sets are that you can keep drive in line as per an automatic gearbox and that you can run system ratios greater than approximately 3:1 over one set. Planetary gear drives are especially useful in applications like high torque gear heads for power drills and the like because of these two factors exactly.


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## major (Apr 4, 2008)

etischer said:


> I think the most interesting thing from the graph was the AC-55 hp curve. AC motors are known for having sustained high rpm power, but the AC-55 looks like one of the worst in the group.





Tesseract said:


> Is that the motor's fault?


Fault? Not really an applicable term, in my opinion. Looks to me like it was a motor designed for a base frequency of 67 Hz at that voltage and is performing as expected. It is not a whole lot different than taking a standard NEMA 256, 60 Hz motor and plotting it against your hot EV motors.


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## etischer (Jun 16, 2008)

major said:


> Fault? Not really an applicable term, in my opinion. Looks to me like it was a motor designed for a base frequency of 67 Hz at that voltage and is performing as expected. It is not a whole lot different than taking a standard NEMA 256, 60 Hz motor and plotting it against your hot EV motors.


The system should be constant horsepower above base speed, the power seems to drop off much faster than that on the AC55.


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## major (Apr 4, 2008)

etischer said:


> The system should be constant horsepower above base speed, the power seems to drop off much faster than that on the AC55.


Hey etischer,

I do not see any "constant hp" regions for any of the plotted motors. Do you? And, as I mentioned, you short change some of the motors when you plot. For instance, you show zero power at 6000 RPM for the AC55. Where did that come from? And you show the curve for the Warp9 72V with a 350 amp limit. Who would use that set-up? Even a Curtis would get 500 amps. Just because the published curves don't show performance points all the out does not mean they go to zero.

I guess you draw this curve up to compare what is available in motors. Fine. But remember, those motors were designed for specific applications for OE customers years ago and for the most part, never meant to go on the market as commodities. Like your motor, by Siemens for Ford, for the Ranger, with a certain gear. And the AC55 appears to have been designed for a peak power at 2000 or 2100 RPM for its intended application. And at 2000 RPM, it beats the Siemens motor by 50 percent on power. 

My point is that because a particular motor is different, it is not a fault, it is just different. If you don't like it, don't use it. 

Regards,

major


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## etischer (Jun 16, 2008)

Im taking data directly from the manufacturers published specifications. The manufacuters data is blank above 5000 rpm; what horsepower value would you suggest I use? 

http://etischer.com/awdev/compare/AC55_DMOC445ProductSheet.pdf

Typically AC motors are constant torque to base speed (typically 1750rpm), and constant horsepower from base speed to max speed (typically 3500 rpm). The constant horsepower range for the siemens motor is 3000-13000 rpm. 

Siemens motor looses 50% power over 10,000 rpm range. 

The AC55 looses 50% power over 1,500 rpm range. 

That is the huge difference I am talking about, power from an AC motor should not drop off so rapidly. I suspect there is some room for improvement in the motor tuning. 

I'm doing my best to compare fairly. If you have data for a motor I'm happy to add it to the comparison. As for the Warp 9 data, the reason I'm using 350A is because that was what the manufacturer published the data for. For what it is worth I also included the motor data for Warp 9 at 144v

http://etischer.com/awdev/compare/003_15_WarP_9_Graph.jpg





major said:


> Hey etischer,
> 
> I do not see any "constant hp" regions for any of the plotted motors. Do you? And, as I mentioned, you short change some of the motors when you plot. For instance, you show zero power at 6000 RPM for the AC55. Where did that come from? And you show the curve for the Warp9 72V with a 350 amp limit. Who would use that set-up? Even a Curtis would get 500 amps. Just because the published curves don't show performance points all the out does not mean they go to zero.
> 
> ...


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## Overlander23 (Jun 15, 2009)

etischer said:


> Im taking data directly from the manufacturers published specifications. The manufacuters data is blank above 5000 rpm; what horsepower value would you suggest I use?
> http://etischer.com/awdev/compare/003_15_WarP_9_Graph.jpg


Maybe leave it blank. The Azure's datasheet indicates that the mechanical rpm limit is 8000 rpm, so clearly it's doing some work at that speed. Assuming anything above 5000rpm is producing zero hp is misleading, IMO... moreso than just leaving the graph blank after a certain point.

Regardless, even if you were to look at the trend from Azure's graph, the values start to go shallow... while the rating at 4000 rpm is about 25kW and the rating at 5000rpm is 18kW, the trend would indicate that at 6000 you'd be at around 15kW, etc...

To me the motors look different from an overall power standpoint, but mainly they look like they're designed for different efficiency ranges (kind of what Major was saying). In other words, the AC-55 is designed for gear ratios of 3-5:1 (as stated in their documentation), but the Siemens is designed for something higher (about 1.75x higher given the difference in peak power points.)

Just as a design point, Azure indicates the AC-55 is supposed to connect directly to a differential (via prop shaft, for instance) doing away with an intermediate gearbox. 

A 27" diameter tire (close to stock diameter on a Ford Ranger) rotates at about 125 rpm per 10mph, or 750rpm @ 60mph. A MY2000 Ford Ranger also has 3.73:1 rear diff ratio, for example. So at 60 mph the AC-55 will be spinning at around 2800rpm. Or, peak kW (2000 rpm) would occur at about 42mph with that gearing setup.

The Siemens motor, on the other hand, will be under-geared unless the rear diff ratio is higher, or another reduction method is employed (such as the manual transmission on your conversion or the optional single ratio box for the motor).

Keep in mind this is all in regards to a truck's 27" diameter tire, not a much small passenger car's tire (which would obviously increase the overall ratio).

The Siemens still rates higher on the power scale, but some of that power advantage might be negated a little by the need for additional gearing.

I guess what I'm saying is that I don't think the two motors are vastly different in capability, but very different in intended design implementation. Though it would appear the Siemens does have a bit of an edge.


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## major (Apr 4, 2008)

etischer said:


> The constant horsepower range for the siemens motor is 3000-13000 rpm.
> 
> Siemens motor looses 50% power over 10,000 rpm range.


Hey etischer,

Your definition of constant must be different than mine 

Call it what you want.

major


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## major (Apr 4, 2008)

etischer said:


> Siemens motor looses 50% power over 10,000 rpm range.
> 
> The AC55 looses 50% power over 1,500 rpm range.
> 
> That is the huge difference I am talking about, power from an AC motor should not drop off so rapidly. I suspect there is some room for improvement in the motor tuning.


Hi etischer,

Tuning? Maybe, but I doubt it. I think the difference is in the way the motor is designed, especially the winding, ie. the volts to hertz ratio.

One could say there is a huge difference between the AC150 and the Siemens. Can you tune the Siemens up to the AC150?

Mr. Overlander23,

Thanks for elaborating.

Regards,

major


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## tomofreno (Mar 3, 2009)

An example of of this sort (design for max power at different rpm) is the HPGC AC31 and AC50 motors. The AC31 came first, with the "flat" part of the torque-speed curve out to about 1800 rpm and max power at about 1900 rpm. Presumably designed primarily for golf cars and lower speed industrial vehicles. 

I sent HPGC a graph of available and required wheel torque for a Suzuki Swift with this motor to show acceleration would drop off precipitously above about 50 mph up a freeway on ramp. They responded they were working on a new motor which would extend the flat part of the curve to higher rpm. They recently came out with the AC50 which extends the flat part of the curve out to 3000 rpm, resulting in max power at about 3200 rpm. This gives much better available torque and power at higher vehicle speeds for a Swift - similar to an 8" series DC motor with 500A controller. It has a bit lower torque at lower rpm than the AC31 (90 versus 99 lb-ft). They explained they gave up some torque at lower rpm to get higher running (higher rpm) torque and power. The two motors are both 8.5" diameter and the AC50 is about 1.5" longer.

So I also think that the Siemens and AC55 were just designed for different applications somewhat like the above example, and there is nothing you could do to make the AC55 run more like the Siemens other than redesign the windings. Which one is "better" than the other depends on your application.

Tom


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## etischer (Jun 16, 2008)

I agree, I'll make the last point blank instead of zero =)

And I also agree, the Azure motor is probably better suited to a lower gear ratio. 



Overlander23 said:


> Maybe leave it blank. The Azure's datasheet indicates that the mechanical rpm limit is 8000 rpm, so clearly it's doing some work at that speed. Assuming anything above 5000rpm is producing zero hp is misleading, IMO... moreso than just leaving the graph blank after a certain point.
> 
> 
> I guess what I'm saying is that I don't think the two motors are vastly different in capability, but very different in intended design implementation. Though it would appear the Siemens does have a bit of an edge.


I think Siemens did their homework and designed a motor from the ground up. It puts out more power across a wider rpm range and has 4x the area under the curve compared to the AC55. 

I think Azure just took an off the shelf motor and made some modifications to it, hence the 1750 rpm base speed.


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## etischer (Jun 16, 2008)

Above base speed is the constant horsepower range. I didn't make the name up, this is what it is called.

If you go to 13,0000 rpm, I agree it doesn't look very constant. But the drop off is 600% better than the AC-55. 





major said:


> Hey etischer,
> Hey etischer,
> 
> Your definition of constant must be different than mine
> ...


----------



## etischer (Jun 16, 2008)

There is a big difference. To me the AC150 is clearly the best motor. 

But, one cannot ignore the fact that the AC55 has twice the power at 1800 rpm, so depending on whats best for you, the AC55 might be a better choice. =)


If you ran the siemens motor at 460v you might get a similar looking curve to the AC-150. That would push the torque peak out to about 7000 rpm. 
It just requires more batteries. When I switch to lithium, I plan to run higher voltage than I am now to push the curve out. 





major said:


> Hi etischer,
> 
> Tuning? Maybe, but I doubt it. I think the difference is in the way the motor is designed, especially the winding, ie. the volts to hertz ratio.
> 
> ...


----------



## major (Apr 4, 2008)

etischer said:


> If you ran the siemens motor at 460v you might get a similar looking curve to the AC-150.


And what if you ran the AC55 at 460v? Then it would look pretty good against the Siemens.

I think we're finally getting to the point where we can agree that these are all different motors designed for different applications. And you can take any one of them and vary the voltage, or gear ratio, or current limit and have them behave differently in a particular application.

So your comparison curve, while interesting, does not represent the full capabilities of the motors. Nor does it indicate any time base; that is how long it can deliver how much power. 

Regards,

major


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## major (Apr 4, 2008)

etischer said:


> Above base speed is the constant horsepower range. I didn't make the name up, this is what it is called.


Hey etischer,

Yeah, _constant hp range_ has bugged me for years. This is where I think it came from. VFDs were being applied to industrial motors. Say a 10 hp, 1750 RPM, TENV motor. The user then could run the motor up to 120 Hz or 3500 RPM (early drives had lower frequency limits). And of course he could run it slower. And the user could run these conditions for extended periods. So to keep the motor from overheating, he had to limit it to 10 hp output above base speed. Hence the _constant power region_ above base speed. And similarly, below base, he had to maintain current, so was told it was a _constant torque_ _region_. The terminology applies to ratings.

This logic falls apart when you start looking at peak power output for these motors.

Regards,

major


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## etischer (Jun 16, 2008)

Yup, it would. The base speed is still half what base speed is on the siemens though. I think for EV's, a flat hp curve is better than one that has a sharp peak. 


In the constant horsepower range, it is probably constant horsepower because the inverter is not capable of outputting more current, and motor is not capable of shedding the increased heat. 

The graph shows the max power the motor is rated for, they are all on a level playing field. You can double the current limit on one motor to make it look better, but then you could double them all. To compare motors, you need to have a level playing field, I'm happy to implement suggestions on how to make it more level. 



major said:


> And what if you ran the AC55 at 460v? Then it would look pretty good against the Siemens.
> 
> I think we're finally getting to the point where we can agree that these are all different motors designed for different applications. And you can take any one of them and vary the voltage, or gear ratio, or current limit and have them behave differently in a particular application.
> 
> ...


----------



## etischer (Jun 16, 2008)




----------



## major (Apr 4, 2008)

etischer said:


> The graph shows the max power the motor is rated for, they are all on a level playing field.


Hey etischer,

I don't think this is true. Most of the source curves do not give any indication of "rating". Your comparison plot is not a level playing field.



> You can double the current limit on one motor to make it look better, but then you could double them all.


If your controller is already pressing the AC motor to its limits on torque, which I think is the case with the 3 AC machines you show, doubling the current limit isn't going to get you anymore.



> To compare motors, you need to have a level playing field,


Agreed. That is what I, and others, have been telling you. But I have no way to supply you "level playing field" data. And neither does anyone else, which I know about.

I thank you for attempting the comparison and the discussion. But it will always take more than a simple chart to make an intelligent decision when it comes to choosing the right motor for a particular application.

Regards,

major


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## Tesseract (Sep 27, 2008)

etischer said:


> ...
> The graph shows the max power the motor is rated for, they are all on a level playing field. You can double the current limit on one motor to make it look better, but then you could double them all....


Sorry, no... perhaps I need to remind you of what I previously wrote:



tesseract said:


> Series DC motors generate torque in proportion to current right up until the point of destruction while* AC induction motors stall at a certain torque (breakdown torque) regardless of how much current you force through each phase leg.* ...


Sooo.... where's that level playing field?


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## etischer (Jun 16, 2008)

Give me data and I will happily add it to the comparison. I cannot add what I do not have. 

My inverter is rated 300A, I cannot double the current limit, I can only increase the voltage which would effectively increase torque by pushing the torque peak further out. 



major said:


> Hey etischer,
> 
> I don't think this is true. Most of the source curves do not give any indication of "rating". Your comparison plot is not a level playing field.
> 
> ...


----------



## etischer (Jun 16, 2008)

Quote:
Originally Posted by *tesseract* 
_Series DC motors generate torque in proportion to current right up until the point of destruction while* AC induction motors stall at a certain torque (breakdown torque) regardless of how much current you force through each phase leg.* ..._

Sooo.... where's that level playing field? 

Pushing a motor to 99% of it's destruction limit is not going to make for a reliable ev, and I wouldn't design a car that pushed the motor to that limit unless it was a drag vehicle. 

I want the comparison to display realistic and reliable power data. Data someone could use to design their ev, and not worry about melting or over heating. 

I have never had my AC motor stall, this only happens in v/hz mode, not vector control.


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## etischer (Jun 16, 2008)

Why is everyone so defensive? I'm doing my best to display accurate information, and asking for your help to make improvements. What would you do differently?


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## Tesseract (Sep 27, 2008)

etischer said:


> Give me data and I will happily add it to the comparison. I cannot add what I do not have.


Here's a data point for you:

http://www.diyelectriccar.com/forums/showpost.php?p=129116&postcount=228

Warp 9 at 2000 rpm. The rest of the information is embedded in the graph. 




etischer said:


> My inverter is rated 300A, I cannot double the current limit, I can only increase the voltage which would effectively increase torque by pushing the torque peak further out.


No, that doesn't _effectively increase torque_; it effectively increases _power_, but upping the voltage will not affect torque. It will allow you to keep the same torque rating up to a higher RPM, but higher frequencies do cause higher losses in the magnetic materials used to construct both rotor and stator, so there is a point of diminishing returns.

In contast, the field and armature currents oppose each other in the commutated DC machine so the behavior of the magnetic structure is very nearly irrelevant (only ohmic losses and shaft torsional strength stand in the way of higher torque).

Not saying one machine is better than the other - they both have their places - but there is a good reason the series DC motor is also called a _traction_ motor, you know...


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## etischer (Jun 16, 2008)

how does "motor effect" from 204-220 seconds "running time" translate? I can put a dot at 100kw 2000 rpm. Stable current is easy when the load and RPM doesn't change. 

I need hp vs rpm data. 

Again, is 1000A sustainable for a daily driver EV? At 50% soc, will you still be able to pull 1000A? 








Tesseract said:


> Here's a data point for you:
> 
> http://www.diyelectriccar.com/forums/showpost.php?p=129116&postcount=228
> 
> ...


----------



## Tesseract (Sep 27, 2008)

etischer said:


> Pushing a motor to 99% of it's destruction limit is not going to make for a reliable ev, and I wouldn't design a car that pushed the motor to that limit unless it was a drag vehicle.


Sorry, thought this thread's title was *Pure horse power DC vs AC*.




etischer said:


> I want the comparison to display realistic and reliable power data. Data someone could use to design their ev, and not worry about melting or over heating.


But you said in a previous post you were basing your graph on the _peak power_ each motor was capable of delivering? Peak implies "not continuous" which means there must be a time limit involved. One does not drive at a constant speed on a constant slope with constant wind at all times, so as long as the motor/controller in question can deliver 20kW continuously it will probably be able to propel any EV down the highway at reasonable slopes and into reasonable headwinds at 65-75mph. It's peak power, though, that determines how well it will accelerate both from a stop and when passing. That is important to most drivers too.




etischer said:


> I have never had my AC motor stall, this only happens in v/hz mode, not vector control.


Hmmm... so what is happening when you accelerate from a complete stop? It's true that an inadequate sized V/Hz mode controller will not be able to get the motor spinning, while a vector mode controller will (albeit slowly), but you most certainly can stall a vector mode controller if the torque required to accelerate the load exceeds the breakdown torque rating of the motor (which depends on the rotor skew and resistance as well as the controller amp limit).

And we aren't getting defensive, just exasperated.


----------



## Tesseract (Sep 27, 2008)

etischer said:


> how does "motor effect" from 204-220 seconds "running time" translate?
> 
> I need hp vs rpm data.


I told you the RPM... the dyno is holding the motor at 2000 rpm during the 1000A part of the run. the legend states that Motor Effect is in kW... 1kW = 1.34hp, you know. So, the controller is delivering ~100kw (105kw, actually) to the motor for approximately 11 seconds. The dyno recorded, IIRC, 88kW of shaft output (~84% efficient).




etischer said:


> Again, is 1000A sustainable for a daily driver EV?


It's not sustainable, no, but it is repeatable. Again, I remind you of the thread's title. Indeed, of the subforum's title! EV _Performance!_ Take that hypermiling crap over to ecomodder 




etischer said:


> At 50% soc, will you still be able to pull 1000A?Can you still pull 1000A from your battery pack at 50% SOC?


Dunno - that depends on your battery pack, now doesn't it?


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## Bowser330 (Jun 15, 2008)

etischer said:


> Range assuming 80% dod would be 35 miles.
> 
> At 60mph Im pulling 60A, about 320 whr/mile.
> 
> ...


80% DOD range 35 miles

Sustaining 60mph takes 18.7kw

Those seem like pretty DC capable performance statistics to me...

OH! No...wait wait...the DC requires a transmission shift or two....oh well then... DC is just the worst!


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## Qer (May 7, 2008)

etischer said:


> What would you do differently?


Not trying to compare apples with _oranges_? Your graph is simply misinformative.


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## etischer (Jun 16, 2008)

Hey, I was just answering the question. Yes, DC can do the same I'm sure. 



Bowser330 said:


> 80% DOD range 35 miles
> 
> Sustaining 60mph takes 18.7kw
> 
> ...


----------



## etischer (Jun 16, 2008)

How am I supposed to plot hp vs rpm if you only give me one point? It can sustain for atleast 16 seconds. 



Tesseract said:


> I told you the RPM... the dyno is holding the motor at 2000 rpm during the 1000A part of the run. the legend states that Motor Effect is in kW... 1kW = 1.34hp, you know. So, the controller is delivering ~100kw (105kw, actually) to the motor for approximately 11 seconds. The dyno recorded, IIRC, 88kW of shaft output (~84% efficient).
> 
> 
> 
> ...


----------



## etischer (Jun 16, 2008)

V/Hz controller is not feasible for an EV. Nobody (execpt for me messing around initially) is doing that. 

I want my comparison to give people a good feel for how fast a car will accelerate using different motors. Using an instantanious peak value is not representative, area under the curve is the best aproximation. 



Tesseract said:


> Sorry, thought this thread's title was *Pure horse power DC vs AC*.
> 
> 
> 
> ...


----------



## tomofreno (Mar 3, 2009)

> I have no way to supply you "level playing field" data. And neither does anyone else, which I know about... it will always take more than a simple chart to make an intelligent decision when it comes to choosing the right motor for a particular application.


 So what data would you examine to make such a determination? First, all would have to agree on what performance is desired for the ev. I'm not certain what eischer meant by "an average ev." I would say the ev should be able to drive at posted freeway speed limits, including on hills up to 6% grade, and keep pace with traffic accelerating up freeway on-ramps, but that likely isn't the present average ev, nor is it what everyone desires. 

Vehicle acceleration depends on difference in required wheel torque and wheel torque available from the motor at the rpm range you want to accelerate over. So it depends on vehicle overall gear ratios and available shaft power over the operating rpm range - presumably with no limitation due to motor overheating with most off-the-shelf controllers as the time period is short ("time base" consideration). I think all would agree you can't really compare just motors, you have to compare motor/controller combinations. 

Maximum cruising speed on the highway will depend on motor constant power rating and vehicle gear ratios. It seems then for such a vehicle constant and peak shaft power would be important. Starting torque also, but it's not a drag racer.

I don't know if this is what eischer had in mind or not. Just threw it out to see if it helps focus the discussion. I made a spreadsheet to do this kind of comparison, specifiying the usual data for different vehicles such as mass, drag coefficient, gear ratios...and compared different motor/controller combinations in different vehicles. As all here seem to be saying, which motor/controller combination approaches the above performance for a given vehicle depends on those input parameters.


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## etischer (Jun 16, 2008)

I agree with your definition of "average ev". It should atleast be able to maintain 65mph on the freeway including 6% grade. 

I think the problem is EV performace depends so much on how hard you are willing to push the current limits. 

Manufactureres are not willing to endorse abusive current limits on their motors, and as such publish rediculously low numbers to limit their warranty liablity. 

I think the most typical yardstick for measuring vehicle performace is 0-60mph. Almost none of the cars in the garage, or evalbum post a 0-60 time though.


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## Bowser330 (Jun 15, 2008)

etischer said:


> I agree with your definition of "average ev". It should atleast be able to maintain 65mph on the freeway including 6% grade.
> 
> I think the problem is EV performace depends so much on how hard you are willing to push the current limits.
> 
> ...


I would say for the average driver, 0-60 performance could be used as a standard.

Also, I would like to clear up some comments that have been made in this thread that I feel are as misleading as that kw/rpm graph...

(1) Of the hundreds upon thousands of DIY DC EVs I have only heard of a few that have had any motors melting or what not.
(2) Those same hundreds upon thousands of people are commuting daily with their EVs going 65mph+ without any issues, besides having the extra AHs they wish they had (price prohibitive)
(3) 1000A for few seconds is not going to melt a DC motor, it wont even significantly shorten its overall life...


About 0-60mph....Please start!

Have you measured your car yet?


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## etischer (Jun 16, 2008)

2001 VW Passat
Siemens/Ford AC motor
4200lbs including driver
0-60 is 16 seconds using only 2nd gear. 
top speed 98.6 mph (would go faster, but I backed off)
65mph on 6% grade uses 70% current limit.
I can also lay down two patches of rubber 15 feet long =)

I've tested 0-60 atleast 50 times over the last 4 months while charting feedback on my laptop.
Here is a typical 16 second plot, again using only 2nd gear. 
Estimated "at the wheel" horsepower was 83.5 hp, estimated battery power 105 hp. 











Magenta: DC Bus Voltage (0-400 VDC)

Red: Motor RPM x 20 (0-8000 RPM) 340 = 60mph

Blue: Motor current (0-400 Amps/Phase)

Lt. Blue: Torque demand 0-160% torque demand



how does that compare with a 90hp rated dc system?


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## Bowser330 (Jun 15, 2008)

etischer said:


> 2001 VW Passat
> Siemens/Ford AC motor
> 4200lbs including driver
> 0-60 is 16 seconds using only 2nd gear.
> ...


I want to start by saying I think trying to compare the characteristics to the letter would be impossible, due to the previously discussed reasons, however generally speaking, I think the following examples are of DC cars that perform in a very similar way....

http://plasmaboyracing.com/bluemeanie.php

168V ADC 9" + Zilla 1000A
2460lbs (w/o Driver?)
0-60 in 5.5 seconds
125mph, Top Speed.
25-30mile range, aggressively driven.

Note: Battery pack weighs 700lbs, if the capacity were doubled, it would have 50-60mile range...
0-60 time would increase but not significantly with the amount of low-end torque from the DC motor.

http://www.evalbum.com/736

156V ADC 9"+ Raptor 1200A
3420lbs (w/o driver?)
0-60 in 8 seconds
75mph in 3rd gear
46mile range to 65-70% DoD (20 miles of which were 65-70mph)
Owner Quote: "Car easly spins tires if I take off to fast."

http://www.evalbum.com/542

144V ADC 8" + Raptor 1200A (limited to 400A)
3260lbs (w/o driver?)
"0-40mph, better than stock civic" (stock civic does 0-60 in approx. 9sec)
72mph in 3rd gear.
45 mile range (@55mph)


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## etischer (Jun 16, 2008)

Plasma boy is using two motors though. Tesla does 0-60 in 4 seconds using only one motor. 

The civic wasn't tested 0-60 or 0-40, no numbers were provided.

I am impressed with the 928 though, 8 seconds is not easy. Looks like he has 4600 miles on it and looks like it has been reliable. It says 3rd gear tops out at 75, and 3rd gear is his highest gear. I can still beat him 0-90 using half the hp 







Bowser330 said:


> I want to start by saying I think trying to compare the characteristics to the letter would be impossible, due to the previously discussed reasons, however generally speaking, I think the following examples are of DC cars that perform in a very similar way....
> 
> http://plasmaboyracing.com/bluemeanie.php
> 
> ...


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## toddshotrods (Feb 10, 2009)

etischer said:


> Plasma boy is using two motors though...


That's not the White Zombie race car, it's another Datsun with:



> 9" series-wound by Advanced DC, model FB-4001


 


etischer said:


> ...Tesla does 0-60 in 4 seconds using only one motor... I can still beat him 0-90 using half the hp


You're whole argument seems to be an attempt to validate your own preference.


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## etischer (Jun 16, 2008)

toddshotrods said:


> You're whole argument seems to be an attempt to validate your own preference.


all in good fun  
Just proving my point that AC motors have a wider power band. I seem to be the only representative from the AC world.

And for comparing 0-60s, the tesla still wins. 

I am impressed with the two cars though. Impressive power from a small motor, and they appear to do so reliably.


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## toddshotrods (Feb 10, 2009)

I have no problem with good fun, and am a very competitive person, but I like to be fair in my arguments.

To prove your point you pit a $100K Tesla, with lithium batteries, against a DIY 72 Datsun with lead. Pit the Tesla against the Smoke Screen S10 if you want to have a reasonable debate.

I'm not ragging on Teslas - I love them, and would love to have one. I am making the same point everyone else here has - you compare apples to oranges and call it a reasonable process. If there is no data available for an apples to apples comparison the end result is invalid. That's like doing a study to find out whether Tylenol or Advil is more effective against a certain type of headache, but substituting aspirin for Advil because you couldn't find any at the pharmacy.


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## Qer (May 7, 2008)

etischer said:


> Just proving my point that AC motors have a wider power band.


Um. Considering electric motors start from 0 (in contrast to ICE's that always have an idle RPM as low end) the power band in an electric motor is infinite and the only thing that matters is different gearing to match top RPM.

AC motors usually have a higher top RPM than DC-motors, that's true, but that's just a part of the apples-oranges thing.

EDIT: Ok, miss in translation. Power band didn't mean what I thought it meant. Never the less, I still doubt that you generally can say that an AC-motor has a wider power band just like that since that, too, will be affected by the controller and battery pack as well.


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## Drew (Jul 26, 2009)

I think what etischer is getting at is what I was talking about in my first post, which is that you still need a gearbox with a DC motor, you don't with an AC because those motors seem to always have something approaching a constant power area of the output range, whereas DC simply has a point of peak power.


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## JRP3 (Mar 7, 2008)

That's not exactly true, some series DC motors have been used with no transmission, just the reduction the differential provides. It may not be the most efficient setup but as long as the current is within component parameters there should not be a problem.


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## Qer (May 7, 2008)

Drew said:


> I think what etischer is getting at is what I was talking about in my first post, which is that you still need a gearbox with a DC motor, you don't with an AC because those motors seem to always have something approaching a constant power area of the output range, whereas DC simply has a point of peak power.


Ok, let's repeat everything once more, because nothing is as fun as beating a dead horse in the summer evening.

First:
power = voltage * current
power out = power in - Losses
power = rpm * torque

With other words, if you pull, for example, 100 kW from the batteries you will get 100 kW minus losses out from the motor. Depending on your set up volts, ampere, rpms and Nm will be different, but in the end it will be the same power no matter what system you're running!

Second, take a look at these graphs:



etischer said:


>





Qer said:


>


What does these two graphs have in common? Constant current. The former is an AC system, the latter a DC system. Why do both have constant current? Because the controller limits the current to protect the silicon. Or at least I'm guessing that's what the AC system does (protecting the silicon that is), I know that's what the DC system does because I wrote the software.

Now, since torque is related to current (yes, even in an AC set up, it might come as a shock but it's true) it means that as long as the current limit is active you get a fixed torque but since power is torque times rpm your power current will ramp up to a certain point where current (and thus torque) can't be kept flat any longer.

In a high power system you will have to limit battery current too, at least unless you can afford those fancy A123-batteries, and that means that once battery current reaches it's upper limit power will be constant (yes, even in a DC-system).

Now, at a certain point the motors back-EMF (yes, even for AC-systems) will start to limit motor current so much that battery current, and thus power output from the battery pack will start to drop and, naturally, so will motor power.

Conclusion: You can't claim ANYTHING without comparing complete systems. Maximum power out will be defined by your pack voltage and maximum current you can draw from it, maximum torque will be defined by the maximum motor current (in a DC system that will be defined by controller, in an AC system apparently the motor will also be a limiting factor) and the only thing that's really defined by the motor is the proportions between rpm and torque and, of course, how long you can keep it up before the motor blows.

Neither can you say that you don't need a gear box in an AC system but you do in a DC system, because that depends entirely on the available power and torque. If the motor is strong enough you can skip the gear box, but if you have a, uh, let's be nice and call it a "budget system" you will need that gear box to keep up with traffic no matter what technology the controller and motor uses. It's not any different from that if you have a serious ICE, like a V8, you can easily skip every second gear and still get decent acceleration, but if you have one of these toy cars with a puny 1.4 litre I4 ICE's you'll have to use every single gear available to you to be able to keep up with traffic.

You CAN say that "This AC system beats this DC system" (or the opposite, of course), like the Tesla will beat the crap out of an ADC 9" with a Curtis 1231C and a pack of Trojan lead-acid, but claiming that "AC is better" is like saying that "Gas powered cars are faster than Diesel powered cars".

¿Comprende?

PS. For the record, the DC system in those graphs generates about 35% more power than the AC, system. Food for thought...?


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## Bowser330 (Jun 15, 2008)

etischer said:


> Plasma boy is using two motors though. Tesla does 0-60 in 4 seconds using only one motor.
> 
> The civic wasn't tested 0-60 or 0-40, no numbers were provided.
> 
> I am impressed with the 928 though, 8 seconds is not easy. Looks like he has 4600 miles on it and looks like it has been reliable. It says 3rd gear tops out at 75, and 3rd gear is his highest gear. I can still beat him 0-90 using half the hp


The blue meanie uses ONE DC 9" motor..and you are comparing that to the 100K$ Tesla *Roadster*? (Tesla is a company not a car, they also make the Tesla *Model-S*)

The civic owner did his own butt-dyno test and determined it felt quicker 0-40 than the stock civic. And I personally believe him based on the general torque profile of the DC motor.

The 928, 3rd gear is his highest gear because he took out the other gears, if he were to have kept them, he would have been able to go higher...Also I have a hard time believing that you would beat him 0-90 if he already has 8 seconds on you from 0-60... its really funny how you started the whole 0-60 comparison and now are jumping to 0-90....


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## etischer (Jun 16, 2008)

I think the DC graph is a bit confusing. The motor was ramped up, and held at a constant 2000 rpm, this is why the current is constant. 

My graph shows an AC motor with constant current across the range from zero speed to 7000 rpm. 

Current would typically drop off with RPM on a DC motor, but AC system as you can see, current is constant from 0 -7000 rpm. Again, AC has more area under the curve. 





Qer said:


> PS. For the record, the DC system in those graphs generates about 35% more power than the AC, system. Food for thought...?


 You're ignoring the entire quote, the civic owner states:
"Accelerates better than a stock Civvy from 0-40; pokier than stock from 40-72.


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## Bowser330 (Jun 15, 2008)

etischer said:


> The reason the DC curve is constant current is because the motor was held at a *constant 2000 rpm.*
> 
> Current would typically drop off with RPM on a DC motor, but AC system as you can see, current is constant from 0 -7000 rpm. Again, AC has more area under the curve.


The white zombie with Kostov-11" motor ran the 1/4 mile in 13.347 sec @ 95.86mph.

The moment when the car crossed the line the power meters read 250V & 620A...

Using the size of his tires and final drive...95.86mph = 6020rpm

250V x 620A = 155kw @ 6020 rpm

Don't forget to plot that....


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## etischer (Jun 16, 2008)

If his top speed is 75, I'll beat him to 90! Just pointing out an advantage of AC motors over DC motors. That's what were here for, to learn. I'm certainly learning more about DC characteristics.



Bowser330 said:


> The blue meanie uses ONE DC 9" motor..and you are comparing that to the 100K$ Tesla *Roadster*? (Tesla is a company not a car, they also make the Tesla *Model-S*)
> 
> The civic owner did his own butt-dyno test and determined it felt quicker 0-40 than the stock civic. And I personally believe him based on the general torque profile of the DC motor.
> 
> The 928, 3rd gear is his highest gear because he took out the other gears, if he were to have kept them, he would have been able to go higher...Also I have a hard time believing that you would beat him 0-90 if he already has 8 seconds on you from 0-60... its really funny how you started the whole 0-60 comparison and now are jumping to 0-90....


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## etischer (Jun 16, 2008)

How about I cut that in half since he is using 2 motors. 

250V x 310A at 6000 rpm. I can do that with my little AC system. 






Bowser330 said:


> The white zombie with Kostov-11" motor ran the 1/4 mile in 13.347 sec @ 95.86mph.
> 
> The moment when the car crossed the line the power meters read 250V & 620A...
> 
> ...


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## Qer (May 7, 2008)

etischer said:


> Current would typically drop off with RPM on a DC motor, but AC system as you can see, current is constant from 0 -7000 rpm. Again, AC has more area under the curve.


And again you're proving that you actually don't know what you're talking about. Current would typically drop off with RPM on a AC system as well, just not below 7000 RPM in this particular example. In this thread it has been shown numeral times that the back-EMF in a DC motor isn't as bad as you preach and that with a big enough pack you can pull full current pretty high up in the RPM's. For example, that typical graph from the White Zombie shows a dropping motor current NOT because the back EMF is killing the current but because the battery current limit kicks in. Take a look yourself:










As you can see, motor voltage and pack voltage only meet once, when the serial/parallel shift kicks in, no other time in the graph is the motor voltage limited by pack voltage and no other time does PWM reach 100% which means that it's NOT the back-EMF that is the limiting factor.

Now, I can't help you if you refuse to see reason, if you fanatically will continue to claim that AC is superior in every aspect I'll leave you to your private religion and from now in consider you a lost case with a distorted view of the world. I will take comfort in the fact that I hopefully have sown some doubt among your disciples.

Oh, and have a nice day.


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## Bowser330 (Jun 15, 2008)

etischer said:


> How about I cut that in half since he is using 2 motors.
> 
> 250V x 310A at 6000 rpm. I can do that with my little AC system.


Well you aren't learning quick enough...

The white zombie had a phase where it ran on a single Kostov-11" motor...thats the information I provided...


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## Tesseract (Sep 27, 2008)

etischer, please refrain from substantially editing your post after writing it. It makes it difficult to respond.



etischer said:


> I think the DC graph is a bit confusing. The motor was ramped up, and held at a constant 2000 rpm, this is why the current is constant.


Rather than attempt to explain this yet again, why don't you imagine a situation in which you floor the accelerator pedal but your motor is so loaded down it couldn't exceed 2000 rpm. Say, for example, driving up a hill while towing a trailer. That wasn't hard to envision, now was it?




> My graph shows an AC motor with constant current across the range from zero speed to 7000 rpm.


It sure does. It looks like the current was constant at 160A... Somehow, your 7000 rpm just isn't as impressive anymore. Not sure what the actual rms voltage applied to your motor was, but let's assume that at 7000 rpm it was the theoretical maximum for your battery pack (220Vrms if the pack is 312VDC). It's not clear whether that is 3 phase current or not... let's assume it is the current through a single phase leg (so the 1.73x multiplier is used). That means the input power to your motor is 220V x 160A x 1.73 or ~61kW. Our input power was 105kW... now, do you still want to claim that just because your motor made it to 7000 rpm it is somehow more powerful that the DC motor we tested? I mean, we were loading our motor down to around 300 ft-lbs of torque; your little AC motor certainly wasn't putting out the equivalent amount of power - ~85 ft-lbs of torque at 7000 rpm.




> Current would typically drop off with RPM on a DC motor, but AC system as you can see, current is constant from 0 -7000 rpm. Again, AC has more area under the curve.


If you have run out of battery volts (ie - hit 100% duty cycle) then sure, motor current will start to drop off as RPM increases (if it increases). But see the aqua line in our graph? That's duty cycle. We were at approximately 60% during the 100kW part of the run and the pack had sagged from 192V nominal to 160V, so we had quite a bit to go. Could we hit 7000 rpm? Nope. But your motor can't take 1000A, either.


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## etischer (Jun 16, 2008)

LOL!! Haha, ok you got me =)



Bowser330 said:


> Well you aren't learning quick enough...
> 
> The white zombie had a phase where it ran on a single Kostov-11" motor...thats the information I provided...


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## etischer (Jun 16, 2008)

Isn't that why he does a parallel series shift? To get more voltage to counter act back emf? And I've always stated DC torque is based on slip speed (difference in battery v and back emf) In this case, yes he has enough voltage to counteract emf at 6000 rpm, 360V



Qer said:


> And again you're proving that you actually don't know what you're talking about. Current would typically drop off with RPM on a AC system as well, just not below 7000 RPM in this particular example. In this thread it has been shown numeral times that the back-EMF in a DC motor isn't as bad as you preach and that with a big enough pack you can pull full current pretty high up in the RPM's. For example, that typical graph from the White Zombie shows a dropping motor current NOT because the back EMF is killing the current but because the battery current limit kicks in. Take a look yourself:


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## Bowser330 (Jun 15, 2008)

etischer said:


> If his top speed is 75, I'll beat him to 90! Just pointing out an advantage of AC motors over DC motors. That's what were here for, to learn. I'm certainly learning more about DC characteristics.


HAHAHA, I would like to see you beat him, once he shifted into his (removed) 4th gear...

I'm glad you are learning about the advantages of DC over AC, I think maybe you could have done some of that before coming out and publishing skewed data (72V vs 312V), but hey, thats just me...


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## etischer (Jun 16, 2008)

I feel like I'm carrying on a debate with 3 or 4 different people now. I think I'm just going to have to agree to disagree and move on. 


Current was 275 A per phase (dark blue), not 160

160 is the pedal position (light blue)



Tesseract said:


> etischer, please refrain from substantially editing your post after writing it. It makes it difficult to respond.
> 
> 
> 
> ...


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## Bowser330 (Jun 15, 2008)

etischer said:


> Isn't that why he does a parallel series shift? To get more voltage to counter act back emf? And I've always stated DC torque is based on slip speed (difference in battery v and back emf) In this case, yes he has enough voltage to counteract emf at 6000 rpm, 360V


If you are quoting my post of 6020rpm, I should edit your comment that the 155kw was attained with a pack of 336V not 360V, just trying to be upfront with the data...


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## Bowser330 (Jun 15, 2008)

Qer said:


> Now, I can't help you if you refuse to see reason, if you fanatically will continue to claim that AC is superior in every aspect I'll leave you to your private religion and from now in consider you a lost case with a distorted view of the world. I will take comfort in the fact that I hopefully have sown some doubt among your disciples.....


+1000000

...Must be the water up there in San Fran...jk


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## etischer (Jun 16, 2008)

Qer said:


> Now, I can't help you if you refuse to see reason, if you fanatically will continue to claim that AC is superior in every aspect I'll leave you to your private religion and from now in consider you a lost case with a distorted view of the world. I will take comfort in the fact that I hopefully have sown some doubt among your disciples.
> 
> Oh, and have a nice day.


 
This is turning ugly. I have never said AC is superior in every aspect, nor do I believe this. Im trying to point out the benifits of AC. There is a reason cars like the EV1, Ranger EV, Rav4 EV, Tesla, Prius, Insight... all use AC motors. Trying to share the things I have learned with my AC conversion since 99% of conversions are DC.


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## etischer (Jun 16, 2008)

I was refering the graph. Battery voltage is 367+ volts












Bowser330 said:


> If you are quoting my post of 6020rpm, I should edit your comment that the 155kw was attained with a pack of 336V not 360V, just trying to be upfront with the data...


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## etischer (Jun 16, 2008)

Give me data, and I'll add it to the graph. 

I posted the motor at 72v and 144v. 144v is roughly equal to the battery capacity in my 312v car since my car is delivering roughly half the current. 




Bowser330 said:


> HAHAHA, I would like to see you beat him, once he shifted into his (removed) 4th gear...
> 
> I'm glad you are learning about the advantages of DC over AC, I think maybe you could have done some of that before coming out and publishing skewed data (72V vs 312V), but hey, thats just me...


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## etischer (Jun 16, 2008)

Why are DC motors not used in production cars like Tesla, Honda, Ford, Toyota, Chevy.... ?


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## Qer (May 7, 2008)

etischer said:


> Isn't that why he does a parallel series shift? To get more voltage to counter act back emf?


Again, no, totally wrong. You series shift the motors to get twice the power and torque at low RPM. When the motors are in parallel, they don't provide more power or change the back-EMF in any way so they're more or less behaving like a single motor would (with the exception of half the internal resistance, of course). The real kick of a siamese motor is the takeoff, those first crazy 3 seconds when the Zombie's front wheels goes air born from the massive torque.



etischer said:


> In this case, yes he has enough voltage to counteract emf at 6000 rpm, 360V


240 Volt. The voltage drop of the pack is something entirely different than back-EMF and shouldn't be included in the formula. At the end of the race the controller has reached 80% PWM so there's still some Volts to be tapped before the constant power region of the setup is passed.



etischer said:


> Why are DC motors not used in production cars like Tesla, Honda, Ford, Toyota, Chevy.... ?


Whatever reason, it's not a decision based on power or back-EMF.


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## major (Apr 4, 2008)

etischer said:


> Why are DC motors not used in production cars like Tesla, Honda, Ford, Toyota, Chevy.... ?


Hey etischer,



> I agree production EVs are and will be AC traction drives, but do not necessarily see this hp curve area as the reason. Simply put, the reason is product validation.


Quoting myself from post #110.

Regards,

major


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## major (Apr 4, 2008)

etischer said:


> all in good fun
> I seem to be the only representative from the AC world.


Hey etischer,

I like the AC drives better. 

Who'd of guessed?

major


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## etischer (Jun 16, 2008)

He has a 360 volt pack, it sags to 240V

I assume he starts the car in series, (each motor sees 120v)
Then shifts to parallel to counter act EMF (each motor sees 240v)

He can pull twice the amps by starting in series, but needs twice the voltage once the rpms increase so he switches to parallel. 

A briliant way to get power out of a DC motor at 6000 + rpm



Qer said:


> Again, no, totally wrong. You series shift the motors to get twice the power and torque at low RPM. When the motors are in parallel, they don't provide more power or change the back-EMF in any way so they're more or less behaving like a single motor would (with the exception of half the internal resistance, of course). The real kick of a siamese motor is the takeoff, those first crazy 3 seconds when the Zombie's front wheels goes air born from the massive torque.


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## etischer (Jun 16, 2008)

Well thanks Major



major said:


> Hey etischer,
> 
> I like the AC drives better.
> 
> ...


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## etischer (Jun 16, 2008)

Qer said:


> Whatever reason, it's not a decision based on power or back-EMF.


I'd be willing to bet it is =) A wide power band is more desireable, and a wide power band is easier to do with AC because power is not limited by Back EMF.


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## Bowser330 (Jun 15, 2008)

The graph that Qer posted is more recent data, with the white zombie's siamese 8" motors and 360V.

I was quoting a previous setup where he had a single 11" and 336V pack sagging to 250 as he crossed the line at 6020rpm and 155kw...

just to clarify...


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## Tesseract (Sep 27, 2008)

etischer said:


> I'd be willing to bet it is =) A wide power band is more desireable, and a wide power band is easier to do with AC because power is not limited by Back EMF.


Like we keep telling you, AC motors don't get to break the laws of physics... they have back EMF, too - why do you think you need more volts to spin them at a higher RPM?

Every motor is a generator; every generator is a motor.

Induction motors make fine generators: just spin them faster than their synchronous speed by their slip percentage and you can extract full nameplate amps from them (the load just needs to have leading power factor; ie - capacitive) and there needs to be a slight amount of residual magnetism in the rotor (which can be produced by briefly touching a 9V battery to any phase pair).

And FWIW, I'm motor neutral... each has it's place in industry (from where I come from) and in industry there is rarely a use where the series DC motor is a better choice than an induction motor. Loads that demand extremely high starting torque and/or must withstand extreme overloading on a periodic basis are where the series DC motor can be a superior choice.

It is true that with certain forms of space vector modulation the AC induction motor can have vastly improved starting and breakdown torque, and even servo-like precision, but the SVM inverter is a far more complicated piece of equipment compared to the usual buck converter employed for controlling the speed and/or torque of a series dc motor.

One other thing w/r/t ac induction motors... keep in mind that the higher the gear reduction ratio the less efficient it will be, and high shaft RPMs (5000+) tend to lose a lot of power churning the lubricant around inside the gearbox. It is _always_ more efficient to mechanically transfer a higher torque than it is a higher speed.


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## etischer (Jun 16, 2008)

Tesseract said:


> Like we keep telling you, AC motors don't get to break the laws of physics... they have back EMF, too - why do you think you need more volts to spin them at a higher RPM?


They don't. They need higher frequency, not voltage. I built my own inverter, I would know.

Voltage applied to my motor at 3000 rpm is exactly the same as it is at 8500 rpm, I could probably spin it up to 20,000 at the same voltage


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## Tesseract (Sep 27, 2008)

etischer said:


> They don't. They need higher frequency, not voltage. I built my own inverter, I would know.


Oh, my bad... I thought _Volts_ had to be kept proportional to _Frequency_ in an ac induction motor... 




etischer said:


> Voltage applied to my motor at 3000 rpm is exactly the same as it is at 8500 rpm, I could probably spin it up to 20,000 at the same voltage


Hmmm... can you extract the same amount of torque from the motor at 3,000rpm, 8,500rpm, 20,000rpm, etc?


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## etischer (Jun 16, 2008)

Tesseract said:


> Oh, my bad... I thought _Volts_ had to be kept proportional to _Frequency_ in an ac induction motor...


 
Nope, they sure don't. I run 200v @ 120hz for 3500 rpm, 200v @ 240hz gives me 7000. 



Tesseract said:


> Hmmm... can you extract the same amount of torque from the motor at 3,000rpm, 8,500rpm, 20,000rpm, etc?


Torque is constant from 0-3500 rpm. Above that it tapers off proportional to RPM, this is the "constant horsepower range". 

At 8500 rpm it still produces 75% of the torque it had at it's 3500 rpm peak. 

Basically there is no reason to shift, there is no power or torque advantage. Again, a very wide power band works well in an ev application


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## Tesseract (Sep 27, 2008)

etischer said:


> Nope, they sure don't. I run 200v @ 120hz for 3500 rpm, 200v @ 240hz gives me 7000.
> 
> Torque is constant from 0-3500 rpm. Above that it tapers off proportional to RPM, this is the "constant horsepower range".


If you continued increasing voltage proportionally to frequencies above 120Hz then torque would not taper off... that was my point. If you keep voltage constant as frequency (rpm) rises then torque must fall. And why do you need to increase the voltage as rpm goes up, or decrease it as rpm goes down? Surely you aren't going to argue that there is no need to decrease the voltage as frequency goes to zero?




etischer said:


> At 8500 rpm it still produces 75% of the torque it had at it's 3500 rpm peak.
> 
> Basically there is no reason to shift, there is no power or torque advantage. Again, a very wide power band works well in an ev application


How can you be in the constant hp region when above 3500 rpm, as you just stated above, yet also claim that torque is only down to 75% of its 3500 rpm value at 8500 rpm? Available torque at 8500 rpm should be less than half that at 3500 rpm. 

Look, I'll grant you that with a well designed VFD and high enough battery pack voltage the ac induction motor is easily usable without a multispeed transmission, but that's not really the point of this thread, now is it?

Indeed, the only parameter that is relevant to this thread's topic is which motor type has the highest overload capacity? Whichever one does is the one that can delivering more hp for a given size/weight.


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## etischer (Jun 16, 2008)

Sorry, I meant to say power, not torque. 

At 8500 rpm it still produces 75% of the power it had at it's 3500 rpm peak. 

I agree, in general, DC motor has more overload capacity, and higher peak hp value. 

Maybe some day someone will publish some data to complete my comparison chart. I agree, the full potential of DC motors are not represented in my chart. I am making a sincere effort to represent DC motors in a fair comparison, so help me out. Give me some data for a Warp 9 and Kostov at 200v, 250v, 300v...

http://etischer.com/awdev/compare/compare2/hp_curves.gif





Tesseract said:


> How can you be in the constant hp region when above 3500 rpm, as you just stated above, yet also claim that torque is only down to 75% of its 3500 rpm value at 8500 rpm? Available torque at 8500 rpm should be less than half that at 3500 rpm.
> 
> Look, I'll grant you that with a well designed VFD and high enough battery pack voltage the ac induction motor is easily usable without a multispeed transmission, but that's not really the point of this thread, now is it?
> 
> Indeed, the only parameter that is relevant to this thread's topic is which motor type has the highest overload capacity? Whichever one does is the one that can delivering more hp for a given size/weight.


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## etischer (Jun 16, 2008)

Qer, 



Qer said:


> Again, no, totally wrong. You series shift the motors to get twice the power and torque at low RPM.


Motors in series will get you half the power, not twice. Each motor would be getting half the voltage in series.



Qer said:


> When the motors are in parallel, they don't provide more power or change the back-EMF in any way so they're more or less behaving like a single motor would (with the exception of half the internal resistance, of course).


Two motors running at 240v can produce more power than two motors running 120v. 

Motors in parallel will cut the back-EMF in half. A voltage source of 120v will not produce much torque on a motor with 119v of back-EMF, this is why he parallel shifts to apply 240v to the motors at high rpm. This is done purely to counter act the torque robbing effects of back EMF, and a cleaver way to maintain torque at high rpm on a DC motor. 






Qer said:


> And again you're proving that you actually don't know what you're talking about. Current would typically drop off with RPM on a AC system as well, just not below 7000 RPM in this particular example.


I do know what I'm talking about because I built my own inverter and you can see the graph of acquired data from my inverter that current is flat (0-7000 rpm). 

I agree, current will taper off, but not with the slope of a DC motor (unless the battery voltage is high enough to counter act the back EMF). At 12krpm, I can still put 56% of peak power in, a DC system would need 500-1000 volts to overcome back EMF. 















Also notice battery voltage starts at 320 and I regen up to 360v (about 50A)


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## JRP3 (Mar 7, 2008)

etischer said:


> Why are DC motors not used in production cars like Tesla, Honda, Ford, Toyota, Chevy.... ?


I can think of a number of possible reasons:
1. Regen
2. Higher voltage
3. No brush wear or potential brush problems, (dust, broken springs, contacts, water, dirt, etc.).
4. Maybe cheaper construction costs on the motor side, though not the inverter, so that may be a wash.
5. Better/easier cooling.
6. Maybe safer if the controller fails.


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## Qer (May 7, 2008)

etischer said:


> Motors in series will get you half the power, not twice. Each motor would be getting half the voltage in series.


That would be the case IF we were talking about a fixed voltage and unlimited current. We don't. We're talking about a fixed current and "unlimited" (to a limit...) voltage. Hence, power doubles.



etischer said:


> Two motors running at 240v can produce more power than two motors running 120v.


No. Power equals voltage times current. Depending on the rpm (and thus back EMF) it will be better to run the motors in series, parallel or it won't make a difference because it's the battery pack, not the motors, that limits the output power.

You still have to compare systems, not individual components.



etischer said:


> Motors in parallel will cut the back-EMF in half.


No. Back EMF is always back EMF, it's a fixed voltage proportional to rpm, it's not a resistance. There's ALSO (on top of the back EMF) a resistance in each motor of some mOhm and THAT will be cut in half if you put two motors in parallel! In real life that won't make any difference before the controller hits 100% pwm in parallel mode, which the Zombie doesn't in that graph.



etischer said:


> A voltage source of 120v will not produce much torque on a motor with 119v of back-EMF, this is why he parallel shifts to apply 240v to the motors at high rpm.


 Yes, that's the point where the advantage of serial motors turns into a disadvantage and that's why he shifts. BUT from that point up to when the controller hits 100% pwm the siamese motor doesn't give more power than a single motor would (well, ok, a little due to decreased efficiency).

The main point of siamese motors is not to counter back-EMF, it's to double the power and torque output at really low rpm's. If you don't need dragster performance at close to zero rpm there's no need to get yourself a siamese.



etischer said:


> I do know what I'm talking about because I built my own inverter and you can see the graph of acquired data from my inverter that current is flat (0-7000 rpm).


Which means that the point where back-EMF starts to kill your current is above 7000 rpm. If you change system voltage that point will move and if you build a different inverter with a different max current your power and torque curves will be rescaled.

Now, if you look at my graph you can see that there's no problem to put 1000 Amps through a WarP 9" at 2000 rpms and a motor Voltage of approximately 90 Volt. That means, theoretically, that since the input Voltage to the controller is 150 Volt (including drop) the motor should be able to keep running with a flat torque up to about 3500 rpm but in theory the batteries has reached their absolute maximum so instead 2000 rpm is the point where the curve for the system (not the motor) turns into fixed power which will last to at least 3500 rpm, probably a bit higher.

That is why I say you can't compare DC motors to AC systems and that is why I over and over again tell you that you have to compare systems and your graph over AC systems versus DC motors is comparing apples with oranges.



etischer said:


> I agree, current will taper off, but not with the slope of a DC motor


Finally. And no, noone has claimed that the two systems will be identical. That's the whole point, they won't.



etischer said:


> At 12krpm, I can still put 56% of peak power in, a DC system would need 500-1000 volts to overcome back EMF.


 A DC motor can't run at 12000 rpm, but since motors only converts electrical power to mechanical power it doesn't matter! Admittedly, you will get lower rpm but you will instead get higher torque since power equals rpm times torque.

"Ye canna change the laws of physics, Captain!" - Scotty



etischer said:


> Also notice battery voltage starts at 320 and I regen up to 360v (about 50A)


That's a totally different topic and also not limited to AC motors. A SepEx, for example, regenerates fine too (lots of electrical Renaults and Citroens over here that regens with SepEx motors) and even a series wound can, in theory, regenerate but it seems to be a hell to implement in real life. Or as Tesseract put it:

"Every motor is a generator; every generator is a motor."

You're still comparing apples with oranges.


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## Qer (May 7, 2008)

JRP3 said:


> I can think of a number of possible reasons:
> 1. Regen
> 2. Higher voltage
> 3. No brush wear or potential brush problems, (dust, broken springs, contacts, water, dirt, etc.).
> ...


In your list I'd say 2 (thinner cabling) and 5 (water cooling) with possible some merit to 3 and 4. 1 and 6 I'd say is system independent.

2, 5 and somewhat 3 are the reasons for why I'd choose AC if I'd decide.


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## etischer (Jun 16, 2008)

I think you are confused Qer.

Lets say a motor spinning at 1000 rpm has 120v of back-EMF and 100 mOhm resistance

Put two of those in series you get 240v back emf and 200 mOhm resistance. If your pack voltage is 240v you can only apply 120v to each motor 
You cannot generate any torque. 
You cannot generate any current.

Put those two in parallel you get 120v back emf and 50 mOhm resistance. 
Your pack voltage is still 240v, but now you can apply 240v to each motor.
This gives you up to 180v above back emf to produce torque with. 


Series connection is for low speed, to limit power within the range the controller can handle. The shortest duration pulse from the pwm would probably damage the controller if it is switching 240v to a stopped motor (0v of back emf). The series system has twice the back emf (120v) as the parallel connection (60v). 


Parallel connection is for high speed, to counter act torque robbing effect of back emf. Power is much greater because each motor has the potential to run at twice the voltage (240v instead of 120v)


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## Tesseract (Sep 27, 2008)

etischer said:


> I think you are confused Qer.


Nope - Qer's right; you are the one that is confused, mainly because you seem to have ignored anything written that doesn't confirm your vision of glorious AC supremacy... 

Two DC motors wired in series gives you twice the hp at low RPM while in parallel will give you twice the hp at high RPM. Deciding when to switch from series to parallel is a matter worthy of debate, but your arguments aren't; to wit:




etischer said:


> Lets say a motor spinning at 1000 rpm has 60v of back-EMF and 100 mOhm resistance
> 
> Put two of those in series you get 120v back emf and 200 mOhm resistance. If your pack voltage is 240v your can only apply 120v to each motor
> You cannot generate any torque.
> You cannot generate any current.


Ummm... wow. Just wow. You were doing fine right up until the last two statements of "fact".... In your example, the two motors in series have a combined back emf of 120V and your battery pack is 240V. In such a case (which is fairly realistic for a warp 9) the controller will be running at 50% duty cycle when delivering its maximum rated amps if the pack doesn't sag at all. Conversely, the pack could sag nearly 50% and the controller could still deliver maximum amps to this pair of motors. As long as the controller does not hit 100% duty cycle neither the pack voltage nor the back emf is limiting the power output.

Your reasoning is faulty in much the way as is this syllogism: Mohammed is an Arab; Some Arabs are Terrorists; Mohommed is a terrorist.

Because you totally blew it here there's no point in responding to the rest of your post. If you happen to make a correct statement I have to assume at this point it's only because you got lucky... "even the blind squirrel finds a nut now and then"...


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## etischer (Jun 16, 2008)

Well yea, I goofed up one number, but the working principal is still correct. 

Simple series and parallel circuits. 

put two light bulbs in series and then put them in parallel. which connection produces more power?

series connection, bulbs will be half as bright becasue they are running at half the voltage. 


*If *you were putting your batteries in series vs parallel, then your theory is sound. 
Twice the amps at low speed, twice the voltage at high speed. Since the graph shows the battery voltage the same before and after the shift, we know this is not how it is being done though. 

Maybe he is running two motor controllers and thats where the confusion lies. 



Tesseract said:


> Your reasoning is faulty in much the way as is this syllogism: Mohammed is an Arab; Some Arabs are Terrorists; Mohommed is a terrorist.
> 
> Because you totally blew it here there's no point in responding to the rest of your post. If you happen to make a correct statement I have to assume at this point it's only because you got lucky... "even the blind squirrel finds a nut now and then"...


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## Tesseract (Sep 27, 2008)

etischer said:


> ...
> put two light bulbs in series and then put them in parallel. which connection produces more power?


Neither connection _produces_ more power... Semantics aside, the power output of the two lamps in total depends on the limiting factor in the source: if the source is voltage limited (e.g. - a PWM converter operating at 100% duty cycle) then the parallel connection will produce more light; if the source is current limited, though, the series connection will produce more light.

I agree that the circuit is simple, but you are still managing to screw it up.

EDIT - Oh, I see you edited your post to backpedal...


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## Qer (May 7, 2008)

etischer said:


> If you were putting your batteries in series vs parallel, then your theory is sound.


Uhm. Changing the battery configuration (provided the pack still contains the same kWh) only changes maximum motor voltage, nothing else differs. In a DC/DC buck converter (which a motor controller essentially is) you convert power to power, like this:

Uout = Uin * D
Iout * D = Iin

where D is duration of the PWM pulse between 0 and 1. This means that you theoretically get:

Pout = Uout * Iout = Uin * D * Iin / D = Uin * Iin

Thus power out equals power in (except, of course, that you have some losses in the conversion).

So if you shift your pack in some kind of series/parallel fashion the only thing you achieve is lower maximum output voltage since Uout <= Uin, the power transformed doesn't change in any way.



etischer said:


> Maybe he is running two motor controllers and thats where the confusion lies.


What are you talking about...? Who runs two motor controllers?


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## etischer (Jun 16, 2008)

Ok, that might be the case if a current limit is factored in. I'm done debating



Tesseract said:


> Neither connection _produces_ more power... Semantics aside, the power output of the two lamps in total depends on the limiting factor in the source: if the source is voltage limited (e.g. - a PWM converter operating at 100% duty cycle) then the parallel connection will produce more light; if the source is current limited, though, the series connection will produce more light.
> 
> I agree that the circuit is simple, but you are still managing to screw it up.
> 
> EDIT - Oh, I see you edited your post to backpedal...


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## etischer (Jun 16, 2008)

Qer said:


> Uhm. Changing the battery configuration (provided the pack still contains the same kWh) only changes maximum motor voltage, nothing else differs.
> What are you talking about...? Who runs two motor controllers?


Lets say you have (2) 120v batteries and each can produce 1000A, and a controller can deliver 1000A. 

connect 1 120v battery to controller A

and the other 120v battery to controller B 

you can lay down 2000A at 120 for low speed. Twice what you could with only one controller




at high speed connect the batteries in series and connect 240v battery to both controllers. 

you can lay down 1000A at 240v for high speed.



This would give you twice the current at low speed.


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## Qer (May 7, 2008)

etischer said:


> Lets say you have (2) 120v batteries and each can produce 1000A, and a controller can deliver 1000A.
> 
> connect 1 120v battery to controller A
> 
> ...


How on earth did you manage to build your own inverter when your grasp of the buck converter is worse than mine? I can blame it on that I'm the software guy, I don't NEED to grasp it since Tesseract is the hardware guy, but...

No, I'm not even gonna touch this one. Here, read up:

http://www.ecircuitcenter.com/Circuits/smps_buck/smps_buck.htm
http://en.wikipedia.org/wiki/Buck_converter


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## etischer (Jun 16, 2008)

If you are really interested, you can read the "motor controller" section of my webpage, I just updated it this weekend with an archive of pics and videos over the last year. 

http://etischer.com/awdev/

Please, enough with the insults already. My comment was simply if you put two battery packs in parallel you can pull twice the amps for low speed, then twice the voltage for high speed. Building a series parallel switching pwm dc motor controller wouldn't be that hard. Besides the advantages mentioned previously, it could also allow some regen capablity in motors which cannot currently do regen (very well). I obviously know more than your willing to give me credit for. 



Qer said:


> How on earth did you manage to build your own inverter when your grasp of the buck converter is worse than mine? I can blame it on that I'm the software guy, I don't NEED to grasp it since Tesseract is the hardware guy, but...
> 
> No, I'm not even gonna touch this one. Here, read up:
> 
> ...


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## Overlander23 (Jun 15, 2009)

OK, let's step back and simplify all of this back to the original subject...

Fundamentally, a 50kW DC motor is putting out the same power as a 50kW AC motor, the only caveat being that the two motors are generating 50kW in their efficiently designed range. I mean, that's seemingly obvious... the kW rating should be independent of the design and a measure of the generated power as tested independently. No?

AC favors speed while DC favors torque. This is largely due to construction and limitations of brushes on commutators (in the case of DC.)

Speed comes from volts and a higher number of winds... Torque comes from fewer winds and higher current... Horsepower comes from the relationship of the two. So high speed and low torque makes the same power as low speed and high torque. It's up to the EV designer to figure out how to tap the characteristics.

This point is hazy with me, but feel free to yell at me if I'm wrong. In an AC induction system, rpm is independent of applied voltage. The shaft speed is dictated by PWM frequency. BUT, rpm is irrelevant if there's nothing behind it. Why spin 50,000 rpm if there's no torque. And that's where voltage plays in generating torque... which will subsequently increase amp draw. Which is why you increase voltage with frequency. Again, I'm well aware this could be completely incorrect.

All the systems we're discussing are motors operated by controllers pulling current from batteries. So there are essentially three potentially limiting parts to the system; battery limits, motor limits, and controller limits.

A siamese motor has the ability to switch between series and parallel windings. This has the effect of favoring speed or torque, depending on the mode... and it's essentially rewiring the motor. It's essentially like changing the motor. User demand dictates the performance of the motor, and the controller dictates the limits (in addition to the physical limitations of the battery and motor itself).

In case of the drag racing example, I imagine you'd start with the motor in parallel. Remember, you have control of the voltage through the controller. You don't have direct control of current (although this is generated through demand from the motor by the user increasing the volts, and the demand on the system to change states.) With the motor in parallel, a large amount of torque can be generated for a given amount of current at the expense of top motor speed. The power is the same as in a maxed out series configuration, but you're biased for torque. Then, as speed off the line increases the motor is switched to series mode (at some point) to bias the power generation to speed. Torque will fall off. BUT POWER STAYS THE SAME.

AC inverters typically handle much higher voltages than DC controllers. Are your average AC inverters also be rated for less amperage then a similar class DC controller? Or are we seeing 1000 amp controllers and inverters, with the controller running under 200v and the inverter running under 400v?


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## Qer (May 7, 2008)

It seems you've done your home work since most of your reasoning looks right to me so I'll just comment those few details where you've missed something. There are other parts where I frankly don't know myself so I'll simply keep quiet about those. 



Overlander23 said:


> In case of the drag racing example, I imagine you'd start with the motor in parallel.


Actually, the opposite.

At 0 RPM the back EMF is 0 and a controller will typically go into current limitation to avoid blowing up. Since power out from the motor corresponds to BEMF * I and BEMF is 0 nothing fun happens, BUT the current is proportional to torque and that's what you want at 0 RPM to get things moving!

Let's say the controller is good for 2kA and the motors are in parallel, then each motor will get I/2 each, which means that your torque will be proportional to I/2 * 2 = I. No difference from a single motor. Now, if we connect the motors in series (so that the full current goes through both motors) then suddenly your torque will be proportional to I * 2! Twice the torque!

That also means that when your BEMF starts to raise you get the power P = BEMF * I * 2, ie twice the power than a single motor and this works until (BEMF + R * I) * 2 reaches pack voltage, ie the controller reaches 100% PWM. R here is the internal resistance in the motor and the Voltage over the motor is BEMF (as we've talked about a few times already) plus the voltage over the internal resistance which is the resistance multiplied with the current, R * I. So the voltage drop over the motor is BEMF + R * I and since the motors are in series that's multiplied with two. The power over R (R * I^2) is, however, only losses and doesn't help propelling the car. It's all going to waste in the form of heat.

When the voltage over the two motors in series reaches pack voltage, the current starts to drop rapidly and that's when you shift to parallel and then the power from the motors drop to BEMF * I/2 since each motor only get half the current. That means that the total power out equals (BEMF * I/2) * 2 = BEMF * I, ie the same as a single motor would generate. This is also the case until the controller hits 100% in parallel mode and it's the voltage, rather than current, that limits the motor power and suddenly the power out per motor is P = (U - R * I) * I where I is (U - BEMF) / R aaaand there somewhere it's not worth bothering anymore. 

Since the motors are in parallel the two R are in parallel as well, meaning the resistance the controller sees is R/2 and thus the current gets twice as high compared to a single motor and power gets twice as high again. So at low RPMs and high RPMs the siamese motor can give twice the power compared to a single motor, but in the mid range the siamese doesn't give any more power out than a single motor (but can keep it up for longer since the heat is divided between the motors). The real advantage is, however, at low RPMs since that will give you a massive start torque which you can see on some of the videos of the Zombie when the car lurches forward, lifting the front wheels off the ground.

And now RL calls. Sorry...


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## Amberwolf (May 29, 2009)

I wish I'd known all that when I created my first ebike motorization scheme on the DayGlo Avenger, with two 12V radiator fan axial-flux brushed DC pancake motors wired in parallel. I'd've setup a relay (contactor) for them to be in series from dead-stops up to the 36V BEMF point, then switched automatically to parallel. Would probably have worked wonders for the system's starup torque, which was terrible. 

I'm sure some of that had to do with them being really small motors for that application, and being friction drive, but still, I'm sure it would have helped *some*. 
________
thai girl Cams


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## Tesseract (Sep 27, 2008)

Overlander23 said:


> ...
> Fundamentally, a 50kW DC motor is putting out the same power as a 50kW AC motor, the only caveat being that the two motors are generating 50kW in their efficiently designed range....


Yes - this is what we've been saying over and over again to etischer with the additional argument (from me) that the series DC motor is likely the pure HP champ simply because it is intrinsically capable of tolerating a much higher short term overload than the AC induction motor.




Overlander23 said:


> ... In an AC induction system, rpm is independent of applied voltage. The shaft speed is dictated by PWM frequency. BUT, rpm is irrelevant if there's nothing behind it. Why spin 50,000 rpm if there's no torque. And that's where voltage plays in generating torque... which will subsequently increase amp draw. Which is why you increase voltage with frequency. ...


Precisely right... The frequency at which you stop increasing voltage (because you've run out of it most likely!) is where the output power plot of the ac motor shifts from constant torque to constant hp (because torque will drop off by the same proportion as speed increases).




Overlander23 said:


> A siamese motor has the ability to switch between series and parallel windings. This has the effect of favoring speed or torque, depending on the mode...


Yep.




Overlander23 said:


> In case of the drag racing example, I imagine you'd start with the motor in parallel.


Nope. You start with the motors wired in _series_ because each motor is generating so little back EMF at startup (0v) to low RPMs the controller reaches full output current at very low duty cycles. In other words, much of the battery pack is not being used at low RPMs.




Overlander23 said:


> Remember, you have control of the voltage through the controller. You don't have direct control of current


On some dc motor controllers this appears to be true (e.g. - Curtis), but there is no reason why you can't directly control current (and we should know, as that's the control method we use  ). Indeed, that is the superior control method for traction applications as torque is proportional to current and torque is the variable you instinctively wish to control with your right foot...




Overlander23 said:


> AC inverters typically handle much higher voltages than DC controllers. Are your average AC inverters also be rated for less amperage then a similar class DC controller? Or are we seeing 1000 amp controllers and inverters, with the controller running under 200v and the inverter running under 400v?


Keeping your qualifier "typically" in mind, these observations are correct. In industrial applications you rarely see inverters rated for higher than 200A per phase because industrial engineers (and the electricians that wire them) hate having to run 2/0 or thicker (like MCM500, etc.) cable, so running at a higher voltage is much preferred to a higher amperage within reason. 

In a vehicle, the number of cell or battery connections that need to made to achieve a higher pack voltage presents a similarly cumbersome obstacle... people just get sick of having to make dozens (or hundreds in the case of LFP) cell/battery cables and, of course, each mechanical joint (post clamp or crimp) is a site of potential failure down the road (ahem). Mainly, though, I believe the reason is that most series DC motors use a single turn for each armature loop and raising the armature voltage requires more than one turn which then means the wire has to wrap around the commutator end in an awkward fashion (I'm sure major can add to this, providing he hasn't ditched the thread out of sheer frustration). 

Of course, ac induction motors don't have this particular problem, but they do have others... like, for example, to get more torque per amp you have to skew the shorting bars in the rotor more and/or increase their resistance. This increases the amount of slip the rotor can tolerate before stalling but the downsides are the speed regulation is worse and rotor losses are necessarily higher. Once again, I defer to major on this sort of stuff...


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## CroDriver (Jan 8, 2009)

Qer said:


> Let's say the controller is good for 2kA and the motors are in parallel, then each motor will get I/2 each, which means that your torque will be proportional to I/2 * 2 = I. *No difference from a single motor.* Now, if we connect the motors in series (so that the full current goes through both motors) then suddenly your torque will be proportional to I * 2! Twice the torque!


Yes, but the thing is that one motor can handle only a certain amount of power. Two motors = double peak power

I choosed a dual motor because I think that one motor can't handle the power I need. First I didn't thought about series/parallel shifting at all but now it seems like a very interesting option. I just have to find a 2K controller. 

BTW. very interesting thread. Thanks for sharing all that info guys!


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## Bowser330 (Jun 15, 2008)

CroDriver said:


> Yes, but the thing is that one motor can handle only a certain amount of power. Two motors = double peak power
> 
> I choosed a dual motor because I think that one motor can't handle the power I need. First I didn't thought about series/parallel shifting at all but now it seems like a very interesting option. I just have to find a 2K controller.
> 
> BTW. very interesting thread. Thanks for sharing all that info guys!


+1 Thank you for that detailed information Tess&Qer, very much appreciated.

What about the single 13" motor of the S10 Smokescreen? That motor helped a heavier car by 1000lbs do the 1/4 mile quicker than the whitezombie...Is it because torque per amp is just plain more on a 13" than two 8"s? (im biased, my donor may only have enough room for one motor)

Also, im assuming when a battery pack sags, that voltage becomes the voltage that BEMF has to overcome, so thats really important for someone who wants their EV to be quick for awhile...


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## Qer (May 7, 2008)

Bowser330 said:


> What about the single 13" motor of the S10 Smokescreen? That motor helped a heavier car by 1000lbs do the 1/4 mile quicker than the whitezombie...Is it because torque per amp is just plain more on a 13" than two 8"s? (im biased, my donor may only have enough room for one motor)


Yes, the 13" motor gives more torque per amp, but on the other hand top rpm is lower so that means the diff (I'm guessing we're talking direct drive without gear box now) needs a different gearing which probably ruins the whole thing by trading torque for rpm (since power = torque * rpm, the laws of physics spoils all the fun, I know).



Bowser330 said:


> Also, how does battery sagging voltage come into the picture...for example, when whitezombie was running single 11" kostov, at 336V he crossed the 1/4 mile with 250V and 620A on his meters...


It sucks. Plain and simple. Since you want to limit battery current (no race can be won with a blown pack) it means that when the voltage drops, your maximum power drops too. Let's say that the Zombie has a maximum battery current of 1000 Ampere, at 336 Volt he'd get a theoretical top effect of 336 kW but since his pack drops to somewhere around 240 Volt his effect in real life drops to 240 kW, naturally. Now, lets say he'd used a better battery pack (like Lithium, or just a more sturdy lead-acid pack) that can take 800 Amps max but only drops to 300 Volt he'd still get 240 kW out despite current being only 80%.

That's, btw, why I keep nagging about that you have to calculate kW and kWh because what propels your car isn't Ampere, it's Power. Range isn't Ah, it's kWh, and top speed isn't Volt, it's kW. You might have to optimize your Volts, Amps and RPMs for as much kW as possible, but it's still, in the end, your kW that propels your car. If you have a controller that can do 300 Amps it will do 300 Amps no matter Voltage so if you add a few more batteries (like gottdi did from 72 to 96 Volt) you get more kW out too and the car will get better performance.

You'd get the same change in power if you changed controller from one that can deliver 400 Ampere continuously rather than 300 (provided the batteries doesn't sag more, of course) but you'd have to gear for a different RPM. 300 * 96 = 400 * 72 = 28.8 kW. That is, theoretically. In real life batteries suck so I'd say 15-20 kW would be more realistic plus that the lower voltage might mean that motor efficiency drops too, but, well, THEORETICALLY it'd work.


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## Bowser330 (Jun 15, 2008)

Qer said:


> Yes, the 13" motor gives more torque per amp, but on the other hand top rpm is lower so that means the diff (I'm guessing we're talking direct drive without gear box now) needs a different gearing which probably ruins the whole thing by trading torque for rpm (since power = torque * rpm, the laws of physics spoils all the fun, I know).
> 
> 
> 
> ...


I mentioned previously that when I calculated the white zombies tire diameter with the speed at which he ran the 1/4 mile, I got 6020rpm...thats pretty nice! (especially with 250V and 620A on tap!) Maybe I should ask Major what modifications I can do to my future kostov-13" to enable the motor to rev up to 6K, of course with the downside being low-end torque but I think the 13" has a bit of it to spare...

Battery sagging does suck and it happens even with the almighty M1 A123 cells.. see link...Discharge Characteristics...at 30A or 13C the 3.3V cell sags to 2.7V so 100 cells in series would sag from 330V to 270V...right..if 13C was demanded of them...

http://a123systems.textdriven.com/product/pdf/1/ANR26650M1A_Datasheet_APRIL_2009.pdf


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## DavidDymaxion (Dec 1, 2008)

Doesn't the 13 inch Kostov have a really low RPM spec? Also, I thought Wayland ran closer to 5000 rpm max than 6000 rpm max. Be careful out there! 

If you really hate battery sag you can get a Zilla with a higher voltage pack, but limit the voltage to the motor, so the motor sees less sag. 



Bowser330 said:


> I mentioned previously that when I calculated the white zombies tire diameter with the speed at which he ran the 1/4 mile, I got 6020rpm...thats pretty nice! (especially with 250V and 620A on tap!) Maybe I should ask Major what modifications I can do to my future kostov-13" to enable the motor to rev up to 6K, of course with the downside being low-end torque but I think the 13" has a bit of it to spare...
> 
> Battery sagging does suck and it happens even with the almighty M1 A123 cells.. see link...Discharge Characteristics...at 30A or 13C the 3.3V cell sags to 2.7V so 100 cells in series would sag from 330V to 270V...right..if 13C was demanded of them...
> 
> http://a123systems.textdriven.com/product/pdf/1/ANR26650M1A_Datasheet_APRIL_2009.pdf


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## Bowser330 (Jun 15, 2008)

DavidDymaxion said:


> Doesn't the 13 inch Kostov have a really low RPM spec? Also, I thought Wayland ran closer to 5000 rpm max than 6000 rpm max. Be careful out there!
> 
> If you really hate battery sag you can get a Zilla with a higher voltage pack, but limit the voltage to the motor, so the motor sees less sag.


 
The website says he had 22" diameter tires with a 4.11 gearset when we drove that car across the line, with a single 11" kostov, at 13.347seconds 1/4 mile @ 95.859mph...

Basic Formula = MPH*Gears*336/Tire Diameter (in) = RPM

95.859 * 4.11 * 336/22 = 6017RPM

He also mentioned when he crossed the line his V = 250 and A = 620 (pack was 336V AGM LA Batteries)

According to what ive seen about the 13" I have to concur with you about the max speed (rpm), however the only graphs Ive seen were at 72V or 144V...im thinking if I up the voltage to nearly 400V the upper rpm will increase as well...not sure though...it worked for the S10 smoke screen although I do think his max was 5000...


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## Drew (Jul 26, 2009)

If you designed a controller for it would there be a benefit to dividing the battery pack in half and switching it from series to parallel in the same way as White Zombie did with the motors?


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## Qer (May 7, 2008)

Bowser330 said:


> Maybe I should ask Major what modifications I can do to my future kostov-13" to enable the motor to rev up to 6K, of course with the downside being low-end torque but I think the 13" has a bit of it to spare...


The problem with high RPM in a big motor is the rotor flings itself apart because of the centrifugal force.

http://en.wikipedia.org/wiki/Centrifugal_force

I guess that's the main reasons AC motors can rotate faster, the squirrel cage is lighter and stronger, which means it can handle more RPMs. If you, somehow, manage to reinforce a 13" for higher RPM you'd still get the same torque though.



Drew said:


> If you designed a controller for it would there be a benefit to dividing the battery pack in half and switching it from series to parallel in the same way as White Zombie did with the motors?


Not really, it only means more contactors, more losses in the cables (since cable losses are proportional to current) and more things that can break. Battery pack delivers power, if you deliver power as U * I or U / 2 * I * 2 ends up the same for the controller.

This is, however, ignoring the fact that switching losses go up with Voltage (see Tesseract, I DO listen! ) and even though switching losses are still a pretty minor loss all considered it will result in more heat disspiation which might be enough to blow the transistors (or force the controller to limit current to protect itself) so in SOME cases switching the pack like you say would actually mean more power.

However, I'm not sure that gain would be enough to compensate for the extra time when the pack is switched or worth the money/problems. No matter how you do it, when you do it there will be an interruption of power while the batteries, or motors, are reconfigured. We believe it can be done much faster than in the Zilla case, but no matter how it's done there will be a total loss of power for a fraction of a second.

Pretty much like when you shift gears on your ICE.


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## Dalardan (Jul 4, 2008)

By splitting the battery pack in half and them placing each half in parallel, you'd get roughly twice the current available at half the voltage. The problem is your controller will have the same current limit. 

Therefore, either your controller will be current limited when the pack is in series, so when the pack is in parallel hafl the current availlable won't pass through the controller. This might slightly augment the efficiency of the battery pack as less current will be drawn from each cell, so less Peukert effect, but I'm not sure it's really interesting from a Pure Power point of view...

Or the controller will be current limited when the pack is in parallel, so when the battery pack is in series, it will only be able the provide half the current limit of the controller. So the controller will be less stressed when the pack is in series, but if one on the parts isn't stressed at it's max level, it's not drag racing, yeah? 

Dalardan


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## Qer (May 7, 2008)

Dalardan said:


> By splitting the battery pack in half and them placing each half in parallel, you'd get roughly twice the current available at half the voltage. The problem is your controller will have the same current limit.


*sigh*

No, no, no and no. Stop thinking in current, 'cause you're only confusing yourself. Battery current is ALWAYS less or equal to motor current, motor voltage is ALWAYS less or equal to battery voltage. The ONLY thing that's equal on both side is power (well, ok, minus losses, but still).

If your motor pulls 1000 Amps at 60 Volt and your pack voltage is 60 Volt your pack current will be 1000 Amps, sure, but if pack voltage is 120 Volt your pack current will be 1000 * 60 / 120 = 500 Ampere. If your pack voltage is 240 Volt, pack current will be 1000 * 60 / 240 = 250 Ampere, and so on. In all these cases the power will be 60 kW on *BOTH* sides of the controller.

Frankly, I don't see any practical use for having the pack split in some kind of parallel/serial way. No matter how you organize the cells it's the maximum power that will limit you.

The only times you have to think in Volts and Amperes is when it comes to limitations. As I said, motor voltage <= battery voltage and that will limit your rpm, there's a limit on how high current the batteries can stand (that C-factor), how much the controller can take and when the motor will start to overheat, but when it comes to power, think power. Not Amps.


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## Dalardan (Jul 4, 2008)

Well, I was speaking of thermal limitations of the components...  You're right, I might have not explained myself clearly enough.

I was saying that if you use a 60V 1000A battery pack with a 1000A controller, you can provide 60kW of maximal power. If you use a 30V 2000A (pack split in 2 then paralleled), but the same 1000A controller, you'll only be able to source 30kW of maximal power because the maximal current will still be 1000A, limited by the controller. Well, I know it's not as simply as that, but it's roughly like that, right?

Therefore, I do think it's useless for a pure power application to split the pack in a series/parallel configuration. I'd say get a bloc of enough parallel cells to provide the maximal current your controlled can handle, then add other of those blocs in series until you are limited by maximal voltage of controller, cargo space or weight limit. 

So I do agree with you, Qer, in a power point of view, there is no interest in dynamically changing the battery configuration during a race.

Dalardan


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## Qer (May 7, 2008)

Dalardan said:


> I was saying that if you use a 60V 1000A battery pack with a 1000A controller, you can provide 60kW of maximal power. If you use a 30V 2000A (pack split in 2 then paralleled), but the same 1000A controller, you'll only be able to source 30kW of maximal power because the maximal current will still be 1000A, limited by the controller. Well, I know it's not as simply as that, but it's roughly like that, right?


I sense a current confusion here because battery current and motor current aren't the same, except at 100% PWM. I've written a long text about it already, but it's too annoying to try to find it again so I'll just give you the PWM-light explanation here:

Usually you talk about a duty cycle (D) between 0 and 1 where 0 is completely off and 1 is completely on. D=0.5 means that the controller spends equal long time with the transistors off as on (ie 50% PWM). Then the following goes:

Umotor = Ubattery * D
Ibattery = Imotor * D
Pmotor = Umotor * (Imotor * D) = (Ubattery * D) * Ibattery = Pbattery

Since D can only be between 0-1 Ibattery is always equal or lower than Imotor and Umotor is always equal or lower than Ubattery. It also means that a 120 Volt pack that is limited to 500 Amps can still provide 1000 motor Amps up to D=0.5 and thus Umotor up to 60 Volt. Above 60 Volt over the motor Imotor will start to drop until it's 500 Amps at D=1.

Also, the maximum current for the controller is measured at the motor end, not the battery end, so a 1kA controller can always provide maximum current at 0 RPM unless the battery pack is REALLY crappy (or severely discharged).

Think of the controller as a gear box. By gearing down rpm (voltage) you gain more torque (current).


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## Dalardan (Jul 4, 2008)

Well, I do remember reading the long text you're talking about. You're right, I was assuming 100% PWM which won't be the case except when motor voltage = battery voltage.

So, the controller can take a 100V 500A input on the battery side and provide a 50V 1000A output on the motor side, thus taking 50kW in and getting 50kW out. It's then useless to switch the configuration of the battery pack as the controller essentially already does this trade of Volts versus Amps. Thanks for the clarifications.

Dalardan


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## DavidDymaxion (Dec 1, 2008)

Re: RPM: Right you are and thanks for the correction -- I was going off his older Hoosier tire's larger diameter. 6k rpm is good news for me, too, maybe now I can get the speeds I want without a gear change.

I would talk to Kostov before assuming the low rpm limit is due to voltage and not mechanically flying apart! Going 11 inch to 13 inch may not sound like much, but diameter goes from 5.5 inch to 6.5 inch. (6.5/5.5)^2 = 1.4, that means the 13 inch has 40% more centrifugal force for the same rpm as an 11 inch. This is a reason some drag racers prefer 2 smaller motors, for more rpm. Theoretically it doesn't matter, as the bigger motor turns slower but has more torque, so you can equalize things with gearing.

Be careful comparing to Berube's Smoke Screen -- he runs a GE, not a Kostov.



Bowser330 said:


> The website says he had 22" diameter tires with a 4.11 gearset when we drove that car across the line, with a single 11" kostov, at 13.347seconds 1/4 mile @ 95.859mph...
> 
> Basic Formula = MPH*Gears*336/Tire Diameter (in) = RPM
> 
> ...


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## Bowser330 (Jun 15, 2008)

DavidDymaxion said:


> Re: RPM: Right you are and thanks for the correction -- I was going off his older Hoosier tire's larger diameter. 6k rpm is good news for me, too, maybe now I can get the speeds I want without a gear change.
> 
> I would talk to Kostov before assuming the low rpm limit is due to voltage and not mechanically flying apart! Going 11 inch to 13 inch may not sound like much, but diameter goes from 5.5 inch to 6.5 inch. (6.5/5.5)^2 = 1.4, that means the 13 inch has 40% more centrifugal force for the same rpm as an 11 inch. This is a reason some drag racers prefer 2 smaller motors, for more rpm. Theoretically it doesn't matter, as the bigger motor turns slower but has more torque, so you can equalize things with gearing.
> 
> Be careful comparing to Berube's Smoke Screen -- he runs a GE, not a Kostov.


So how do a GE And a Kostov 13" differ? 
Are the GEs stronger? Why? Can I upgrade the Kostov to have the same amount of strength?
Wont the cent. forces on a 13" Kostov apply to a 13" GE?


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## Qer (May 7, 2008)

Bowser330 said:


> So how do a GE And a Kostov 13" differ?
> Are the GEs stronger? Why? Can I upgrade the Kostov to have the same amount of strength?
> Wont the cent. forces on a 13" Kostov apply to a 13" GE?


Different motors, different characteristics. Why did you expect two different 13" motors to be identical? 

We've just started to run a Kostov 9" in the dyno instead of the WarP 9" and they also behave different, of course. Especially when you start to push it. We don't have any hard numbers or so, but they definitely differ. Which is best? Well, how long is a piece of string?


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## DavidDymaxion (Dec 1, 2008)

Dennis Berube is the real expert on the GE motors. I don't think he is here on DIYEC but hangs out on the EVDL and NEDRA Yahoo list.

I would guess a GE and Kostov 13 incher would have similar RPM limits, but it could be one is built tougher than the other.


Bowser330 said:


> So how do a GE And a Kostov 13" differ?
> Are the GEs stronger? Why? Can I upgrade the Kostov to have the same amount of strength?
> Wont the cent. forces on a 13" Kostov apply to a 13" GE?


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## Bowser330 (Jun 15, 2008)

Points taken... Thank you.

I guess I may have to rethink my Kostov 13" purchase, maybe rummaging for a GE 13" is a better idea...

in any case, as its been mentioned, the motor is only one part of a three part system...

With Lithiums getting more affordable and available, its come down to the availability of High Voltage High Amperage Controllers...I do know that there are plans for one, so I guess i have more time to save up my pennies...


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## Qer (May 7, 2008)

Bowser330 said:


> I guess I may have to rethink my Kostov 13" purchase, maybe rummaging for a GE 13" is a better idea...


Depends. You gonna build a racer or an every day car? Personally I think a Kostov 11" will be great (and that's only for the possibility to test regen, if I wasn't part of making a controller I wouldn't bother) and I'm even considering a Cherokee. 

On the other hand, deciding isn't my strong side. I'm still pondering what, why and, mostly, when...


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## Bowser330 (Jun 15, 2008)

I am looking for smokescreen power...single motor..

_*Quote from EVDL:*_
_My S 10 runs 11.08 at over 120mph in the qt.mi.(.4 SEC quicker than zombie) It has the official nedra record! It is direct drive with a 3.25 rear ratio.and 28in tall tires.I use the 13 inch motor up to 5500rpm. _
_Dennis Berube_

120mph x 3.25 x 336/28inches = 4680 RPM (Motor)

_*Quote from EVDL:*_
_The 13 inch motor in my S 10 (without tranny) has not gotten over 138 F either on the street or track. The temp. is taken on the field coils. The truck weighs over 3300lb and is driven in phoenix. My house is a good 200 feet higher than Phoenix so the ride home is always uphill. *This motor came out of **a large Clark forklift and has been mech.and elect. balanced to suit the load.(for instance:field poles were brought closer to armature for more torque *__*lower in rpm band)*_

So does this mean if the field poles were brought *farther* from he armature you would increase torque *higher *in the rpm band? 

I also had started a thread awhile back trying to put together a list about how to strengthen a DC motor to allow for higher voltage, I guess they can be used for higher rpm as well...

Here is the list I had gathered from our fellow members...

A: Thorough cleaning from original usage wear and tear...

1: Advance Timing/Interpoles

2: Insulation (liberal nomex paper wrapping)

3: Larger/powerful forced cooling blower (electric)

4: Newer Harder "Heavy Duty" Brushes (specific to other parts in the motor e.g. commutator)

5: Add extra banding (Kevlar) 

6: High temp wiring

7: Better bearings

8: Trimming of unrequired metal weight (Jim H. trims some metal pieces off the motors to lighten them up...his website has specifics)


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## Bowser330 (Jun 15, 2008)

Why cant a racer be an every day car too?

Its all about kw right? so...if cruising at highway speeds,lets say 70mph, takes 21kw....then a 21kwh pack should be able to get about a 70 mile range (100%DoD) Taking into consideration that jack-rabbit starts and cruising at lower speeds will cancel eachother out...

3.2V 60AH Lifepo4 cell, 3C cont. 20C pulsed, 66$

100 series = 320V
2 parallel = 120AH
200 cells x 66$ = $13,200 (w/o BMS)
360A = cont.
2400A = pulsed
1000A = 10sec?? (If the 320V sagged to 290V, 1000A might be still be pulled by 5252rpm) at that rpm 400ftlbs (13" motor) = 400hp
38.4kw = 128 mile range (100%DoD) @ 70mph

All the claims are just calculations, until its actually on the road, who knows...


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## JRP3 (Mar 7, 2008)

With a high C rate cell like A123 or Altairnano you can generate the short term power for a pass yet not have much kwh for range, and not carry unnecessary weight.


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## major (Apr 4, 2008)

Tesseract said:


> Mainly, though, I believe the reason is that most series DC motors use a single turn for each armature loop and raising the armature voltage requires more than one turn which then means the wire has to wrap around the commutator end in an awkward fashion (I'm sure major can add to this, providing he hasn't ditched the thread out of sheer frustration).


Hi Tesser,

Been on a road trip and not able to get on-line. Yeah, a bunch of stuff posted here since I left. Haven't had time to read it all, and probably won't as I have another trip in a day or two. Personal and day job business.

With the DC armatures in the sizes used by EVers, single turn designs are used when possible because it allows the use of rectangular cross section conductors. This facilitates assembly, especially the connection to the commutator. Generally speaking, this means a more robust machine compared to the multi-turn armature where in most cases the comm connects are soldered. The rectangular conductor in a rectangular lamination slot also gives a better fill factor opposed to round wire in a tear dropped shaped slot.



> Of course, ac induction motors don't have this particular problem, but they do have others... like, for example, to get more torque per amp you have to skew the shorting bars in the rotor more and/or increase their resistance. This increases the amount of slip the rotor can tolerate before stalling but the downsides are the speed regulation is worse and rotor losses are necessarily higher. Once again, I defer to major on this sort of stuff.


Don't follow the logic here. Rotor resistance does doesn't change the breakdown torque value. It does change the slip. Skewing will increase the rotor resistance, but is not used to purposely alter resistance. Skewing is used to reduce cogging and noise.

Regards,

major


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## CroDriver (Jan 8, 2009)

Bowser330 said:


> 3.2V 60AH Lifepo4 cell, 3C cont. 20C pulsed, 66$


What cell has that high C ratings?


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## Tesseract (Sep 27, 2008)

major said:


> ...Rotor resistance does doesn't change the breakdown torque value. It does change the slip. Skewing will increase the rotor resistance, but is not used to purposely alter resistance. Skewing is used to reduce cogging and noise...


Higher allowed slip generally means more torque before the rotor stalls, right??? 

And what is the actual cause of the rotor stalling if not saturation, as I always...well... assumed it to be (since the amp/torque relationship seems to go exponential around the 150% mark which is exactly how a transformer behaves when it saturates)???

Free us from our delusions, oh mighty captain.. er.. major!


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## major (Apr 4, 2008)

Tesseract said:


> Higher allowed slip generally means more torque before the rotor stalls, right???


Hi Tesseract,

Talking about induction motors of design types A and B, which we are, at a fixed frequency, slip increases as load increases. This continues until breakdown. On a RPM vs torque plot, breakdown looks like a knee. If the load is increased to this point, the motor will stall because the actual stall torque, or starting toque is less than breakdown torque.

Slip is a consequence of the load increase and should not be viewed as the reason. In other words, the idea of increasing rotor resistance to increase slip to get more torque is illogical.



> And what is the actual cause of the rotor stalling if not saturation, as I always...well... assumed it to be (since the amp/torque relationship seems to go exponential around the 150% mark which is exactly how a transformer behaves when it saturates)???


This is difficult for me to explain. But you can imagine a circuit where the power is limited by the load impedance, right? Saturation is not occurring. A similar thing happens in the induction motor. It is not saturation which limits torque, but the electrical characteristics of the motor. To saturate the induction motor, you simply have to increase the voltage at a fixed frequency, regardless of load. If fact, that is how you test for the sat curve. Plot current vs voltage at a fixed frequency. If the voltage for the given frequency is correct, the induction motor will not saturate regardless of load.

It is a different animal, but saturation does not cause your DC motor to stall, right? It stalls because the load has exceeded the limit of electrical characteristic of the motor. In the DC case, it is resistance. In the AC case, it is impedance.

Here again, not a great explanation, but all my weary mind can offer up.

And it has been my experience when using VFDs on induction motors, you get anywhere near breakdown, you get an OC (over current) fault real fast. 

Regards,

major


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## Bowser330 (Jun 15, 2008)

CroDriver said:


> What cell has that high C ratings?


http://www.thunder-sky.com/pdf/TS-LFP60.pdf


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## CroDriver (Jan 8, 2009)

Bowser330 said:


> http://www.thunder-sky.com/pdf/TS-LFP60.pdf


Can't believe this.. The same cell but doubled C ratings. 

http://www.thunder-sky.com/pdf/20092201189.pdf

That are the cells I bought (111 of them). Some people mentioned that even the 10C rating is to optimistic. After everything I heard and read I won't push them over 5C


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## Bowser330 (Jun 15, 2008)

CroDriver said:


> Can't believe this.. The same cell but doubled C ratings.
> 
> http://www.thunder-sky.com/pdf/20092201189.pdf
> 
> That are the cells I bought (111 of them). Some people mentioned that even the 10C rating is to optimistic. After everything I heard and read I won't push them over 5C


 
To be honest I am pretty sure that "pulsed" means milli-seconds...

Thats why I wrote:

3C = continuous
20C = pulsed
8.33C (1000A) = 10 sec??? (still a guess)

I guess you could set your amp-limit to 5C, then, using your BMS you could see if any of the cells went out of balance or something, and then ramp it up to 6C and check, etc...until you find what the maximum C is where you truly have an issue....

I guess this is one reason why the A123 cells are better...

Another thing that is important is, whats the point of all that Amperage if its not usable (just spins wheels)...

I would be interested in a wheel slip sensor which would cut amperage by 100A (example) every few milliseconds, until wheel slip is no longer detected, sort of like a launch-control, so it limits amperage to the amount that will actually be useful, with limited slip... (a little slip is good)..


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## Tesseract (Sep 27, 2008)

major said:


> ...at a fixed frequency, slip increases as load increases. This continues until breakdown.


Yep... my misunderstanding (which I have had for many years, I regret to say) was that one intentionally designed the rotor for higher slip to allow higher torque, and I got the whole rotor resistance idea from the common practice of adding resistance in series with the wound rotor synchronous induction motor to increase starting torque. I put 2 and 2 together and got something like pi, I guess.




major said:


> This is difficult for me to explain. But you can imagine a circuit where the power is limited by the load impedance, right? Saturation is not occurring. A similar thing happens in the induction motor. It is not saturation which limits torque, but the electrical characteristics of the motor. To saturate the induction motor, you simply have to increase the voltage at a fixed frequency, regardless of load. If fact, that is how you test for the sat curve. Plot current vs voltage at a fixed frequency. If the voltage for the given frequency is correct, the induction motor will not saturate regardless of load.


Okay, I'll buy this for a dollar, but I still want to know what happens when the rotor saturates, anyway (even if it it is because too high a voltage for the frequency has been applied)? Conversely, when too _low_ a voltage is applied for the frequency (as when operating in the "constant hp" region") it would appear there would be a point at which the impedance limits current so much that the breakdown torque is less than the starting torque, and so a momentary overload above full running torque could plunge the motor into the pullup region of its operating curve... bad news, I'd imagine, for the motor, no?


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## JRP3 (Mar 7, 2008)

Bowser330 said:


> http://www.thunder-sky.com/pdf/TS-LFP60.pdf


Wow, they upped their max C rate to 20C AND number of cycles to 80% 3000 70% 5000!


----------



## major (Apr 4, 2008)

Tesseract said:


> I put 2 and 2 together and got something like pi, I guess.


Metric units 



> but I still want to know what happens when the rotor saturates, anyway (even if it it is because too high a voltage for the frequency has been applied).


Well, it makes the induction motor unhappy. It gets noisy. And messes up the waveform badly. It still runs but, unlike the series motor which seems to run fine when saturated, behaves badly. Since there is no good reason to run an induction motor into saturation, I have always avoided doing so. 

Did you ever hook up a 120V transformer primary to 240V?



> Conversely, when too _low_ a voltage is applied for the frequency (as when operating in the "constant hp" region") it would appear there would be a point at which the impedance limits current so much that the breakdown torque is less than the starting torque, and so a momentary overload above full running torque could plunge the motor into the pullup region of its operating curve... bad news, I'd imagine, for the motor, no?


Above base frequency, the flux is reduced. Sometimes actually called field weakening the induction motor. This reduces the breakdown torque as well as the starting torque. I think it is not so much that the machine itself limits current, but that you have to. Otherwise, like you say, it hits the breakdown point and stalls while drawing a bunch of amps.

And never say _constant hp _to me again 

Regards,

major


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## Qer (May 7, 2008)

major said:


> Did you ever hook up a 120V transformer primary to 240V?


Dad once did the mistake to connect his shaver to 220 Volt when it was set to 110 Volt. It SCREAMED. Everyone in the house came to the rescue since we wondered what the h just happened and who was dying.

I'd never imagined such a small little gadget could produce that kind of racket. No, I don't think I'll try connecting a transformer (especially not a big one) the way you suggest...


----------



## piotrsko (Dec 9, 2007)

Qer said:


> Dad once did the mistake to connect his shaver to 220 Volt when it was set to 110 Volt. It SCREAMED. Everyone in the house came to the rescue since we wondered what the h just happened and who was dying.
> 
> I'd never imagined such a small little gadget could produce that kind of racket. No, I don't think I'll try connecting a transformer (especially not a big one) the way you suggest...



the big 5kw isolation transformer we used hums loudly and will blow the service breaker or inline fuse when some of our idiots forget to switch them back to 240. Every once and a while if the breaker is for a larger circuit you get the dreaded burnt smell that lasts for a day or so.


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## CroDriver (Jan 8, 2009)

JRP3 said:


> Wow, they upped their max C rate to 20C AND number of cycles to 80% 3000 70% 5000!


I would really like to know if they just wrote some new specs or the cells have been modified...


----------



## Bowser330 (Jun 15, 2008)

CroDriver said:


> I would really like to know if they just wrote some new specs or the cells have been modified...


Hey Crodriver, so are Kostov-motors.com only connecting your motors, or are they also making them stronger?

If so, do you know what modifications they are making? Can you help us be mentioning them here?


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## tomofreno (Mar 3, 2009)

> But you can imagine a circuit where the power is limited by the load impedance, right? Saturation is not occurring. A similar thing happens in the induction motor. It is not saturation which limits torque, but the electrical characteristics of the motor.


 My (meager) understanding of this is that leakage flux increases with slip resulting in increasing rotor reactance and less induced current for a given voltage.

Tom


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## CroDriver (Jan 8, 2009)

Bowser330 said:


> Hey Crodriver, so are Kostov-motors.com only connecting your motors, or are they also making them stronger?
> 
> If so, do you know what modifications they are making? Can you help us be mentioning them here?


Hi. I *think* that the motors will stay stock. But I'm not sure since they knew from the beginning for what I will use them and the voltage and current they will have to handle...


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## ubergeek63 (Oct 12, 2009)

Tesseract said:


> Yep... my misunderstanding (which I have had for many years, I regret to say) was that one intentionally designed the rotor for higher slip to allow higher torque, and I got the whole rotor resistance idea from the common practice of adding resistance in series with the wound rotor synchronous induction motor to increase starting torque. I put 2 and 2 together and got something like pi, I guess.
> 
> 
> 
> ...


Percent of saturation goes up with current, current gues up with voltage and down with frequency. Rerating a 10HP AC motor can result in 100HP peak and 50HP continuous. The reduced weight translates directly into increased range.

Dan


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## ubergeek63 (Oct 12, 2009)

CroDriver said:


> Can't believe this.. The same cell but doubled C ratings.
> 
> http://www.thunder-sky.com/pdf/20092201189.pdf
> 
> That are the cells I bought (111 of them). Some people mentioned that even the 10C rating is to optimistic. After everything I heard and read I won't push them over 5C


"Simple" changes in purity and electrodes can effect this since the C rate is fairly proportional to interna; resistance at a given cell size and chemistry.

Dan


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## ZX-E (Aug 31, 2009)

Wirecutter said:


> Actually, it's quite a bit more. The Tesla is closer to 200 HP.
> 
> 
> 
> ...



Actually it looks like the Tesla is rated at 300 hp: http://www.teslamotors.com/performance/acceleration_and_torque.php. From what I've heard the motor is air cooled and about the size of a watermelon. If this is just a question of pure horsepower, are there any DC motors with a similar peak power to size ratio that can still run safely at the claimed power? Obviously the Tesla can.


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## ZX-E (Aug 31, 2009)

That's the sport model . 295 ft-lbs @ 5100 rpm.


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## ubergeek63 (Oct 12, 2009)

ZX-E said:


> Actually it looks like the Tesla is rated at 300 hp: http://www.teslamotors.com/performance/acceleration_and_torque.php. From what I've heard the motor is air cooled and about the size of a watermelon. If this is just a question of pure horsepower, are there any DC motors with a similar peak power to size ratio that can still run safely at the claimed power? Obviously the Tesla can.


There are a few details that you are neglecting:

1: Cars only need peak power for short periods of time
2: Cars need high torque more often than high power
3: IC engines suck at delivering high torque at both low and high RPMs
4: AC motors excel at both
5: ratings are not what they appear

The Tesla roadster only uses a 20-30HP motor though they would like you to think it is special. Stock 30HP AC motors can be run at close to 300HP peak until they overheat using a technique known as rerating. If you actually go lookup the specs, a 250HP motor is in a 449T frame and weighs in at ove 2000lb.

http://energy.ece.illinois.edu/chapman/papers/IEMDC 2003 2.pdf


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## JRP3 (Mar 7, 2008)

ubergeek63 said:


> The Tesla roadster only uses a 20-30HP motor though they would like you to think it is special.


I'm not aware of another 75 lb motor that can do 14,000 RPM and 300 hp.


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## tomofreno (Mar 3, 2009)

> Cars only need peak power for short periods of time


 Yes, but it is nonetheless required if you want to accelerate as in appears crodriver does. As JRP3 points out that combination of weight and peak power is unusual.


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## ZX-E (Aug 31, 2009)

ubergeek63 said:


> There are a few details that you are neglecting:
> 
> 1: Cars only need peak power for short periods of time
> 2: Cars need high torque more often than high power
> ...



Sorry, but I don't see how I was neglecting any of those things. I just want to know if there's a DC motor that can compare to it. Simple as that.


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## major (Apr 4, 2008)

ZX-E said:


> I just want to know if there's a DC motor that can compare to it. Simple as that.


About the closest thing I've seen documented is Mike's CrazyHorse Pinto here: http://www.diyelectriccar.com/forums/showthread.php?t=16474&highlight=crazyhorse+pinto He has the dyno charts about midway thru. True, it is a pair, but what the H. And if Mike had the Tesla battery, I think he could beat the peak power. But you never know when Mr. Zorch will raise his ugly head 

major


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## JRP3 (Mar 7, 2008)

But probably more than 3 times the motor weight.


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## major (Apr 4, 2008)

JRP3 said:


> But probably more than 3 times the motor weight.


Glad you said that JRP,

I haven't looked, but it would be interesting to compare the 1/4 mile times of the Tesla to Mike.

Which does relate to your point.

major


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## paker (Jun 20, 2008)

So is anyone considering the AC motor, Curtis programmable controller combo from High Performance Golf Cars that Jack Rickard was showing in one of his Friday videos? For about $4800 it sounds quite interesting. If I get financially stable again to the point I can actually start a conversion this is what I'd consider using.


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## tomofreno (Mar 3, 2009)

Yeah. Bought one 4 months ago and have it in a Swift. Ran for the first time last week. Then the charger died on first startup, and Voltblochers killed two of my cells. JRP3 has a thread on HPGC motors on this forum. I have a build thread on the Swift. You might look around a bit.

Tom


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## ZX-E (Aug 31, 2009)

tomofreno said:


> Yeah. Bought one 4 months ago and have it in a Swift. Ran for the first time last week. Then the charger died on first startup, and Voltblochers killed two of my cells. JRP3 has a thread on HPGC motors on this forum. I have a build thread on the Swift. You might look around a bit.
> 
> Tom



Good god man. What did the Voltblochers do? I know they get pretty hot.


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## JRP3 (Mar 7, 2008)

I think a few of them just drained some cells while sitting, and without realizing it Tom drove the car and killed them.
Major,
I think NEDRA shows 12.64 for a Tesla Sport quarter. I saw 12.4 for the crazyhorse pinto.


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## CroDriver (Jan 8, 2009)

Maybe DC strikes back in a few days 



























































It's amazing how outdated the available technology is (except controllers). There is a lot room for improvements. I have seen sooo many imperfections in the current designs that I'll develop a lot stuff on my own with some partners


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## tomofreno (Mar 3, 2009)

> Good god man. What did the Voltblochers do? I know they get pretty hot.


 Evidently some are at least partially conducting when they are supposed to be off. Evcomponents said they had had around 10 other people call complaining of dead cells with VBs. They are going to recall VBs, and are currently investigating whether it is a design, assembly, component, or some other flaw. There is more about it on my "SwiftE" thread. I only drove the car around the driveway for a couple minutes, so the cells had to be pretty drained prior to that. The other 32 cells and VB's seem to be fine.


----------



## DavidDymaxion (Dec 1, 2008)

It isn't exactly apples-to-apples to compare just the weight of the motors only for AC to DC. The AC Propulsion motor controller weighs something like 70 lbs, the motor about 110 lbs, package weight is 180 lbs.

Contrast that to an 11 inch Kostov (180 lbs) and a Z1k (15 lbs), which produces similar power, or go with a Z2k (30 lbs) which produces double the power.

Does anyone know what the inverter and cooling system weigh on the Tesla?


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## JRP3 (Mar 7, 2008)

DavidDymaxion said:


> It isn't exactly apples-to-apples to compare just the weight of the motors only for AC to DC. The AC Propulsion motor controller weighs something like 70 lbs, the motor about 110 lbs, package weight is 180 lbs.


Except the ACP controller is also a charger, and a DC/DC converter, so that's not apples to apples either.



> Contrast that to an 11 inch Kostov (180 lbs) and a Z1k (15 lbs), which produces similar power, or go with a Z2k (30 lbs) which produces double the power.


Just because the controller can make the power doesn't mean the motor can handle it. I don't think a Kostov, or any motor, can do 1000 amps at high voltage for more than a few seconds, let alone 2000 amps.


> Does anyone know what the inverter and cooling system weigh on the Tesla?


Probably less than the ACP unit since they don't use the inverter and motor as a charger any more.


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## DavidDymaxion (Dec 1, 2008)

Those are good points, but a DC system still compares favorably to AC. Throw in 10 lbs for a DC-DC converter and 30 lbs for a charger -- the DC motor + Zilla 2k combo is still more hp/lb than AC Propulsion, and likely more than Tesla.

The http://www.NEDRA.com guys know all about high Amps. The Killacycle puts about 900 Amps through each 8 inch motor. John Wayland put 1200 to 1800 Amps through his single Kostov (once he put at least 1200 Amps into his Kostov for 30 to 40 seconds before it blew). Dennis Berube puts 1500+ Amps through his GE 13 inch. You are right about the few seconds thing, though, they do this for a drag strip run of 8 to 12 seconds. In fairness, the Tesla or ACP systems couldn't handle those Amps for more than a few seconds either (if you could double or triple the inverter output).

Don't get me wrong, I love the slightly higher efficiency of AC, broad torque curve, and effortless regen. If you want to go fast, though, and don't care about regen, you are better off putting the money into A123 batteries than an expensive AC system.



JRP3 said:


> Except the ACP controller is also a charger, and a DC/DC converter, so that's not apples to apples either.
> 
> Just because the controller can make the power doesn't mean the motor can handle it. I don't think a Kostov, or any motor, can do 1000 amps at high voltage for more than a few seconds, let alone 2000 amps.
> Probably less than the ACP unit since they don't use the inverter and motor as a charger any more.


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## CroDriver (Jan 8, 2009)

DavidDymaxion said:


> ...In fairness, the Tesla or ACP systems couldn't handle those Amps for more than a few seconds either (if you could double or triple the inverter output).


Yep, there are some reports that the Tesla Motor (or inverter?) overheats if pushed hard for a few minutes.

I don't like this whole apple-orange thing. It's all about power, weight and efficiency!

We shouldn't care if it is a common-rail-bi-turbo-diesel, a steam engine or an AC or DC electric system.

I would love to have a liquid cooled 400kW motor with regen but there simply are non available (at least not for a reasonable price) so I built a DC racer.

This are the only AC systems with 100+ kW I know:

1. AC propulsion - not available for DIY-ers
2. UQM 150 - 35 k$ - not available for DIY-ers
3. Siemens 200kW liquid cooled AC motor - no inverter, not available for DIY-ers
4. Brusa 400V/100kW inverter + HSM 40kW continuos, 82kW peak motor - 42.100 € (!!)

It's not hard to make the DC decision with this prices


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## JRP3 (Mar 7, 2008)

DavidDymaxion said:


> The http://www.NEDRA.com guys know all about high Amps. The Killacycle puts about 900 Amps through each 8 inch motor. John Wayland put 1200 to 1800 Amps through his single Kostov (once he put at least 1200 Amps into his Kostov for 30 to 40 seconds before it blew). Dennis Berube puts 1500+ Amps through his GE 13 inch. You are right about the few seconds thing, though, they do this for a drag strip run of 8 to 12 seconds. In fairness, the Tesla or ACP systems couldn't handle those Amps for more than a few seconds either (if you could double or triple the inverter output).


Tesseract killed a Kostov with about 10 seconds of 900 amps at about 200 volts
http://www.diyelectriccar.com/forums/showpost.php?p=136717&postcount=401

The Tesla is a much higher voltage system so doesn't need to deal with as much amperage.


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## DavidDymaxion (Dec 1, 2008)

The graph is longer than 10 seconds -- was it ramping from 0 to 900 Amps for 10 seconds, and then ran another 10 seconds at 900 Amps? BTW, the Kostov internal fan isn't great, you really should run one with an external blower. Was this one externally cooled? Was it the 9 inch or the 11 inch? (These would be good data points for me to know!) It is noteworthy that Wayland had racing mods done to his motor, I have heard the stock Kostovs aren't as robust. Was the blown motor stock?

It's true that higher voltage lets you run lower current for the same power. The Tesla has a 375 Volts nominal pack. John Wayland ran a 336 Volt pack, Berube runs a 348 Volt pack. So yes the Tesla is higher voltage, but not much higher. While Advanced DC motors don't like really high Volts, the Kostov and GE motors have been run at AC Voltage levels.


JRP3 said:


> Tesseract killed a Kostov with about 10 seconds of 900 amps at about 200 volts
> http://www.diyelectriccar.com/forums/showpost.php?p=136717&postcount=401
> 
> The Tesla is a much higher voltage system so doesn't need to deal with as much amperage.


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## Tesseract (Sep 27, 2008)

DavidDymaxion said:


> The graph is longer than 10 seconds -- was it ramping from 0 to 900 Amps for 10 seconds, and then ran another 10 seconds at 900 Amps?


Very good questions, as without knowing the answers this really isn't fair to Kostov.

So the motor was on our dyno for testing/calibrating controllers prior to shipment and just prior to the zorch event I had done my usual test sequence which is to run the motor with enough loading for the duty cycle to hit 40% at a current of 300-400A to calibrate the internal current sensor against my Fluke. Then I ramp the current up to whatever max the uncalibrated throttle will allow (usually 850-950A) a few times in a row for around 2-4 seconds each time, then let the motor run less loaded at 200A and 3000 rpm for a couple minutes to resurface the brushes some and equalize any hot-spots (I know this doesn't do much, but it makes me feel better anyway...  ). 

So that's more or less what I had just done when Seb came along and called me a *bleep* for "babying the controller" then took over the throttle and ran the motor at 900A until it blew up (~10-12 seconds). 




DavidDymaxion said:


> BTW, the Kostov internal fan isn't great, you really should run one with an external blower. Was this one externally cooled? Was it the 9 inch or the 11 inch?


I'd say the internal fan of most motors is just a step above useless unless you run the motor at or above some minimum speed all the time. I totally agree that if you have a high power controller you should just forget the internal cooling fan and use a blower, regardless. 

This was a stock Kostov 9"/144V motor, so it was being EXTREMELY abused. While it was costly for us to obtain this data, it was valuable if for no other reason than we can suggest sensible limits to program into the Soliton1.

Oh, and one other thing... I don't know for sure, but I somehow doubt the Tesla can run at 300hp or whatever it's MAX is for more than a few seconds, either. I mean, even if the motor was 96% efficient (doubt it) you'd still have to get rid of ~9kW in waste heat. 

(this argument is still going on? wtf?)


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## JRP3 (Mar 7, 2008)

Tesseract said:


> (this argument is still going on? wtf?)


It never ends! Too much fun to argue


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## DavidDymaxion (Dec 1, 2008)

Tesseract, many thanks! This is great info. I want to push my Kostov hard, but hopefully short of destruction!


Tesseract said:


> Very good questions, as without knowing the answers this really isn't fair to Kostov.
> 
> So the motor was on our dyno for testing/calibrating controllers prior to shipment and just prior to the zorch event I had done my usual test sequence which is to run the motor with enough loading for the duty cycle to hit 40% at a current of 300-400A to calibrate the internal current sensor against my Fluke. Then I ramp the current up to whatever max the uncalibrated throttle will allow (usually 850-950A) a few times in a row for around 2-4 seconds each time, then let the motor run less loaded at 200A and 3000 rpm for a couple minutes to resurface the brushes some and equalize any hot-spots (I know this doesn't do much, but it makes me feel better anyway...  ).
> 
> ...


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## Tesseract (Sep 27, 2008)

DavidDymaxion said:


> Tesseract, many thanks! This is great info. I want to push my Kostov hard, but hopefully short of destruction!


No problem... They can take some pretty serious abuse. I briefly - as in half a second briefly - ran one at 145V/1200A (174kW) with an unlocked Soliton1 and while the light show was vigorous, the Kostov 9 took it. So, yeah, it was a well-abused motor before Seb blew it up.


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## major (Apr 4, 2008)

Tesseract said:


> ......- ran one at 145V/1200A (174kW).....


You guys do realize that this is input power and the numbers discussed on the Tesla and ACP are output


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## DavidDymaxion (Dec 1, 2008)

It's fun to throw the numbers around... But do realize the Wayland White Zombie Datsun and Berube Smoke Screen truck are doing 0 to 60 and the 1/4 mile faster than the Tesla (and Smoke Screen weighs more!)... So it looks like they are winning for output power, too!  Input power is easier to measure.

Interesting data point: ACP says it's 150 kW system is rated for 50 kW continuous. That means less than about 160 Amps continuous if you don't want eventual overheating.


major said:


> You guys do realize that this is input power and the numbers discussed on the Tesla and ACP are output


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## major (Apr 4, 2008)

DavidDymaxion said:


> So it looks like they are winning for output power, too!


David,

That would be torque. The whole point of the thread http://www.diyelectriccar.com/forums/showthread.php/torque-irrelevant-relevanti-36904.html 

But we don't need to start into that here. However, from what I've seen, I seriously doubt that a Kostov 9 or 11 inch would have greater power output than the motor in the Tesla, let's say qualified for 10 seconds or longer.

And you mention 50 kW continuous for the ACP. That is output power. Show me a DC motor with that high of a continuous rating which will fit into a car, let alone of similar size to the ACP.

Regards,

major


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## JRP3 (Mar 7, 2008)

Let's also remember, ACP does not = Tesla. Tesla has changed and improved the ACP design. Lighter motor, higher output, and no longer uses the motor and controller for charging.


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## ubergeek63 (Oct 12, 2009)

ZX-E said:


> Sorry, but I don't see how I was neglecting any of those things. I just want to know if there's a DC motor that can compare to it. Simple as that.


See my link... there are many that do the difference is not a special motor but a special controller. ANY 12 wire 60/60Hz 3PH 30HP AC motor wired for low voltage operation operated at high frequency and high voltage will perform similarly, though you do want a premium efficient type to start with.

But to answer your question, it is an effect of the AC nature that allows this to work so there is no way to make a DC motor do this even with rare earth magnets.

Dan


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## ubergeek63 (Oct 12, 2009)

tomofreno said:


> Yes, but it is nonetheless required if you want to accelerate as in appears crodriver does. As JRP3 points out that combination of weight and peak power is unusual.


Not a problem at all. Did ANYONE read the PDF at the link I posted? 

Minor motor modifications and major controller modifications get large peak power increases such that the AC motor horse power rating can be sized for the continuous duty, IE cruising requirements instead of the peak requirements that you need to size a IC engine for.

Dan


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## major (Apr 4, 2008)

ubergeek63 said:


> Not a problem at all. Did ANYONE read the PDF at the link I posted?


Yeah, Dan, I read it. Interesting. All they are doing is changing the design voltage of the windings by coil connection. When was the last time you were able to buy a 30 hp motor rated for 120 Vac or 60 Vac? Minor modifications the manufacturer should do for you, I think is what the paper said. You want to bet?

Even changing the winding, you'll fall way short of the Tesla (or ACP) motor. If was that easy, you'd think there would be some competition for those guys. Love to see you do it. Go ahead, make my day. 

Regards,

major


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## JRP3 (Mar 7, 2008)

Mine too


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## Electric Car-Nut (Jul 5, 2009)

Wirecutter said:


> Thanks for that, major. Great laugh. I've seen that number before, too, but when you put it that way, it really does sound ridiculous.
> 
> A coworker once ran the numbers on an EV with 200+ mile range and a 5 minute (or similarly very short) recharge time. Using conservative estimates for vehicle weight, it turned out that it took an incredible amount of power draw to acheive the stated recharge time, simply by virtue of replacing enough energy to move a car 200 miles in such a short time. (edit: Tesla -> 53kWh battery. To replace that 53kWh (or 3.18 megawatt-minutes) of energy in 5 minutes takes a 636kW draw, assuming everything's 100% efficient, which it's not. My house has 200A service, which at 220v works out to 44kW.)
> 
> ...


Friends of mine who drive locomotives for CSX have told me that they run 5,000 hp with the 8 wheel locos and 7,000 hp with the 12 wheel locos, but I never asked how many motors were driving the wheels, might be one for each wheel...


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## ubergeek63 (Oct 12, 2009)

major said:


> Yeah, Dan, I read it. Interesting. All they are doing is changing the design voltage of the windings by coil connection. When was the last time you were able to buy a 30 hp motor rated for 120 Vac or 60 Vac? Minor modifications the manufacturer should do for you, I think is what the paper said. You want to bet?
> 
> Even changing the winding, you'll fall way short of the Tesla (or ACP) motor. If was that easy, you'd think there would be some competition for those guys. Love to see you do it. Go ahead, make my day.
> 
> ...


sorry i was snooping for a while as well as working on things. Actually they are talking about taking a 230/460V motor and wiring the phases in parallel

Gonna keep trying to look a mfg to see if they have a 12 wire motor.

Dan


----------



## major (Apr 4, 2008)

ubergeek63 said:


> Actually they are talking about taking a 230/460V motor and wiring the phases in parallel


Dan,

From your source: 




> we began with a motor that had been factory configured for a dual 115 V/ 230 V 60 Hz rating


​

Show me where to get a 115V 3 phase 30 HP induction motor.​ 
Regards,​ 
major​


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## ubergeek63 (Oct 12, 2009)

major said:


> Dan,
> 
> From your source:
> 
> ...


And the very next sentence is: 

(a low-cost modification of winding taps compared to the
catalog 230 V/ 460 V connections)

Or, in other words, "readily doable but not stock".

Dan


----------



## major (Apr 4, 2008)

ubergeek63 said:


> And the very next sentence is:
> 
> (a low-cost modification of winding taps compared to the
> catalog 230 V/ 460 V connections)
> ...


And my point is that you will not find a motor manufacturer willing to do this unless you're bringing them an order for 5,000 motors. If you can find differently, please let me know as I am interested in a few. 

And furthermore, even if you get that far, you will be a long way from the machines of the Tesla and ACP.


----------



## dataman19 (Oct 7, 2009)

I take stated motor horsepower ratings with a grain of salt over my shoulder.
..
Electric power is different that ICE power. The torque curves show they are different.
..
Most ICE automobiles are grossly over powered - a known fact. They are overpowered so that they accelerate to max speed in the shortest time span. - When was the last time you heard someone walk into a dealership and ask them "which one of these has the slowest acceleration and best gas mileage?" _ NOT!
...
The reason ICE [powered vehicles have transmissions is because the ICe engine has a torque curve. And a transmission lets you operate that vehicle to maximize the use of that engine torque curve to accelerate and maintain speed. But probably less than 20% of the engines power is used to maintain speed (unless going up hill, etc).
..
This is probably why so may EV builders are getting by with less than 40 HP rated motors. The secret in electrics is in the controller. A fact stated on this forum over and over again.
..
As for the water cooled AC motors - No they are not water cooled just because they run hotter. They don't run any hotter than a comparatively built DC motor - but.... The AC Motor is more tightly constructed and does not have as much air circulation. It is made so because it is used in tight enclosures with little or no air circulation (so even if it were more loosely built - it wouldn't get the cooling effects anyway).
..
The other point is that AC Drive motors are used in a more demanding environment (enclosure has already been covered) that includes heavy debris, dust, grease, oils, solvents, etc. In this same environment an air cooled DC motor would soon fail (even if it were not totally clogged with debris).
...
Yes the AC Motor does not have any brushes to wear out - but then there are brushless DC Motors out there too.
..
The main reason that DC motors are so popular with the EV DIY crowd is their economy. The reason they are so pupular with the EV drag racing crowd is somewhat the same - economy. Fry a DC Motor and controller and you have fried a 4K investment (maybe 9K). Fry an AC Motor and Controller and you could easily be frying a 12K Investment.
..
dataman19


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## JRP3 (Mar 7, 2008)

dataman19 said:


> As for the water cooled AC motors - No they are not water cooled just because they run hotter. They don't run any hotter than a comparatively built DC motor - but.... The AC Motor is more tightly constructed and does not have as much air circulation. It is made so because it is used in tight enclosures with little or no air circulation (so even if it were more loosely built - it wouldn't get the cooling effects anyway).


There are a lot of air cooled AC motors, including the ACP, Tesla, and the HPG motor that I'm using.


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## volksracer (Mar 22, 2010)

Man, this is deja-vu. IMO. Coming from a long time car (ICE) guy, this AC vs DC proponents, sounds like the people who compare the OHV Pushrod V8 engines to modern fuel injected turbo charged/Hi-rev 4-cylinder. It's ironic really, I mean you can make good performance from both, sure one is "more efficient" but, the contrasts have already been made and it's the persistence and development by individuals that will make make motors better. Both by cost and simplicity, or technology and complexity. Good luck guys, and great info.


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## RogueThunder (Jul 31, 2009)

Must say, interesting thread, took me almost a week to read through the whole thing. Alot of good information that if taken with a proper couple grains of salt... Is quite useful.

Before reading this thread, I was partial to AC, but with no great dislike of DC.
Now I'm partial to AC and Brush-less DC, with no dislike of DC but little to say about it(It works.), wondering when/if the costs will even out XD...

In my case I suspect it will be more a matter of which I get ahold of in my random wandering of salvage yards that ultimately will determine which I fiddle with xD...
From what it looks... DC and AC are roughly matched, for their various... fairly even flaws.
-----------------------------------------------------------------------
And... on side tangents...


dataman19 said:


> ... When was the last time you heard someone walk into a dealership and ask them "which one of these has the slowest acceleration and best gas mileage?" _ NOT! ...


*chuckles* I've watched someone walk into a dealership and ask for "The best gas mileage and I don't care about acceleration." ... You have no idea how hard I facepalmed. 
I'm all for efficeancy. But I drove a badly abused Geo Metro ONCE in driving school back a few years ago. After it failed to make 65mph, going down hill on a mid length onramp. I *cough*forcefully*cough* requested they never schedule me for that vehicle ever again... At first they tried to tell me driving crappy cars was a good learning experience. I told em yeah, I learned to never step foot in a Geo Metro who's engine had been burned out... ... ... twice, I like actually being able to make freeway speeds coming down a hill -.-...
XD They never did try to schedule me with that car again.


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## JRP3 (Mar 7, 2008)

Interestingly Tesseract recently posted that a series DC motor has about a maximum of 1hp/lb peak. AC certainly beats that power to weight ratio.


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## tomofreno (Mar 3, 2009)

> AC certainly beats that power to weight ratio.


 As has been said before, it depends on the controller. The AC50/Curtis 1238 doesn't come close to that. From a practical viewpoint, even if the Tesla, MiniE, or AC propulsion motor/controllers do, it doesn't help diyers. I really like AC with electric braking, but there is no doubt that if a diyer wants high acceleration, and they don't have tens of thousands to spend on a motor/controller, DC is the way to go.


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## etischer (Jun 16, 2008)

dataman19 said:


> As for the water cooled AC motors - No they are not water cooled just because they run hotter. They don't run any hotter than a comparatively built DC motor - but.... The AC Motor is more tightly constructed and does not have as much air circulation. It is made so because it is used in tight enclosures with little or no air circulation (so even if it were more loosely built - it wouldn't get the cooling effects anyway).



I think the reason AC motors are available water-cooled and brushed DC motors aren't is this:

AC motors have the coils (where heat is generated) on the outside where water-cooling is easy. 

DC motors have the heat generating coils in the middle of the motor, on the spinning rotor, which is nearly impossible to water cool. 

A motor's hp rating is based on how much heat it can dissipate and it's efficiency. When the heat is generated on the outside of the motor, it has more effective cooling.


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## JRP3 (Mar 7, 2008)

tomofreno said:


> As has been said before, it depends on the controller. The AC50/Curtis 1238 doesn't come close to that. From a practical viewpoint, even if the Tesla, MiniE, or AC propulsion motor/controllers do, it doesn't help diyers. I really like AC with electric braking, but there is no doubt that if a diyer wants high acceleration, and they don't have tens of thousands to spend on a motor/controller, DC is the way to go.


I wasn't talking about affordable, just the best power to weight ratio possible. Seems as if AC is a clear winner. A full power DC system running at 1hp/lb isn't going to be cheap either, but at least you can get your hands on one.


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## Tesseract (Sep 27, 2008)

JRP3 said:


> Interestingly Tesseract recently posted that a series DC motor has about a maximum of 1hp/lb peak. AC certainly beats that power to weight ratio.


I also stated that said rule of thumb only applied to the massaged-over forklift motors that are available to us in the 9" and 11" sizes. 




etischer said:


> I think the reason AC motors are available water-cooled and brushed DC motors aren't is this:
> 
> AC motors have the coils (where heat is generated) on the outside where water-cooling is easy.
> 
> ...


Sorta... In an AC induction motor the losses are fairly well balanced between the rotor and stator. Do not think that there are no losses in the rotor - it is, after all, a single turn secondary that has been shorted so there are tremendous currents circulating.

In a well-designed DC motor the same applies - losses are evenly balanced between rotor and stator - but the real problem during overload is that the brushes get hotter faster than the rest of the armature (rotor).

It is obviously impractical to cool the rotor of either motor type. 

The switched reluctance motor DOES possess the benefit of very low rotor losses, and it is very easy to design and construct, too, but that's a whole 'nother topic.


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## DavidDymaxion (Dec 1, 2008)

NEDRA racers are getting 2 hp/lb -- but they fry their motors occasionally, too.


JRP3 said:


> Interestingly Tesseract recently posted that a series DC motor has about a maximum of 1hp/lb peak. AC certainly beats that power to weight ratio.


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## CroDriver (Jan 8, 2009)

DavidDymaxion said:


> NEDRA racers are getting 2 hp/lb -- but they fry their motors occasionally, too.


Where do they get 2hp/lb? From the batteries or at the output shaft?


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## DavidDymaxion (Dec 1, 2008)

Using ET and trap speed (perhaps the most honest estimate of power), let's look at an example:

Killacycle, 7.864 s @ 169 mph, about 800 lbs. Using this calculator: http://www.dragtimes.com/horsepower...ubmitButtonName=Calculate+Horsepower+Estimate :
313 hp for 100 lbs of motor.

White Zombie: 
11.466 s @ 114 mph, about 2100 lbs
260 hp for 175 lbs of motor.

So it looks like about 3.1 hp/lb for Killacycle, and 1.5 hp/lb. for White Zombie.


CroDriver said:


> Where do they get 2hp/lb? From the batteries or at the output shaft?


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## major (Apr 4, 2008)

DavidDymaxion said:


> Killacycle, 7.864 s @ 169 mph, about 800 lbs. Using this calculator: http://www.dragtimes.com/horsepower...ubmitButtonName=Calculate+Horsepower+Estimate :
> 313 hp for 200 lbs of motor.
> 
> White Zombie:
> ...


David,

So a pair of 6.7 inch motors weigh 200 and a Siamese 8 weighs 175 

And your calculator is likely making assumptions about power plant performance based on ICE and transmission clutch/torque converter assumptions. I don't think these give an accurate representation of the electric motor as used for the power plant.

Regards,

major


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## JRP3 (Mar 7, 2008)

I think Major is questioning the 200lbs for the two 6.7 motors. I've never heard of a 100lb 6.7 motor.


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## DavidDymaxion (Dec 1, 2008)

Thanks for the clarification. All fixed in the original post now: http://www.diyelectriccar.com/forums/showpost.php?p=173844&postcount=323

Major: Yep, electric and gasoline motors are not perfectly apples-to-apples comparisons. Can you suggest a better yet easily measured metric than using 1/4 mile data?


JRP3 said:


> I think Major is questioning the 200lbs for the two 6.7 motors. I've never heard of a 100lb 6.7 motor.


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## major (Apr 4, 2008)

DavidDymaxion said:


> Yep, electric and gasoline motors are not perfectly apples-to-apples comparisons. Can you suggest a better yet easily measured metric than using 1/4 mile data?


How about dynamometer tests  The 1/4 mile time is not a true measure of power. This was demonstrated by the example in the thread http://www.diyelectriccar.com/forums/showthread.php/torque-irrelevant-relevanti-36904p3.html posts # 22, 23 & 25. More power does not win the 1/4 mile race. Gettin' goin' faster sooner is a big factor. And that is torque.

Power is power. Easily measured with a dynamometer. The 1/4 mile race is another animal all together. It all depends on what you want to consider important 

Regards,

major


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## DavidDymaxion (Dec 1, 2008)

Major: Agreed a dyno is a more scientific measure of power. Here are a couple of additional thoughts:

Few of even the hardcore NEDRA racers have done a dyno, so it makes it hard to compare to their cars -- but they do publish their 1/4 mile stats.







Among my gasser racer buddies very few have done dyno pulls, far more have done 1/4 mile runs (even for autocrossers and road racing track racers). A dyno is great for calculations, but lacks critical mass for comparisons between hobbyist vehicles. My other observation is that among those that do dyno runs they don't do very many. It's much easier to find "Modification A, 1/4 mile stats A, Modification B, 1/4 mile stats B, etc." kinds of blogs than similar for dynos.

Also, for about the price of a dyno run, you can buy a gtech or iphone app that measures acceleration vs. time -- this is would be an easier and cheaper way to do a bunch of power measurements than a dyno, while providing the same information. (Yes, I know using an accelerometer is less accurate, but I won't lose sleep over a couple percent.) If you wanted to get fancy, you could combine accelerometer data with GPS and coast-down data and outdo the dyno for data to play with.









major said:


> How about dynamometer tests  The 1/4 mile time is not a true measure of power. This was demonstrated by the example in the thread http://www.diyelectriccar.com/forums/showthread.php/torque-irrelevant-relevanti-36904p3.html posts # 22, 23 & 25. More power does not win the 1/4 mile race. Gettin' goin' faster sooner is a big factor. And that is torque.
> 
> Power is power. Easily measured with a dynamometer. The 1/4 mile race is another animal all together. It all depends on what you want to consider important
> 
> ...


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## major (Apr 4, 2008)

DavidDymaxion said:


> NEDRA racers are getting 2 hp/lb --


David,

This is what you said. And the discussion was about the electric motor. Power is the output from the motor. I don't think these guys are actually seeing 2 hp/lb.

I think Mike pushes his Siamese 9's about as hard as anybody. Here is his dyno run. http://www.dragtimes.com/1978-Ford-Pinto-Dyno-Results-Graphs-15453.html Granted this is power measured at the wheels, so motor output may be a few percent higher due to loss in the rear end and tires. But a little over 300 hp. And his combined motor weight is likely a little over 300 lbs.

If you want to claim electric motor power (or power density), then measure motor output power, not race times. If you want to claim race times, then measure race time, not power.

That's all I'm saying. 

major


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## CroDriver (Jan 8, 2009)

major said:


> David,
> 
> This is what you said. And the discussion was about the electric motor. Power is the output from the motor. I don't think these guys are actually seeing 2 hp/lb.
> 
> ...


Almost all NEDRA guys used Lead Acid so far so they couldn't push more power trough the motor. My car with the two custom 11" HV motors will have a 350V/4000 Amp capable pack (sagging to 260V at 4000 Amp).

I'll make a dyno test when I finish it (should be in two months).


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## major (Apr 4, 2008)

CroDriver said:


> My car with the two custom 11" HV motors will have a 350V/4000 Amp capable pack (sagging to 260V at 4000 Amp).
> 
> I'll make a dyno test when I finish it (should be in two months).


I can hardly wait, really.


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## Bowser330 (Jun 15, 2008)

CroDriver said:


> Almost all NEDRA guys used Lead Acid so far so they couldn't push more power trough the motor. My car with the two custom 11" HV motors will have a 350V/4000 Amp capable pack (sagging to 260V at 4000 Amp).
> 
> I'll make a dyno test when I finish it (should be in two months).


From what i've read 1000A through an 11" motor is about 300ftlbs of torque...so...4000A = 1200ftlbs???

You better find a performance dyno...thats some serious torque...


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## CroDriver (Jan 8, 2009)

Bowser330 said:


> From what i've read 1000A through an 11" motor is about 300ftlbs of torque...so...4000A = 1200ftlbs???
> 
> You better find a performance dyno...thats some serious torque...


One motor will power two wheels so I think that almost every dyno can handle one motor. I can simply turn off the other and have a FWD or RWD or AWD car by pressing a button.


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## DavidDymaxion (Dec 1, 2008)

Sadly, sometimes we have to infer things from the available data.  Don't worry, we agree that a dyno is awesome, controlled, repeatable, scientific, etc. If Bill Gates wants to fund dyno time for every EV, I certainly wouldn't stop him! 

You might have missed the edit on my original post. What I said was from quarter mile times I'm estimating the Killacycle has 3.1 hp/lb! That's even more than 2 hp/lb! How could the Killacycle be seeing less than 2 hp/lb for the motor if you put it on a dyno, with those 1/4 times and speeds? I know the killacycle has been on a dyno, but couldn't find data for that -- does anyone know what the killacycle dyno numbers were, better yet the dyno chart?

I wouldn't assume Mike's single data point represents the peak of DC motor performance for hp / lb of motor. Since we're taking about the peak of what is possible, the Killacycle is a better data point.

Just for fun, let's compare Mike's dyno chart to his 1/4 mile hp estimate. His dragtimes webpage says the dyno peak was 314 hp. Using his published stats of 12.470 s @ 104.47 mph, and Mike says his car is 3200 lbs, I'll estimate 3400 lbs with the driver. The drag times calculator estimates 325 hp at the flywheel. Mike doesn't run a tranny, just the rear end losses, so I'd guess his driveline losses to be around 8% (half of typical number since no tranny). 325 hp * 0.92 = 300 rwhp.

The dyno says 314 hp. An estimate from the 1/4 mile time is 300 rwhp. That's a 5% error, really not too bad.

Thanks Major for pointing out the weight error on the Killacycle motors, and the link to the Crazy Horse 1/4 mile and dyno data. It was illuminating!


major said:


> David,
> 
> This is what you said. And the discussion was about the electric motor. Power is the output from the motor. I don't think these guys are actually seeing 2 hp/lb.
> 
> ...


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## Bowser330 (Jun 15, 2008)

CroDriver said:


> One motor will power two wheels so I think that almost every dyno can handle one motor. I can simply turn off the other and have a FWR or RWD or AWD car by pressing a button.


Very true, you could dyno two wheels and then just adjust the dyno chart/graph by multiplying all the data points by 2, haha.


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## Tesseract (Sep 27, 2008)

DavidDymaxion said:


> ...
> You might have missed the edit on my original post. What I said was from quarter mile times I'm estimating the Killacycle has 3.1 hp/lb! That's even more than 2 hp/lb!...



Smaller motors, to a point, will deliver more power per pound. The 1hp/lb rule of thumb mainly applies to the 9" and 11" sizes, okay?

Also, I stipulated that my definition of peak power is that which can be SAFELY sustained for 10 seconds... and it wasn't in _this_ thread, which is obviously about something completely different.

Bottom line: if you are building a drag racer then you should expect the occasional zorched motor. Indeed, you are probably doing something wrong if you don't destroy the motor every run (you certainly aren't extracting the "maximum" power from the motor if you don't end up destroying it).

Given that the WarP11HV is wound for higher voltage, and it has demonstrably higher losses at the same current as compared to a WarP11, I fully expect CroDriver to blow up both motors the first time he floors it.


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## CroDriver (Jan 8, 2009)

What do you think, could a camera filming the commutator and ramping the power up slowly (maybe adding 100 Amps each run) help?



Tesseract said:


> Given that the WarP11HV is wound for higher voltage, and it has demonstrably higher losses at the same current as compared to a WarP11, I fully expect CroDriver to blow up both motors the first time he floors it.


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## major (Apr 4, 2008)

CroDriver said:


> What do you think, could a camera filming the commutator and ramping the power up slowly (maybe adding 100 Amps each run) help?


Hi Cro,

That would be a cool way to be on the safe side. Also it is really tempting to take it directly to the track and see what she'll do. But new motors should be broken in. Getting a good film on the commutator surface is crucial for tolerance of overload currents. This could take many hours of running under normal loads (currents). And then after an intense overload, it should be run at normal loads for a period to re-establish the comm condition.

But that is just me, a motor dork, talking. I doubt many heed such advice. But that just keeps the rebuilders busy 

And I hope the chrome doesn't interfere with the camera 

major


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## DavidDymaxion (Dec 1, 2008)

Go Cro go! A dyno chart would be great to see! You'll have a great machine.



Tesseract said:


> Smaller motors, to a point, will deliver more power per pound. The 1hp/lb rule of thumb mainly applies to the 9" and 11" sizes


Thanks for the clarifications. This is a good thing to know. Maybe I'll do four or more 6.7 inch motors in my next EV (although I wouldn't expect to be able to reliably do Killacycle levels of power). FWIW, I'm planning to do about 1 hp/lb in my 11 inch motor. Wish me luck! So what's the optimal motor size for power density? Too small and friction eats up too much of the power, too large and scaling laws make it heavy for the size.



Tesseract said:


> ... Also, I stipulated that my definition of peak power is that which can be SAFELY sustained for 10 seconds ...
> 
> Bottom line: if you are building a drag racer then you should expect the occasional zorched motor. Indeed, you are probably doing something wrong if you don't destroy the motor every run (you certainly aren't extracting the "maximum" power from the motor if you don't end up destroying it).


Agreed!


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## CroDriver (Jan 8, 2009)

major said:


> But that is just me, a motor dork, talking. I doubt many heed such advice. But that just keeps the rebuilders busy


Thanks for the advice Major, I will definitely do that



major said:


> And I hope the chrome doesn't interfere with the camera


You really like the chrome housing


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## Tesseract (Sep 27, 2008)

DavidDymaxion said:


> ...
> Thanks for the clarifications. This is a good thing to know.


Well... the clarifications _were_ in the original post from which JRP3 paraphrased me...

The 1hp/lb approximation



DavidDymaxion said:


> Maybe I'll do four or more 6.7 inch motors in my next EV (although I wouldn't expect to be able to reliably do Killacycle levels of power).


I hope you arrange the shafts in parallel with stacked belt, chain or gear drive to a larger root diameter common shaft rather than bolt them all together in a straight line. The shaft of a single 6.7" motor isn't going to take the combined torque from 4 motors for very long. 




DavidDymaxion said:


> FWIW, I'm planning to do about 1 hp/lb in my 11 inch motor. Wish me luck! So what's the optimal motor size for power density? Too small and friction eats up too much of the power, too large and scaling laws make it heavy for the size.


Unless our resident motor dork knows otherwise, I don't think there's any rule of thumb that can be used to predict the optimal motor size for power density... there are simply too many trade-offs at work.


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## nzev (Nov 20, 2008)

Jease!! the people on here who a avid AC lovers need to get a grip!! how much money do you have??? DC is faarrrrrrrrrr cheaper than AC for matched performance. Undoulbtably AC is best for OEM's, but OEM's will never make a tyre eating, axle braking beast that the average Jo could afford......


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## JRP3 (Mar 7, 2008)

nzev said:


> Jease!! the people on here who a avid AC lovers need to get a grip!! how much money do you have??? DC is faarrrrrrrrrr cheaper than AC for matched performance. Undoulbtably AC is best for OEM's, but OEM's will never make a tyre eating, axle braking beast that the average Jo could afford......


I doubt the average Jo can build "a tyre eating, axle braking beast that the average Jo could afford" either. That kind of power takes money, no matter the technology. Besides, this thread isn't about the most cost effective way to do something, it's called "Pure horse power DC vs AC". Nothing about price.


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## aeroscott (Jan 5, 2008)

nzev said:


> Jease!! the people on here who a avid AC lovers need to get a grip!! how much money do you have??? DC is faarrrrrrrrrr cheaper than AC for matched performance. Undoulbtably AC is best for OEM's, but OEM's will never make a tyre eating, axle braking beast that the average Jo could afford......


As you might have figured I'm into airplanes , especially home-built . I know a hand full of people that built and spent over $500,000 on their all carbon fiber wonders( 275 mph cruse) . I buy the way am not wealthy in fact under employed . I have demonstrated many times that with enough knowledge( never enough) and a little money( never enough ) we can do what almost all say is imposable.


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## DawidvC (Feb 14, 2010)

> "a tyre eating, axle braking beast that the average Jo could afford"


Series dc motors are designed to deliver large amount of torque. Normal operation for ac motors does not need that large amounts of torque, so they deliver less. If you want an ac motor that is designed to deliver large amount of torque, several manufacturers have what they call torque motors ( I wonder why ) available that deliver ridiculous amounts of torque. These are special motors, so the market is smaller, so the motors are more expensive. If you have the money, I have a 250kw 1500Nm nominal ac motor that will twist even a truck axle. Secondhand, and rewound (Class H, S1 duty). It only weighs 350kg

Dawid


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## electrabishi (Mar 11, 2008)

JRP3 said:


> I doubt the average Jo can build "a tyre eating, axle braking beast that the average Jo could afford" either. That kind of power takes money, no matter the technology. Besides, this thread isn't about the most cost effective way to do something, it's called "Pure horse power DC vs AC". Nothing about price.



For not a lot of $$ you can put in a system with single DC Controller and two DC motors that will twist off stock 28-spline axles on a Ford 9" Rear end as well as stress fracture the gear case housing. Knowing that it happens I went with 35-spline axles (31-spline would likely have sufficed - but the 35- was the same price) and Strange nodular iron gear case. Just the money I have into the rear end is about the same as the two motors I put in. So while the cost of the motor and controller system the average joe needs to eat tires and break axles is not all that much (if they go with a DC system), the cost from that point to keep from eating tires and breaking axles is what will drive up the cost of the rest of the project. 

Mike


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## toddshotrods (Feb 10, 2009)

electrabishi said:


> ...the cost from that point to keep from eating tires and breaking axles is what will drive up the cost of the rest of the project.
> 
> Mike


That's when you try to lift your nose, like an airplane ready to jump into the sky!  You can also cut back on half the cost of that by selecting hard compound tires, if you're more into impressive smoke shows than impressive times slips! Keep 'em spinning and the axles should last a bit longer.  They also have those neat tires that give off colored smoke...


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## electrabishi (Mar 11, 2008)

toddshotrods said:


> That's when you try to lift your nose, like an airplane ready to jump into the sky!  You can also cut back on half the cost of that by selecting hard compound tires, if you're more into impressive smoke shows than impressive times slips! Keep 'em spinning and the axles should last a bit longer.  They also have those neat tires that give off colored smoke...


Ha ha  the broken axles were experiences of others. I haven't broken anything yet..... except a few blown up batteries.... and some vaporized tool tips..... uh and oh yeah maybe some pretty well worn in Hoosiers in two seasons... but thats all  And I ain't necessarily into the smoke shows, its just what happens when you get those Hoosiers all hot and sticky...so you can lift your nose "like an airplane ready to jump into the sky!" 

Mike


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## toddshotrods (Feb 10, 2009)

electrabishi said:


> ...I went with 35-spline axles (31-spline would likely have sufficed - but the 35- was the same price) and Strange nodular iron gear case...
> Mike





electrabishi said:


> ...I haven't broken anything yet...


A little off topic, but still somewhat relevant, do you know how much your whole assembly (the current one) weighs? I plan to go the same route (35-spline/nodular iron) eventually, and just wanted to see how much weight comes with it.

Also, what rear end housing do you have?


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## electrabishi (Mar 11, 2008)

toddshotrods said:


> ... do you know how much your whole assembly (the current one) weighs? ...
> 
> Also, what rear end housing do you have?


Ordered the Ford 9" housing from Dutchman Motorsports with the Strange N- case, Detroit Lockers, 35- spline axles, and 11" (stock) drum brake assembly for a total of $3172. Total weight is 220#. 

Housing is 45#
chunk is 75#
Axle (short) 18#
Axle (long) 22#
Drum brake set 60#

They're fun to play with and they do take a beating. Everyday joe driver won't break it. Heck every day drag racer joe won't break it either. Its something I totally don't have to worry about. 

Mike


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## toddshotrods (Feb 10, 2009)

electrabishi said:


> Ordered the Ford 9" housing from Dutchman Motorsports with the Strange N- case, Detroit Lockers, 35- spline axles, and 11" (stock) drum brake assembly for a total of $3172. Total weight is 220#.
> 
> Housing is 45#
> chunk is 75#
> ...


Awesome information, thanks a million! It's actually a good bit lighter than I planned - always a good thing. I should also be able to lose some weight in the brakes (Wilwood discs planned). 

Sorry for the detour guys, back to the horsepower wars!  But, if you think about it, what good is pure horsepower if you can't apply it?


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