# 2 x Warp 9 vs 1 x Warp 11



## major (Apr 4, 2008)

m.137 said:


> It looks like (according to the graphs) that the warp 11 motor is almost as efficient as the warp 9 (how does that work with 2?)......


Hi m,

First off, the efficiency curves published for those which I have seen are inaccurate. It would be foolish to make design decisions based on those down to less than 10%.

Secondly, if you have one motor which is 80% efficient at 10 hp and combine it with a second motor which is 80% at 10 hp, then you get 20 hp at 80% efficiency.

Regards,

major


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## DIGGER11 (Mar 16, 2010)

Hi M.,
I am considering the same issue of 2 Warp 9's v 1 Warp 11.

I am leaning towards 2 Warp9's for the following reason;
1. I am going Direct Drive so need more torque to get the thing moving
2. Direct Drive gives me more room in the transmission tunnel to mount the rearmost TransWarp9.
3. Warp11's are big and take up more of the battery room in the engine bay.
4. Zilla 1k and 2k controllers have auto serial/parallel switching which will make great use of the 2 motors.
5. Zilla also has reverse ability.

If battery and controller technology improves in say 5-10 years time, I can take out one of the Warp 9's and move it to another car - giving me 2 EV's ! I don't think DC motor technology is going to improve much compared to battery and maybe controller technology.

Just my thoughts and I am definitely no expert.


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## CroDriver (Jan 8, 2009)

Hi.

I have made a performance graph for the 11" HV based on the available data. I don't know if it's accurate but I guess it's better than nothing:

http://www.diyelectriccar.com/forums/showthread.php?t=41328


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## Bowser330 (Jun 15, 2008)

DIGGER11 said:


> Hi M.,
> I am considering the same issue of 2 Warp 9's v 1 Warp 11.
> 
> I am leaning towards 2 Warp9's for the following reason;
> ...


What he said.... 

However I am not sure how comfortable those warp-9s will be in parallel mode, with full voltage being applied to them...


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## DIGGER11 (Mar 16, 2010)

Bowser330 said:


> What he said....
> 
> However I am not sure how comfortable those warp-9s will be in parallel mode, with full voltage being applied to them...


I assume the Zilla will limit the amps ? Is that what you mean ?


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## EVfun (Mar 14, 2010)

Why so much motor? Are you planning to convert a large vehicle? The motor just converts electricity to horsepower, within reason size doesn't matter.

It does matter some, larger motors tend to be more efficient but... running a motor well outside of its continuous power rating (either higher or lower) tends to result in reduced efficiency. 

If the motor is to small it is going to overheat (and almost certainly be operating well outside of its efficient range, see above 

A larger motor is heavier and excess weight tends to be damaging to vehicle efficiency (part of the reason Lithium batteries are becoming so popular.) A larger motor tends to make more torque per amp, but it equally makes less rpm per volt. You don't get more power because your motor is bigger unless the other one cannot handle turning the controller up.


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## DIGGER11 (Mar 16, 2010)

EVfun, Yep a large car. For a variety of reasons I just don't like smaller cars (being 6ft 5" and 16 stone probably doesn't help).
I have a 190E Mercedes that I was going to convert but it is just too small for me to drive comfortably on a regular basis.
I am therefore looking at a 300E Merc or a 5 Series BMW. I realise these are both "too heavy" and are rear wheel drive and nearly all Auto's - but I want to build what I want to drive. It will not be a build in theory that is just done to save money, but a practical car I can use every day.
At about 1800kg completed and with Direct Drive, I am sure a Warp11 or dual Warp 9's will be required as will plenty of LiFePo4's.


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## Tahoe Tim (Feb 20, 2010)

I think two 7's are better compared to a single 11.


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## major (Apr 4, 2008)

Bowser330 said:


> However I am not sure how comfortable those warp-9s will be in parallel mode, with full voltage being applied to them...


Hey Bowser,

With regards to voltage, 2 in parallel is the same as a single. I don't get what you mean by uncomfortable 

major


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## Bowser330 (Jun 15, 2008)

major said:


> Hey Bowser,
> 
> With regards to voltage, 2 in parallel is the same as a single. I don't get what you mean by uncomfortable
> 
> major


Always nice to be addressed by a true master...

I always thought in series mode the voltage was shared e.g. 300V pack would be 150V each motor x2 = 300V, such that the amperage could be 2000A each and really be a torque monster...then when you switched to parallel mode, both motors received 300V and the 2000A peak capable pack was shared to each motor, 1000A peak for each...

So seeing as this is a daily driver....I was stating originally that if in parallel mode each motor were to experience the full 300V, even at 50% pwm, it would be quite a burden at 150V..I always thought those Warp9s were maxed out at 150V?

Am i wrong in my understanding of the above?


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## DIGGER11 (Mar 16, 2010)

Not to butt in or be off-topic, but for effective series/parallel switching of dual motors, do you need a 288v battery pack ?
My plan was only144v. Would 144v work for dual motors ?


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## BiGH (Aug 7, 2009)

I think to use the series mode requires the higher voltage. you could use just parallel, however i'd be wary putting high voltage. Get a motor that supports the voltage you're looking for. 

Also being a heavy car, the amperage requirements are going to be intense for your car. I'd recommend choosing a higher voltage as there will be less complications. high amps kills batteries faster, requires more cable.

if you're going to look at the series/parallel switching of the zilla, i'd consider talking to a motor place about motors designed for the voltage you're looking at using (that being said i don't think your voltage is high enough for decent performance in a large heavy car).


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## major (Apr 4, 2008)

Bowser330 said:


> I was stating originally that if in parallel mode each motor were to experience the full 300V, even at 50% pwm, it would be quite a burden at 150V..I always thought those Warp9s were maxed out at 150V?


Hi Bowser,

With a 300V battery and 50% PWM, the motor voltage is 150V. This is true if you have one motor or two in parallel. 

It is common to have battery voltage higher than what can be tolerated by the motor. The controller is used to limit the voltage to the motor. Afterall, what would be the motor RPM with such a high voltage applied? 

Regards,

major


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## major (Apr 4, 2008)

DIGGER11 said:


> Not to butt in or be off-topic, but for effective series/parallel switching of dual motors, do you need a 288v battery pack ?
> My plan was only144v. Would 144v work for dual motors ?


The concept should work for any voltage pack.


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## major (Apr 4, 2008)

Two Warp9s with a Zilla 2k is what Mike uses in the CrazyHorse Pinto. He has posted dynamometer plots and linked to those in the Performance sub forum. Maybe someone could find that and post it here.


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## CroDriver (Jan 8, 2009)

Hi Major,

I would like to ask you a little off topic question since you're our motor expert.

My calculations tell me that I won't have much power above 4500-5000 RPM from my 11" HV. Field weakening would help but I don't know if this is possible since I'll push 2000 Amps trough the motor.

Will "over voltaging" the motor help? Jim Husted suggested 280V as a limit.

There is no concern of too high RPMs since every motor will be directly bolted on a differential, without gearbox and clutch. 

The factory claims 9000 RPM as a limit. My car would drive over 350 km/h (218 mph) at 9000 motor RPMs 

Thanks.


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## major (Apr 4, 2008)

CroDriver said:


> My calculations tell me that I won't have much power above 4500-5000 RPM from my 11" HV. Field weakening would help but I don't know if this is possible since I'll push 2000 Amps trough the motor.


Hi Cro,

I have no doubt what-so-ever that field weakening is useless at 2000 amps 

I have to leave on a trip. Maybe more later.

major


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## Bowser330 (Jun 15, 2008)

major said:


> Hi Cro,
> 
> I have no doubt what-so-ever that field weakening is useless at 2000 amps
> 
> ...


Hi Crodriver,

I just checked the history of the Whitezombie and John Wayland had experiemented with field weakening but he removed it...
http://www.plasmaboyracing.com/reviews.php


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## Bowser330 (Jun 15, 2008)

major said:


> Hi Bowser,
> 
> With a 300V battery and 50% PWM, the motor voltage is 150V. This is true if you have one motor or two in parallel.
> 
> ...


Thanks...I guess I really don't yet understand the relationship of pwm%, Voltage, amperage, Rpm, and throttle%...


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## EVfun (Mar 14, 2010)

DIGGER11 said:


> Not to butt in or be off-topic, but for effective series/parallel switching of dual motors, do you need a 288v battery pack ?
> My plan was only144v. Would 144v work for dual motors ?


Well... yes... but it depends on voltage  You can do duel motors at any voltage but you don't need to do series/parallel switching at just any voltage. 

If the voltage is low for the motors I would recommend they be wired in parallel and not switched. The motors need to 'see' all of the pack voltage so they can pull a decent rpm. The motors would launch faster in series, but 'fall asleep' at 1500 rpm and have to be switched into parallel when you are barely across the intersection. 

If the voltage is considerably higher than the motors can handle they can be wired in series and not switched. That way they will only see half the applied voltage. You can't apply 180+ volts to an ADC 8 inch motor without a serious risk of turing the commutator into a ball of plasma (followed closely by flying molten copper.)


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## Olaf-Lampe (Feb 24, 2010)

m.137 said:


> Hello everyone, I think this is the first time i have ever posted on a forum. Normally I am using the power of google to find my answers. The last time some one asked this question the answer came back as, "Well there are no good controllers for the warp 11 so go for 2 warp 9s"
> 
> Here is what I want to do. I am in the process of getting a car to restore (now that I have the money, time, and a garage) and I want to slowly get it ready to be a 100% EV with the next generation of batteries. It seems to me, once the battery tech gets much better, then we will have cheap powerful EVs that can dive 300 miles on a single charge. Until then, I want to put a tow a diesel generator so I can take the EV on road trips. That being said, I need enough power to tow a few hundred pounds. Also, since this is a long term project I am not going to get set on just one kind of battery. I am however still trying to figure out what I need in terms of a motor. Since it is so important in the planning process I am trying to figure it out now.
> 
> It looks like (according to the graphs) that the warp 11 motor is almost as efficient as the warp 9 (how does that work with 2?) and just weights more, so at highway speeds it shouldn't be that much more of a power hog. Any thoughts on the pros vs cons would be greatly appreciated.


Hi m.
what made me smile a bit was the point where you want to choose 'next generation batteries' but on the other hand you want to compare two "stoneage" DC -brushed motor concepts. 
Don't get me wrong, IMO there are plenty of good reasons to use DC-brushed motors, but why don't you look for ACPM or ACIM-motors or switched reluctance motors ( which will be next generation motor design )? That would be a consequent concept for a car.

Most modern battery/inverter concepts coming up have chosen the high voltage/low amp path. For good reason, 'cause one bad cable/battery connection can easily ruin a 2000A setup. ( and ruin the whole car as well  )

Just my two cent
Olaf


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## DIGGER11 (Mar 16, 2010)

EVfun said:


> Well... yes... but it depends on voltage  You can do duel motors at any voltage but you don't need to do series/parallel switching at just any voltage.
> 
> If the voltage is low for the motors I would recommend they be wired in parallel and not switched. The motors need to 'see' all of the pack voltage so they can pull a decent rpm. The motors would launch faster in series, but 'fall asleep' at 1500 rpm and have to be switched into parallel when you are barely across the intersection.


But isn't this the advantage of dual motors and the Zilla's automatic pre-configured series / parallel switiching ?
Series connection to get the thing moving, then at 1,500rpm (which is 30mph with my diff ratio) the Zilla (seemlessly ?) switches to a parallel to keep the car accelerating.

I know that Direct Drive is derided for street use, but with twin Warp 9's, additional air cooling, a Zilla and enough batteries I am sure it will work pretty good (albeit an expensive soultion).


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## EVfun (Mar 14, 2010)

I would reconsider the diff ratio for direct drive! The White Zombie runs shorter gears and generally the gear ratio should get taller the higher the performance (higher top speed, shorter duration so heating is less of an issue even with big amps.) 

I don't have any issue with direct drive EVs using series wound motors but it has to be applied with care. It works better if you have a fairly high system voltage. The goal is to make more of your power with voltage because motor heating is almost entirely related to amps.

If you really want to run the motor that slow you will need series/parallel switching. At least the motors will see a little voltage at neighborhood speeds. I think the results will be inefficient and likely to burn up the motors in town. Motor amps will be high in series and parallel at road driving speeds.

If I knew what a custom made adapter for my early Datsun was actually going to cost I would have put duel 6.7 inch motors in place of the single 8 inch and stock 4-speed I used. I would have replaced the stock 4.11 to 1 rear axle ratio (with P165/80R13 tires) with a 4.86 early Datsun pickup. It would have been about the same cost.


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## DIGGER11 (Mar 16, 2010)

I don't want to run the motors slow - but the Mercedes I am looking at converting only comes in a 3.6 Diff Ratio (as the highest numerical ratio) and auto trans only.

I am thinking that Dual motors will provide more torque and be a bit easier on them as they will both be absorbing 1/2 the load at low revs.

Not trying to build a racing machine - but I don't want any less power/drivabiltiy than the original.

If it is Amps that destroy the DC motors, then shouldn't I just run them in parallel all of the time to increase the volts but not the Amps ?


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## EVfun (Mar 14, 2010)

They will be sharing the load all the time, in series and in parallel. 2 will go longer without overheating than one, but if the rpm is too low it will happen even with 2 motors. I really cannot recommend 3.6 gearing and a pair of 9's. 

Lets look at a situation that calls for 10 kW of power. With the 2 motors in series the controller dishes out 100 volts at 100 amps. Each motor sees 50 volts at 100 amps. We switch to parallel and the controller puts out 50 volts at 200 amps. Each motor sees 50 volts at 100 amps. Nothing changed except the controller losses are likely a little higher in parallel. The power needed is set by the vehicle requirements. The motors rpm is set by the fixed gearing so to make that power we can calculate the torque required (horsepower = torque * rpm / 5252.) Amps sets the motor torque and sufficient voltage has to be applied to get the motor to take those amps at the required rpm (as it works out, horsepower = volts * amps / 746 plus some extra to make up for losses because motors aren't 100% efficient.)

What kind of voltage are you planning to run? Is there some other final drive that can be swapped into the Mercedes? I'm a fan of direct drive but setup is more critical because you can't just pick another gear if it works better (well, not easily.) Perhaps one large motor that isn't designed for high rpm would be a better choice. An issue here is limited real world experience, there are few EVs on the road right now with larger motors.


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## DIGGER11 (Mar 16, 2010)

thanks Evfun,

I would use a TransWarp11 if it would work (or evena 13 if it fitted). 

Where I live I either drive 5 minutes to the shops, or a bit further to the golf course - not many traffic lights, so not much stop/start stuff. It is also fairly flat, so as long as the car gets going at a reasonable rate of knots from standstill then I will be happy. Also need the ability to go Freeway speeds for about 20 minutes (down to the beach). 
So 3,000 RPM for 100kmh sounds reasonable to me. 

Voltage will be as high as is necessary. I am not really that restricted by $'s other than I don't really want to waste money by spending it on things that are useless.

If it cost me say $5,000 more to make the car nicer to drive then I would do it. 
Cannot find a manual transmission nor a lower final gear ratio than 3.6 - hence the desire to spend the money on more batteries/better controller/bigger or dual motors, to make it all work.

It looks like my thinking is in it's infancy, so I might need to build it and then tweak the parts it the acceleration is no good. I only really need to keep up with the traffic from standstill - but would prefer to maintain close tot he existing acceleration.

From reading this forum, I am sure that 2 Warp9's or one Warp 11 will work fine at 3,000RPM at 100kmh for my 1500kg build. Range is not that important to me (but can easily be increased by spending dollars on more batteries).

Unfortunately I am hung-up on the saying "convert a car to electric that you will be happy to drive for many years" ( 100+ hrs of time + about $20,000 in costs ).
I have owned 8 Mercedes in my life (ranging from old to new) and kind have got to like them.

I was going to build a gas powered Kit car like a GT40 Replica, but am not really into sports cars, so am going to spend my time on building an electric Mercedes instead.


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## EVfun (Mar 14, 2010)

It's not 3000 rpm at 60 mph that I find concerning. Its the 0 to 1000 rpm as a vehicle accelerates from 0... 5... 10... 15... 20. That is going to take some serious motor amps. I think you will need a 2000 amp Zilla controller. The battery amps won't need to be very high, but the motor amps from a stop will be.


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## Tesseract (Sep 27, 2008)

Olaf-Lampe said:


> Hi m.
> what made me smile a bit was the point where you want to choose 'next generation batteries' but on the other hand you want to compare two "stoneage" DC -brushed motor concepts.


Oh, I suppose you could argue that the induction motor is more advanced than brushed DC... after all, it was invented by Nikola Tesla in 1883 while the modern (commutator) brushed dc motor was invented by Siemens in 1880... So, a whole 3 years more advanced.




Olaf-Lampe said:


> Don't get me wrong, IMO there are plenty of good reasons to use DC-brushed motors...


Yep - reasons such as you can actually buy them and they deliver about 2x the power for 2/3rds the cost of an equivalent AC setup... AC *is* coming to the DIY market, but I don't expect it to displace DC anytime soon. 'specially not the cheap bastards that hang out around here 




Olaf-Lampe said:


> ...but why don't you look for ACPM or ACIM-motors or switched reluctance motors ( which will be next generation motor design )? That would be a consequent concept for a car.


I agree that SRMs will likely dominate EV traction applications... eventually. SR motors are very simple to design and build which makes them significantly less expensive... eventually. However, the software required to control them is quite a bit more complex than even FOC of an induction motor.... 




Olaf-Lampe said:


> Most modern battery/inverter concepts coming up have chosen the high voltage/low amp path. For good reason, 'cause one bad cable/battery connection can easily ruin a 2000A setup. ( and ruin the whole car as well  )


One bad cable/connection can ruin EITHER setup. 

Also, there are practical (not to mention regulatory) limits to how high of a voltage you can run... Insulation breakdown and bearing failure of inverter-driven motors caused by high dV/dt comes to mind.


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## DIGGER11 (Mar 16, 2010)

Fair Enough,

You don't think a Zilla 1k with a burst of 500 amps per motor will cut it ?


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## Tesseract (Sep 27, 2008)

DIGGER11 said:


> I don't want to run the motors slow - but the Mercedes I am looking at converting only comes in a 3.6 Diff Ratio (as the highest numerical ratio) and auto trans only.
> ...
> Not trying to build a racing machine - but I don't want any less power/drivabiltiy than the original.


A single 9" motor and 1000A controller will likely deliver more than enough power for what you want, then. You will probably need to idle the motor to maintain pressure in the auto trans. I know at least one guy here has done so with a Zilla (TheSGC) while the Soliton1 (disclaimer - I make, so not even remotely unbiased) has an idle regulation routine built-in.

You need higher amps for good acceleration and higher top speed, but the latter is also affected by the available voltage. From Soliton1 log files we see that it takes a solid 180V to maintain 5600 rpm at 500A load (Amps = torque in all motors). So, a pack voltage of 192V is what I feel is a good starting point for a modern conversion to be able to perform well on the highway and not require too much current even when accelerating with 1000A from a stop (when motor voltage is much lower)




DIGGER11 said:


> If it is Amps that destroy the DC motors, then shouldn't I just run them in parallel all of the time to increase the volts but not the Amps ?


No, it is POWER that destroys motors. Sure, too much amps at low RPM for too long - like towing a trailer or being stuck in one gear (ie - direct drive) can overheat them, but so can too high of a voltage even at modest currents (leading to flashover, also called "zorching").

Running the motors in parallel theoretically splits the CURRENT between the two in half (tiny variations in resistance can shift a surprisingly large fraction from one motor to the other, though). Running in series more closely splits VOLTAGE between the two in half. From tests on our dyno it appears that being able to switch between series and parallel isn't really worth the $400 worth of contactors required (and that is why that feature has dropped so far down the priority scale for the Soliton1).

Series/parallel switching is definitely worthwhile for drag racing, though.


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## Coulomb (Apr 22, 2009)

Tesseract said:


> Insulation breakdown and bearing failure of inverter-driven motors caused by high dV/dt comes to mind.


Ok, I'll bite: how does high dV/dt or other "AC-ness" cause bearing failure? Through induced current?


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## Tesseract (Sep 27, 2008)

It's a pretty well-documented phenomenon. Essentially, the faster the switching and/or the higher the bus voltage, the more current is capacitively coupled through insulators that were never meant to be capacitors, such as the enamel coating on the windings and the oil film inside the bearings.

From the book "High Power Converters and AC Drives": dV/dt effects


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## Tahoe Tim (Feb 20, 2010)

> Lets look at a situation that calls for 10 kW of power. With the 2 motors in series the controller dishes out 100 volts at 100 amps. Each motor sees 50 volts at 100 amps. We switch to parallel and the controller puts out 50 volts at 200 amps. Each motor sees 50 volts at 100 amps.


I don't think you got this right. In parallel the controller would still deliver 100 volts and 100 amps, 100 volts and 50 amps to each motor, right? Isn't the point of series/parallel to deliver half voltage and full amps off the line and them switch to full voltage/half amps when up to speed? 

It doesn't surprise me that someone who doesn't offer this feature in their controller will poo-poo it. I sincerely believe that acceptance of electric cars for the masses MUST eliminate all the extra steps required to drive the car including shifting and make it as simple and pleasant as driving a golf cart. At least it's my goal.


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## JRP3 (Mar 7, 2008)

Tahoe Tim said:


> I sincerely believe that acceptance of electric cars for the masses MUST eliminate all the extra steps required to drive the car including shifting and make it as simple and pleasant as driving a golf cart. At least it's my goal.


For EV's to gain broader acceptance they need longer range and a cheaper price. OEM's eliminate shifting by using higher RPM AC motors.


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## EVfun (Mar 14, 2010)

Tahoe Tim said:


> I don't think you got this right. In parallel the controller would still deliver 100 volts and 100 amps, 100 volts and 50 amps to each motor, right? Isn't the point of series/parallel to deliver half voltage and full amps off the line and them switch to full voltage/half amps when up to speed?
> 
> It doesn't surprise me that someone who doesn't offer this feature in their controller will poo-poo it. I sincerely believe that acceptance of electric cars for the masses MUST eliminate all the extra steps required to drive the car including shifting and make it as simple and pleasant as driving a golf cart. At least it's my goal.


I don't offer any controller, plus I'm a user and big fan of the Zilla, so I don't know what you are talking about with the second paragraph.

To address your first paragraph, 100 volts at 50 amps is a very different rpm than 50 volts at 100 amps (the first case is a much higher rpm.) Since nothing changed the motors rpm, and nothing changed the motor power output (they are still providing 5 kW each), the voltage and amperage each motor is seeing is unchanged (any such change results in a change in torque, rpm, or both.)


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## EVfun (Mar 14, 2010)

DIGGER11 said:


> Fair Enough,
> 
> You don't think a Zilla 1k with a burst of 500 amps per motor will cut it ?


Otmar doesn't recommend the 1000 amp Zilla for direct drive duty except in lightweight EVs. If the designer doesn't recommend it I certainly won't! The low motor rpm is going to make the problem worse.


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## DIGGER11 (Mar 16, 2010)

Tesseract said:


> A single 9" motor and 1000A controller will likely deliver more than enough power for what you want, then. You will probably need to idle the motor to maintain pressure in the auto trans. I know at least one guy here has done so with a Zilla (TheSGC) while the Soliton1 (disclaimer - I make, so not even remotely unbiased) has an idle regulation routine built-in.


thanks for your advice (and disclaimer!) Jeffrey, 

Have actually had a bit of an eye on you Soliton1 Controller as the ability to idle with the Auto-trans is very tempting.
I am thinking of going with a single warp motor, and will add another if performance is not up to scratch.
Looking at battery choices and cost, a 1,000amp controller will be more than enough for me for the forseeable future.
The voltage advice sounds good too.


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## DIGGER11 (Mar 16, 2010)

EVfun said:


> Otmar doesn't recommend the 1000 amp Zilla for direct drive duty except in lightweight EVs. If the designer doesn't recommend it I certainly won't! The low motor rpm is going to make the problem worse.


This Volvo over in Perth is not light and apparently goes o.k..

I think Zilla are being a bit conservative.

http://www.evworks.com.au/vehicles.php?id=6


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## Tesseract (Sep 27, 2008)

Tahoe Tim said:


> I don't think you got this right. In parallel the controller would still deliver 100 volts and 100 amps, 100 volts and 50 amps to each motor, right? Isn't the point of series/parallel to deliver half voltage and full amps off the line and them switch to full voltage/half amps when up to speed?


It appears that both you and EVFun are only considering the situation where both motors are wired in series or parallel - ie, the static condition - and not when/why/if it makes sense to switch between those two configurations. It takes a minimum of three SPST contactors (rated for the full motor current) to be able to switch between series and parallel, and, of course, the controller must support it, so the real question becomes: what advantage does s/p switching deliver over simply connecting the motors permanently in either series or parallel?

Series connection delivers far more brute force acceleration at the expense of needing to "shift gears", so to speak, much earlier. This is because you get twice the torque for a given motor current but twice the BEMF, so you run out of RPM 4x as fast (ie - when the controller hits 100% duty cycle so it can't apply any more voltage and yet motor current is declining due to rising BEMF). Thus, wiring the two motors in series is the equivalent of a really low first gear. Note that if you can already break the tires loose from a dead stop with your EV then doubling the amount of torque won't really help you all that much.

When the motors are in parallel a given amount of current is split between the two motors, so the total torque is the same as with one motor but each motor is much more lightly loaded. This makes the motors happier and it also let's them rev to twice the RPM they could otherwise achieve with a given pack voltage. This acts like a modestly tall gear, say 4th-ish. In my opinion, if you need the power output from two motors then it is hard to beat simply wiring them in parallel permanently.

Now, as to the whole switching thing. Those three contactors really ought to be rated for the full motor current (so, with a Z2K that would be 2000A capable contacts!) which means you need to go with quadruple EV200s in each position or Tyco (nee Kilovac) "Bubbas" (which are $1200 ea.). It's pretty obvious when you would want to switch from series to parallel; it is much less obvious when you would to switch back. A simple rule would be to only switch back to series when both RPM and motor current are zero, otherwise remain in parallel. Driveability with this rule could suffer somewhat in stop-and-go traffic if the s -> p shift point is repeatedly encountered. Keep in mind that some time needs to be allowed for the contactors to change states and stop bouncing. The Zilla allots 300ms to this, IIRC.

So, there's a little context as to why I said that s/p switching isn't worth the hassle/expense for a daily driver. If you are driving full throttle down a track for 10-15 seconds at a time (ie - drag racing) and have the budget to match your ambitions, then that's a whole 'nother story. Of course, when it comes to buying three Bubba contactors at $1200-$1400 each or buying a second controller most people choose the latter (or they go with woefully undersized contactors like the Albright SW200). 




Tahoe Tim said:


> It doesn't surprise me that someone who doesn't offer this feature in their controller will poo-poo it....




Don't assume that not having a feature is the same as not being able to have it... upgrading the code that runs the Soliton1 is easier than uploading a picture to this forum. S/P switching is on the list of things to add, it's just a little bit lower in priority than other features (and other products that we are working on now... or not now because I took the time to respond to your snarky post).


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## EVfun (Mar 14, 2010)

Tesseract said:


> It appears that both you and EVFun are only considering the situation where both motors are wired in series or parallel - ie, the static condition - and not when/why/if it makes sense to switch between those two configurations.
> [snip]
> 
> When the motors are in parallel a given amount of current is split between the two motors, so the total torque is the same as with one motor but each motor is much more lightly loaded. This makes the motors happier and it also let's them rev to twice the RPM they could otherwise achieve with a given pack voltage. This acts like a modestly tall gear, say 4th-ish. In my opinion, if you need the power output from two motors then it is hard to beat simply wiring them in parallel permanently.
> [snip]


You do a nice job of describing why to switch the motors into series mode. I'm going to have to take issue with "each motor is much more lightly loaded" (in parallel.)

Let look at the case of an direct drive EV going down the road at some speed (perhaps 40 mph.) The driver has a switch to manually shift the motors between series and parallel. The power required is set by the vehicle and speed, switching the motors between series and parallel doesn't change the power required to go 40 mph, so both motors see the same load (half the total required) wired either way.

Now I'm going to get more controversial. In the case above, each motor has the same volts and amps applied to it in both series and parallel operation. The load hasn't changed and each motor provides half the power required. The motor's rpm hasn't changed. If you know a motor's rpm, load, and have the motor performance curves available you can determine the applied volts and amps. It's not negotiable, if you change the motor voltage the motor amps will change and the motor power will change. This will cause the motors (and vehicle) to accelerate or decelerate until a new equilibrium is reached. 

As silicon gets cheaper I expect series/parallel shifting to fade away. Series parallel shifting of a Z1k gets you almost the same result as using a Z2k and wiring the motors in parallel (and double throw contactors are expensive.) All you have to do is program the Z2k with the same battery current limit and twice the maximum motor current limit as the Z1k with S/P shifting. Each motor gets the same motor amps in parallel as it would in series with the Z1k. The Z2k will actually be slightly faster because there will be no shifting time and the peak power will be flatter instead of 2 peaks. Series parallel shifting of a Z2k gets you almost the same result (just slightly slower) than using 2, Z2k's.


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## Coulomb (Apr 22, 2009)

Tesseract said:


> It takes a minimum of three SPST contactors (rated for the full motor current) to be able to switch between series and parallel


Two double pole double throw contactors would do it. Perhaps a reversing contactor could be adapted.



> what advantage does s/p switching deliver over simply connecting the motors permanently in either series or parallel?


I think it's brilliant (but shame about the contactor requirements). It means that you get a single 2.0:1 reduction gear for high torque applications (climbing gutters, steep driveways with heavy loads), and yet get full maximum speed.



> Series connection delivers far more brute force acceleration at the expense of needing to "shift gears", so to speak, much earlier. This is because you get twice the torque for a given motor current but twice the BEMF, so you run out of RPM 4x as fast


I'm not into DC, but surely it's 2x as fast as if you had a single motor or two motors in parallel. The double torque comes from the two motors; each motor is only delivering its own maximum torque. So each motor sees half the controller voltage, and everything else is the same. So this is a 2.0:1 reduction gear, not 4.0:1.



> When the motors are in parallel a given amount of current is split between the two motors, so the total torque is the same as with one motor but each motor is much more lightly loaded. This makes the motors happier and it also let's them rev to twice the RPM they could otherwise achieve with a given pack voltage.


This is because any extra torque robs the series DC motor of RPM, am I right? The magnitude of the effect would vary depending on the motor characteristics, and how battery limited the vehicle is (perhaps the battery can supply enough current for about 1.5 motors, for example, rather than the 1.0 you seem to be assuming).

You presumably don't get the same effect with series operation, assuming that the battery has enough current to operate one motor by itself.



> This acts like a modestly tall gear, say 4th-ish.


Well, call it first overdrive; fourth gear is straight through or very close to it for many 5-speed gearboxes.



> In my opinion, if you need the power output from two motors then it is hard to beat simply wiring them in parallel permanently.


I was going to say that you then get no extra torque at low speed. But series DC motors give you that anyway, and there is the extra effect you mention (assuming it's real; I need to think more about it) from paralleling them. But it's a pretty mild effect. With two motors, you presumably have a fair bit of torque available, so you may get away with never multiplying that torque with a gearbox or series connection.



> Now, as to the whole switching thing. Those three contactors really ought to be rated for the full motor current (so, with a Z2K that would be 2000A capable contacts!)


Well, the controller could help by making sure the contactor never switches under load. But yes, each contactor would have to carry the full controller current (in series operation only, which is likely to be for a short period of time).

I agree that the contactors is definitely the achilles heel of the series/parallel switch, and I suspect it's the reason most direct drive setups don't use it.


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## Tahoe Tim (Feb 20, 2010)

Nothing controversial in what you just wrote. I'm still trying to wrap my mind around the Zilla series/parallel logic but from an ECONOMY point of view. 

Hypothetical car:
Two 7 inch motors and a TS100AH battery set at 144 volts. Zilla 1K LV controller. Assume 60MPH load of 100kwh (did I get the units correct?)

vs

1 - 11 inch motor that provides the same off the line performance as two 7's in series. In series, what system would it take to match the 11 against two 7's? what pack size? which Zilla?

1 - 11 inch motor that provides the same top speed as two 7's in parallel
what pack? which zilla?


I thought that a single 11 inch would require twice the AH pack and larger controller to get off the line. Or, is my logic completely off!


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## Tesseract (Sep 27, 2008)

EVfun said:


> ...
> Let look at the case of an direct drive EV going down the road at some speed (perhaps 40 mph.) The driver has a switch to manually shift the motors between series and parallel. The power required is set by the vehicle and speed, switching the motors between series and parallel doesn't change the power required to go 40 mph, so both motors see the same load (half the total required) wired either way.


Yep.




EVfun said:


> Now I'm going to get more controversial. In the case above, each motor has the same volts and amps applied to it in both series and parallel operation. The load hasn't changed and each motor provides half the power required. The motor's rpm hasn't changed. If you know a motor's rpm, load, and have the motor performance curves available you can determine the applied volts and amps. It's not negotiable, if you change the motor voltage the motor amps will change and the motor power will change. This will cause the motors (and vehicle) to accelerate or decelerate until a new equilibrium is reached.


If the gear reduction ratio is fixed and the vehicle speed is fixed then the motor RPM and torque must be fixed as well (ergo, V and I are fixed, too).

But if either series or parallel connection of the motors can maintain said 40mph, then why choose one mode over the other? This is what I meant when I said you were only considering a static condition: ie - one in which power output is constant, not increasing or decreasing.

That is to say, I totally agree there is no difference in total power and losses in either the series or parallel configuration, but that was more or less my point in the first place! 

I.e. 500A through two motors in series is the same as 1000A through two motors in parallel (torque-wise). 100V across two motors in parallel is the same as 200V across two motors in series (RPM-wise). If the controller can deliver either combination then there is no meaningful difference between the two configurations.


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## Tahoe Tim (Feb 20, 2010)

I want to modify my hypothetical car above to include a steady economical acceleration from 0 to 60.

Again, can I run a smaller pack and controller with two 7's and gain the 
2 to 1 "shift" as I accelerate to freeway speed?


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## major (Apr 4, 2008)

The controller has a particular rated maximum current, say 1000A. That is motor current. The series to parallel switch gives you twice the low speed torque for your 1000A than would be available if the motors were in parallel. And you still get the high speed power when you switch to parallel you could not get with the motors in series.

The S to P arrangement is done to overcome controller limitations.

Sure you could use 2 controllers rated at 1000A each or a 2000A controller with the motors in parallel. And you'd think that would double your high speed power. But can the motors take that high current at that high a voltage and RPM?

So even if you spend the bucks to double the controller amps, you may have to limit the power anyway.

major


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## major (Apr 4, 2008)

Tahoe Tim said:


> Or, is my logic completely off!


Yeah Tahoe,

You are using charge (Ampere hours) for some unknown reason. That may enter into the ability of the battery to deliver current (Amperes), but not necessarily into the torque equations needed for acceleration.

For equal acceleration of equal mass, the power and energy requirements from the battery are equal and it makes little difference if you use one motor or two. This assumes similar efficiency for the motors, which is reasonable, and equivalent driveline configurations.

Regards,

major


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## EVfun (Mar 14, 2010)

Tahoe Tim said:


> I want to modify my hypothetical car above to include a steady economical acceleration from 0 to 60.
> 
> Again, can I run a smaller pack and controller with two 7's and gain the
> 2 to 1 "shift" as I accelerate to freeway speed?


It is not going to change the required pack size. The pack size (kWh capacity) is going to set your range. Your pack may also set your peak power if you have to turn down the controller to limit amps to a level that won't harm the pack.

Series parallel shifting will let you get away with a smaller controller because it will allow you to go through your peak power twice. A transmission will let you do it 3 or 4 times and a usable one is often included as part of the vehicle being converted. 

No matter how you play with the parts, the electrical power into the motor is going to equal the horsepower coming out of the motor (minus a little for losses.) 746 watts equal 1 horsepower. Allowing for losses it is easy to just estimate that 1 kW in will get you 1 HP out.


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## DIGGER11 (Mar 16, 2010)

EVfun said:


> Allowing for losses it is easy to just estimate that 1 kW in will get you 1 HP out.


25% losses ? Is that the motor or the controller ?


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## major (Apr 4, 2008)

DIGGER11 said:


> 25% losses ? Is that the motor or the controller ?


Hi DIG,

This is a pretty common estimate from the battery to the motor output shaft. So includes motor, controller, contactors, fuses and cables. As with almost all efficiency figures, it actually depends on many things including the load, or operating conditions. So this 1 kW from the battery giving you 1 hp from the motor is pessimistic at rated loads and speeds but optimistic at overload or low speed operation. Just an easy rule of thumb.

major


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## EVfun (Mar 14, 2010)

DIGGER11 said:


> 25% losses ? Is that the motor or the controller ?


At peak power the motor may very well only be 75% efficient. A little better for a low peak power EV and perhaps worse for the street/race EVs. The goal is to have your best efficiency closer to the continuous power requirements because you don't spend a lot of time at peak power. Most of the series wound motors in street conversions will have a peak efficiency around 90%.

Edit to point out Major gave a better answer 11 minutes before my answer


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## Tahoe Tim (Feb 20, 2010)

I'm starting to get it. The size of the contactors was mentioned as a downside of series parallel. I looked at the Zilla series/parallel/reverse wiring diagram that sent me down the thought path that if a vehicle was light enough, I could build a twin 7's motor with a Zilla 1k controller without a transmission or a clutch.

Any thoughts on contactors required for a light car build? Again, I am thinking about a 144v, 100ah pack.


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## major (Apr 4, 2008)

Tahoe Tim said:


> Any thoughts on contactors required for a light car build?


I would think Albrights would fit the bill. Or if you want to do some leg work, maybe some eBay, surplus or used lift truck contactors might work. The Zilla will only switch under no load, so you just have to choose for rated current (make sure it is DC rated) maybe a little higher. 200 amp contacts would likely do. Then you need the proper coil voltage. 12 volts for the Zilla to control, I think.

There was a guy on eBay selling Kilovacs (EV200) for like $40. You need more of those because they are SPST as opposed to reversing sets. But they'd do the job.

Don't think I know of anyone doing dual 7 inch motors with Zilla 1K LV and a S/P switch. Sounds kool to me. If you end up doing low speed travel for any length of time, better do a forced air cooling job on the motors. They won't self ventilate well creeping around.

Regards,

major


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