# New build, AC or DC advantages or dis...



## S1lv3r (Aug 2, 2012)

Hello everyone, I have been planning on this build for quiet some time. Years actually. I have done alot of reading and I did not find too many places with clear advantages and disadvantages of using DC or AC power. I know some things are price. it seems that DC power requires a little less money but for the extra cash you get better maintenance options and even some effeciency by going the AC route. AC route is costly with controllers but they give you big gains in use of the motor and its longevity. These are clear to me but what about power? I have read that DC motors tend to drop power and torque in the high rpm range... moreso than AC motors. Is this accurate or did I misunderstand something? 

I had purchased an AC motor and a VFD. My requirements have changed and now my AC motor is waaaay too weak to fulfill this duty. I was originally going to make a motorcycle conversion using 2x2HP motors but I think I am going to need at least 20 - 50HP now. So I pose another question.

How much HP do I actually need??

The weight of the build will be around 1,000-1,200lbs with no rider. This is just an estimate but I would want to build something in this size range and I would want it to travel at least 120 miles with stop and go driving. Acceleration does not have to be sportscar type but a good quick get-up-n-go would be nice. 

I have been pricing Siemens motors, GE motors, and others but they range in price from 4k to 10k$ This is waaay out of my price range. I have found some local ads for cheaper but i dont know if these can be used for my project. 

These are local and I dont know if they will work what do you guys think?

This set is non-tested and a huge risk... But I will post anyway for opinions

































This is a set that has a tempting price tag. They seem to want to get rid of these so I am highly considering them.

General Electric AC Motor - 
Condition: Used 
Works well
Model # 5K1445CA1
Type K 
Frame 445S
Volts 208-220/440
Cycles 60
Amp 182/91
Speed 1770 
Phase 3

General Electric DC Motor 
Model # 5CD444G3
Wound - Compound 
200 AMP
250/250 Volts 
50 KW
1750 RPM 


























The plates are a little worn or alot worn but any opinion on these would be helpful. 

i do realize that the heavy cast iron case for the motor is not optimal but if these are cheap enough and they will work, cant I just take them out of the cast iron shell and put a thinner steel shell on them?

As far as controllers go They are pricey indeed but if it needs to be spent then I think that is a good pplace to do so. Again any info on this project is much appreciated. I am about to start spending my saving on this project and I dont have much. any guidance and all opinions are valued. thank you.

I will add more to this topic in a little while. I just need to gather more of my thoughts.

Ok here are some more of my thoughts... I want the system to be regenerative to get the range I desire. Or even more range, that would be awesome. I looked in the Zilla controllers but those are for DC and I am not leaning towards DC power at the moment. They are also very expensive. I would need a 2k$ controller minimum. For that kind of money I can probably find a nice Siemens controller like the one mentioned at this link http://www.metricmind.com/ac_honda/motor.htm at the bottom of the page. It has some cool features like regenerative braking, torque n power control, voltage conversion to run 12v Dc electronics, 100kW power rating and its water cooled. This would allow for upgrading, if needed, to a larger motor later. However I do not have that amount to spend on just the controller.

the motor on that page is also very appealing but it is 10k$ Whoa!!

For Energy I am unsure how to go the most cost effective way. It really depends on which power source I choose to go. AC or DC and I have not completely decided yet so I cannot begin to develop that system. I can do one for each but I will need more time. I am in the process of doing a cost analysis on each of the drive systems but again that will take me a couple of weeks at this point. Between work and family I can only devote about an hour or so every other day. Today I am splurging on my research here with you guys 

The whole time that I had planned this project before is no longer applicable due to changes in design so I now have to start from scratch, taking with me small tidbits from the previous design. Any help and advice will be appreciated as stated above. I know alot of legwork has to be done and I dont intend for everyone here to do the work for me but any help at all is greatly appreciated.

working out the Power equation given in the stickey now to see if I can get a round about estimate of power.

took a shortcut I found on a website called engineering toolbox. The online cal stated that it would be 125HP and 93.4kW to attain a 110km/h speed in 6 seconds. This would happen in roughly 97meters. I changed the time to 10 seconds and it reduced this down to 75.1 HP and 56kW at 153 meters. The second calc more around the feasible range I desire. I am unsure if this is only taking into account mechanical energy though so i will work out the formula given either way to see the difference if any.

Ok a little confused... 
Power in Watts = ((Mass in kg) (9.8m/s²) (Velocity in m/s) (Rolling Resistance)) + ((0.6465) (Coefficient of Drag) (Area in m²) (Velocity^3))

Power in Watts = ((550 kg) (9.8m/s²) (3.06 m/s) (118)) + ((0.6465) (0.5) (1.47 m²) (Velocity^3))

Area in m^2 ~ about 1.47m^2

Now velocity... this is where I lose it. I already entered the velocity in m/s how do I get the Cubed velocity??

The portion of this equation after the + symbol looks alot like the equation for "drag at high velocity" found on wikipedia

Ok so This is what I plugged in
Power in Watts = ((550 kg) (9.8m/s²) (3.06 m/s) (118)) + ((0.6465) (0.5) (1.47 m²) (3.06^3)) and I got 1.94624e6 or ~195kW pretty large amount of power. i dont think thats correct though.


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## major (Apr 4, 2008)

Hi S1,

Pretty long post there. Here's a couple of things. AC vs DC: See http://www.diyelectriccar.com/forums/showthread.php?t=76971 And on your calcs, check the rolling resistance value. It looks like about a 1000 times too big.

Welcome aboard,

major


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## S1lv3r (Aug 2, 2012)

Thank you Major for the reply. Here is how I calc the RR. 

N= m*g = 550kg*9.8m/s^2 and C = 0.01 giving me ~ 118

The "rolling resistance coefficient", is defined by the following equation[5]:







is the rolling resistance force (shown in figure 1),







is the dimensionless *rolling resistance coefficient* or *coefficient of rolling friction* (*CRF*), and







is the normal force, the force perpendicular to the surface on which the wheel is rolling.







is the force needed to push (or tow) a wheeled vehicle forward (at constant speed on the level with no air resistance) per unit force of weight. It's assumed that all wheels are the same and bear identical weight. Thus:







means that it would only take 0.01 pound to tow a vehicle weighing one pound.

Sorry for the long post I just wanted to make sure I got everything I needed across  Maybe even a little too much.


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## major (Apr 4, 2008)

S1lv3r said:


> N= m*g = 550kg*9.8m/s^2 and C = 0.01 giving me ~ 118


Math police  550 * 9.8 * 0.01 = 53.9 not 118. That is the force in Newtons.

When you go to the power equation, do not multiply by 550 and 9.8 again.

And 3.06 m/s = 11 km/h.

IMMIC (If My Math Is Correct)  I did not go through the entire post and calculations of yours. Just that part where rolling resistance and coefficient appeared confused.

Good luck with it.

major


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## S1lv3r (Aug 2, 2012)

Lol, math police. Yeah ur right don't know how I miscalculated that but I sure did step in it. I used the 3.06 m/s from a website calculator so that figure may also be incorrect. It was late and I did not have my ti89 handy so I took a quick shortcut. I will be doing the math over to get an accurate number. Do u have any opinions on the motors posted above? I'm going to read the link u posted on ac dc right now to get more insight. Thank u major for ur posts so far.

Ok, just read entire post and I would have to say I like sticking to the AC power. I do remember reading an article that the inventor (or someone the like) of DC power spent a lot of time trying to refine it and on his deathbed anounced that he had one regret and that was not to go to the AC power and spending his time on it. I don't know the names of these people but I believe I read that on Wikipedia somewhere. 

Either way, it seems that AC power offers a lot. DC is popular it seems but AC seems to be more of a precise power system. There are variables u can change to get a different drive experience and that is very appealing to me. I am at this point going to focus on using an AC power source, with that said are the motors above recommended or should I try to find a new one. I was looking at Siemens 1ph8 models but I'm sure those are about 10k$ maybe a two year old comparable model maybe it will be cheaper. I have looked into their simatic controllers. Simatic being the name if the model line I think. These have all sorts of functions built in, they have the regenerative braking which is a big plus. Before I was trying to design a whole other system that would handle hat task but this way I can just use the existing motor for that task. 

It is expensive but I feel it may be worth it. And according to some folks AC is the future of the EV car so why not learn that subject matter thoroughly by diving right in?


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## PStechPaul (May 1, 2012)

OK, a quick reality check. For a build of 1400 lb including rider, you might be able to cheat the usual 330 Wh/mile down to 200, but that is really optimistic. If you want to go 120 miles on a charge you will need a 24 kWh battery pack. I think you will be lucky to get that for $10,000. Here is an example:
http://www.batteryspace.com/lifepo4-battery-12.8v-40ah-512-wh-40a-rate-with-pcm---replace-sla.aspx

That battery is $380 for 512 Wh ($0.74/Wh) so using these a 24 kWh pack would be almost $18,000. It's 13.4 lb so the pack would be 628 lb. That's half the weight of your proposed vehicle. 

For power needed, let's use the higher figure of 330 Wh/mile at 60 MPH so you will use about 20kW, or 26HP continuous. You really don't need a bigger motor because you can get 2x to 3x peak torque from it. A larger 40-50HP motor such as what you show may actually have less losses running at 25HP than the "right-sized" motor, but you add a lot of weight. I figure probably 10lb/HP so your motor is probably 400-500lb, especially for a premium efficiency inverter duty motor. But I think the 40HP motor is a good choice. Weight is not a huge factor in overall efficiency if rolling resistance is optimized. I really think a 1500lb vehicle could be pushed with well under 100lb thrust on a smooth flat surface. 

Aside from rolling resistance, the biggie is how steep an incline you want to be able to climb, and how fast. You can always get plenty of torque by using a transmission, so in low gear you may have a top speed of 20 MPH at which point the wheels will be turning at about 300 RPM. Your 40HP motor has a rated torque of 118 lbft at 1800 RPM (which works out to 40.44HP), so you can get a wheel torque of 700 lbft. This is a thrust of about 700 lb which will allow your vehicle to climb an incline of about 45 degrees. Since you can get peak torque of 2x to 3x you could literally climb a wall. Or you could add some weight to your vehicle. You will need a frame and transmission and other necessities, and I think that will add at least 500 if not 1000 pounds. Especially to make it street legal. 

You probably already blew your budget with the batteries. 120 miles is a very high bar. 30-40 miles may be more practical and you can always add capacity when and if you can get a great deal on batteries. You will also need a controller, but I think you can find one on eBay for around $1000. You really don't need any more than 40HP, and 25-30HP will probably be fine. You can probably double up on the IGBTs for $300 or so. 

HTH!


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## S1lv3r (Aug 2, 2012)

Thank you PStechPaul, I will be looking more into the battery option. I had read that out of everything battery setups are the most expensive. I had not yet caluclated what range I would be looking into since I had not definitively decided wether to go AC or DC. 

At this point AC sounds best due to the above mentioned options. I have read your recommendation of Galiebs book and intend to do some reading on the subject just to become more familiar with the motors and their specific functions.

I live in the City so there are many overpasses that I would drive over. Work is about 16 miles away with about 6 overpasses. With morning traffic takes me thirty-five minutes to arrive at work and about forty-five in afternoon traffic. I estimated the 120miles just to be sure I could get there and back home without a charge because I dont believe they will allow me to charge the vehicle at work every day. So that value can be played with. 

If I understood you correctly I can use less power with a larger motor but will add that motor weight to the total weight being rolled around so the larger motor gain is minimal?

I have been searching eBay and other liquidation sites to see if I can find a suitible VFD for an AC setup or even a motor. Out of all the VFD's I have found handling 100kW the cheapest was around 2k$. I have been looking into something larger than what I actually need. I will continue to look with these new specs in mind and see of one under 1k$ is attainable. Also as far as motors go, I have seen some that are in the 150-200lb range. This seems reasonable for the motor weight to me. Although BRUSA has some that are nice but i have no idea what their cost is. They also have the Drive available. It seems like a very nice "all you need for the Driveline package". But I bet the cost is higher than I can afford.

I will continue to read and then see what new stuff I learn. Thanks again to all posters. Keep them coming if you think of something not mentioned thus far.


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## PStechPaul (May 1, 2012)

It seems like the largest drives under $1000 are about 15HP. It's also hard to find 240VAC drives over 25HP at reasonable cost. Like this:
http://www.ebay.com/itm/25-hp-Yaska...154?pt=LH_DefaultDomain_0&hash=item519ca9bf02

If you really plan to add enough batteries for 120 miles (or even 50 miles) you might as well go to a 600V system and usea 480V drive. Here is a 40HP 460V drive for $1200.
http://www.ebay.com/itm/IDM-CONTROL...740?pt=LH_DefaultDomain_0&hash=item1c181ba72c

Here's a pretty good deal on a 30HP motor for $400:
http://www.ebay.com/itm/260882263403?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1438.l2649


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## DDDvvv (Apr 2, 2012)

if going the ac route, i dont think the 40hp controller will work. it will be tripping the hardware overcurrent fault, everytime you try to move the vehicle from rest. the guy in this link tried just that ;
http://bmpenterprises.net/blog/2010/01/08/lessons-learned-using-industrial-vfd-for-motor-controller/
only difference is, he used a 30hp vfd, and his donor car is a feather-lite mini cooper.

the guys running successful ac vfd conversions recommend a vfd rating of 3 times your induction motor hp. if using that 30hp ebay motor, then go for a 90hp or more vfd.

this seller is selling a 100hp drive for $999 or best offer, http://www.ebay.com/itm/261017688785?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649 to show an example of whats available.


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## PStechPaul (May 1, 2012)

I have not actually used an industrial VFD in a vehicle, except my little tractor, and it was very limited in power. But my VFD has a lot of settings which I think would avoid the hardware fault trip. That is usually caused by an actual short circuit and not locked rotor current. Generally a locked rotor will draw only 6-8x nominal current, and there is a time/overcurrent module which acts like a thermal motor starter and trips after a few seconds. 

There is also a ramp-up and ramp-down time setting, but I think for vehicular use it is usually set to 0 or a minimum like 0.1 second. You should be able to achieve DTC by feeding the output of the torque sensing circuit to a PID loop with the throttle position and setting a torque limit below the breakdown torque. 

I don't have a high current power source capable of being used for such a test with my 2HP drive, although I might be able to run it on a 240VAC single phase 30A circuit which should give me 7200W or almost 10HP. I could lock the rotor on one of my motors and see what happens. I really doubt that it will trip the hardware overcurrent fault. But it might be a problem that is seen with high capacity battery packs, which can provide 30C or more. Even there, the inductance of the motor should slow down the saturation of the stator enough for the PWM and current sensors to detect maximum current (torque) and reduce the PWM width accordingly. 

If you find a seller who has both a motor and a controller, and an industrial mains supply, I would ask them to connect the motor to the controller and lock the rotor and see what happens. Locked rotors and high inertial loads (such as flywheels and EVs) are common situations in industry and a controller that kept tripping would be a nuisance and indicate either a bad controller, bad motor, or improper settings. 

Also I just checked the figures in the cited post and the 30HP (40kW) 460V controller should be good for about 50A per phase, so the 80A hardware protection limit seems suspect. Normal peak torque of a 30HP motor would be about 3x or 150A. Locked rotor might be 6x or 300A. So hardware protection should be more like 400A. 

My VFD has an overload torque of 150% for 1 minute and 200% for 0.5 seconds. To put this in perspective, a 30HP motor at 3600 RPM has a nominal torque of 44 lbft so it should give 88 lbft for starting. Assuming a drivetrain ratio of 10:1 that's 440 lbft *nominal* at the wheels which should be enough to push a 2000 lb vehicle up a 20% slope or accelerate at 0.2G. This is 9.8/5 = 1.96 m/s/s so in 10 seconds you will be going 18.6 m/sec which is 70km/hr which is fast enough for most purposes. And that is not even flat out. 30HP is plenty, unless you have direct drive, of course. Or maybe I made an error in my math. 

JMHO.


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## S1lv3r (Aug 2, 2012)

Thank you guys kindly for writing. This thread is really putting into perspective what it takes to get going in these EV's. I was calculating a minimum of 60-75 HP to get to have a comparable driving experience to a 4 Cylinder engine. I am currently trying to discuss possible drivetrains with friends to see what we can actually build according to my budget. I will be reading some more. Read a few hours this weekend just to become more aquainted with the AC asynchronous induction motor. I like that there is almost no maintenance involved in this motor. Induction is a pretty impressive phenomenon. I really like the AC road but WOW, three times the rating for the VFD sounds something fierce. I have looked alot at pricing and these controllers are a very substantial investment. I am certain I would not use 70% of the capabilities offered by these industrial controllers.

I actually started looking into what functions I would actually use and I wondered treading the waters of putting one together. I read in one of the threads here that you could build your own although I'm sure it would have less functions.

Just a thought, would it be very difficult in you guys' opinion to build a VFD that handles: motor HP and Torque control, regenerative braking, motor diagnostics and functionality (power consumption, real time volts, amps, watt usage) and battery bank levels?

Its just a question though. Have not really looked into building one yet so i dont know how much of an endeavor it would be.

I imagine transformers a plenty will be used, some relays, capacitors, sine wave, and freq manipulation, programmed chips etc... wow my mind is going haywire trying to come up with the major components off the top of my head.

I'll search the threads some to see if anyone has accomplished this feat. Thanks again everyone for your input. I am putting these posts into my research so that I may make the best decision for functionality. I will conitnue to read Gottlieb and other motor pdf's I have found online. Google is amazing!!


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## S1lv3r (Aug 2, 2012)

Just thought I'd post this link to give any readers interested in my findings some info. So far it seems that AC is a good choice but maaaan the budget seems to be telling me that I may end up with a DC series Wound system. At least for the first build. As someone had suggested in one of their posts on the forums... start with a DC system and then move onto a more elaborate AC setup when you have the basics down(and possibly more money). It seems thats where I'm headed but the tunnel is dark and I cant tell what the light at the end is yet. 

http://www.electric-cars-are-for-girls.com/electric-car-motors.html


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## steven4601 (Nov 11, 2010)

Depending on your budget..
The cheapest new AC traction kit with batteries (rental) you can find is likely the Renault Zoe coming out September. .But it may be silly to hack it apart as its a hip & quick extra compact car.


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## Siwastaja (Aug 1, 2012)

Disclaimer; I don't have real experience yet on using an industrial AC induction motor, but we plan to rewind one and use it so I've been doing some research on the subject. So I will comment about your idea of using an industrial ACIM which indeed has potential to be a very economical solution.


I think that a nominal 40 HP (as in the first picture) industrial ACIM will be very plentiful for any normal sized car.

They are designed to run years or even decades continuously at that power rating, sometimes with a bit hindered ventilation etc.

Magnetic saturation of the core limits maximum power at a certain frequency, but the catch is here; if you increase _frequency_, you can increase the power at the same rate (by increasing voltage at the same time) without this happening. Frequency too high gives new types of losses, but this shouldn't happen before 200 Hz or so. So you should be able to at least double the power by doubling the frequency; possibly even more. (This is exactly the same reason as switch mode power supplies are very small; they can use physically small transformer core - less iron - due to high frequency used.)

This is also why a 4-pole motor (~1800 rpm) should be preferred over 2-pole (~3600 rpm): you get your preferred maximum rpm (somewhere around 4000-5000 rpm, or more if you are brave enough) at somewhere around 150 Hz, not 70-80 Hz as you would with a 2-pole, so you have more power reserve to use.

Still, even though your motor efficiency wouldn't fall (at least very much) even when overpowering, you are still generating more heat. The chances are, these motors may be conservatively designed so it wouldn't become a problem. But, if you can come up with solutions for driving the heat out of the windings, you can probably increase the overpowering factor.

Anyways, I would guesstimate you can safely double the nameplate power for an industrial 4-pole ACIM used at higher frequency, and this is for a CONTINUOUS reading. You can probably double that again to get the peak reading. This also boils down to the simple reality that the physical motor size is really quite good measure for the real power available; these motors are big so you can get a lot of power from them. Of course, a bulky cast iron enclosure not present in EV-specific motors hinders this evaluation.

The actual problem here is the voltage. For most industrial motors, the nameplate power is achieved when connected in delta, and if the voltage here is around 400V, you would need a DC bus voltage of about 600V just for the nameplate frequency and rpm. Then, if you want to double it, you would need a 1200 V battery!

If you find a motor with a nameplate value at 230V, you are much better off, but still a bit far from REALLY usable, IMO, unless you are really ready to design a high voltage system.

This is why you should find a very special motor with lower voltage rating to begin with, or to rewind an industrial motor, or if you are VERY VERY lucky, you might find an industrial motor where you can change the existing windings from series to parallel. Or, you can just live with getting 40 HP or a bit more off a 40 HP motor and shifting gears while you drive. This would be a simple conversion and comparable to those DC conversions in performance/driving experience.

We have a 2-pole 13 kW (nominal continuous) @ 440V 50 Hz delta ACIM we are currently rewinding. We have removed half of the existing windings now. It HAD two groupings of windings that could have been changed from series to parallel, but the connections were impossible to reach without destructing the windings, and changing it to 220V wouldn't have been enough. Furthermore, we are planning to change it to 4-pole. So we will be DIYing a full rewind.


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## Tesseract (Sep 27, 2008)

Siwastaja said:


> ....
> Magnetic saturation of the core limits maximum power at a certain frequency, but the catch is here; if you increase _frequency_, you can increase the power at the same rate (by increasing voltage at the same time) without this happening. Frequency too high gives new types of losses, but this shouldn't happen before 200 Hz or so. ...


Core losses increase at (approximately) the 1.6 power of frequency, so driving a 50Hz motor with 200Hz while keeping V/f proportional will result in 9x more core loss. Common industrial motors won't tolerate that for more than a few seconds.


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## steven4601 (Nov 11, 2010)

Banter.
Larger AC traction motors have slip frequencies less than a few hertz. Core losses come mainly from their magnetising currents. 
You referring to the stator losses which is valid, however those losses are not dramatic compared to the copper losses. Additionally those are very easy to cool in watercooled ac motors.


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## Siwastaja (Aug 1, 2012)

Tesseract said:


> Core losses increase at (approximately) the 1.6 power of frequency, so driving a 50Hz motor with 200Hz while keeping V/f proportional will result in 9x more core loss. Common industrial motors won't tolerate that for more than a few seconds.


Do you have a source for this? Every material I have came across have shown that the core loss is a small fraction (like a few percent) of the total losses at 50/60 Hz compared to I^2R losses, and therefore they would start coming really into play somewhere about or after the 200 Hz mark; I still believe doubling the frequency (hence tripling the core loss) would be fine, 200 Hz starting to be a borderline condition. This is what I based my comment on. Of course I might be wrong and don't have time to try to find the sources again...

Anyway, I agree there can be a factor of uncertainty here. Motors designed only for 50/60 Hz use may use too thick laminates or inferior core material, because the don't NEED any better. OTOH, they might be designed for higher frequencies than absolutely needed and most probably have some leeway in order to make the motor more efficient even at 50/60 Hz. A "premium efficiency" branded motor should be a good sign here.


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## PStechPaul (May 1, 2012)

I don't have direct experience with overclocking ACIMs except as a low power short term experiment, but I think it should be reasonable to be able to overclock to 3x or 180 Hz without serious problems. A premium efficiency large motor might be 94% efficient, and probably half the losses are in the copper. So if there is 3% core loss at 60 Hz, it should be no more than 6% at 180 Hz if the 1.6 power is correct. 

I think the future of traction motors will be switched (or synchronous) reluctance types. But for the DIYer it will be much more cost-effective to use surplus ACIMs which are probably 1/5 to 1/10 the cost of and SRM, especially when you add the controller. But I'm trying to make my own SRM and there are some demos showing how simple, versatile, and powerful they are:





 




 




 




 
And for the corporate schtick from ABB:





 
I think this technology deserves its own thread, however. Once I get my motor running I'll start one and post videos. But here is a start, showing an initial idea for the rotor and stator pieces. The laminations for a 6.5" diameter 2" thick motor can be purchased from www.eMachineShop.com for about $400:


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## Tesseract (Sep 27, 2008)

steven4601 said:


> Banter.
> Larger AC traction motors have slip frequencies less than a few hertz. Core losses come mainly from their magnetising currents. You referring to the stator losses which is valid, however those losses are not dramatic compared to the copper losses. Additionally those are very easy to cool in watercooled ac motors.


Yes, I am referring to the stator, and while it is true that you *can* use liquid cooling for the stator (much more easily than the rotor, anyway), in a common industrial motor - which is what is being discussed - all you are going to get for cooling are some crappy cast iron fins. But feel free to prove me wrong with empirical evidence. AC induction motors have some very real advantages, but like any motor they are limited in the amount of overload they can handle; driving an ACIM over base speed while fully fluxed is a great way to cook it.


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## Siwastaja (Aug 1, 2012)

Tesseract said:


> Yes, I am referring to the stator, and while it is true that you *can* use liquid cooling for the stator (much more easily than the rotor, anyway), in a common industrial motor - which is what is being discussed - all you are going to get for cooling are some crappy cast iron fins. But feel free to prove me wrong with empirical evidence. AC induction motors have some very real advantages, but like any motor they are limited in the amount of overload they can handle; driving an ACIM over base speed while fully fluxed is a great way to cook it.


I agree somewhat, and even if the core losses wouldn't become the problem, resistive copper losses still increase.

At higher RPM, the fan also works harder to remove heat, but I suspect that the internal heat transfer from the stator windings to the cast iron frame will be the limiting factor, and heavy mountain climbing might require external cooling as the rpm is low but power is high. (This is true to any air cooled motor.)

Still, (1) heat transfer increases as the temperature increases; (2) motor has quite a bit of mass, even in the windings, to average out the temperature. These motors are specified to work for hundreds of thousands of hours uninterrupted with max power. I really doubt that just doubling the power, even for longer runs such as hours on a highway, would heat up the windings enough to bring the varnish near failure point. It probably is just at the region of increased wear rate; but high-power usage hour count will be very very low in a typical EV application. 

I suspect that the products sold as "EV" motors (DC or AC), even the high-end ones are just specified with different tolerances and tested more in this specific application. After all, there doesn't seem to be any special magic there, at least with the cheap ones; they are small and still rated at higher power, and that power cannot come from anywhere else than just rating them differently, for this specific purpose that differs from industrial use.

Also, a failure in an industrial motor in its intended use may cost millions or billions; this is the reason they need to have more leeway in ratings.

But with no overload or overclocking testing done (edit: or published) by the mfg, it will be more about luck. And I would be very careful with the temperature anyway, for the reason that many older industrial motors may not have winding temperature sensors in them.

We need test results to give some kind of starting point. I hope we can provide some in the future.

Anyway, if we get back to the OP's question, a 40 HP(cont) industrial motor as shown will be more than enough anyway for any normally sized car, and it should be able to get to highway speeds easily. Doubling the power momentarily for joining the highway will probably be on-specs anyway, and this should go even without increasing frequency much; so you if you can afford that weight on the car and can physically install motor that large, you don't even need to overrate it.


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## aeroscott (Jan 5, 2008)

how about the guys down under that had less heat overclocking a high eff. motor


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## PStechPaul (May 1, 2012)

Apparently they do a lot of rewinding and overclocking on the Australian forum:
http://forums.aeva.asn.au/forum_pos...=38371&title=getting-the-right-windings#38371

This article may be useful:
http://www.reliance.com/mtr/b7100_1.htm

This is a rather detailed study of core loss vs frequency and flux:
http://eprints.gla.ac.uk/3438/1/flux_and_freq.pdf

Others:
http://www.reliance.com/prodserv/motgen/b7097_2.htm

This paper estimates core losses to be 20-25% of total losses. 
http://220.156.189.23/energy_managers_auditors/documents/guide_books/3Ch2.pdf

So since the copper losses go up by the square of current and core losses increase by perhaps even less than the square of frequency, it seems that higher frequencies would contribute less to overheating than higher current (torque boost). Also the internal fan should be more efficient at higher speeds so that will help as well. You run a risk anytime you push a machine past its design limits, but ultimately the consequences are determined by temperature, which is easily monitored. The failure mechanisms are generally insulation deterioration and bearing overheating and wear.


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## aeroscott (Jan 5, 2008)

PStechpaul , thanks for finding those links .


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## Tesseract (Sep 27, 2008)

Siwastaja said:


> Do you have a source for this? Every material I have came across have shown that the core loss is a small fraction (like a few percent) of the total losses at 50/60 Hz compared to I^2R losses, and therefore they would start coming really into play somewhere about or after the 200 Hz mark; I still believe doubling the frequency (hence tripling the core loss) would be fine, 200 Hz starting to be a borderline condition....


The 1.6 power rule is a heuristic, or simple shortcut, for estimating the sum of hysteresis and eddy losses vs. frequency in the armature* of any motor (or transformer) made with silicon steel laminations.

I don't have a reference for this specific heuristic because it is one of those useful things I've picked up over the years but can't remember where. I'm not planning on writing a paper on it so a citation is not too important to me. I understand that it might be important to you, however, so feel free to ignore it. You're loss... ahem... because here is a good paper on calculating the core losses in a squirrel cage induction motor:

Iron Losses in Induction Machines


* - Yes, AC motors have an armature; it is defined as the source of the rotating magnetic field, while the field is defined as source of the static magnetic field.


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## Hollie Maea (Dec 9, 2009)

PStechPaul said:


> You run a risk anytime you push a machine past its design limits, but ultimately the consequences are determined by temperature, which is easily monitored.


We need to be cautious with this statement. There are two equivalent limits. The maximum current is limited by temperature, but also the maximum voltage is limited by rating insulation. Again, in a mission critical industrial machine, the insulation ratings, like the temperature ratings, are likely to have a lot of leeway. But if you are going to overclock a machine at constant V/Hz, then the voltage could be an issue as well, and it would be nice to at least have a ballpark estimate of what the insulation can handle. Further complicating the issue is that at higher temperatures insulation rating degrades so there is some interplay at work here when you increase both the voltage and current.

All this said, as far as the OP is concerned, by all means do an AC build if you can. You can get a better car for the same money with DC right now, but your future conversions will be AC and it's good to start going down that road now if possible.


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## ruckus (Apr 15, 2009)

Well, this thread starts out looking at specific junk motors on ebay and then launches into a lot of theoretical maybe's, if's, and possibly's.

If you want to build something get a motor and hook it up. There is a ton of theory out there that doesn't matter at all when you are looking at an old greasy motor for $150. A specific motor on Ebay will do what it does. Under-sizing the motor seems to be a common mistake (ask me how I know). So go big, but also keep an eye on weight. No need to lug around a train motor. 100-300 lbs is the ballpark.

If you want a very accurate calculator of rolling resistance and kw needed, use this one over at Ecomodder: http://ecomodder.com/forum/tool-aero-rolling-resistance.php

Obviously this is continuous kw/hp needed for a given speed. I would add at least 20% for loads, head winds, hills, etc. Again, better to have a bit extra than to overheat.

If you want to calculate gearing and speeds use this calculator: http://www.rocky-road.com/calculator.html

Rated rpm is very important. If you have 2 motors both rated at 30hp but one is 1800rpm and the other is 3600rpm, the 1800rpm motor will have double the torque. Either way you can compensate with gearing, up or down. On some motors like servo-motors you can change the working rpm by just switching around a couple of wires on the winding connections. Again, weight is probably the best indicator of a motor's capability. If it doesn't weigh at least 100 lbs you probably don't want it unless you are building a motorcycle/trike.

Good luck.

edit- oh yeah, on the ac-dc thing. If you are buying used parts I think AC is cheaper right now cause they are under the radar. Everyone is already wise to DC and the prices are consistently pretty high on Ebay. Sometimes used industrial AC drives are sold with the matching controller. That would likely be the way to go.

one of many examples on Ebay: http://www.ebay.com/itm/Powertec-20...aultDomain_0&hash=item2a1b74e4f7#ht_638wt_952


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## Tesseract (Sep 27, 2008)

Hollie Maea said:


> We need to be cautious with this statement. There are two equivalent limits. The maximum current is limited by temperature, but also the maximum voltage is limited by rating insulation. Again, in a mission critical industrial machine, the insulation ratings, like the temperature ratings, are likely to have a lot of leeway....


I generally agree with this statement but with the caveat that the PWM waveform from the inverter - particularly if the switching transitions are fast - causes capacitively coupled current to flow through the insulation of the stator windings which results in additional heating (ie - "dielectric heating", literally). Also, these same capacitively-coupled currents are what cause bearing erosion in AC motors, though you don't often see this happening until you get up to around 500-600V for the DC bus.




ruckus said:


> Well, this thread starts out looking at specific junk motors on ebay and then launches into a lot of theoretical maybe's, if's, and possibly's.


The sole reason I responded to this thread was to disabuse people of the notion that it is okay to run *any* kind of motor at 4x its rated power for long periods of time. And that is exactly what is being talked about here: driving a 50Hz ACIM at 200Hz while maintaining the same V/Hz ratio - even if the stator was rewound for a lower voltage and higher current. If you weren't asking 4x the power from the motor at 200Hz then you wouldn't need to supply it with 4x the voltage, either.


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## ruckus (Apr 15, 2009)

Tesseract said:


> The sole reason I responded to this thread was to disabuse people of the notion that it is okay to run *any* kind of motor at 4x its rated power for long periods of time.


Couldn't agree more. At 4x power 30 seconds is an eternity.


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## PStechPaul (May 1, 2012)

Tesseract said:


> I generally agree with this statement but with the caveat that the PWM waveform from the inverter - particularly if the switching transitions are fast - causes capacitively coupled current to flow through the insulation of the stator windings which results in additional heating (ie - "dielectric heating", literally). Also, these same capacitively-coupled currents are what cause bearing erosion in AC motors, though you don't often see this happening until you get up to around 500-600V for the DC bus.


Agreed. There are motors specifically made for PWM duty, and it's all about the insulation and the high frequency harmonics and capacitive current flow and dissipation factor. And there are also special drive cables optimized for this. Has anyone tried adding a low-pass filter from the controller to the motor? 

I did not know about the bearing erosion problem. Is that caused by torque ripple or induced currents through the bearings?



> The sole reason I responded to this thread was to disabuse people of the notion that it is okay to run *any* kind of motor at 4x its rated power for long periods of time. And that is exactly what is being talked about here: driving a 50Hz ACIM at 200Hz while maintaining the same V/Hz ratio - even if the stator was rewound for a lower voltage and higher current. If you weren't asking 4x the power from the motor at 200Hz then you wouldn't need to supply it with 4x the voltage, either.


I definitely agree. However, I think most motors will have minimal core loss up to about 120 Hz, so doubling the power by overclocking 2x should be OK for continuous operation. If you use a 240/480V motor the insulation is already rated at 480V or even 600V so you should be able to use V/F up to that point. For short term current overload it seems that 1.5x is OK for about 30 seconds and 2x is OK for 2-3 seconds or so. 

Under normal driving conditions, including extended hill climbing, the motor should be rated for the continuous power needed. Overclocking (2x) and current (torque) overload (2x) might safely give 4x power for short bursts, but I think it's better to gear down and overclock rather than run at overcurrent because the resistive losses are larger and increase per power of 2 rather than 1.6.


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## Ivansgarage (Sep 3, 2011)

Ok guys how many amps (draw) do think it takes to mantain
60 mph? On a 10 hp of the self ac 3phase motor.

The ac-50 was originaly a 7.5 hp motor (8" diameter)


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## ruckus (Apr 15, 2009)

Ivansgarage said:


> Ok guys how many amps (draw) do think it takes to mantain
> 60 mph? On a 10 hp of the self ac 3phase motor.
> 
> The ac-50 was originaly a 7.5 hp motor (8" diameter)


You mean kilowatts?

The amperage is dependent on the vehicle you are pushing and the voltage (not the motor size). Using this calculator for your average smallish car (like a Honda Civic): http://ecomodder.com/forum/tool-aero-rolling-resistance.php
I get about 9600 watts @ 60 mph. So let's round that up to 10 kw (13hp).

Sooo... what's your voltage????? That is what determines the amps, not the hp rating of the motor. (volts x amps = watts / 1000 = kw)

10kw @ 120v = 83 amps
10kw @ 240v = 42 amps
10kw @ 360v = 28 amps
10kw @ 440v = 23 amps
10kw @ 640v = 16 amps

Use the calculator. Estimate your vehicles speed in watts. Multiply by 20%. Divide by the voltage. Boom, you have the amps. simple.

A small motor and a large motor will use the same amps in this case at first. But the small motor will quickly start to get hot. This increases the amps needed to produce the same power. Eventually it will overheat. 

Go big. Go higher voltage. This reduces amps and thus heat. My advice.


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## adeyo (Jun 6, 2012)

ruckus said:


> Go big. Go higher voltage. This reduces amps and thus heat. My advice.


Ok, in light of this, please comment on a baldor high efficiency (94%) 230/460v 60Hz 1780 rpm 60 HP motor weighing ...gulp...800lbs. Is there any way to shed weight with a rewind or ditch the cast iron casing for something else? This even possible? Could I lower the voltage to 72 or 144? (Can't figure how to fit batteries unless it's a lower voltage...can't afford lith)...let's say I keep higher voltage, how high do I need to go with an inverter? ...what size vfd is best if I go this route? ...what would one of you guys do with this motor if you were in my shoes? and how do I run it with keeping battery costs realistic?


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## PStechPaul (May 1, 2012)

I think your motor is twice as big as it needs to be unless you have a vey heavy vehicle. Of course if you have a lot of lead batteries that will add to the weight. Since you shoud be able to maintain 60 MPH with well under 20 HP, a 25-30 HP high efficiency motor would be better. Maybe you can sell your 800lb pig and buy a 400lb piglet and come out a few dollars ahead. 

You will need to have a pack voltage of at least 200 VDC (including sag) for a 240 VAC inverter, and 320 VDC is recommended. You might be able to get a motor shop to rewire the motor delta rather than star for a nominal 138 VAC.


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## ruckus (Apr 15, 2009)

Sure, I'll shed some light on that beast... forget it. You want 1-300 lbs, 400 max. Everything else is a waste of time. Motors are everywhere, pick the right one or you will regret it.

Not sure how yer gonna get high voltage with lead. Small batts? Is it worth it? If this is a budget project there are other ways to go such as salvaging some production hybrid packs. Many are thrown out with only a bad cell or two. Often they just need a good balancing. Used Lithiums? Anything but lead will put you ahead.


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## adeyo (Jun 6, 2012)

ruckus said:


> Not sure how yer gonna get high voltage with lead. Small batts? Is it worth it? If this is a budget project there are other ways to go such as salvaging some production hybrid packs. Many are thrown out with only a bad cell or two. .


Originally, I was thinking Trojan T-1275's (if I can remember correctly...good power density). But I do have access to many totaled hybrid vehicles battery packs. (Usually, packs unharmed) What are the best kind for an ev conversion and basically, how would you approach that??









PStechPaul said:


> You might be able to get a motor shop to rewire the motor delta rather than star for a nominal 138 VAC.


What are the trade offs? 138 volts sounds good to me. Still too much weight? Brand new, it lists at over $6k...baldors web site. My cost 1k. Ultimately, this will be in a large donar truck. Right now, old Volvo with blown engine.


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## S1lv3r (Aug 2, 2012)

Wow this thread really got away from me. I guess that will happen when you dont check back for a couple of weeks. I have been busy taking care of life duties but have managed to look into a purchase and I came accross a deal that I think will be SOLID for this project build. This maybe better posted in another forum but since this thread is running I'll post it here.

A local seller is willing to sell me a Warp 9 (dont know what year model though), an Alltrax controller (again no model # yet), mounts, charger, and transmission for 2k. This seems like it is the missing puzzle piece for this build. 

So is it the general consensus that this is a good deal? Depending on model numbers and year of production??

I will be visiting the sellers shop sometime this week to look at their EV conversions and check out the items for sale. I can take pictures for the forum if it is ok with seller. He stated that he just finished a microbus and an EV 4x4 rail type buggy.

Of course there is still battery packs to look into but that is the next objective.

I read through all the posts during my absence and there was alot of great information posted. Thank you all for your time and knowledge. I had not been able to go through all links posted but I will definitely be doing so in the near future. 

I apologize in advance if posting the deal I found on this thread is unacceptable. I will repost in proper "motor" thread if necessary. Thanks again everyone.


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