# AC Induction motor rewind for higher frequency / power - need help



## samborambo (Aug 27, 2008)

I realise we've mentioned this idea before when comparing 400Hz aircraft motors to standard 50Hz induction motors. I've approached a motor rewinder about rewinding a secondhand AC induction motor for lower voltage (230VAC, 320VDC at the inverter). It's quite cheap compared to buying a brand new custom spec one from ABB. NZ$1500 vs NZ$3500

Since I'm having the motor rewound for lower voltage anyway, I think it'd be worthwhile doubling pole pairs, halving the winding BEMF and doubling the frequency to give me close to double the power at the same rated speed while avoiding core saturation. Maybe even go for a factor of four.

I realise there are issues with AC skin effect losses and winding window constraints but the real unknown is whether there will be prohibitive iron losses in the core. Is the standard electrical steel used in motor cores good for 100, 200 or even 400Hz?

Sam.


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## major (Apr 4, 2008)

samborambo said:


> Is the standard electrical steel used in motor cores good for 100, 200 or even 400Hz?


Hi Sam,

As Lee says, good thing about standards; there are so many to choose from. Who knows what steel is in there?

My advice is to use a 4 pole machine up to 400 Hz. With most operation below 300 Hz. From experience starting with NEMA "premium eff" motors. Whatever that really means 

Regards,

major


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## samborambo (Aug 27, 2008)

Thanks major. The premium efficiency motors, as I understand it, are just more copper and iron to reduce losses even further. Since I'm not increasing the flux density in the iron, increasing the electrical frequency would probably have the same effect on premium efficiency motors as it would standard motors.

I think I'd be pushing my luck going for a factor of 4 - effectively an 8 pole motor. That'd be a large and uncommon stator.

Performance based on the 18.5kW ABB motor:

Torque: 72Nm continuous, 274Nm peak (3.8x)
Speed: 3000RPM base, 6000RPM max
Stator: 2 pole, 230V p-p, 50Hz base, 100Hz max

So I want to use a similar frame (132mm) secondhand motor wound to produce:

Torque ~100Nm continuous, ~300Nm peak (3x)
Speed: 3000RPM base, 6000RPM max
Stator: 4 pole, 230V p-p, 100Hz base, 200Hz max

That's about 31kW continuous, 94kW peak.

How does that sound?

Sam.


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## major (Apr 4, 2008)

samborambo said:


> How does that sound?


Sam,

Don't change a 2 pole stator to a 4 pole winding. The steel shape is all wrong. Start with a 4 pole and change the turns and wire size (effective) to get your new base V and f. Same with the rotor, although not as critical as a 2 pole will just have extra thick end rings most likely. Although many times the air gap diameter is different between the 2 and 4 pole designs. KISS. You be more likely to like the results.

For maximum torque density you're best off with 4 poles, maybe 6. 2 poles and 8 and higher actually decrease torque density. If you can do a stable drive for it, shoot for a base of around 200 to 300 Hz for one power dense machine. And then figure out how to cool it.

I really don't follow your math and don't want to get into all that. Just relating some experience here.

Regards,

major


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## Bowser330 (Jun 15, 2008)

samborambo said:


> .....
> 
> So I want to use a similar frame (132mm) secondhand motor wound to produce:
> 
> ...


It sounds amazing and would really change the DIY EV landscape if used readily available AC motors could be affordably rewound and respec'd for EV operation.


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## samborambo (Aug 27, 2008)

Bowser330 said:


> It sounds amazing and would really change the DIY EV landscape if used readily available AC motors could be affordably rewound and respec'd for EV operation.


There's no reason why you can't rewind an induction motor for lower voltage / higher frequency. I've found a cheap motor from CMG - 4 pole, 400VAC, 50Hz, 1450RPM, 11kW, 132MB frame (roughly an 8" small flange), 61kg. Rewinding that for 230VAC, 100Hz would yield around 22kW at 2900RPM with very little increase in weight, maybe a couple of kg extra copper. CMG offer high power density windings (non-specific, some design consideration must be made) to allow for higher peak power. I'd expect to get at least 70kW out of it.

Here's the kicker: Off the shelf those motors are US$500. CMG will wind it to a custom voltage as a factory option.

What voltage would you guys like to use? I assume you'd use a DMOC445 or Kelly controller? 

Sam.


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## Bowser330 (Jun 15, 2008)

samborambo said:


> There's no reason why you can't rewind an induction motor for lower voltage / higher frequency. I've found a cheap motor from CMG - 4 pole, 400VAC, 50Hz, 1450RPM, 11kW, 132MB frame (roughly an 8" small flange), 61kg. Rewinding that for 230VAC, 100Hz would yield around 22kW at 2900RPM with very little increase in weight, maybe a couple of kg extra copper. CMG offer high power density windings (non-specific, some design consideration must be made) to allow for higher peak power. I'd expect to get at least 70kW out of it.
> 
> Here's the kicker: Off the shelf those motors are US$500. CMG will wind it to a custom voltage as a factory option.
> 
> ...


Sounds like a perfect economy motor. Would it be possible to have CMG wind a larger motor something with a peak of 150kw or 200kw?

I am not sure what the peak amperage tolerances are of the AC motors in question but if they could tolerate 500A for peak power output then I guess a voltage of 400V is something that would work to create 200kw...

The question about what controller to use is another one all together. I know that a member "etischer" did create a custom AC controller and I have heard rumblings from the Soliton1 camp that they were going to build one....

(1) Custom AC inverter based on modified VFD controller ~2000$
(2) Custom wound AC Motor rated to 400V 500A peak, 200kw ~3000$

5000$ guesstimate for 200kw AC EV drive?

Is this possible?


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## samborambo (Aug 27, 2008)

Bowser330 said:


> Sounds like a perfect economy motor. Would it be possible to have CMG wind a larger motor something with a peak of 150kw or 200kw?
> 
> I am not sure what the peak amperage tolerances are of the AC motors in question but if they could tolerate 500A for peak power output then I guess a voltage of 400V is something that would work to create 200kw...
> 
> ...


The CMG SLA series don't go bigger than a 160 frame. The ABB IPM motors are typically longer and have higher peak power but are 3 times the price of CMG. Do some hunting through motor catalogues for a motor with a high torque to weight ratio and have it rewound for a lower voltage. Industrial induction motors tend to be quite wide which maybe a constraint for you. The frame number is the measurement in mm from the shaft centre to the base. Some of the ABB motors can be 600mm - 700mm long.

Just a quick glance through the ABB IPM 4 pole motors shows the 3GAA-132-316-**E 15kW 132 frame motor is capable of 4x overload off the shelf. That's 60kW @ 1500RPM base speed in a 97kg package. If the motor was wound for full power / voltage at 4500RPM base speed the frequency would be 150Hz. The peak power would be 180kW. ABB recommend not running these motors above 4500-6000RPM but that's usually on a radial load, eg: a pulley and belt drive. If you're coupling directly into a gearbox the radial load should be zero, meaning you should be able to get some very high speed out of the rotor.

Sam.


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## Bowser330 (Jun 15, 2008)

samborambo said:


> The CMG SLA series don't go bigger than a 160 frame. The ABB IPM motors are typically longer and have higher peak power but are 3 times the price of CMG. Do some hunting through motor catalogues for a motor with a high torque to weight ratio and have it rewound for a lower voltage. Industrial induction motors tend to be quite wide which maybe a constraint for you. The frame number is the measurement in mm from the shaft centre to the base. Some of the ABB motors can be 600mm - 700mm long.
> 
> Just a quick glance through the ABB IPM 4 pole motors shows the 3GAA-132-316-**E 15kW 132 frame motor is capable of 4x overload off the shelf. That's 60kW @ 1500RPM base speed in a 97kg package. If the motor was wound for full power / voltage at 4500RPM base speed the frequency would be 150Hz. The peak power would be 180kW. ABB recommend not running these motors above 4500-6000RPM but that's usually on a radial load, eg: a pulley and belt drive. If you're coupling directly into a gearbox the radial load should be zero, meaning you should be able to get some very high speed out of the rotor.
> 
> Sam.


So if the ABB is 3X more than the 500$ CMG so...1500$?. Does ABB make the motor to your specific specs e.g. free high power winding? or would you have to pay another XXXX$ to rewind it for performance?
180kw! in a 97kg package! NICE! and if the RPM could stretch up to 80000rpm thats a huge power band to work with...
5:1 Ratio with 25" diamter wheel would result in....
1000rpm = 14.9mph
~4000rpm = ~60mph
8000rpm = 118.9mph
Definitely direct drive capable....

Problem still is which controller to use (custom build) since the off the shelf variety might not be suitable for 180kw peak...


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## Tesseract (Sep 27, 2008)

samborambo said:


> There's no reason why you can't rewind an induction motor for lower voltage / higher frequency.


Sure there is... an increase in core losses. Specifically, eddy current losses from the laminations being too thick and, to a lesser extent (unless you go crazy), hysteresis losses from the wrong alloy of silicon steel.

An excellent online reference geared towards engineers is:

http://info.ee.surrey.ac.uk/Workshop/advice/coils/power_loss.html

That said, merely doubling the frequency to 100/120Hz is unlikely to cause a huge increase in core losses in modern motors, especially those designed for use with inverters.




samborambo said:


> I've found a cheap motor from CMG - 4 pole, 400VAC, 50Hz, 1450RPM, 11kW
> ...
> Here's the kicker: Off the shelf those motors are US$500. CMG will wind it to a custom voltage as a factory option.


Good find, Sam.




samborambo said:


> What voltage would you guys like to use? I assume you'd use a DMOC445 or Kelly controller?


Sheesh... talk about pearls before swine... Anyway, winding for a lower voltage makes it easier to overload it with practical size battery packs. My vote is to rewind for 200Vrms so that standard IGBTs could be used and still allow a moderate amount of overexcitation (i.e. - maintaining the proportionality of V and F above the base speed).


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## JRP3 (Mar 7, 2008)

I'd look into the new Sevcon AC controllers: http://www.diyelectriccar.com/forums/showthread.php/sevcon-ac-controllers-39558.html


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## Bowser330 (Jun 15, 2008)

JRP3 said:


> I'd look into the new Sevcon AC controllers: http://www.diyelectriccar.com/forums/showthread.php/sevcon-ac-controllers-39558.html


Good point i totally forgot about my post in that thread!

300V 800A for one minute controllers...240kw perfect for the modified ABB motors we are talking about...

The most expensive HPGC motor setup is about 5000$ and for ~50HP and 110ftlbsTQ

This setup might cost a little bit more but @ 180kw is 240hp!


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## samborambo (Aug 27, 2008)

Bowser330 said:


> Good point i totally forgot about my post in that thread!
> 
> 300V 800A for one minute controllers...240kw perfect for the modified ABB motors we are talking about...
> 
> ...


I saw those Sevcon controllers the other night when doing some research. They'd definitely do the job - auto learning the motor characteristics on start-up means you won't have any compatibility problems. You'll probably have to sell a kidney or two. Can someone investigate price on these inverters please?

The 800A, I assume, is the phase current. That would be theoretically 800A x (300VDC/1.414) x 1.73 = 294kW. Modern direct torque vector drives can also achieve around 15% more AC voltage because the vector space is hexagonal, better utilising the DC source voltage. That'll help keep the power flat at maximum above the base speed.

240VDC with 3x speed would be a good compromise. A 4 pole motor wound for 170VAC at 4500RPM/150Hz. That's 57VAC at 1500RPM/50Hz, a rewinding factor of 7 from the stock 400VAC.

I've spoken with both ABB and CMG over the past few months about motor options. CMG seem more flexible in options for their motors like flying leads instead of a cable box, mounting options, buried stator temperature sensors, winding wire options, etc.

Plus CMG is farken cheap. How does this power density and price compare with a DC motor?

Sam.


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## Bowser330 (Jun 15, 2008)

samborambo said:


> I saw those Sevcon controllers the other night when doing some research. They'd definitely do the job - auto learning the motor characteristics on start-up means you won't have any compatibility problems. You'll probably have to sell a kidney or two. Can someone investigate price on these inverters please?
> 
> The 800A, I assume, is the phase current. That would be theoretically 800A x (300VDC/1.414) x 1.73 = 294kW. Modern direct torque vector drives can also achieve around 15% more AC voltage because the vector space is hexagonal, better utilising the DC source voltage. That'll help keep the power flat at maximum above the base speed.
> 
> ...


If the Sevcon will cost a kidney then maybe a custom AC inverter then? by modifying a VFD like what etischer has done...by developing an AC inverter for the 90hp Ford Siemens motor...http://etischer.com/awdev/

If CMG can make these high power motors for a "good price" and the inverter can be built for a "good price" then this could be a game changing EV kit! Hey if the price is consistent with DC then a lot of people would consider making an AC DIY EV...


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## samborambo (Aug 27, 2008)

Tesseract, you're right about the core losses, especially eddy current loss. Eddy current loss increases proportional to the square of the frequency. That means at 3x frequency, eddy loss is 9x. Better cooling of the core?

Eddy loss is also proportional to square of the thickness of the laminations. Eg: 2mm laminations reduced to 1.4mm would halve the eddy loss. CMG might have some thinner lamination options.

Sam.


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## Bowser330 (Jun 15, 2008)

http://www.evalbum.com/2688

Well look what I found, a member of the Australian Electric Vehicle Association (AEVA), Brisbane branch, has had CMG rewind an AC motor for him...


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## samborambo (Aug 27, 2008)

Here's an inverter that would work for a 230VAC/320VDC motor setup:

https://i-store.hitachi.us/ISDWebStore/Shop?op=pd&item=SJ300-550LFU

US$3096 seems pretty cheap for a 55kW / 78kW (60 secs) inverter. They're also designed to have a DC accumulator on the DC bus so using it in an EV shouldn't be too hard. Talk to Hitachi about it.

Sam.


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## Bowser330 (Jun 15, 2008)

Why isn't this getting more traction with the DIY community?

Why aren't more people rewinding aluminum AC motors for EV use?


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## few2many (Jun 23, 2009)

Hey guys, check this out. The guy didnt rewind the whole motor, but identified the series windings and changed them to parallel. Kinda like the star to delta, but going a few steps farther.http://www.aeva.asn.au/forums/forum_posts.asp?TID=1237


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## Amberwolf (May 29, 2009)

Bowser330 said:


> Why isn't this getting more traction with the DIY community?
> 
> Why aren't more people rewinding aluminum AC motors for EV use?


Maybe lack of cheap AC controllers to run them?
________
condo for sale in Pattaya


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## Tesseract (Sep 27, 2008)

Bowser330 said:


> ....
> Why aren't more people rewinding aluminum AC motors for EV use?





Amberwolf said:


> Maybe lack of cheap AC controllers to run them?


Bingo! I'd take it a step further and say that there isn't a decently powerful ac controller specifically for EVs available at any price, much less a cheap one.

Moreover, an ac controller (er... inverter) will always deliver less power for the same amount of active silicon than it's DC counterpart. Some people will be willing to pay more for the perceived benefits of AC, though, so we have been running some numbers. Using the same IGBT modules as in the Soliton1 (3 instead of 2, of course), we could just barely squeak out 200kW according to my calculations (and the maximum current would have to be moderately reduced at low RPMs to prevent overheating, or else we would have to raise the minimum speed of the motor... which might make for an unpleasant driving experience).

So, the Soliton1 can deliver 300kW with its 2 IGBT modules* while the AC inverter with 3 of the same modules might be good for 200kW (and without nearly the same operating margin of the DC controller). Granted, the AC parameters aren't optimized like the DC ones, and with some tailoring of the operating envelope of the inverter I could probably get more output on the upper end of the RPM range at the expense of less current at the lower end, but that may not be a good tradeoff. 



* - okay, realistically you'd have to use 400Ah LFP cells to keep the sag low enough to hit 300kW, and you'd need something like 4 WarP 9s to take it for longer than a few seconds, but you COULD hit it, is my point.


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## JRP3 (Mar 7, 2008)

That's the thing, most EV's don't need a 200kw system, let alone a 300kw system. ACP and UQM run around 150kw and give plenty of performance for most applications, you just can't get them. If you could do a 100-150kw controller for less than $4k I think you'd have a winner.


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## JRP3 (Mar 7, 2008)

Besides, are you going to let Otmar beat you to the punch with a Tri-Zilla ?


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## Tesseract (Sep 27, 2008)

JRP3 said:


> Besides, are you going to let Otmar beat you to the punch with a Tri-Zilla ?


Oh, the one that he's been threatening to make for the last 5 (or is it 10?) years? Hah.


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## major (Apr 4, 2008)

Tesseract said:


> Moreover, an ac controller (er... inverter) will always deliver less power for the same amount of active silicon than it's DC counterpart.


Hey Tesseract,

Mind if I comment 

What you say is true and important if you're one of those "save the silicon" types. But be aware that the function of the silicon is different in the AC inverter than in the DC converter. In the AC inverter, it not only controls the voltage and current as in the DC, but also provides the commutation for the electric machine. So that extra silicon in the controller replaces the carbon and copper associated with commutation in the DC machine. Worth the cost? Maybe if you're among the "save the carbon" crowd.

Regards,

major


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## Bowser330 (Jun 15, 2008)

Well the AC revolution has begun...

(1) Etischer built a DIY AC Inverter that fully powers his 90hp Siemens motor. Older posts showed he had an intention to build kits and sell them, the 5,000$ price range was mentioned...

(2) Paul Holmes the builder of the DIY DC Controller (on ecomodder.com) has started another build thread for an AC Inverter...His intentions are to build a kit where a DIY'r can build an AC inverter for less than 2,500$ (he mentions that price because there is another DIY AC inverter kit for 2,500$, although I cannot find it, anyone have a link?)

(3) Australian EV Association has growing post counts about rewinding AC motors and/or using VFDs in EVs, etc.


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## Bowser330 (Jun 15, 2008)

JRP3 said:


> That's the thing, most EV's don't need a 200kw system, let alone a 300kw system. ACP and UQM run around 150kw and give plenty of performance for most applications, you just can't get them. If you could do a 100-150kw controller for less than $4k I think you'd have a winner.


+1 winner..


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## few2many (Jun 23, 2009)

And several people on Austalian ev are doing modified industrial inverters.


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## steiner (Dec 8, 2008)

Bowser,

I have seen Pauls thread on the DIY DC controller and have heard of the AC inverter he is working on but haven't been able to find the thread. Do you have it by chance?

Thanks...


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## jackbauer (Jan 12, 2008)

http://ecomodder.com/forum/showthre...eap-3-phase-inverter-ac-controller-10839.html

Question. If say a 415v 22kw delta wound motor were to be reconnected for approx 207v delta could it be used with an industrial inverter with the appropriate settings and dc bus to match?


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## Bowser330 (Jun 15, 2008)

few2many said:


> And several people on Austalian ev are doing modified industrial inverters.


Got any links or methods to find those threads?


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