# Permanent Magnet motor pros/cons?



## Richard Ward (Jul 14, 2008)

Hi all, I'm in the early planning stages of an EV conversion (lightweight city-car, max. speed 40 mph, range 30-35 miles) and was wondering about the merits of a motor like this. One big advantage is it only weighs 11 kg (22 lbs), with a small car like I have in mind weight saving is paramount to getting a useful perfomance/range.
My donor car in mind (still looking for one) is a Reliant Fox pick-up, gf body, galvanised steel frame, guw 1410 lbs, only made about 1000 of them (which is why I'm still looking......).

Richard
Bristol UK


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## MalcolmB (Jun 10, 2008)

Hi Richard

The Reliant Fox looks like a very practical lightweight choice. Good luck with finding one! The Lemco motors are very good, though I do know someone in Leeds who has already managed to burn one out in a Mini conversion.

The AVT site (http://www.everything-ev.com/12v72v-200mm-85kw14kw-light-weight-pancake-pm-motors-p-288.html) reckons that the motor is good for vehicles up to 500 kg in weight, so it sounds as if you would be pushing it a little. How about using two of them? (expensive I know)

I agree with you totally on keeping weight as low as possible, but personally I'd be prepared to compromise a little when it comes to the motor. What sort of speed are you hoping for?

Are you planning to keep the gearbox? I think this would be almost essential to minimise time at high current (and hence overheating). Some effective forced air cooling would be also be good, such as a heater blower fan ducted into the commutator housing.


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## MalcolmB (Jun 10, 2008)

Just remembered this: http://www.evalbum.com/1529 conversion by Greg Fordyce just over the border in Scotland.


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## Richard Ward (Jul 14, 2008)

Hi Malcolm, thanks for those links. There's a lot of good stuff on the everything-ev site, this kit looks like it uses the LEM 200 pm motor, and is apparently good for 750 kg, which is my target for the Fox conversion.

I also found a couple of pics here and here, showing a Fox conversion with a Lynch motor, exactly what I want to do. This car was for sale a few weeks ago, before the bug bit me.

I feel absolutely committed to light weight, I have to admit to being a bit mystified when I read of people planning to convert vehicles weighing in at 3500 - 4000 lbs and above. Just no point in dragging all that weight around, especially since it probably means retaining power steering, etc. I think its much more sensible to go back to the way small cars were 20 or 30 years ago, simple, light weight, easy to work on and now green as well!

Would still be interested to hear from real-world experience about pros and cons of pm motors in general (just remembered another pro, regen braking).

Richard
Bristol UK


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## major (Apr 4, 2008)

Richard Ward said:


> Would still be interested to hear from real-world experience about pros and cons of pm motors in general (just remembered another pro, regen braking).
> 
> Richard
> Bristol UK


Hi Richard,

I recommend you go with a sturdy wound field motor. Those PM motors may look good on paper but in the real world fall short on durability. EV propulsion is a tough application, often loaded with overloads. PM motors in general are too fragile. You show a few sites of them in cars or in builds of cars. How do these actually work out for those guys?

Light weight may be a fine goal, but the vehicle has to support a heavy battery, so be careful. Look at the rated weight after you install every thing. Is the structure adequate? Brakes? And the motor is not a place to save a few pounds.

That PM motor you show is expensive. And after you fry it, probably not repairable. A good wound field motor will take a lot more abuse, and if it does fail, can be repaired.

Regards,

major


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