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Right Size AC Motor for an Electric Car

by Steve
(Woodstock, NY, USA)

Is there a simple way (formula) to estimate the correct size for a 3-phase AC induction motor for an EV conversion given the weight of the vehicle?


Hi, Steve!
The new edition of "Build Your Own Electric Vehicle" by Seth Leitman says to figure on 6-8 hp (continuous) per thousand pounds total vehicle weight (include passengers and cargo), more if you want to drive on the freeway.

Your voltage matters, too. Since horsepower increases with voltage, a 72v system with exactly the same motor will have less horsepower than a 144v system.


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Electric Car Motor Size: 3 phase AC

by Gary Palmer

AC Electric Car Motor

AC Electric Car Motor

How big of a 3 phase AC motor do you need to power a medium size electric car, and how much AC power is required to run this motor - not using DC and an inverter, but true AC power in kw?

(Sorry if the question is stupid, but I am not a electrical kind of guy.)

Hi, Gary -
It's not stupid, but it IS a little bewildering. How are you going to power it if not with batteries?

Well, I guess that's your business; )

Here's the motor that's powering Eric Tischer's VW Passat, which is a medium sized car - it's the motor that powered the Ford Ranger EV:

215 - 380 Volt, 282 Amp RMS (400 peak)
6 pole, 3 Phase AC Induction
67 Kw peak (33 Kw continuous)
3500 - 9700 (13,000 Max) RPM
Weight: 178 lbs


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Conversion Question: AC Motor Size

by Alex
(Puerto Rico)

I'm new to this EV/hybrid thing and would like to ask a few questions before I start buying the wrong stuff.

1) How do I know which AC motor to use depending on the vehicle weight?

2) Is it possible to make a "hybrid vehicle" by using a AC motor and a small gas generator to provide the electricity needed?

Hola, Alex!
For AC motors, first determine your donor car's factory curb weight (not gross vehicle weight).
If it's between 2000 and 2400 pounds, choose the Solectria AC24 motor.
If it's between 2400 and 3500 pounds, choose the Solectria AC55 motor.

Wasn't that easy?

You can read all the technical data you want about these two motors at Electro Automotive's data page.

The hybrid question?
Yes, it can be done, and it has, many times. However, if you intend to use your generator a lot, rather than plugging in most of the time and using the generator only as an emergency range extender, then a small gasoline or diesel car engine would be better.
Because generators don't have the same pollution control that car engines have evolved, since they're not required to have it...and so consequently, they're terrible polluters, comparatively.


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