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Building an Electric Mazda RX-7

by Dominic
(Philadelphia, PA)

I was thinking of converting an rx7 the year around 94 I like the body style.

It needs to travel a distance at least 100 mile per charge, and it needs to run on the Highway also so the speed need to be at least 55 mph.

What size motor would be needed?
The AC motor you wrote about was good but do I need something better/bigger or is there something better out there?
And what kind of battery would be ideal?

Hi, Dominic -
The older Mazda RX-7 is beautiful, isn't it? Here's a video of an electric RX-7 beating the pants off a Dodge Viper. That just NEVER gets old; )

On to your questions:
Yes, the RX-7 is a good choice, but with the comparatively light bone structure of a sports car, you'll need to really think about the battery weight you want to put in it.

To get this kind of range out of a freeway-able EV, you don't have much choice but to go with an AC drive system. AC motor systems are typically run at 300 or so volts, which means you'll need at least 26 batteries.

There are generally only two sizes of AC motor for electric cars; the one for light cars, and the one for heavier cars. You've got a comparatively light car, so the Siemens AC24 is probably the one the dealer will recommend - about 9", 85 pounds though I've seen a sports car with the AC55 motor, the bigger one.

Your challenge will be to get enough batteries into your car to provide the Amp-hours you need to go 100 miles comfortably without exceeding a reasonable weight limit. It might not even be possible with lead. The majority of these sporty or small AC conversions seem to have Lithium (either LiFePO4 or Li-Po) batteries, I notice after a look around the EV Photo Album.

Consider this: If you're willing to charge up at work, you can use lighter batteries (fewer amp-hours) than if you actually need to go 100 miles between charges.

Update 2011: Check out the AC-50 motor from HPEVS. It's a great choice for cars like your RX7.

Good luck with your project!


Edit: I should have said "Azure Dynamics/ Solectria AC24" - not Siemens.

Thanks to JD Kennedy from for pointing this out; )

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Model/Mfr Correction
by: J.D. Kennedy

Are you talking about the Azure (formerly Solectria) AC24 and AC55? I'm not aware of any Siemens motors by those model numbers - I think they prefer much more complex numbers. I would almost recommend the UQM PowerPhase 125 (smaller, lighter, more powerful), but I'm not sure if these are available to just anyone. All I've seen is vague volume pricing.

See my product and instructional reviews at:

Hi, JDK -
Oops; )
Good save. I did mean the Azure Dynamics/Solectria, not Siemens.


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