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Friday, October 22, 2010

Electric Car Motors

What kinds of electric car motors are the most popular? There are a lot of electric motors out there, but just a few make up the majority of the motors being used in electric cars. When people choose a motor for their car, they're balancing factors like cost, availability, and the "do it yourself factor" - the confidence that they can get all these expensive gizmos installed and not just wind up with a project scattered all over the garage...a well-known cause of marital discord!

#1: DC Series wound electric car motors

If you want to know the technical stuff about these, like what they look like when they're turning, where the commutator is located relative to the brushes...no problem. Check out Ian's excellent EV motors page at ZEVA, he's covered that brilliantly. After you're done watching the rotor go 'round, come on back, I'll be right here; )

The Good: All the torque is available from a standstill.

You've no doubt heard about this famous characteristic of electric cars. It's really a characteristic of these series wound DC electric car motors, though, rather than electric cars in general. These motors happen to be popular for electric drills, too, and that's why.

The Bad: Not your best hill-climbing device.

The Electrical Engineering training series says, quote: "Series motors cannot be used where a relatively constant speed is required under conditions of varying load." Unfortunately, that pretty much sums up what an electric car would be doing in hilly terrain, like my neighborhood. The DC series motor in your NEV might not climb those hills too briskly. Oh, you noticed this already? So did Zenn and Miles, actually...and this year(2008), their new cars have AC drive systems installed.

The Ugly: These always have to be run under load.

Meaning, when you're installing your shiny new Netgain motor in that Chevy S-10 you've so carefully de-ICEd, you don't wanna hook the motor up to 120 volts and just whizzz it out attached to nothing (you know, to hear what it sounds like running); it'll take your head off. Apparently it turns with enough force to even damage itself if you run it without a load!

The Advanced DC Series wound motor is by far the most popular of the electric car motors, according to the EV Photo Album, followed by GE and Netgain.

#2: Permanent Magnet DC electric motors

These are the second most popular electric car motors in the EV Photo Album, but that's not necessarily because they're the best thing going.

The biggest drawback with permanent magnet DC motors? They're noisier. Like all brushed DC motors, the brushes generate electrical radio interference. But unlike other types of brushed electric motors used in electric cars, like the series wound DC motors above, which have windings which provide natural filtering of electrical noise, the PM motors have no natural filtering effect in their design...so they're noisy.

Most of the EVs with Permanent Magnet DC motors you find in the EV Photo Album belong to "small-ticket" EVs: bikes, motorcycles, scooters, and the like.

#3: 3-Phase AC induction motors

Third most popular electric car motors, but if all motors cost the same, these would be the hands-down winner. Why? Because they're better. (There, yes, I said it. I took a stand; )

"AC motor" doesn't mean it runs off the AC power at the house, plugged into the wall with a very long extension cord; ) No. It uses batteries like the DC motor does. An inverter takes the place of the controller you see in DC drive systems. The system overall is a bit more expensive, primarily because of these sophisticated inverters...but you get your money's worth.

I'm very enthusiastic about these, it's no secret! Why?

Because the terrain around my house is hills, hills, and then a couple more hills after that. An AC drive system is a lot better suited for this type of terrain than a DC drive system.
An AC system will treat your poor gas-guzzler's tranny a lot more gently than a DC system.
You can move a lot heavier car with an AC drive system.
The range is better with an AC drive system, for a couple of reasons. First, because it uses the batteries more efficiently, and second, because of excellent regenerative braking, which acts just like a generator to put energy back into your batteries.

All these things add up to an electric car that's considerably more like the familiar gas-gobbler's performance.

Metric Mind's FAQ has a lot more to say about the advantages of AC drive systems over the typical series wound DC electric car motors and controllers you often see in electric car conversions.

Go from "Electric Car Motors" to learn more about the AC vs DC debate.