The Motor: HPGC AC-50

A quick look at EVAlbum will show that lot of people use less expensive series wound DC motors made by companies like ADC or NetGain. A long time ago I decided on using AC drive, but it was just too expensive.

A DC system is cheaper because it's simpler, but it also has certain limitations that are hard to ignore. There are a lot of technical challenges to getting a DC system to do regenerative braking effectively without destroying the brushes. Plus, eventually, the brushes in the DC system will wear out anyway and need replaced.

In contrast, a 3 phase AC motor has no problem doing regen. I prefer a simple and reliable system for regen. Let the motor do the braking. I'm not changing brake pads all the time. Plus, an AC motor uses induction to transfer power to/from the rotor, so it doesn't even have brushes that can wear out. Part of the idea with an electric car is less maintenance. Let's really try and minimize it.

There also exists a type of DC motor that doesn't use brushes. Some electric bikes, like mine, use these. I am talking about brushless permanent magnet motors that even can do regen well with the help of a good controller. You just don't see any PM DC motors that are big enough to push a car to highway speeds.

This is sidebar but, on their Scion EV, ChargeCar was creative by mechanically tying 4 PM DC motors together, but that vehicle can only go about 40 mph. In their defense, this car is used for data collection and research into intelligent vehicle control algorithms, and their goals with that car are very different than the goals of building a daily use commuter EV.

Back on topic, an AC system is still more expensive, although it's getting cheaper. AC systems used to cost 2-3 times or more of the cost of a comparable DC system. Now, you may only pay 50% more for the AC system. So, unless you're really budget constrained, you should consider AC, as it will a be a more efficient conversion.

I've seen the AC-35 motor used in a Honda Civic conversion done by ChargeCar at CMU. The car can accelerate from 0-20 mph in about 2 seconds and has been driven at over 70mph on the highway. Taking that the Civic's stock curb weight is 2600 lbs and the CR-V weighs around 3200 stock, plus the fact that I'm installing a bigger battery than the Civic has, I think it's better to go with the slightly bigger motor that has more torque, so I'm thinking the AC-50 motor will work best. I ran it by ChargeCar's mailing list and Ben, who worked on the Civic, agreed.

[ power curves for the AC-50 at 550 amps. I plan to use a 650 amp controller -more on that later-, so I'll get more power than this is showing.]

In my next post, I'll talk about the controller.