Electric Vehicle Frequently Asked Questions

MOTORS

What motors are available?

The most popular motors for EV's are series wound brushed DC motors. It used to be that these were salvaged aircraft starter/generators, or motors cannabalized from other sources, but most on-road EVs now almost universally favor the "advanced DC," or "WarP" (a.k.a. Netgain - www.go-ev.com brand motors. These motors are designed for EV's, and are available in sizes that are right for most conversions.

That said, there are also conversions using shunt wound and separately excited brushed DC motors, but these require specialized (and thus more expensive) controllers. AC motors are coming down in price, and while their performance characteristics are different from the traditional series wound DC motors, they have advantages, too. They require specialized controllers, and are typically more expensive than their DC counterparts. The reasons to use different types of motors would usually hinge around some of the unique features they can offer, such as regenerative braking.

It is generally agreed that the series wound DC motor most closely matches the torque-speed requirements of everyday driving.

Which is better, AC or DC motor?

As with most decisions in building an EV, this depends on what you want to put into and get out of your EV. This issue has been hotly debated on the EV discussion list many times.

AC systems tend to be more expensive, but are slightly more efficient overall, and easily incorporate regenerative braking. Most AC systems require the use of a high voltage (216 or more VDC) battery pack. Finally, most AC systems incorporate all the electronic components in one box, making the underhood arrangement simpler.

DC systems are cheaper at the moment. The required brush servicing is around 50,000 to 100,000 miles, and can be done in minutes at a competent electric motor shop. It is really not much of a hassle. Either high or low voltage components may be used. It is relatively difficult to incorporate regenerative braking when using a series wound DC motor (although it has been done). Other kinds of DC motors better lend themselves to regenerative braking, but require specialized controllers, driving the cost back up.

The most arguable difference is in performance. While DC motors have their best torque at low speeds, AC motors have their best torque at higher speeds. AC motors also can typically spin a lot faster. This can eliminate the need for a multi-gear transmission, and allow the substitution of a single-speed lightweight gearbox. It would then go in reverse electronically.

Can I use a surplus aircraft starter/generator for motor?

possibly contact the owner to find out how.