CHOOSING A DC MOTOR & CONTROLLER FOR AN EV.
By Edward Booth, November 2008-11-18
Choosing the traction motor for an EV can be quite simple, if you follow a logical decision-making path.
It should be said at the outset, that AC motors are more efficient than their DC counterparts, but they are also much more expensive. DC remains the system of choice for most home builders with a limited budget.
In many ways, DC is a little easier for the not-so-technically minded, but DC can be more dangerous volt-for-volt than AC. Over about 80volts, neither is “safe” without following the strictest protocols.
The controller is a bit more difficult to choose. You need to decide whether you want regenerative braking, and what your maximum and cruising current draws will be. If in doubt, err on the high side. It is very frustrating to have the performance throttled by lack of current, and continuous over-drawing of current can damage the controller or cause it to shut down.
The Choice of Motor.
There are many brands and types on the market, but it is advisable to stick to those that are well supported, and have a good track record.
Permanent magnet motors (Perms) are very efficient in their optimum rev range, but less so out of it. They tend to be a bit on the small side and are prone to overheating. They are best suited to motor bikes or similar, where their small size makes them attractive.
Be aware that the Perm PMG132 has a design that can retain carbon dust from the brushes, and in damp weather, this can cause arcing in the brush housing. The Company were unhelpful, and denied fault, so be warned!