On Mon, 22 Aug 2005 11:27:55 GMT, Ignoramus32687
wrote:

I had a visitor yesterday who responded to my craigslist ad about a
free 200V 7.5 HP 3 phase motor. A pleasant, intelligent young man. I
asked him what he was doing with the motor, and he replied that he was
going to build an electric motorcycle. His plan is, apparently, to
have a motorcycle based on batteries, inverter, phase converter, and a
3 phase motor drive. I just could not believe what I heard. (and still
have doubts about his veracity) Am I going crazy or does this sound
like a completely insane idea to you?

Maybe he enjoys doing things in an unusual way. It's not a project
I would want to help him with, though. Induction motors are not
well-suited for propulsion because of the rather narrow speed range in
which they develop much torque. DC motors or switched-reluctance
motors are much better suited for variable-speed, have much better
low-end torque , and they tend to be lighter weight for given HP.

Brushless DC motors are really polyphase machines, but they are not
induction motors; they have either a permanent magnet field or a
driven wound field. SR motors are also polyphase machines with *no*
field. They pack a lot of power in a small, lightweight motor -- but
torque ripple can be a problem. A guy I know developed SR motors
and controls for a bus running in (I think) Taiwan. The Maytag
Neptune washing machine originally used an SR motor, maybe it still
does. Got rid of the transmission.

For the curious:
http://www.freescale.com/webapp/sps/...Pb02R&tid=tMfp

Batteries: a 105 amp-hour 12-volt deep cycle battery weighs about 50
lb, contains about 101 hp-minutes. At 7.5 HP this would be about
13 minutes of operation -- at 100% efficiency. Having all those
conversion will reduce efficiency quite a lot. More importantly a
105 AH battery will NOT supply 466 amps, which is 7.5 HP at 12 volts.
They're better suited to loads of up to 50 amps. He'd need 8
batteries (400 to 500 lb worth). Maybe a forklift battery.....
hey, Ig, do you see any submarines in your surplus shopping
adventures?