Victor Tikhonov wrote: > Since it was stated that the voltage defines top speed, my point was > to highlight the difference: for DC motor it's enough to apply > a voltage and it starts running (characteristics aside). > In general - under some load - the more voltage, the faster it runs. > > In case of AC it's not enough to apply AC voltage it has to be > [the right] frequency as well. Also increasing [AC] voltage will not > make AC motor run faster. *You* need to take care of frequency > increase to achieve that. This is different from DC motors where > the frequency converter (commutator) is part of the rotor and you > have no control over that (cannot control frequency and voltage > separately as you can for AC motors.
My concern is that we're throwing around generalities about motors as if AC vs. DC is the main consideration, when in fact, it's only one of many important factors. This is bound to confuse our EV newbie! Motors and their controllers are intimately intertwined. Any motor can have any torque-speed characteristics, depending on its controller. So you have to consider them as pairs. I think Victor is comparing a brushed series DC motor with PWM controller to a 3-phase AC induction motor with sinewave inverter controller. Several things are changing between these two cases; for example: - AC vs. DC - brushes and commutator vs. electronic commutator - wound field vs. induction field - simple vs. complex controller You can't attribute the performance differences between the two systems to just one factor, like AC vs. DC. That would be like attributing the difference in performance between two completely different cars all to the tires. For the newbies, just consider the motor+controller to be a "black box". You put electricity in, and get horsepower out. How much depends on how much power your batteries can supply. Efficiency is 75-90%. Weight is 1 to 2 pounds per horsepower. Higher tech systems work better but cost more. -- Lee A. Hart Ring the bells that still can ring 814 8th Ave. N. Forget your perfect offering Sartell, MN 56377 USA There is a crack in everything leeahart_at_earthlink.net That's how the light gets in - Leonard Cohen
