Michael Ross wrote: > " battery amps would be lower than motor amps at low RPMs" > > That sounds like nonsense to me, but I don't have the whole circuit > in front of me.
It is absolutely correct. The PWM motor controller behaves similarly to a variable transformer, but with DC input and output. DC motor RPM is proportional to voltage; at low motor RPM, the battery pack voltage is reduced by the motor controller so that less than full pack voltage is applied to the motor. Aside from a relatively small loss due to inefficiency of the controller, power out to the motor is (approximately) equal to the power into the controller from the battery. Assume the battery does not sag so we have full pack voltage into the controller and further assume that the voltage applied to the motor is half of the pack voltage. For approximately equal power in and out of the controller, the current in the motor loop will be twice that in the battery loop. As long as the voltage at the motor is less than the battery voltage, the current in the motor loop is greater than that in the battery loop. Once the motor voltage (speed) increases to the point of being equal to the battery voltage, the motor current and battery current are equal. Cheers, Roger. _______________________________________________ UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub http://lists.evdl.org/listinfo.cgi/ev-evdl.org For EV drag racing discussion, please use NEDRA (http://groups.yahoo.com/group/NEDRA)
