Quote:
Originally Posted by byte312
Interesting thought. I think just regulating voltage from a series string of batteries might help keep the car runnng at a constant speed for a longer time. What if you have 120 volts to start and the motor only needs 96v. If you can use a regulator to hold the output at 96 you can discharge 24 volts before the car slows down. Changeing from series to parralled or vice versa will not change available watts but you can choose either higher current or higher voltage.
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That's a slightly misleading explanation.
If you need 96V from a 128V battery, the motor controller uses a 75% pulse. During the 25% 'off' period the motor current is provided by diodes or diode-like freewheel switching. Also during the off period the controller's smoothing capacitors recharge to provide part of the current for the next pulse.
As the voltage drops, the pulse width increases to compensate. Less of the current comes from the freewheel devices, and more current comes from the batteries.
A modern controller can do this very efficiently, at a frequency so high the motor current is almost constant. This is *far* more efficient than slowly switching banks of batteries in various combinations of serial, parallel and anti-series. (Anti-series is reversing/recharging one bank to effectively drop the voltage across the motor.)