Quote:
Originally Posted by princeton
Has anybody thought about a reverse circuit?...
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That's real easy and isn't part of the motor controller. If you look at nearly any wire diagram from Curtis, Alltrax, or any of the other commercial motor controller manufacturers, they all show how you can have a "reversing contactor" as part of the circuit.
A reversing contactor normally completes the circuit, but has a second set of power connections, that when actived, breaks the circuit, and then reconnects it with the polarity reversed.
On a permanent magnet motor, you simply reverse the positive and negative, to make the motor spin the other way.
On a series-wound motor, it's just slightly more complicated - you need four power connectors going to the motor (two for the field, and two for the armature) and the reversing contactor just reverses one or the other to make the motor spin in reverse. (If you reversed BOTH the field and armature, the motor would still spin the same direction.)
If you look at a typical electric forklift, that's exactly how they work. The motor is connected to the wheels through a differential, and reverse is done electrically through a reversing contactor. Drive motors will always have four power connector on them. Series-wound pump motors sometimes only have two, as those motors are usually designed just to run one direction.
Also, be careful of brush timing is you want to reverse your motor. If you advance your brushes for higher voltage, they will be retarded for reverse!
Some commercial motor controllers also have a pin in for when you are in reverse. When the controller knows you are in reverse, the controller limits speed to half.
On my Electric Geo Metro (With an Open Revolt controller) I just use the mechanical reverse gear, and I have every bit as much speed/power in reverse as I do in forward - actually even more, as reverse gears tend to be even lower than 1st, and I NEVER use first gear in my car because of how much torque the motor has.