I'm trying to create a circuit that will allow for switching the direction of a wheelchair motor. I originally was using a regular relay to switch the motor on and off, but after killing 3, I determined that the motor drew too much current (I'm running it at 12V DC). I have since used a starter solenoid, which has worked fine, but these are expensive and are only SPST. Now I need to be able to switch the direction of the motor, and I am having a hard time figuring out a way to do this. Any thoughts? Thanks.
To switch the polarity you need either one DPDT relay to switch direction PLUS a SPST relay to turn the juice on or off, or a pair of SPDT relays. For the latter, if both relays are pulled in or dropped out nothing happens. Pulling one or the other in drives the motor in one direction or the other.
Semiconductor switching of traction motors is not for the faint of heart- you would likely need to massively overrate the switching devices to keep them from failing. That's certainly my experience. And failing 'on' with a wheelchair motor could conceivably be dangerous- propelling the hapless operator unexpectedly into some place they don't want to be.