Quote:
Originally Posted by bluetwo
Just thought I'd throw it out there that reversing an electric motor is as simple as reversing the polarity. Meaning, swapping the positive and negative wires, in so doing the motor will spin backwards with the same power and torque.
Anyone who's really smart on this stuff stop me if I'm wrong though, by all means and I know it gets way more complicated when you're talking about the more sofisticated motors like in todays hybrids.
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This is true in several cases, but I've proven it untrue in several cases as well.
For instance, I have a drill motor that will run in reverse, but it will die running in reverse as well.
Backstory - I've used a 12V drill motor wired to a car battery (via alligator plugs) for years now. It's always been reliable, never had a problem with it. I built one for a friend of mine, as well, because it's a much longer lasting setup, with 0 charging time (in most jobs).
When I built his, I accidentally switched the colored clips, so that black was actually positive, and red was actually negative. This was a brand new drill, which had been tested on a normal battery only. Instead of letting me switch the clips, he just reversed the motor gear (reversible drills have transmissions, they spin the same direction either way.), so that he was hooking up the leads red to positive, and black to negative, and then using reverse for forward, and vice versa. About 2 hours later, the drill wouldn't run, and had finally let out the magic smoke.
I never thought reversing a motor would cause this to happen, so I rebuilt the drill... sure enough, it happened again, with the new motor.
Moral: Not all motors are reversible. The ones that are make nice brakes, though, such as those which are normally used in forklifts. Reversing the polarity on those motors (which are specifically designed for this, as they reverse polarity to move in reverse) will act as a brake. The more current you apply, the faster you stop, up to the maximum rating of the motor.