Reversing the Direction of An Induction Motor?

Question

I have this motor I salvaged from a dryer, and I'm interested in reversing the direction of spin because it spins in the direction opposite of typical machine threads. The Capacitor is shown at the bottom of this picture(relative to the picture, just above the white letters):

The cyan and white-red wires are AC lines. I can't figure out what the purple wire is, and the dryer wiring diagram says nothing about the motor aside from how it is wired in the dryer. Additionally, the connector that connects to the terminal block does not have a wire for the purple pin, leading me to believe that it is used in starting the motor. Using an ohmmeter, the purple wire is connected to all of the ac lines.

Answer 1

It looks like Charles' point that you can't get to the windings is the case. There looks to be three wires coming from the windings and no starter switch. so you have this case:

So it looks like the white/orange is tied to the two windings, main and aux, (the lower line). So unless you can reach into the windings and reverse one of those, you can't reverse it. If you can, you want to bring another wire out so you can separate the connection from main and aux. from the white/orange.

Answer 2

In order to reverse a single-phase motor, it is usually necessary to reverse one winding with respect to the other. If you don't have access to both ends of the windings, the motor can not be reversed. That is likely the case for a dryer.

Some motors that are designed for reverse operation have two identical windings. In that case, the capacitor can be connected to either winding for either direction. That is certainly not the case for a dryer.

If the motor runs in the "wrong" direction for its original use, the capacitor may now be connected to the "wrong" winding.

Answer 3

A tumbler dryer motor needs to run in both directions to tumble the laundry as intended. Usually the schematic is as follows:

^{simulate this circuit – Schematic created using CircuitLab}

So one coil is connected to AC directly while the other is connected through the cap. By selecting which one the tumbler control logic can change the direction from time to time.

Answer 4

Single-phase motor rotation direction is based on the initial direction given by the starter winding, nothing significant about the main winding will favor initial movement.(180 degree pole reversal has no rotational aspect and the magnetic field is zero twice per cycle) Direction can also be reversed by starting it with a mechanical spin in the desired direction. Did this dryer have an auto start or manual starter button? Most old dryers that I have used require the user to hold a starter button until the motor has enough momentum for the main winding to operate.

Just in case this is a commercial dryer motor(only induction was mentioned). 3-phase induction motors do not have starter windings because the rotation direction is inherent and can be reversed simply by reversing any two of the phase wires.(120 degree pole changes are clearly rotating either clockwise or CCW, and the magnetic field is never zero at any point in the rotation.)