SparkFun Forums 

Where electronics enthusiasts find answers.

By navillus5
I was tasked this evening with a request to fix my son's window fan. It is a dual fan unit with a three position switch - Off, Low, High.
I thought that it would be a simple fix - a loose wire or a broken switch - no such luck. So I am now on a quest to figure out what has happened to this "simple" device.

The unit contains a pair of two-speed shaded-pole motors that are controlled by a three position rotary switch - I have included photo of the motor and a wiring diagram below. I have not been able to find that much information about two-speed shaded-pole motors, but I would think that the three wires indicate a motor winding with a middle tap. I have measured the resistances between each wire and there is only continuity (11.3 Ohms) between the red and blue wires. This is the case for both motors.

If I connect the red and blue wires to ac power, the fan runs but it also gets very hot, very fast - definitely not a preferred operating state.

So my question is - am I missing something obvious, or did both motors fail in the same way at the same time?
As I finish writing this, my wife popped her head in to tell me that some of the Amazon reviews for this item mentioned sudden failure. :shock:

Any insight would be appreciated!
shaded-pole motor.jpg
wiring diagram.jpg
You do not have the required permissions to view the files attached to this post.
By n1ist
Both motors are in parallel, so an overvoltage could have blown both at the same time, or possibly the same mechanical fault exists; there may be a broken connection from the black or red wire to the winding. The two connections are black/blue and black/red. blue-to-red isn't rated for line voltage; that's why it gets hot.

By navillus5
Thanks for the reply. I got busy with other stuff and my wife bought a replacement fan, so I almost forgot to check for a reply to my post!