I just stripped my broken microwave and got this handy dandy SM16F BY36P1A3 synchronous motor out of it. Now that I have the motor, I would very much like to use it to control a door lock. The issue is, while I can get the motor to move in either direction, the way it switches is seemingly random. Just whenever I flip my on/off switch it could either go CW or CCW. My theory here is that the phase of the signal determines which way it'll go. But it could also be where the rotor stops and has to start from right? So my issue becomes A) determine, somehow, which of my theories may be correct, and B) find a way to time when the AC signal starts, or when the rotor stops.

The input is from the outlet, stepped down to around 21VAC, so it's not like I can control when the incoming signal starts and stops too easily
Does anyone have any prior experience with these motors? Can someone help me control this motor in either direction I want?

 

How many leads?

Was there a cap in the circuit?

 

This thread should be of interest.

 

There are two leads on the motor, which, in initial experiments, was connected directly to the transformer, which was connected directly to the outlet.

 

They start in random directions.

I have one on a piece of workshop equipment that I prefer to rotate clockwise. I just put a bit of torque on it in the clockwise direction with my fingers when switching it on, then it starts up and runs clockwise.

 

There are two leads on the motor, which, in initial experiments, was connected directly to the transformer, which was connected directly to the outlet.

For the turntable that wants random maybe?
Built in alternate start?

New one for me.

A motor that does not have a bias for starting should not start at all. imo

 

New one for me.

A motor that does not have a bias for starting should not start at all. imo

Observe your microwave closely...

 

Observe your microwave closely...

That's why I suggested the turn table.
Is that how they work? Random? Alternate?

 

How about a strategically placed PM to get it under control?

 

The same principle used in the older wall clock synchronous motors, they had a spring/kick start to make sure it started in the right direction, often the start mechanism would wear and the clock would run backwards.
As RB says, you have to tension bias it at start up.
Max.

 

How does the MW motor start?
Random or alternate?

No I never looked!

 

Then go and look.

 

That's why I suggested the turn table.
Is that how they work? Random? Alternate?

Yeah, every microwave I've ever had, started randomly like that.