Electronics > Projects, Designs, and Technical Stuff

Synchronous motor pinout and run capacitor?

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profdc9:
I found the following motor on ebay that looks interesting for a project:

https://www.ebay.com/itm/352546431397

It says it is a two-speed motor, and there appear to be four connections to it.   I would guess it might be something like this:

http://www.seekic.com/circuit_diagram/Basic_Circuit/Single_phase_motor_two_speed_circuit_with_auxiliary_winding_connecting_to_tap_directly.html

One would be live connection, another would connect the capacitor, and two would switch the neutral between the two speeds.  Is it likely to be true?  Would there be a way to figure this out by measuring the inductance of the windings, and estimating the capacitance needed?  Would a polypropylene capacitor work, perhaps of 3 microfarads or so.  I would guess that the capacitance is pretty low given its low hp.

Benta:
The "two speeds" are because it's rated for 50 and 60 Hz. Induction motor, might have an internal cap, might not. Name plate does not give enough information.
The wire connected to the housing suggests an earth connection, this could explain the 4-pole connector.

duak:
As Benta says, this is a motor that runs at a speed determined by the line frequency.  I don't believe it is a synchronous motor where the RPM is exactly locked to the line frequency, rather, it is an induction motor where the RPM is lower and depends on the load.  Do you need to vary the RPM?

Here's a description of the general type: https://www.beckettcorp.com/support/tech-bulletins/an-introduction-to-psc-motors/  You should be able to determine the two windings by their resistance.  There is a type of the these called reversible PSC motors where the windings have the same impedance.  In this case, it doesn't matter which winding is used as the main.

Do you need to reverse the motor on the fly?

Your run capacitor value is in the right ballpark.  Polypropylene is a good choice.  I would go for at least a 400 VDC rating.

When it's all done, check the AC current to see that it's not higher than what is shown.

profdc9:
My main interest in the motor was to find a motor that can rotate an object (about 200 to 400 g) at approximately 1800 rpm, an object probably closed to balanced but not perfectly so, but the speed does not need to be precisely that value.  I do not need to reverse the motor, but I would like the speed of the motor to be somewhere close to 1800 rpm and be relatively constant.

I was considering a smaller DC brushed motor but I am not sure that a smaller DC brushed motor is heavy duty enough to hold a 400 g load steady and rotate it with some small imbalance.  The motor I am looking at is probably a little overkill but it seems to be a good surplus find.
 

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