Motor Start Capacitor placement

Thread Starter

basplin

Joined Jan 8, 2023
6
Hi all - electronics newbie here. I hope this is the right place to ask my question. I’m working on a project that is utilizing a continuous-duty hysteresis synchronous motor. The motor runs clockwise, but I need it to run counter clockwise, which I achieved by reversing the black and blue wires as shown in the schematic. Only issue is now the capacitor doesn’t seem to be having an effect - the motor starts slowly, instead of immediately at or near the rated speed as when wired like the schematic. When I reversed the black and blue wires, do I also need to move the capacitor to a different place in the circuit as well? I already tried reversing the polarity of the capacitor (although the schematic doesn’t indicate that polarity is important). Thank you in advance!2618AC3D-CC9F-4392-8F86-169DFEB805AB.jpeg
 
Last edited:

MrChips

Joined Oct 2, 2009
31,087
I recently had a similar but not identical situation. In my case, I had access to all four wires to the two windings. I was able to reverse the connections to one winding.

In your case, unless you have access to the leads that are connected to orange, I don't see how you can reverse one winding.

Measure and compare the DC resistance between BLACK and ORANGE, and BLUE and ORANGE.
 

Thread Starter

basplin

Joined Jan 8, 2023
6
I recently had a similar but not identical situation. In my case, I had access to all four wires to the two windings. I was able to reverse the connections to one winding.

In your case, unless you have access to the leads that are connected to orange, I don't see how you can reverse one winding.

Measure and compare the DC resistance between BLACK and ORANGE, and BLUE and ORANGE.
So by swapping black and blue, I'm reversing both windings, right? What would be achieved by only reversing one?

Black & Orange: 99.5Ω
Blue & Orange: 19.0Ω

What am I looking for with the resistance measurements?
Thanks!
 

MrChips

Joined Oct 2, 2009
31,087
So by swapping black and blue, I'm reversing both windings, right? What would be achieved by only reversing one?

Black & Orange: 99.5Ω
Blue & Orange: 19.0Ω

What am I looking for with the resistance measurements?
Thanks!
I am just following up on what Max suggested. I was thinking of switching the mains from (6) to (0).
So the windings are different and you cannot swap windings.
I think you are out of luck here.
 

MaxHeadRoom

Joined Jul 18, 2013
28,829
The black orange is the start winding and requires the cap in series, as Mr. chips intimated, you require access to the common ends of the windings in order to reverse one or the other.
 

MrChips

Joined Oct 2, 2009
31,087
Just a question for my knowledge base.
If the capacitor is a start capacitor, where is the centrifugal switch?
 

Thread Starter

basplin

Joined Jan 8, 2023
6
Thank you both for the replies!

Just to be clear, I was able to reverse the rotation of the motor using MrChips’ suggestion, switching the mains from (6) to (0). What I’m wondering is how to get the capacitor to start the motor right at top speed rather than it start slowly and eventually get there. Are you saying that there is no way to do this with the reversed mains?
 

MrChips

Joined Oct 2, 2009
31,087
I don’t have enough knowledge about how AC induction motors work.

If this is not a start capacitor, then is it a run capacitor that creates a phase shift?

Maybe when you switch the two windings the value of the capacitor is incorrect.

Also I think that you will lose torque since the motor was not designed to be reversed.
 

MisterBill2

Joined Jan 23, 2018
19,453
We need one more resistance reading to verify what seems like the reasonable guess, which is that you need access to all four winding ends because one is a start winding and the other is a run winding. so what is the resistance between the black and blue wires? If it is about 119 ohms then the current analysis is totally correct.
 

MaxHeadRoom

Joined Jul 18, 2013
28,829
Just a question for my knowledge base.
If the capacitor is a start capacitor, where is the centrifugal switch?
Not all motors disconnect the start cap, they are called PSC, 'Permanent start cap motors', also some motors that have two caps, one is a start cap that is disconnected after a second or so by centrifugal switch or external current relay, the other stays in permanently. initially they are both in parallel.
The switched start cap is generally a bi-polar with dry electrolyte, and cannot stay in circuit for more than a second or two.
 

MaxHeadRoom

Joined Jul 18, 2013
28,829
We need one more resistance reading to verify what seems like the reasonable guess, which is that you need access to all four winding ends because one is a start winding and the other is a run winding. so what is the resistance between the black and blue wires? If it is about 119 ohms then the current analysis is totally correct.
Its seems obvious from the OP answer which is the start & run winding
The numbers given:
Black & Orange: 99.5Ω
Blue & Orange: 19.0Ω
Also from the DWG, Shows the black-orange pair to be the start winding! ;)
It could be a motor that is intended for fan usage and therefore does not typically require reverse.
 

Thread Starter

basplin

Joined Jan 8, 2023
6
Black and Blue measures at 117, so it sounds as though the analysis here is correct.

One more question… since it appears the motor isn’t designed to be run in reverse, any idea how much torque I’d be losing doing so?
 

MisterBill2

Joined Jan 23, 2018
19,453
Its seems obvious from the OP answer which is the start & run winding
The numbers given:
Black & Orange: 99.5Ω
Blue & Orange: 19.0Ω
Also from the DWG, Shows the black-orange pair to be the start winding! ;)
It could be a motor that is intended for fan usage and therefore does not typically require reverse.
NO, it is not obvious, because the 19 ohms could be a tap, or a second winding. Is the drawing the actual motor or is it what the TS found in a web search???
Certainly the best guess is a separate winding, proof positive would be in that third resistance reading. I discovered exactly that on a transformer a month ago. It looked like a 12/220 primary but it was not, although the colors on the wires implied it was.
 
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