Electronics > Repair

Problem with air compressor pump motor

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shockpoint:
Hi all.

I have a compressor motor head exactly like the one in this video.
In this video, the construction of the windings shows that the run winding has both in and out terminals as RED. and the start winding has both in and out terminals as BLACK.
Based on my multimeter check, on my own unit, the black wires do NOT have continuity with one another and neither do the red. The only continuity is between one black-red and another black-red. So I believe on my unit the color is arranged differently.
So please note that in my below diagrams, the black and red refer to what I believe to be the arrangement of the winding terminals on my particular unit.
It is a 580W, 230V AC pump that is most likely a permanent start capacitor motor. The nominal current on this is 3.8A.
The capacitor is 25uF rated for 450V and I bought it new and verified that it works.

I have an issue with mine that I cannot figure out.
I have tried wiring my motor in two ways.
The first way I tried is to wire it in the way suggested in the video above, which is summarised in the line diagram as shown below (first picture attached). Note again that in the schematic, the black and red denote what I believe to be the in and out terminals for each winding, and not differentiating the start winding and the run winding as in the video.

Key:
L = line, N = neutral. There is a ground wire, and it is connected to AC GND.

This method resulted in:
- the circuit breaker tripping
- There was no audible hum in the motor
- motor not rotating
- motor bearings are movable with hand, no seizing noted

The second way I wired it is according to the technician at the store (my compressor is out of warranty and I want to know what is the problem with this motor so for those reasons I would prefer not to take it into the store as they are unlikely to offer more help), who told me that:
- the two red wires, contrary to the video above, were actually meant to be directly connected to the capacitor, while the two black ends are meant to be connected to L and N (with a green for GND of course).
- this also resulted in a circuit breaker trip.
- this arrangement does not make any sense on a line diagram. See the second photo, which is essentially what I think the technician is telling me. Although on the shop units I have seen this to be the case. Here is a photo of the shop unit. https://ansaleeov.xyz/product_details/38663846.html (see photo 3 for annotated picture)
As you can see, coming from the side of the compressor through a bunged hole, are two black sheathed cables. the thin one threaded under the compressor unit goes to the capacitor (this sheath contains the two red wires). The thicker sheath going to the pressure switch  contain the two black wires and a green-yellow ground wire.

My areas of confusion:
- I have measured the black and red wires on a multimeter. On black-red pair 1, I am getting 13 Ohms. On the other black-red pair 2, I am getting 1-2 ohms. Are these expected values for the main and auxiliary windings? Based on the video above the construction selects 21AWG for the main winding and 23AWG for the auxiliary winding each with different winding dimensions, so I have reason to believe that this possibly could affect the reading but I am not sure if a 12 ohm difference is reasonable. Assuming a current of 3.8A, 13ohm*(3.8A)^2 (power) results in a heat dissipation in watts of 187.7watts. This seems a bit high to me. The alternative winding, 2ohm*(3.8A)^2 = 15.2 watts seems more reasonable.
- when the motor is hand turned, the 1-2ohm resistance winding stays a CONSTANT 1-2ohms. The 13.3ohm winding fluctuates wildly, going from 0 dead short to 60 ohms. *** does this suggest that the 13.3ohm winding is faulty
- Between the black and black wires, there is no continuity. This would suggest that black-red pairs are end terminals of each of the windings in the motor (main and auxiliary).
- However, if the capacitor was meant to be connected directly to the red pair of wires, and the L/N wires straight to the black terminals, then this means that the wiring diagram would look like this (second photo). This line diagram does not make sense to me as a PSC motor and I cannot see how the capacitor could possibly generate a phase shift to kick start the motor.

I have no idea which way is the right way to wire it.
And I also have no idea what to think about the motor windings themselves - are they actually bad? I thought the windings should be relatively similar in terms of resistance.

Please help! any ideas pointing me in the right direction would be much appreciated

andy3055:
That 2nd diagram is not correct.  In your 1st diagram, insert the capacitor in series with the lower resistance winding and swap the N and L connections. If that still trips, it is possible that you have a bad winding. Do these connections without other switches or sensors etc. to eliminate any possible interactions.

shockpoint:

--- Quote from: andy3055 on May 14, 2024, 04:04:10 pm ---That 2nd diagram is not correct.  In your 1st diagram, insert the capacitor in series with the lower resistance winding and swap the N and L connections. If that still trips, it is possible that you have a bad winding. Do these connections without other switches or sensors etc. to eliminate any possible interactions.

--- End quote ---

Thank you for your response
I will give that a go tomorrow morning.
would you care to explain your reasoning behind the swapping of the L and N terminals and the capacitor in series with the lower resistance? I'd like to try and understand your thought process of debugging and diagnosis

andy3055:
Usually, they he winding with the higher resistance is the main winding and it can be directly connected across the power. Compare that to the running winding of a motor with a starting winding that gets disconnected  by a centrifugal switch that gets activated when the motor speeds up. The starting winding is in series with the capacitor. In some cases, there is no centrifugal switch and the so called starting winding is always on but with the cap in series. The high value of the cap proves it.  In the case of the winding that falls out of the circuit, the cap would be a smaller value. As a practice  the cap is on the line side. I cannot think of a good reason for that because electrically, it doesn't make a difference.

andy3055:
When I was an apprentice in my twenties, I had a book on electric motors. It used to be a well known series of books. Audels electric motor handbook... I think it was.

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