Electric Motor Capacitor Failure

[RCP]

A few weeks ago I asked for help with the 2hp, 220V, 1750 RPM single phase motor. Based on input from the group I installed another start capacitor. I have now failed the second capacitor. I do not see or smell anything wrong with the motor, but it turns slowly and will not run the compressor.
I guess I need to start looking for another motor?

 

[wore out]

(quoted from post at 10:27:10 01/13/23) A few weeks ago I asked for help with the 2hp, 220V, 1750 RPM single phase motor. Based on input from the group I installed another start capacitor. I have now failed the second capacitor. I do not see or smell anything wrong with the motor, but it turns slowly and will not run the compressor.
I guess I need to start looking for another motor?

Check to be sure the start switch and centrifugal mechanism are intact and the start switch contacts are not welded closed.

As the motor speeds up, the start switch needs to be ''kicked out'' or the capacitor will fail.

On the other hand, there MAY be shorted windings that cause the motor not to speed up enough to open the start switch, causing the capacitor to fail.

There's a small chance that the new capacitor was simply faulty.

 

[Russ from MN]

One time I had a capacitor start shallow well water pump fail to start, and I just connected the 2 capacitor wires together, and it started, but not as quickly as it should, I got a new capacitor and all was well. Does that make sense, that they will start, with no load, and not as quickly, with the wires just connected?

 

[MarkB_MI]

There are two types of motor capacitors: start and run. As you might guess, the start capacitors are only intended for intermittent service and will quickly fail if used as run caps. If your replacement was physically smaller than the original capacitor, you probably replaced a run capacitor with a start capacitor.

 

[John T]

RCP, does the motor have BOTH a START and a RUN Capacitor??? Some have ONLY a START capacitor. If it has a Start capacitor and is a split phase the START WINDING is what gets it initially spinning the right direction until a certain RPM at which time the centrifugal switch opens to take the start winding and start capacitor out of the circuit. A bad start winding orrrrrrrrrr a bad centrifugal switch orrrrrrrrrr a bad start capacitor can cause it not to start.

John T

 

[RCP]

There is only one capacitor, so I assume it is a start capacitor.

 

[buickanddeere]

Voltage rating and mfd of the old and new caps ?

 

[Charles in Aus.]

(quoted from post at 06:04:22 01/14/23) There is only one capacitor, so I assume it is a start capacitor.

There are also Start/Run combination capacitors that do both jobs , having o ly one capacitor fitted doesn't necessarily mean it's a start only .
My fiacc compressor uses one .

 

[wore out]

(quoted from post at 12:56:40 01/13/23)

(quoted from post at 06:04:22 01/14/23) There is only one capacitor, so I assume it is a start capacitor.

There are also Start/Run combination capacitors that do both jobs , having o ly one capacitor fitted doesn't necessarily mean it's a start only .
My fiacc compressor uses one .

That would be a 3-terminal capacitor, correct?

 

[John T]

If its only one unit, it could be a START Capacitor. Again it,,,,,,,, PLUS the start winding in which its a series component,,,,,,,,,PLUS the Centrifugal Switch (closed until X RPM then it opens) all need to be working and make up a continuous series starting circuit. If theres NO start winding circuit (cap OR switch OR start winding) she may just hum when voltage is applied to the run winding.. On some motors with an open start winding or cap or the switch is open you can give them a spin and they may take off and run..

Best I have to offer see what the other fine gents have to say it was over 50 years ago I was an engineer with the Century Electric Motor Company but Ive forgotten most all that motor stuff since lol Sure the new cap was the right one ????

John T NOT any motor expert so no warranty trust the experts over me

 

[John T]

No idea about his but Ive seen such animals

John T

 

[Charles in Aus.]

(quoted from post at 07:13:58 01/14/23)

(quoted from post at 12:56:40 01/13/23)

(quoted from post at 06:04:22 01/14/23) There is only one capacitor, so I assume it is a start capacitor.

There are also Start/Run combination capacitors that do both jobs , having o ly one capacitor fitted doesn't necessarily mean it's a start only .
My fiacc compressor uses one .

That would be a 3-terminal capacitor, correct?

Not sure Woreout I'll check later today .

 

[38orange]

RCP, Did you use the 680mfd capacitor wore out recommended? If you picked a lower rating, the motor would spin slowly and eventually capacitor would fail or breaker/overload would trip. Since you haven't smelled anything with motor, you still have hope.

One item no one has mentioned is the unloader valve. If unloader valve is stuck, the motor runs slowly until capacitor fails or breaker/overload trips. I'm guessing this isn't your problem since I believe your tank has zero pressure in it right now. But if tank has pressure, consider this and troubleshoot be letting all air out of tank. If motor starts and you don't hear the short woosh of air when motor stops, you found the problem.

 

[RCP]

I used a 750 capacitor.

The flywheel of the compressor is easy to turn by hand, I also bled the air out of the tank to see if that helped. Even before the second capacitor failed, the motor was slow to spin up to speed.

I checked voltage at the motor, and I had 208 volts when trying to start the compressor.

 

[RCP]

This is a two terminal capacitor.

 

[MarkB_MI]

> There is only one capacitor, so I assume it is a start capacitor.

That would not be a safe assumption. Some motors have a single run capacitor that also serves as a start cap.

 

[stevieb49829]

Does your centrifugal switch inside the end of the motor work correctly. It sounds like the motor is trying to run without switching to the start windings. Could be the centrifugal switch, or a connection to it. steve

 

[Janicholson]

I don't like the 208 volt number much. That much less than todays normal 240 might be an issue. Jim

 

[Charles in Aus.]

Only two wires to the start/run capacitor on my compressor Wore Out .
No centrifugal switch either.

Best photograph I could take without dismantling it. It's hot here today , 45C , 113F , not conducive to getting the tools out .

This post was edited by Charles in Aus. on 01/13/2023 at 09:34 pm.

 

[wore out]

(quoted from post at 16:01:47 01/13/23) > There is only one capacitor, so I assume it is a start capacitor.

That would not be a safe assumption. Some motors have a single run capacitor that also serves as a start cap.

That would typically be a PSC motor with NO centrifugal start switch, IMHE.