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How hot should a capacitor get + another issue

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Forum topic by Robert posted 12-02-2020 02:37 PM 256 views 0 times favorited 8 replies Add to Favorites Watch
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Robert

4330 posts in 2456 days


12-02-2020 02:37 PM

This is a bit of a long story, I’ll keep it as short as possible.

5HP single stage compressor.

Backstory: Last summer I heard a racket from my shop. Opened the door and it sounded like my compressor was about to come apart, smoke was everywhere.

I took it to a compressor shop they said it was the unloader valve. They replaced the shutoff switch with a Pumptrol because they did not have the right IR switch in stock. I told them I was afraid the compressor pump may have been damaged, they didn’t have much of a comment, just see how it runs.

Well it is working, sounds normal, so I figure the pump is probably ok.

A few months after the repair, and one day I flipped the lever to off and it literally disintegrated. A the time I felt it had to be heat I’ve never seen anything like that. Anyway, I replaced it with the same model switch the shop put in.

A couple months later, and I hear the unloader valve leaking air and the motor would not shut off. PSI was about 100. Shutoff is 125. I did some checking and the label says its rated for 20A @ 240. So I’m thinking it is not the right size, hence overheating due to current load.

Question #2. There are 2 capacitors, I assume a start and run.

I had to press the reset button on the motor yesterday. After a few minutes of running, I noticed one of the capacitors gets very hot.

I’ve had to press the red reset button 3 times in the last couple months. Would a bad capacitor cause this?

To the point: I’ve ordered an OEM switch and plan to replace the capacitor.

Am I on point or are there other things to consider?

-- Everything is a prototype thats why its one of a kind!!


8 replies so far

View Rodango's profile

Rodango

22 posts in 204 days


#1 posted 12-02-2020 03:31 PM

All I can say is that I replaced a start capacitor on a lab freezer that had failed with a larger, higher capacity model that was designed as a replacement item. It has worked fine ever since—4 years. I was leery about the potential for electric shock doing this, and putting on a larger one and harming the motor. I learned to use a long handled insulated screwdriver to kill the charge on the old cap while disconnecting it to make it safe. I had to study how to hook it up as the wires looked different, but on the new one it had one or two extra leads that weren’t used in my application.

Good luck, HTH

-- I won't even try to tell other people how to live their lives: they're not listening and I'm probly wrong.

View nicksmurf111's profile

nicksmurf111

377 posts in 2426 days


#2 posted 12-02-2020 03:54 PM

Have any pictures or model numbers? I don’t want to make any assumptions. What kind of compressor is this? Is it wired to a disconnect or is it a portable unit with a plug and a fake 5hp label?

-- Nicholas

View CaptainKlutz's profile

CaptainKlutz

4015 posts in 2470 days


#3 posted 12-02-2020 04:15 PM

Comments FWIW:

1) Red button is thermal overload breaker.

These can go bad over time. They are not designed to be used very often; and have low (50-100) cycle lifetime expectancy, though they will last many decades unused. One failure mechanism being they trip at lower current that specified the more often they trip.
Need to measure current draw to determine if you have overload breaker is failing, or you have excessive motor current which needs corrected.

2) Which capacitor is getting hot?

- IF start cap is hot: can be several things wrong. Could mean it is leaky and needs replacement. But can also overheat start up cap when centrifugal switch is not working properly. Can listen to motor start up, and should hear click from switch 0.5-1 second after start; roughly when motor reaches ~1000 rpm. If you don’t hear switch working properly, then using a new capacitor will get just as hot and die again. Most centrifugal switches are adjustable. Best to remove motor end cap, and check switch contacts for wear, and set for proper operation. FWIW – Non-working centrifugal switch can also cause excessive current draw due start cap in circuit while motor is running. This might explain thermal overload breaker issue also?

- If run cap is hot: replace the cap as it is failing. Run capacitors don’t see same kinds of stress as start cap. So if new capacitor has excessive heat; might have issue with winding or wiring internally. A leaky run cap will also draw excessive current, but only when motor is running steady state; not start up phase like start cap. When does the thermal overload breaker trip; start up or running?

Best Luck.

-- If it wasn't for bad luck, I wouldn't have no luck at all, - Albert King - Born Under a Bad Sign released 1967

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Robert

4330 posts in 2456 days


#4 posted 12-02-2020 04:24 PM

Ingersoll Rand 5HP Model SS5L5 pump.

I don’t know which capacitor it is. Facing the pulley it is the one on the right (I believe its a Baldor motor).

I’ll check it for leakage. As I recall I replaced it once already.

Are the aftermarket cheap capacitors ok?

I don’t have a disconnect the breaker is 20’ away.

-- Everything is a prototype thats why its one of a kind!!

View nicksmurf111's profile

nicksmurf111

377 posts in 2426 days


#5 posted 12-02-2020 04:38 PM

Yes, you can get generic capacitors from a supply store or online as long as they are the same size/rating.

Just wondering since you are having issues with heat: are you sure your supply lines are correctly sized?

-- Nicholas

View CaptainKlutz's profile

CaptainKlutz

4015 posts in 2470 days


#6 posted 12-02-2020 04:45 PM

The run cap is usually the smaller of the two capacitors.
IMHO – If already replaced start cap once, absolutely need to check centrifugal switch on back of motor.

As long as voltage rating of replacement cap is same or higher; cheap caps work.

The lifetime of start capacitor is determined by: number of start cycles, time between start cycles as it needs to cool down, and operating temperature.
Have seen cases where starting a large DC blower with high mass impeller 10 times repeatedly in one minute; will over heat the start capacitor creating a short and/or create leakage.
Start up heating is the reason for overlap in pressure switch, as it reduces number of start cycles, and gives components time to cool down between starts. Start capacitor/switch issues are one big disadvantage to single phase high HP motors. They don’t exist on 3 phase motors.

Cheers!

-- If it wasn't for bad luck, I wouldn't have no luck at all, - Albert King - Born Under a Bad Sign released 1967

View Rodango's profile

Rodango

22 posts in 204 days


#7 posted 12-02-2020 05:00 PM

CaptainKlutz: Learning a lot here, thanks for the info. Are start/run capacitors and/or centrifugal switches used on 3-phase motors?
I ask because I’m looking at the potential of getting some used 3-phase equipment and need to figure out what to look for. Thanks.

-- I won't even try to tell other people how to live their lives: they're not listening and I'm probly wrong.

View CaptainKlutz's profile

CaptainKlutz

4015 posts in 2470 days


#8 posted 12-02-2020 05:28 PM

Are start/run capacitors and/or centrifugal switches used on 3-phase motors? – Rodango
No.

-- If it wasn't for bad luck, I wouldn't have no luck at all, - Albert King - Born Under a Bad Sign released 1967

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