Compressor motor overheating

[shoot summ]

I recently replaced my compressor pump, thread is here:

http://www.garagejournal.com/forum/showthread.php?t=278440

Things were going along well, compressor ran fine, had several instances running high volume tools where it performed well.

Recently I started tripping 1 leg of the circuit, my fault as I hadn't coupled the breakers. I checked the wiring, and everything was fine. I installed the correct breaker to make sure I didn't have a bad breaker.

Now I'm tripping the thermal overload on the motor. It always happens near the end of the cycle, I can cycle a couple of times, then it trips. The motor is very hot to the touch.

None of the wiring is even warm to the touch, so I don't believe I have a voltage issue although I've going to put a meter on it tonight. I'm also going to check the pressure switch contacts to insure they are good.

So my thoughts are a potential problem with the motor, or I'm just running the motor too hard and perhaps need to back the max pressure down on the switch(I'm going to try this anyway).

The motor is probably 10+ years old, and the PO had the compressor outside. The bearings feel OK with no play or drag. Could something in the motor cause the issue?

This pump will supposedly go to 200psi, I'm currently cutting it off at 150psi.

 

[A_Pmech]

Put an amp clamp on one leg of the motor and check the peak current just before cut out.

My guess is you're running the pump too fast.

 

[Finky198]

The leads going into you motor could have vibrated loose
I installed our compressor about 6mo ago and it recently started tripping the breaker and getting hot I pulled both the compressor and wall pannel and what do you know the terminal loosensed up causing poor connection after a few cycles it would cut out

Its posible that your rpm needs to change as it's a new pump with different specs or the motor doesnt have the torque to turn the pump at hight pressure

It Same reason why big chainsaws a decompression button to ease pull starts and why gas compressor have an Unloader valve

And I hate to say this but

If the pump went already the motor could be next : (

 

[shoot summ]

Sorry, forgot to mention, pump is rated at 850-900RPM and I am running it about 830.

Going to check all of the connections tonight, and will put an amp clamp on it as well.

I do actually suspect the motor, just want to validate it before I drop more $$'s.

Thanks for the suggestions.

 

[larry_g]

Sorry, forgot to mention, pump is rated at 850-900RPM and I am running it about 830.

Going to check all of the connections tonight, and will put an amp clamp on it as well.

I do actually suspect the motor, just want to validate it before I drop more $$'s.

Thanks for the suggestions.

Most pumps are rated at some various horse powers and speeds. Are you sure that the 850-900 is the rating for 5 hp and not 7.5 hp? The listing says a 24 cfm pump and that is a lot for a 5 hp motor to do. Most 5 hp pumps are in the range of 17 to 20 cfm.

Bottom line is the current the motor is pulling. If the motor is good and pulling to many amps then you have to slow the pump or lower the pressure at cut out.

lg
no neat sig line

 

[shoot summ]

Checked all of the connections, all good.

Cycled the compressor 3 times messing around with the amp probe. I suspect I'm not doing something right as the reading I interpret is 30 amps...

I have this clamp:

http://www.amazon.com/dp/B00K0U1N5G/?tag=atomicindus08-20

First time I have used it, picked it up in a package deal some time ago. I remember the guy told me to be sure I zero it. So I clamped it onto the wire without the compressor running, zeroed it, started it up and got a solid 3.0 on the meter.

Going to remove the belts and see what I get.

 

[merr6267]

I had a really odd occurrence one time with a 220v circuit, and that was that one leg of the breaker had very high resistance. The voltage drop across one of the legs of the breaker was very high. The breaker would trip, and the motor would get hot, as it wasn’t getting full voltage. We changed breakers and all was ok. This would apply at your compressor switch (starter) as well.

I could be wrong, but I believe that the current (amps) on each leg should match, as the 110v legs are complimentary, which gives the 220v total.

This is in addition to the mechanical pump speed and other considerations.

Good luck,
Phill

 

[A_Pmech]

Remember that current goes up with pressure as the amount of power required by the pump increases.

 

[404]

For the time being, lower the cut out pressure.

 

[shoot summ]

Played with it a little tonight.

Lowered the cut out pressure to 140psi, no control over the cut in, it seems to be 100psi.

Ran an orbital sander for awhile, compressor cycled 5-6 times no problem, I was thinking "BINGO". So I decided to do a little media blasting. Before I started I decided to clean the filter on the dust collector on the tank. I guess my PSA for today is to check your filter, holy **** that thing was packed full. No wonder it seemed like the motor was straining. Anyway, with great suction and much better visibility I started blasting. Compressor kicked on, I'm running the blaster constant and the compressor is holding right at 100psi. After about 5 minutes the thermal overload trips.

So I'm thinking I am running the motor too hard. I'm going to try a 1" smaller pulley and see what happens.

 

[pcmeiners]

"I interpret is 30 amps"
A 5 hp motor should start out 20 -22 amp, at presure cut off, if I remember correctly, it draws a couple amps more, so max should be close to 25 amp. If it above this your expecting too much from the compressor, lower the rpm via motor pulley size for permanent fix.

"listing says a 24 cfm pump" 24 cfm = 7.5 HP, 5hp=18-19 cfm

 

[larry_g]

So I'm thinking I am running the motor too hard. I'm going to try a 1" smaller pulley and see what happens.

Why are you guessing at this stuff? If your really running at 30 amps and should be at ~20amps then you need to slow the pump down by 30%. Find a drive pulley that will spin your pump at ~ 550 rpm ( .66 X 850rpm) and you should be good. Don't guess at this, do the math or call the mfg and ask what speed this compressor should run with a given HP motor and what ever cutout pressure you choose.

Reread posts #5 and #11. If you don't understand say so and we'll try to make it simpler.

lg
no neat sig line

 

[Charles (in GA)]

Most pumps are rated at some various horse powers and speeds. Are you sure that the 850-900 is the rating for 5 hp and not 7.5 hp? The listing says a 24 cfm pump and that is a lot for a 5 hp motor to do. Most 5 hp pumps are in the range of 17 to 20 cfm.

Bottom line is the current the motor is pulling. If the motor is good and pulling to many amps then you have to slow the pump or lower the pressure at cut out.

lg
no neat sig line

Larry has it right. A 24 cfm pump is looking for 7½ hp. You need to slow it down to run it on 5 hp (assuming you have a real 5 hp motor, which should be drawing about 22 amps.

Charles

 

[shoot summ]

Smaller pulley showed up today.

While I had the pulley and belt off of the motor I decided to run the motor and and check the current draw.

First thing I noticed is the motor is noisy, sounds like a bearing, but everything is tight. Not a terrible noise, but not smooth and quiet.

Without any load on the motor it appears I am pulling 27 amps. Again this is assuming that the cheap amp clamp I am using is reading correctly, that I'm using it correctly, and that I'm interpreting the reading correctly...

The new 3" pulley should put me at 615 rpm or so. I didn't have a pending project that would allow me to put a load on the compressor to see if this resolves it. The current draw under load was 29 amps(with all of the disclaimers above...).

I've got 2 additional actions I'm going to take. I have a buddy that has a good amp clamp, going to impose on him to drop by soon to check out the current draw. And I'm going to contact Eaton for some Tech support on how I should be driving the pump, and what I should expect from it.

 

[shoot summ]

Just an update. I haven't followed through on my action items, I replaced the pulley and haven't had an issue since. I haven't gone full out and run the DA for really extended periods. I have run an orbital, the DA, and done some blasting in the media cabinet and haven't tripped the thermal, and the compressor is easily keeping up.

So it does look like I was running it too fast, thanks for all of the suggestions,

 

[sberry]

What is the fla ratng on the motor tag?

 

[shoot summ]

What is the fla ratng on the motor tag?

Not really sure what you are asking?

 

[sberry]

Unhook the motor and see what it draws, it should be 22 or so, you are simply overloaded at 27.

 

[shoot summ]

Unhook the motor and see what it draws, it should be 22 or so, you are simply overloaded at 27.

See post 14, I already did that, draws 27 with no load...