Coleman portable Compressor trips circuit breaker

4 years 1 month ago #1287 by mikebolden@sbcglobal.net

What I have:
Coleman 5hp, 25gal horizontal tank, 90 on-120 off, belt drive, single stage, 120 volt, portable
Model MP0502513

What it does:
When I got this one, it did nothing. I checked the capacitors and they both tested defective so I replaced them.
Now it will run.
At initial power, it starts and builds up pressure and turns off as it is supposed to but the unloader did not work (no hiss on shut off).
I put my amp meter on it and it starts at about 8 amps and gradually increases to a little over 16 at shut off.
The problem occurs at restart. When it restarts, it is drawing 80-90 amps for a few seconds until it trips the breaker.
I tried cleaning the unloader in ultrasound but it still was sticking. Since it was cheaper to replace the entire pressure switch with an unloader rather than just the unloader, I replaced the entire unit.
The check valve. I know this problem usually occurs with a bad check =valve. What I don’t get is why does it work ok when starting from no pressure but fail when starting at restart which is 95psi (my new pressure switch is set at 95-125). I made an assembly to hold the check valve and applied air to itb from another source. It works like it should – passes air in one direction but not the other. This proves it can work but maybe something is happening when it is working at a higher speed.
I have so much time and energy and money in this thing that I hate to give up but I’m running out of things to try.

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4 years 1 month ago #1290 by MTR-Admin

Thanks for the post Mike,

I would typically say yes, the Check Valve seems to be defective; however, you've ruled this out as it does operate as a one-way valve and let's air through to the tank, but not back.

Just to confirm, the Unloader Valve does operate as it should on shut-off, and discharges the air from the line as it should? If so, there's no reason the compressor should have a difficult time on re-start as there is presumably no air in the Discharge Tube or on the pump head.

Something is clearly causing it to struggle on re-start and usually that's either due to back-pressure from the Check Valve or the Unloader Valve not functioning on shut-off.

- MTR

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4 years 1 month ago #1292 by MTR-Admin

Just to confirm the Check Valve is working correct for a 100% certainty, do the below test:

1) Let your unit pump up from 0 PSI.
2) Turn it off.
3) Find the supply line from the pump to the tank.
4) Remove the supply line from the pump head.
5) If you hear air coming from the tank you have a defective check valve.

- MTR

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4 years 1 month ago #1313 by mikebolden@sbcglobal.net

Sorry to be so slow in getting back. I did the test of opening the tube to the head when the tank is full and the compressor is off. There is no leak at that connection. I have also replaced the check valve just to be sure and still get the same results. I put an amp meter on the power cord (I have a plug that sandwiches into the power cord) and find that on start up, it is drawing 75 - 85 amps for about 1.5 seconds and switches to about 11 amps. The 11 amps slowly increases until it reaches cut out pressure. At cut out, it is drawing about 17 amps. I have compared this to another similar (5hp direct drive) compressor and get approximately the same readings readings. On restart, it is drawing about 80 amps until the breaker trips.

Now I'm thinking motor. Do these motors have a centrifugal contact where after a certain speed the start circuit is disabled. On start up the current draw drops off quickly but on restart, it does not. Maybe the motor is not reaching a high enough rpm to force the start circuit contacts to open the start circuit.

Thanks, Mike

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4 years 1 month ago - 4 years 1 month ago #1317 by MTR-Admin

No worries Mike.

Well, if the motor is original, it should not be drawing more than 30 amps or so on start up, according to the manufacturer.
There is a centrifugal switch in the motor and this COULD be causing the high amp draw, certainly. At this point it's best to have an electric motor repair shop take a look at the motor.

The centrifugal switch mechanically opens and closes the starting circuit and the run circuit; it is easy to check and is located on the motor shaft internally usually at the end where the cover for the wiring is located. The switch uses weights to open and close contacts when the motor shaft spins or is at rest, this mechanical switch is subject to wear.

But, how hard is the pump to turn by hand? What size is the breaker that trips? Does the breaker only trip when the unit gets to 90 psi? Basically, we need to determine whether this is a motor or a pump issue.

As long as you have no obstructions in the pump head, the supply tube or in the check valve of the unit, I'd rule out the pump or other components.

Make sure you can turn the pump flywheel by hand easily (with the belt removed). Also, make sure there is no more than 1/2" deflection in the belt when you press down on the center.

I hope this helps.

- MTR

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4 years 1 month ago #1320 by mikebolden@sbcglobal.net

this compressor has:
new capacitors
new pressure switch with unloader
new check valve
new line from unloader to pump head
new line from check valve pump head

I don't have much experience with this stuff so I am not sure about the pump. With the belt off, I can turn it but it requires some effort to overcome the compression in the pump. When I had the belt off, I did not open the line to the head and try to turn it without compression. I would say it feels similar to turning the blade on a small lawnmower engine. Belt is good.
With everything new, I'm fairly certain that everything external to the pump is clear. I do not know how to tell about the pump internally.
Given the way it is acting, I'm leaning toward the motor. When it starts from empty tank, it draws high (75-80) amps current for about 1.5 seconds and then switches to about 11 amps. On cutin, it draw 75-80 amps but never switches so after about 3-4 seconds, the breaker trips.
The breaker is a 20 amp and I made sure it is good by swapping it.
I tried different tank pressures on restart. Up to 40 psi, it will restart. At 50 and up, it trips the breaker which makes me think it can't get up enough speed to release the start mechanism.

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