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  • Help with compressor motor problem

    I have a tank-type compressor with a 2HP motor that has been running fine for 40 years with little use in a home shop basement. Suddenly it has begun to shut off after running about 15 minutes due to overheating. It doesn't feel very hot, however the reset button pops out and I have to wait about 30 minutes to an hour before pushing in the reset button. Then it runs fine for about another 15 minutes or so and quits again. I hate to buy another motor if its something repairable like another reset button. Before I begin tearing it down, I would appreciate some of you motor savvy guys suggesting possible problems I should look for.

    Thanks!

  • #2
    My first step would be to measure the current while it is running and compare to the motors data plate.
    If it is in the normal range, I would then look for a replacement overtemp switch and replace that.
    If this is a capacitor start motor I would check to see if the centrifugal switch is sticking closed all the time.

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    • #3
      If it's running for 15 minutes, I'd start there. That isn't normal.

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      • #4
        It might not be the motor. Is the compressor ok or putting too much load on the motor?

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        • #5
          If it is a reset on the motor itself, then with it taking 40 min to cool off, it would seem to be a "real" overheat situation. The overheat sensors can get bad contacts and trip lower than intended, but when they do that it takes only a few minutes to come back on, in general.

          If the reset is on a motor control box, then it is possible that the trip mechanism is messed up. usually those also take less than 40 min to cool off, though.

          if you do have a "real" overheat situation, then if it is a single phase motor, see if the start switch is working right. It should disconnect the start winding after only a few seconds. If it fails to disconnect, it will overheat the motor. But, the start capacitor will usually fail long before 15 minutes.

          possibly the motor is working way too hard, as it might if one of the windings of a dual voltage motor is bad or poorly connected. Usually that happens when used at the lower of the two voltages.

          Or, the pump may have an issue, and the motor is working extra hard on account of that.

          Bad pressure switch might cause it to run too long, as well as being dangerous if there is also a bad relief valve. The high back pressure might make the motor work extra hard

          Any pics of the setup? Pics of motor nameplate?
          Last edited by J Tiers; 06-16-2017, 08:51 PM.
          CNC machines only go through the motions

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          • #6
            Hi Planeman 41

            A couple of things to check. first as lakeside said it could be either the comp or the motor. remove the belt and just run the motor and see what the current draw is. hand operate the comp and make sure it has not got bad bearings or internal failings. if they check out OK then put the belt back on and see what the motor current draw is to the name plate as mentioned before. Isolate the air tank from the shop if it is plumbed, so you are just filling the tank, it should not take 15 min to fill a tank for this size of comp from flat to 125 psi. If it is it, maybe the comp has got bad valves or rings and not being able to build up pressure very well. Also check for any leaks in the tank since it is quite old, it could have a leak in it. I will assume that the tank is NOT full of water and you drain it regularly.
            If all this still does not answer the problem give us a shout back. either way let us know how you come out.

            TX
            Mr fixit for the family
            Chris

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            • #7
              Could also be the check valve.
              I just need one more tool,just one!

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              • #8
                One more thought: 40 years I would say the motor is worn out. Take the side load off the motor and check to see if the motor shaft is grounding out inside.

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                • #9
                  Originally posted by outlawspeeder View Post
                  One more thought: 40 years I would say the motor is worn out. Take the side load off the motor and check to see if the motor shaft is grounding out inside.
                  2 HP motor... I'd be surprised if it did not have ball bearings, and so would not "wear out" like a sleeve bearing.

                  By "grounding out" I assume you mean "rotor rubbing". The rotor won't "ground out" in any electrical sense. A rubbing rotor can suck up some power, and heat the motor by friction.
                  CNC machines only go through the motions

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                  • #10
                    All are great ideas! Thanks for he suggestions. I think I will begin with checking out the compressor oil and looseness first. If it is binding, it may be the problem. Then on to the motor to investigate the above thoughts. Will report back. I need to first get through my immediate need for the compressor in finishing spraying a project which will take an hour or so spaced over a couple of days allowing for motor cool offs. Then on to solving The problem.

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                    • #11
                      That may solve your problem by itself..... using an overheating motor often results in needing to replace it.
                      CNC machines only go through the motions

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                      • #12
                        This probably isn't for your specific motor, but I have changed a couple of these little dudes in the past. Some of them just seem to get weak over time (the bi-metallic disc). If everything else checks out that the others have mentioned, you might bypass the thermal for a time to prove or disprove it as the culprit.

                        https://www.suppliesdepot.com/buy/pr...temsperpage=60

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                        • #13
                          I think I have figured out my problem. While sitting on the "porcelain throne" (I do my best thinking while on the throne for some reason) it occurred to me that the problem of my motor overheating began to happen AFTER I installed an air hose automatic reel. It came with 50 ft. of hose. Rather than get rid of my existing 50 ft of hose, I connected the old 50 ft. hose to the hose reel which came with 50 ft. of hose - which makes 100 ft of hose. I knew I would lose some pressure at the far end so I turned up the pressure on the compressor air regulator. For a long time I only used the compressor for short intervals to blow down dust and the like. The first time the motor quit was when I was painting the hood of an old truck I keep. This took some time and the motor overheated. The same is happening now when spray painting as it is taking some time. I believe the turned up air pressure is overloading the motor. I will remove one of the 50 ft lengths of hose and replace the section between the compressor and the reel with a short 5 ft length of hose.

                          Now the question is . . . . WHERE TO FIND ONLY 5 FT. OF HOSE WITH CONNECTIONS ?

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                          • #14
                            That will do it. Max HP required is proportional to pressure. My compressor is rated 5-10hp at 30cfm. It's happy with 7.5hp at 125psi, but to get to 175 I really need 10hp (I have tested the 7.5hp motor to that, but it draws 30 amps instead of 24 ). If I wanted to run a 5hp motor and keep the 125psi, I'd need to drop the pulley size (compressor rpm) and lose cfm accordingly.

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                            • #15
                              Originally posted by Planeman41 View Post
                              I will remove one of the 50 ft lengths of hose and replace the section between the compressor and the reel with a short 5 ft length of hose.

                              Now the question is . . . . WHERE TO FIND ONLY 5 FT. OF HOSE WITH CONNECTIONS ?
                              Cut your hose off at the five foot mark, buy two hose fittings and end up with a five and a forty five foot hose.

                              Steve

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