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Thread: Air Compressor "thermal overload protection" issue

  1. #1

    Air Compressor "thermal overload protection" issue

    I purchased a nice 5hp 60 gal "fatboy" style air compressor for my workshop a few years ago. Finally getting around to getting it hooked up.

    Upon closer inspection, I didn't see any "red" reset button on the motor itself which would indicate a "thermal overload" circuit. I'm worried that this motor does not therefore have it. I went to my local large tool store which sells many compressors. They said if there is no "red button on the motor" it probably doesn't have one. They further said with compressors this is pretty important.
    They suggested I buy an "accessory overload switch and have my electrician wire that in". I asked how much and they said about $250.00 for the switch!
    I looked on Amazon and I can buy a 5hp Leeson compressor motor with the overload protection button circuit for about $330.00 (yes I'm up here in the frozen North.) I went back to the store I originally bought it from and see all the newer models do in fact have the obvious red overload button.

    Wondering if it is certain that without a reset button it is certain the existing motor on the compressor is in fact without the circuit?

    Is it critical to have a "thermal overload" capability?

    Is this "thermal overload switch" really this expensive? (I've tried to google it but haven't really found what it is they are referring to)

    and lastly, am I doomed and should just drop the $330 and buy a new motor? (which of course I really don't want to do!)

    I'm not savvy to electrical issues, but have access to a pal who is reasonably handy. I'm a pensioner so money isn't exactly growing on trees (which right now are covered in snow anyways!)

    Any help / advice so very appreciated.

  2. #2
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    my compressor has thermal protection without the red reset button it will shut down and when it cools then starts

  3. #3
    Have you read the motor plate on your existing? Does it say anything like duty cycle or time rating?

  4. #4
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    Did you throw the owner's manual away? If not, why don't you read that and see what it says about thermal overload? I think that would be a more valuable source of information than speculation from strangers who don't even know the brand of compressor you are talking about.

  5. #5
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    The motor nameplate will indicate whether it has thermal overload protection.

    Looking for a red button only proves that it has a manual reset type, many are auto reset and have no button. The motor nameplate will indicate "thermally protected" if it has built in overload protection.

  6. #6
    Scott, Look at your compressor's motor to determine FLA (Full Load Amps). Then ask your pal if you can install an inexpensive compressor overload protector switch like one of these:

    https://www.amazon.com/uxcell-Circui.../dp/B01N7WG7Y7

    https://www.amazon.com/BIN-BON-Compr.../dp/B07G73TBRH

  7. #7
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    This thread brings up some interesting issues. When a motor's intended service could include a locked rotor, it would need a thermal protection. An example: a sump or garbage pump that might pull in some debris. But, for an air compressor, that may or may not be needed. I know that I have some motors that are thermally protected (because they have the red button) and suspect that others w/o the button may have the thermal protector built into the motor. But I have never thought of the safety aspect. My air compressor is "live" when I'm home but I always shut it off if I'm on vacation.

    When a motor is in a locked rotor condition it is drawing extra current. So, if the breaker amperage rating isn't too high, perhaps that could cause it to trip. On my radial arm saw, if I'm doing some heavy ripping sometimes I trip the thermal protector and sometimes I trip the breaker - - it is kind of a "jump ball" which one pops first.

  8. #8
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    Hi Brice, thermal overload is intended more for real motor overloads where the motor is producing more output power than it's rated for.

    Motors require overload protection except for specific motors and applications as per the electrical code.

    Normally breakers for motors are much larger than the long term trip rating of the overload relay......Rod.

  9. #9
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    First off, what are you going to do with your compressor? Moderate to light air tool use, some light spraying, filling a low tire? If this is the case, don;t worry about.

    The thermal overload switch is is basically a thermometer that measure the temperature of the motor. When the motor gets too hot from over use, it shuts the motor off so it does not get damaged.

    If you are not going to be running the compressor on a heavy duty cycle (i.e. cycling on and off every 5 minutes or having it run continuously trying to support the load of two spray guns), you will never come close to tripping the overload switch.

    Alternatively, if you do have a heavy duty cycle, you could just run the motor until it burns out, then get a new and bigger compressor (since this one is undersized for you needs) with an overload switch.

  10. #10
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    For compressors the heat problem is only an issue if the motor is started too often. Something like more then 10 starts per hour is not good. A true compressor duty motor is designed to deal with excess heat from frequent starts.
    I would reduce the max pressure to 120-150PSI. If you are running air motors maybe 100PSI minimum or about 80-90 if not. This will reduce the starts per hour. You can also reduce the motor pulley diameter to make it quieter and run cooler with reduced output.
    I would use it as is until the motor fails which will be 10-20 years as is in a home shop. How long are you planning to live?
    Bill D.

  11. #11
    Thanks for the replies that are helpful.
    Art: I appreciate your "read the manual" comment (that's really helpful) but I wouldn't have posted if I had the information available. I'm not particularly savvy regarding reading motor info plates nor am I capable of tearing off the motor covers to look for whatever it is I should be looking for. I would't know what to look for. Hence why I posted.
    Rod/Jerome: I contacted the actual motor manufacturer located in Wisconsin and they told me they were surprised that my retailer had put this particular motor on a compressor. They looked it up by way of model # and advised it in fact has NO TOPS (thermal overload protection system).
    Bill: Well, I'm hoping to outlive the motor!! (wishful thinking perhaps) But I'd be thrilled with it lasting 20 yrs. (I myself should be so lucky)
    Todd: The purpose of this compressor is basically light use general shop. It'll run air nailer's when req'd, it will run the odd air tool, and it will hopefully be used for an air source for a plasma cutter in the future. Yes tires in the driveway and other uses like that. Certainly not production shop continuous use.
    Brice: Like you, I unplug my smaller 120V air compressors when not using them. This 5hp 230V one was going to be hard wired to a dedicated circuit. Maybe I'll run a "50A 230v plug and receptacle instead & simply unplug it when I'm leaving the shop, it certainly would be an option. (If I always remember)
    Karl: Thx for the links, I'll ask my 'Sparky" about those as they are certainly low priced. My plate mentions 28.2FLA if I read that right.

    Doing a bit more checking and watching some "Youtube" on this issue it seems like a viable approach would be to buy a good quality 5hp 230v magnetic switch ($100-150)and wire it in between the regulator and the motor. (if I recall that right). Apparently magnetic switches often also have "TOPS" built in. So have an exterior reset button while others need the cover removed for a manual reset. They actually bolt (or screw) the mag switch onto the front part of the compressor frame so it is sturdy and accessible. It didn't look too difficult to wire in. I'll sit down with my pal and run these ideas past him. My fear would be to leave the compressor live and have a line blow while I'm out. The machine runs continuously and reaches a meltdown. If all goes well it only cooks the motor but I suppose there is a small risk of it getting so hot as to possibly cause a fire. No doubt insurance investigators would blame me for this for not having a "fail safe" installed since the motor has none. I do plan to put a ball valve shut off immediately after my "whip". I was told to use a whip so as to isolate vibration to my lines. I think I'd actually prefer to have the shutoff before the whip in case the whip burst as the compressor would of course just continue to run. Not certain if having it, the shutoff first attached to the tank output is asking for trouble/ failure from vibration?
    Thank you for the ideas and thoughts on this. Hopefully this thread might help others who find themselves without a "TOPS" on their electric motors.

  12. #12
    You could install a Manual overload switch for about a hundred bucks. It's just a toggle switch with an overload heater switch in it. Any electrical supply house or Grainger will have them. Just make sure you purchase the proper size heater . Used them all the time when I was working.

  13. #13
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    Scott
    You're kind of over thinking this and developing a solution, before you have a problem.
    is the compressor manufacturer still in business? If so have you contacted them?
    Can you tell us the manufacturers's make and model of the compressor, and motor you have?

    I'm 60 years old and have been working around machinery my entire life. Work and personal.The only motor I have ever "routinely" reset, was the motor on my old Performax sander. I've never reset the thermal on my air compressor.
    Install your compressor on the correctly sized, breaker protected circuit, and use it. If the issue develops, address it then. I don't think i will.
    "The first thing you need to know, will likely be the last thing you learn." (Unknown)

  14. #14
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    Quote Originally Posted by Mike Cutler View Post
    Scott
    You're kind of over thinking this and developing a solution, before you have a problem.
    is the compressor manufacturer still in business? If so have you contacted them?
    Can you tell us the manufacturers's make and model of the compressor, and motor you have?

    I'm 60 years old and have been working around machinery my entire life. Work and personal.The only motor I have ever "routinely" reset, was the motor on my old Performax sander. I've never reset the thermal on my air compressor.
    Install your compressor on the correctly sized, breaker protected circuit, and use it. If the issue develops, address it then. I don't think i will.
    If I'm understanding correctly, you are suggesting Scott use the compressor without OL protection? If so, I'm going to strongly disagree with this.

    If it is a machine that is always attended while in operation, then only the motor is at risk. But it's still a bad idea. An air compressor though, can be running when nobody is around and if things go wrong & the motor sets whole place on fire. There was a thread on one of the woodworking forums in the last couple of years where just that happened.

    The argument that a compressor should always be shut off when not being used is no good, because there is a good chance that is not always going to happen. Then in the middle of the night a leak develops & the compressor is running continuously...

  15. #15
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    Quote Originally Posted by Frank Pratt View Post
    If I'm understanding correctly, you are suggesting Scott use the compressor without OL protection? If so, I'm going to strongly disagree with this.

    If it is a machine that is always attended while in operation, then only the motor is at risk. But it's still a bad idea. An air compressor though, can be running when nobody is around and if things go wrong & the motor sets whole place on fire. There was a thread on one of the woodworking forums in the last couple of years where just that happened.

    The argument that a compressor should always be shut off when not being used is no good, because there is a good chance that is not always going to happen. Then in the middle of the night a leak develops & the compressor is running continuously...
    I have a relay that is controlled by my light switch when I leave the shop I shut off the lights and the compressor shuts down also. I also have a solenoid that shuts the air off

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