1. We want to thank the professional machinists that belong to our site for sharing their expertise and insight. It really helps those of us who are hobbyists to improve our work, and pass on your skills to us. Thank you and God bless you!
    Dismiss Notice

Overload relay keeps tripping.

Discussion in 'ELECTRICAL ISSUES - POWER YOUR MACHINES & SHOP' started by Brandon, Nov 3, 2012.

  1. Brandon

    Brandon Active User Active Member

    Likes Received:
    0
    Trophy Points:
    16
    City:
    Buffalo
    State:
    New York
    I'm having an issue with my Harrison M300. I was wondering if anyone can narrow it down for me, or has had a similar occurance. The motor overload relay trips after a minute or so of running with no spindle load. I figure that it is because I'm using a static phase converter, but I'm not so sure. The lathe is new to me, and I was only able to hear it run for a short period of time before I bought it.
    Thanks
     
  2. strantor

    strantor Active User Active Member

    Likes Received:
    0
    Trophy Points:
    16
    City:
    Katy
    State:
    Texas
    sounds like a bad motor to me.
    Motors can have insulation faults and still run, but they trip the overload as you are seeing.

    do you have access to a megger?
     
  3. Brandon

    Brandon Active User Active Member

    Likes Received:
    0
    Trophy Points:
    16
    City:
    Buffalo
    State:
    New York
    I'm not familiar with the term megger.
     
  4. strantor

    strantor Active User Active Member

    Likes Received:
    0
    Trophy Points:
    16
    City:
    Katy
    State:
    Texas
    AKA insulation tester
     
  5. Brandon

    Brandon Active User Active Member

    Likes Received:
    0
    Trophy Points:
    16
    City:
    Buffalo
    State:
    New York
    Ah, gotcha. No I don't. Just a simple ohm meter.
     
  6. Cal Haines

    Cal Haines Moderator Staff Member Moderator

    Likes Received:
    4
    Trophy Points:
    18
    City:
    Tucson
    State:
    Arizona
    I don't know anything about your particular machine, but if the machine was running on 480 at some point in the past and the motor was rewired for 240, it's very possible that someone forgot (or didn't know that they needed to) change the heaters in the overloads. The motor draws twice as much current running on 240, so it can easily trip the overloads if they are set for 480.

    Cal
     
  7. Tony Wells

    Tony Wells Administrator Staff Member Administrator Active Member Director

    Likes Received:
    17,821
    Trophy Points:
    113
    Location:
    Tyler, Texas
    City:
    Tyler
    State:
    Texas
    If you have a clamp on ammeter, like an Amprobe, it would be good to see the no load current draw of the motor. Of course, running on a converter could very well be part or all of the problem if something were wrong with the converter. Have you checked the line voltage on each leg? A serious imbalance could cause some problems as well.

    Although a megger will tell you about the condition of the insulation of the motor, you can also check for leakage which will sometimes result from poor insulation. Check for voltage (AC) between the motor frame itself, cleaning the paint off or finding a good bare spot, and the power supply ground wire. Not the neutral, but the ground. In theory, there would be zero volts measured at that point, but if the insulation is "leaking" a small voltage may be present. Start on a high range on the meter, about the supply voltage(which we hope isn't there) and work your way down until you can measure it if it is there. Might only be a few volts. That presents a load that shouldn't be there.

    It's also possible, though less likely, that there is a problem with the relay. That's why you need to do these other checks.
     
  8. Brandon

    Brandon Active User Active Member

    Likes Received:
    0
    Trophy Points:
    16
    City:
    Buffalo
    State:
    New York
    Hmmm, excellent points... no I haven't checked the legs off of the converter for an imbalance, and the other funny thing is, the heater is an adjustable Klockner Moeloner. It's highest setting is 6.6A. The motor tag says it draws 8.8A. I wonder if that might be a problem... Thanks for your help everyone. It looks like I might have a sleepless night tonight, but I'm going to start poking around bright and early in the AM. I'll keep you updated.
     
  9. Brandon

    Brandon Active User Active Member

    Likes Received:
    0
    Trophy Points:
    16
    City:
    Buffalo
    State:
    New York
    So here's what I saw. L1 has 119V L2 is at 118V and L3 is 170V. There are 0 volts between the frame and ground. I don't have a clamp on ammeter, but I see one in my immediate future. Would 50 or so volts effect a motor? As I'm thinking about it, the overload breaker is doing it's job and protecting the motor correct?
    Thanks again to everyone that helped.
     
  10. Tony Wells

    Tony Wells Administrator Staff Member Administrator Active Member Director

    Likes Received:
    17,821
    Trophy Points:
    113
    Location:
    Tyler, Texas
    City:
    Tyler
    State:
    Texas
    I'd think that perhaps the suggestion that the motor was wired for 480 is worth exploring, in the light of the heater it has. Check the tag on the motor and see if the current draw spec falls within the range of the heater at 480. Also, when you get a clamp on meter, you can see if it is within spec (8.8 amps). If so, you have the wrong heaters installed. You can't run that motor that way.
     
  11. Brandon

    Brandon Active User Active Member

    Likes Received:
    0
    Trophy Points:
    16
    City:
    Buffalo
    State:
    New York
    Ok, it's drawing 10.8a 11.2a and 0 on the third leg while it's running. Way out of the 6.6 breaker's limit. The motor tag says it's supposed to be drawing 8.8... :dunno:
     
  12. Cal Haines

    Cal Haines Moderator Staff Member Moderator

    Likes Received:
    4
    Trophy Points:
    18
    City:
    Tucson
    State:
    Arizona
    We need to understand why you're seeing 0A on the third leg. Are you running off or a rotary phase converter (RPC), static converter, or what? Some "static converters" are nothing more than a set of motor starting caps and let the motor run on two phases once it's running.

    Your overload relay is not going to work in this application. I would expect the machine to draw about 4.4A at 480, so the overload would have worked fine there. You should consider getting a correctly sized unit.

    Cal
     
  13. Tony Wells

    Tony Wells Administrator Staff Member Administrator Active Member Director

    Likes Received:
    17,821
    Trophy Points:
    113
    Location:
    Tyler, Texas
    City:
    Tyler
    State:
    Texas
    Since you reported 170 volts on the third phase, that suggests to me that there may be an open winding, but I fail to understand how it would start. Might be worth taking to a motor shop to ensure the motor is not the source of the problem. But most assuredly, that heater is going to be wrong for an 8.8 amp nominal draw. The reasons the other two legs are drawing more may be related to a problem with the third winding.
     
  14. Brandon

    Brandon Active User Active Member

    Likes Received:
    0
    Trophy Points:
    16
    City:
    Buffalo
    State:
    New York
    I'm running a static phase converter 220v. For what I paid for it, most likely nothing more than starting caps. I'm looking for a motor for a RPC. I thought this static phase converter get me by for a little bit. I was also worried that I would have to buy 2 motors instead of one.
     
  15. Cal Haines

    Cal Haines Moderator Staff Member Moderator

    Likes Received:
    4
    Trophy Points:
    18
    City:
    Tucson
    State:
    Arizona
    Tony,

    The 170 may be because the motor is providing the voltage, along the lines of an RPC idler motor. I suspect that his static converter is only connecting the third phase during startup.

    Brandon,

    You can check for an open winding with your Ohmmeter. With the motor leads disconnected you should see about the same resistance between any two of the three wires going to the motor itself. While you're at it, check to make sure you have infinite resistance between any of the 3 wires and the motor's case.

    You can also swap T3 with T1 or T2, start her up and check the current again. The motor will probably run backwards, but it will tell you if the third set of windings are OK. (T1, T2 and T3 are the designations for the three phases on the load side of the contactor.)

    Cal
     
  16. joe_m

    joe_m Active User Active Member

    Likes Received:
    0
    Trophy Points:
    36
    City:
    Huachuca City
    State:
    Arizona
    I'm not an electrician, but I stayed at a Holiday Inn last night....

    I don't think there is any problem with the motor or the wiring. I think that it's the result of trying to run that motor on a static phase converter and nothing else.
    There are a 1,350,000 (according to Google) explanations of static vs rotary vs VFD on the net, and after reading 1,299,000 of them the symptoms being shown are just what I'd expect to see.

    This site has a rather clear explanation of what it is: http://www.phaseconverter.com/what-is-static.html#faq

    And the same site says this could be one of the effects:
    Static phase converters are designed to start three phase electric motors to run on single phase power. The machinery they are setup to run must be able to operate on two thirds to one half of their rated motor horsepower. If this is not the case then when the machinery is put under its full rated load the motor or machinery will most commonly stall-out or overheat and even burn out.

    That's my guess. It's just a guess. Perhaps a call-out on Craigslist would find someone nearby with a rotary phase converter of the correct size that would let you test it out to confirm before swapping out parts/wires.

    good luck
    Joe
     
  17. Cal Haines

    Cal Haines Moderator Staff Member Moderator

    Likes Received:
    4
    Trophy Points:
    18
    City:
    Tucson
    State:
    Arizona
    It depends on the design of the static converter. Some have a potential relay that connects one or two starting capacitors to the third phase to get the motor started, then disconnect the starting caps, leaving the third phase without power. Others add two run capacitors that stay connected to the motor to power the third phase. It just depends on what he's got. There's not a whole lot of difference between a low end static converter and the motor starter part of a typical rotary phase converter. Something like a PhasePerfect, the provides true 3-phase, is another animal altogether.

    Brandon,

    This might be a good time to consider going with a variable frequency drive (VFD). This one has built in overload protection, so you can ditch the static converter, the undersized starting relay and add variable speed control for under $200:
    http://www.factorymation.com/FM50_230V/FM50-202-C.html

    Cal
     
  18. Brandon

    Brandon Active User Active Member

    Likes Received:
    0
    Trophy Points:
    16
    City:
    Buffalo
    State:
    New York
    A VFD is an alternative that I haven't given much thought. I would figure I would have to wire the VFD directly to the forward and reverse contactors... Hmmm....
    Thanks to everyone that took the time to help me out.
     
  19. Hawkeye

    Hawkeye Active User Supporter Active Member

    Likes Received:
    20
    Trophy Points:
    38
    City:
    Kelowna
    State:
    British Columbia
    If you go with a VFD, you can bypass the forward and reverse contactors. The VFD will handle reversing and give you very nice speed control.
     
  20. Pacer

    Pacer Active User Active Member

    Likes Received:
    1
    Trophy Points:
    38
    City:
    Greenwood
    I have limited experience with a static converter, but 2 incidents similar to your description turned out to be the converter was the problem - 1hp rated converter would do this trying to drive a 1hp motor. I ended up using a VFD.

    But I think I would want to confirm the the motor is OK -- I have a small elec shop near and 2-3 times I have had an unknown motor that I would drop by there and have him 'check' it out. One was a suspected 440v and he confirmed this and suggested he could "pick" (I think that was the term?) the wires and change it to 220v - I said OK and for $60 he did it and every thing was OK. Another was a scrap yard find and he just plugged it into 3ph and it was fine - charged me $10.
     

Share This Page