Overload relay keeps tripping.

Brandon

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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
 
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?
 
Ah, gotcha. No I don't. Just a simple ohm meter.
 
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
 
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.
 
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.
 
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.
 
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.
 
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