# Overload relay keeps tripping.



## Brandon (Nov 3, 2012)

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


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## strantor (Nov 3, 2012)

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?


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## Brandon (Nov 3, 2012)

I'm not familiar with the term megger.


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## strantor (Nov 3, 2012)

Brandon said:


> I'm not familiar with the term megger.



AKA insulation tester


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## Brandon (Nov 3, 2012)

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


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## Cal Haines (Nov 3, 2012)

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_


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## Tony Wells (Nov 3, 2012)

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.


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## Brandon (Nov 3, 2012)

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.


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## Brandon (Nov 4, 2012)

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.


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## Tony Wells (Nov 4, 2012)

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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## Brandon (Nov 4, 2012)

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...


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## Cal Haines (Nov 4, 2012)

Brandon said:


> 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...


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_


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## Tony Wells (Nov 4, 2012)

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.


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## Brandon (Nov 4, 2012)

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.


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## Cal Haines (Nov 4, 2012)

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_


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## joe_m (Nov 4, 2012)

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


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## Cal Haines (Nov 4, 2012)

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_


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## Brandon (Nov 4, 2012)

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.


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## Hawkeye (Nov 4, 2012)

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.


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## Pacer (Nov 5, 2012)

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.


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## rdhem2 (Nov 5, 2012)

As a retired electrician wannabe machinist all I can politely say is all those phase converters and static units are obsolete pieces of s--t.  VFD is the only way to go as they offer overload protection, and direction control as mentioned but so much more.  1 phase to 3 phase conversion to 5 hp is the largest I ever installed for 240v rated motors.  Also infinate speed control from 0 to name plate rating.  Under voltage/over voltage protection, phase failure protection, your motor never had it so nice.  Preset speeds can be set up via switches for different operations.  Ramp up to speed time curve for gentle start ups and ramp down time curves for a nice easy stop.  

Now the down side, these VFD's use very high voltages and frequencies to do their job.  Old, older motors have insulation for the windings that is not rated for this use.  Most motors will stand up in my experience, but early failure is also possible but slight.  Operating the drive in constantly below 25-30 Hz is not generally recommended as the cooling fan on the motor is less efficient and the motor will overheat from thermal problems, not electrical problems.  If you must operate at that speed, gear it down.

All things weighed out, the Variable Frequency Drive is the way to go.  These come in two basic styles, constant torque, and constant horse power, tell the salesman you want one for conveyor duty (constant torque), or fan duty (constant horsepower).   Lathes, mills, drills, etc utilize the constant torque version as the load is variable.  Fan duty the load is constant.  You have reached the limit of my talents but I believe by experience I am correct.  :thumbzup:


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## Brandon (Nov 5, 2012)

The VFD is the way I'm heading.  As for what Pacer said, I'm am running a 3hp phase converter on a 3hp motor.  The way I figure, if the motor is kaput, I'm still going to need a way to control the new motor.  I was considering a RPC so that I would also be able to run my mill. That being said, I can buy 2 VFD's for the price that I will end up paying for a idler motor for a RPC.  On top of that, I would have reverse and variable speeds on my mill. The tricky part will be the Gorton's feed motor, but that hill will be climbed after I start making chips with the lathe...   
Thanks again.


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## rdhem2 (Nov 5, 2012)

Brandon;
Here is a crazy idea my man.  If the motors are close to the same amperage rating why not buy one VFD and put a plug on it (female) and plugs on each machine (male) so they can only couple to each other.  Chances are you don't run both at once anyway so just do the old switcheroo and get by with one VFD until you can get a second?  Remember to size for the larger of the two loads if you do.  A small differance in amperage is not that critical.  This is only really important if you run at full load for long periods of time.  Continous duty is rated at something that operates for periods of four hours or longer at a time.  HTH.          :LOL:


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## strantor (Nov 5, 2012)

rdhem2 said:


> Brandon;
> Here is a crazy idea my man.  If the motors are close to the same amperage rating why not buy one VFD and put a plug on it (female) and plugs on each machine (male) so they can only couple to each other.  Chances are you don't run both at once anyway so just do the old switcheroo and get by with one VFD until you can get a second?  Remember to size for the larger of the two loads if you do.  A small differance in amperage is not that critical.  This is only really important if you run at full load for long periods of time.  Continous duty is rated at something that operates for periods of four hours or longer at a time.  HTH.          :LOL:


you could do that, but you'd have to re-enter the motor nameplate parameters and/or autotune the drive every time you swap over.


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## Pacer (Nov 5, 2012)

> you could do that, but you'd have to re-enter the motor nameplate parameters and/or autotune the drive every time you swap over.



While I have nothing to back it up, it seems that perhaps the VFDs arent especially sensitive to this - say two 2hp motors or a 2hp & a 1 1/2hp with similar amp requirements (which many of the 3ph motors are) I say this because I am seeing this written about being done more and more. In my own case I have bought 3 different machines - 2 lathes with a 1hp and a 1 1/2hp,  and a mill with a 2hp - and used my existing mill 2hp VFD to run them off an extension cord for testing/demonstrating with out any hint of a problem.


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## strantor (Nov 5, 2012)

Pacer said:


> While I have nothing to back it up, it seems that perhaps the VFDs arent especially sensitive to this - say two 2hp motors or a 2hp & a 1 1/2hp with similar amp requirements (which many of the 3ph motors are) I say this because I am seeing this written about being done more and more. In my own case I have bought 3 different machines - 2 lathes with a 1hp and a 1 1/2hp,  and a mill with a 2hp - and used my existing mill 2hp VFD to run them off an extension cord for testing/demonstrating with out any hint of a problem.



I also can't _exactly_ back it up. I've never tried swapping different motors of different ratings without entering nameplate data and autotuning. For all I know, it could work just fine on the fly like that. However, I have set up a lot of VFDs on a lot of motors, and read a lot of *caution: _____*, *warning______*, and *note:_______* in VFD manuals that contributes to what I'm saying. If those features and parameters were not important, they would not be part of the VFD. The VFD needs to know specific things about the motor that it's controlling, like inductance, resistance, etc. Different motors of the same model, manufacturer, and production batch can different inductances. Inductance limits how fast current can rise. VFD needs to know fast current can rise in the specific motor, or else it could overshoot and kill the IGBTs. - that's just the one example I can think of ATM, I'm sure there are more good reasons.


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## Brandon (Nov 8, 2012)

UPS just dropped off my new Teco VFD, I slapped it on real quick and it works awesome. All three legs are pulling 6 amps and the motor is happily humming away.  Now all I have to do is hook it up right and make it all look pretty.

:ups:
Thanks again to everyone.


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