J/P motor tripped - what should I check
#11
This morning Ken Vick was over to take advantage of the 14" capacity of my "new" Mini Max J/P. He had some very nice 9 - 10" mahogany boards to joint. I set the machine up for about a 1/32" cut and Ken pushed them through and I caught them on the outfeed end. I think he had taken about 10 passes total when the motor suddenly stopped in mid cut. First I thought he might have accidentally hit the off button, but he hadn't. Then I found the machine wouldn't start again when I pressed the start button. After maybe a minute I tried again and it started back up and ran fine for the remaining couple of passes he needed to make.

The prior owner installed a 16 amp thermal overload relay on it at some point (from SCMI which makes Mini Max). I don't know if it was to replace one that was originally on the machine or he added it. He also installed a new start/stop switch at some point. The motor is 230 V, single phase, rated at 16.5 amps. We certainly weren't asking much of the motor when it quite running. Anyone have a clue what's going on and what to check? Thanks much.

John
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#12
Loose connection on switch? Bad run Cap?

Once Favre hangs it up though, it years of cellar dwelling for the Pack. (Geoff 12-18-07)  



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#13
Turns out that what I thought were two separate units (overload protection and new start/stop switch) is actually one unit, an AEG Mbs25 with an overload relay adjustable from 10-16 amps. I checked and it is set at 16 amps. The motor is rated at 15.6 amps, which I assume is at full load. The motor plate says it is 2.2 KW, which converts to 2.9 HP. The AEG literature says the MBS 25, 10-16 amp is for a 2 HP motor at 230 V, and for a 3 HP motor it should have a 16-20 amp relay.



Could it be as simple as the 10 - 16 amp overload relay being too small? I don't have an ammeter so I have no easy way to check the actual amp draw. Thanks.

John
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#14
I think you're on to something. Any kind of circuit breaker/overload device that is near its limit can trip on repeated loads. And motor startup pulls a lot of current.

However, if this is the original equipment, they might have been trying to tell you something. I probably would live with the occasional trip unless it's a real problem to you. And even then, I am not sure I would increase the amps of the overload
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#15
Yup too low. Need a new higher amp overload. I remember a post from way back where someone had the same problem with theirs.

Had an ac guy keep complaining that there was something wrong with the power to his RTU and that's why it kept tripping the overload. Come to find out he had it adjusted too low. He kept thinking the numbers on that unit referred to actual amps when it was just 1 to 10 on the unit. Funny how everyone blames the electrician when their equipment trips breakers or overloads...
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#16
I borrowed an ammeter from Ken Vick and the motor read 16.25 amps under no load and around 18.5 - 19.5 when I planed a board with a pretty healthy cut. I rechecked the plate on the outside of the machine and saw it said 16.5 amps, not 15.6 as I first thought. Dyslexic I guess. So then I decided to open up the machine and check the plate on the motor itself. Hmm. 18.5 amps.

So unless I'm missing something, I need a starter with a higher overload rating, yes?

John
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#17
What's the voltage at the receptacle (or even better, inside the motor control) under heavy load and when it's off? The voltage under that load may be sagging unacceptably under load, causing an increase in current over what would be needed at a higher (less mushy) voltage, and the tool may benefit from a shorter and/or heavier branch circuit.

And did you turn the adjustment up higher? Those little adjustable overload threshold controls are not likely to be all that precise, and may have drifted over time.
Tom

“This place smells like that odd combination of flop sweat, hopelessness, aaaand feet"
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#18
Voltage inside the AEG unit was 239 - 240 V with no load and 238 - 239 V under load planing. The receptacle the machine is plugged into has a 30 amp line feeding it as I used to run my 5 HP planer from it.

The overload adjustment seems very light, almost like nothing is moving underneath. I have it set at 16 amps but it will go higher into a zone with no markings. I don't know if that means it really is going to a higher amp rating or nothing is happening. Any idea? I suppose I could turn it down to 10 amps and see if it trips quicker which should prove it's doing something. Or?

Thanks all for your help.

John
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#19
I didn't realize it was a 240V machine. It's pretty hard to pull the voltage down with 240V, as it's the percentage of rated motor voltage that counts. And you're real close.

If it were me, I'd turn it higher and give it a go. You're casting about as it is, by necessity as there's no real calibration to that OL unit (unlike separate heaters in NEMA controls), so why not cast a bit higher? You've satisfied yourself that you're not overloading or otherwise passing excessive current through the motor, so turning the threshold up a bit isn't going to hurt anything.

You certainly can turn it down and see what happens. I might also do that, just to get a feel for what the response is. But that's me. I do things like that. Often when I shouldn't.
Tom

“This place smells like that odd combination of flop sweat, hopelessness, aaaand feet"
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#20
Thanks Tom, much appreciated. And I have a high level of curiosity, too; definitely not always a good thing. But I'll give your recommendations a go, both higher and lower and report what I find.

John
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