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Ok, who's the electrical expert?

My edge sander is tripping the circuit breaker constantly. The longer I wait between uses, the more time I get before it trips, but it's gotten ridiculous. Letting it sit overnight buys me about 5 minutes, and walking away for an hour gets me a minute and a half.

I've tried other circuits with nothing else running on them. It's the sander. I think it's having a harder time turning and that's creating a higher than normal load which is worse when the motor and breaker are warm. Of course, I'm no expert. I don't hear any noise that would indicate worn bearings or the like. Could this be a bad run cap?

Thanks in advance for any help.

John

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John Watkins
CNC Guitar Parts

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Wisdom is justified by her children

John, I’m no electrician, but you are correct, something is causing a greater flow a amperage.
And, unfortunately, there are a lot of reasons for this happen, and it’s difficult to diagnose without
an on site inspection.

I think there is someone here at the olf who is an electrical engineer, who would be of more help!

A couple of questions though;

What is the rated amps for the sander?
What is the rated amps on the circuit you are using?
How long has this been giving you trouble?
Do you smell anything when you operate it?
Have you noticed a decrease in rpm’s from the way it used operate?

Robert

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Everything has beauty, But, not everyone see's it!

It's not completely clear whether you mean that it's blowing the circuit breaker at the panel, or the thermal overload breaker on the machine/motor.
At any rate, I second Max's idea about overheating as the first guess.
Take the sanding belt (and drive belt if it uses one) off, give everything a good cleaning (blow the motor out with compressed air), and then see if it will run without overheating.
With the sanding belt off, you can easily check the non-driven roller for problems as well.
Keep us posted- stuff like this is a pleasant change from my usual problems which are of the patchy finish or mystery binding crack type!
Cheers

John

John, I must have posted the same time as Max1157.

That’s a good place to start. It’s the simplest approach and just may solve the problem. A good
cleaning with compressed air will usually do well, where the brushes are in contact with the armature.

Robert

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Everything has beauty, But, not everyone see's it!

Guys, thanks for the quick responses. The motor is 20A and the circuit is 30A. It's one of the bigger motors in the shop. Coincidentally, it's the exact same motor that's on my bandsaw as they are the same brand and the bandsaw only blows the circuit under really heavy loads. The edge sander will blow it if you just turn it on and walk away for a couple of minutes.

The motor is pretty well sealed, so there isn't much opportunity for cleaning it out. The moving parts are free of dust or obstruction and I can spin it easily by hand when it's off. There's no "train transformer" smell when it runs.

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John Watkins
CNC Guitar Parts

I think as a temporary solution, I'm going to try rewiring it for 220v and plug it in where my vacuum pump normally is. That's a 30A 220V circuit with nothing else on it, so if it blows that, we'll know there's a serious problem.

I have about 4 hours of edge sanding that I have to get done today, so at least that'll get me back in business right away.

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John Watkins
CNC Guitar Parts

John,

I think you had it in your first post. Bad run cap. They often cause the motor to draw excessive juice when bad.

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now known around here as Pat Foster
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http://www.patfosterguitars.com

If it is a bad run cap, the 220 change may not help.  I used to have an old AC compressor that would, every few years, start blowing the circuit, and it was the run cap in every case.  When replaced, it would give me a few good years.  I finally replaced the whole system, but did go through several run caps.

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Waddy

Photobucket Build Album Library

Sound Clips of most of my guitars

No one asked what size the wire in the circuit to the sander was. So, what size is the wire from the breaker to the sander plug? Should be #10 AWG, for a thirty amp circuit.

Secondly, is the sander hard-wired or plug connected? If plug connected, is the plug and receptacle in good shape? If not try hard-wiring the device, that will eliminate an over-heating plug.

Circuits are only designed for 80 percent of the stated size, so it won't overheat the circuit breaker and continually trip. 80 percent of 30 amps is 24 amps. John you stated that the motor was 20amp/110volt so that is in tolerance.

Again, wire size is critical, does the connecting cord to the machine get hot? If so, it may not be large enough, it should be #10 AWG also, check that.

Fifthly, repeated tripping of an otherwise good circuit breaker in a panel, can degrade it's performance. They are cheap, replace it and see if it helps. An electrician service call ain't cheap, breakers are, try it.

Good luck with solving the problem John.

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http://www.dickeyguitars.com

I have the older Powermatic sander (same as a Jet) and had to wire it 220 after overheating melted part of the wiring. It still tends to overheat, but I don't trip breakers anymore since the conversion. You can sort of tell when the motor is getting taxed and let it cool down. Unfortunately, these motors are not made for heavy duty usage and loads.

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"I want to know what kind of pickups Vince Gill uses in his Tele, because if I had those, as good of a player as I am, I'm sure I could make it sound like that.
Only badly."

Hi Don.

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http://www.dickeyguitars.com

Guys, thanks for the additional input. Don is spot on. It is a Powermatic and switching it to 220v has (at least for now) completely fixed the problem.

It has no run cap, but I took the start cap out and went to my local electric motor repair place where it tested fine. Go figure.

Thanks again for all the help. For now, I'm back in business. Now to burn that midnight oil and try to get back on schedule....   

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John Watkins
CNC Guitar Parts

BTW, when I fulfill my dream of having VFDs on all of my tools, this won't be an issue!   

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John Watkins
CNC Guitar Parts

John--I occasionally lust after a VFD on my edge sander in particular, even to the point of considering the required retrofit with a three phase motor. It would be great to slow it down for some jobs to prevent burning and there are even times when reversing would be handy. Sooner or later, the machinery builders are going to figure this out. The VFD's do require 220VAC single phase at a minimum for conversion to 3 phase.   I'm thinking that the less expensive three phase motors would partially offset the cost of the VFD on OEM applications.
I believe there are some 120VAC variable speed controllers out there now but the cost is prohibitive.
Nelson