3 phase motors running in reverse suddenly - help

Today I went to use my planer (3 phase, 9 HP) and when it wouldn’t feed the board, I realized that the motor (cutterhead and feed works) was running in reverse. Strange. There was way more contact “chatter” (clicking) than usual from the starter when starting the planer with subsequent test starts to confirm motor direction 2 or 3 times it clicked a lot, started to rotate for 2-3 seconds then turned itself off. It did eventually start and run but was confirmed to be running in reverse.

Confused, I then tested the table saw (3 phase, 5 HP) and had no problems starting it but it was also running in reverse. This would indicate that the change is coming from the rotary phase converter - detailed below.

I have not switched any leads in the last week since I last used the machines (that were running in normal rotation) and I’m the only one in my shop.

I am familiar with changing 2 of the leads to change direction (normally) when wiring a 3 phase machine.

I have a Kay Phasemaster RPC that is rated for up to 10 HP from any single motor. It is on a 60 amp single
phase breaker from my 200 amp panel and has never given me any issues before. It has always started the planer (largest load by far) just fine.

What would cause sudden change of motor rotation in this situation??

I called my electrician and chatted with him about it; he seemed stumped. he walked me through a few multimeter tests that I did on the RPC itself - ohm test of the fuses, checking voltages on the 3 phase output side. Unless I’m an multimeter idiot, then I think the fuses tested good. On the RPC output side, the voltage from 2 of the legs was steady fluctuating around 240 (+/- 2) and the 3rd leg tested closer to 230 V (+/- 2).

I have not changed any leads on plugs/receptacles at this point. I could, of course, try that on the (1) 3 phase 30 amp receptacle I have on the output side of the RPC and see what happens, but figured I’d ask here before I did that.

I can’t understand why the direction change would happen suddenly like this on its own. The starter clicking / chatter / resistance / whatever you want to call it was also new and seems related, but I’m no electrician and only have the most basic understanding enough to wire simple things like receptacles, plugs and sometimes switches.

Any help is appreciated. Electrician can’t come until Thursday at the earliest and the downtime is not so good for the commission work I was starting on when this happened! Thanks in advance !

is the rpc spinning backwards also?

very strange.

Adam, thanks for the reply. I don’t know how to visually see which way the RPC motor is rotating either now or before as its integrated into the box of the entire unit. There are some cooling vents on either end of the enclosure but the motor is pretty much fully enclosed.

Not sure how one would test that other than visually identifying and I’ve never made note of which way it spins previously to compare to now as you can’t see it.

It works properly now. I reset the 60 amp single phase breaker to the RPC (which I had already done once earlier before posting) I also went through each connection at all cords, plugs and receptacles and tightened everything down super tight. Nothing felt loose, though. I didn’t change locations / wiring of any leads.

Both the table saw and planer spin in the forward direction and not getting any starter chatter / resistance on the planer starter now, which is normal.

I’m thoroughly confused, but happy (for now) that it seems to be working. If anyone has any thoughts or theories I’m all ears and would be good to continue the thread should this pop back up for me or anyone else in the future.

I would give Kay a call. Not that I think there is anything wrong with the rpc but they know the converter and 3 phase

Sounds like it was single phasing....Rod

Quote:

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Originally Posted by Rod Sheridan

Sounds like it was single phasing....Rod

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Rod, I read about this online when trying to troubleshoot but do you care to elaborate on how this could be happening?

Thanks,

While it’s working check the 3 phase output from the RPC again and write it down for future reference.

Hi Phillip, I suspect that the starting capacitors didn't engage and the phase relationship of the derived phase was very close to one of the other phases and the RPC started in reverse....Rod

Thanks Rod for that explanation.

I called Kay Industries and talked to a helpful fellow there who walked me through how to test the capacitors with a multimeter. The RPC was manufactured in 2005 and I’m the second owner, as far as I know and it looked like the riveted lid to access them had never been opened.

My multimeter testing concluded that 6 out of the 8 total caps were faulty and I placed an order for (8) new ones from Kay that should arrive Friday - about $250 worth of damage. I will check back in after I have the new ones installed. Hopefully that’s the problem and the new caps will resolve it.

Rod is absolutely correct as you have discovered. His explaination was perfect. That is the downfall of large caps that get used often, they do tend to wear out over time. I'm glad you found the smoking gun, it sucks having an issue like this and not having an answer as to what happened.

You might want to get one of these, or a similar tester. I used one frequently when working on 3 phase equipment. Now retired, I gave mine away.

Charley

amazon.com/Phase-Sequence-Rotation-Tester-120-460VAC/dp/B00OT5CPOQ/ref=sr_1_4?crid=2FKW1WRX3G1JD&dchild=1&keywords=ph ase+sequence+and+motor+rotation+tester&qid=1616727 740&sprefix=phase+sequence%2Caps%2C177&sr=8-4

I replaced all 8 caps and fired it up. It seems to be be operating fine now. There is also reduced “chatter” in the motor during start up. There used to be 1-2 seconds of a fairly abrasive chatter when starting the RPC. After replacing caps, I heard the same sound only for a split second.

Thanks to all for the help in this thread. Calling Kay Industries was tremendously helpful and easy...go figure! I’m so used to troubleshooting old machines and things without any factory support (mainly bc they no longer exist or support the vintage stuff) that it wasn’t my first thought to call the manufacturer.

Good to hear.I also have a phase master RPC and have spoken to the guys at Kay about my electrical service. They are very knowledgeable about their products and it’s needs.
A great US company.

there was a post on here a while back that said if you have auto braking on machines it toasts caps and there is some ongoing maintenance routine for them.