Rotary Phase Converter running hot

borne2fly · Jul 20, 2017

American Rotary Phase converter, 7.5hp. It's too hot to touch after running for maybe 15 minutes, even with no output load at all.
I've been running it from the 220V dryer outlet for ages, but only recently noticed it heating up. Has anyone else seen this sort of thing happen?

Porschefix · Jul 20, 2017

I have one too, not running that hot. Give American rotary a call, they have always been helpful to me. Phase Converters | Power Transformers | Power Accessories | American Rotary

redlee · Jul 20, 2017

Have you checked your power supply?
Might not be the converter at all.

Gordon Heaton · Jul 20, 2017

What's the temperature where the idler is located? If hot there, have you checked it before under the same conditions? The idler will warm up even when unloaded.

Rescue35 · Jul 20, 2017

Electric motors typically get to hot to touch. I've seen plenty running 150-165 F for years.

Sent from my SAMSUNG-SM-G890A using Tapatalk

metalmagpie · Jul 20, 2017

If it didn't used to get hot but now does, you most likely have a problem that you should fix before proceeding. I suggest you don't ignore this.

I take it the noise is just the same? This isn't some bearing heating up?

Is the input fused? If you have a short inside it should be blowing fuses if so. If not, go inside the box and find where the power wires come in. They probably connect to some capacitors. Look for caps with swollen cans. Use your nose and smell for hot electric stink. Look for frayed or loose wires. Could be a mouse nest, or even a wasp nest. It's OK to blow things out with compressed air. Take pictures and post them but do NOT use photobucket to do so. Don't worry, it can be fixed.

metalmagpie

jim rozen · Jul 20, 2017

This is an easy one. Look at the nameplate on the idler. It will list a working temerature that is
predicated on the wire insulation inside the unit. Call this T1

Put an actual thermometer on the outside of the case and measure the actual temperature of the
unit while it is working. This is T2

If T2 less than T1, then your job is done. There is no problem. Report back it T2 greater than T1.

johansen · Jul 20, 2017

my guess is start capacitors left in circuit. check the contactor/start relay. the caps will probably be hot as well.

SeeandSee · Jul 20, 2017

All my rotary converters run hotter with no load than under load..

moonlight machine · Jul 20, 2017

My 20 hp AR is warm after using it all day. You can hold your hand on it.

pianoman8t8 · Jul 21, 2017

Both my 10hp and 20hp RPC's, when running all day, are only "warm". They are also fan cooled though. Does it sound any different than normal? If your start caps are left on due to a bad relay, you should be able to hear that.

Dodge1 · Jul 21, 2017

Had same result... when you first start up, the circuit should switch in the start or boost capacitor. As soon as the output voltage across the motor climbs above about 80-90%of V out. (This depends of either it being 230 volt 3 phase or 415 volts 3 phase) then and on reaching this level, you should be able to hear the start contactor switch out and the boost light if you have one go out.
If you don't have a light or cannot hear the noise of the contactor switching out check the output voltages phase/phase. If the start capacitor is in all the time then one phase voltage will be significantly raised.
It needs to be checked so that you don't burn out your motors or cook the phase converter transformer,

FredC · Jul 21, 2017

Just had an irrigation pump motor go out. It was an open frame motor and our pesky mud dobbers built a nest on the rotor, water hit the nest and it sand blasted the windings as it was flying out.
If your phase convertor is out side and has an open frame look in to that as well as the capacitor issue mentioned earlier. Also check the windings to ground resistance, you may have a partial short.

Bill D · Jul 21, 2017

I would use a shop vac to remove any dust around the motor. feel for a good airflow while it is running. I do notice my machines run hotter when it is over 110 outside. Part of that is ambient temperature and I think some is the power company has a hard time keeping the voltage up when air conditioning demand goes up so high.
Bill D
Modesto, CA

comstockfriend · Jul 21, 2017

SeeandSee said:
All my rotary converters run hotter with no load than under load..

Yes, my Ronk RPC says in the instructions that better to shut it off if not running any equipment on it. Efficiency drops and heat builds up.

Bob-J-H · Jul 21, 2017

Have your motor meggered, the windings may be going bad. Bob

SeeandSee · Jul 21, 2017

comstockfriend said:
Yes, my Ronk RPC says in the instructions that better to shut it off if not running any equipment on it. Efficiency drops and heat builds up.

Yep, my Haas Rotary manual sez the same thing. My brother re-wound large mining motors for awhile and he said that "back-splash" when not under load causes heat in the windings..

JST · Jul 21, 2017

comstockfriend said:
Yes, my Ronk RPC says in the instructions that better to shut it off if not running any equipment on it. Efficiency drops and heat builds up.

The issue probably is balance caps. They raise voltage by partially resonating the circuit, and quite a bit of current can flow through them, and the windings. When you have a load on it, the resonance is less effective, and the voltage across/current through capacitors and windings is reduced. Depending on how much the voltage is boosted, current can be near full load value with no load on the converter.

Same general effect as raising the mains voltage, because the mains voltage IS effectively raised.. You can get to levels that really work the stator iron, or even saturate it.

Newman109 · Jul 21, 2017

My homebuilt RPC uses a 7.5 hp Baldor motor that I got cheap at a second-hand store. It was new old stock in the original box. When first run, it ran rather hot, couldn't hold your hand on it. It was also noisy with an unpleasant whine.

I disassembled the motor and discovered that the grease on each of the open roller bearings was caked and hard. I cleaned them and re-lubricated with the recommended grease; Mobil Poly Rex. (Blue grease).

That cured the problem. No more undue noise and it runs very cool.

Just a thought to check the condition of the bearings. If they are sealed, see what shape they are in.

All other suggestions about balancing caps or start caps remaining in circuit are certainly prime suspects.

borne2fly · Aug 21, 2017

My apologies for not responding sooner, got swamped by work. I want to thank everyone for your suggestions, and I have managed to follow up on a few.
I checked the phase voltages .... 238V, 251V, 248V. The weakest of the three (238V) was the single-phase input from the outlet. Not sure if this voltage imbalance would cause a heating issue. Also inspected the caps ..... they all look like new, no leaks, no bulging, etc. The relay kicks out on startup as it should, so it's not a stuck relay. I have yet to actually measure the temperature, that's next. I'm starting to think this thing might be running properly, and I'm just worrying about nothing. Wouldn't be the first time.

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