RPC idler motor running hot...why???

Quick question, I purchased and American Rotary RPC panel for a 5hp idler motor. I hooked everything up and fired the RPC up. It is not under any load at this time. After about 30 minutes of running the idler motor seems to be running at a very,very warm temp. You won't burn your hand if you touch it but the temp. seems to be running higher that it should. The wiring is sized right and it isn't warm at all. The current temp is about 40 degrees so it isn't warm in the garage. The bearings in the motor are new and I gave the motor a good cleaning so it spins freely.

Any thoughts?

E

Installing new bearings means you disassembled the motor. Check that you
assembled it with the cooling fan, if any, facing the right direction. Were there
any spring washers, spacers, etc on the rotor spindle that are in the wrong place?

You can't put your hand on a surface of 120 deg F, so the surface is below this. The motor is running at about 10% of its full power i.e. 370W, so don't expect it to be cold. Don't worry its OK.
Frank

chuckey said:

You can't put your hand on a surface of 120 deg F, so the surface is below this. The motor is running at about 10% of its full power i.e. 370W, so don't expect it to be cold. Don't worry its OK.
Frank

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You won't burn your hand if you touch it but the temp. seems to be running higher that it should. The wiring is sized right and it isn't warm at all. The current temp is about 40 degrees so it isn't warm in the garage.

Click to expand...

Sounds like he is running at least a 60* temp rise. That sounds pretty hot to me for an idler.

Is this motor TEFC?

This is one thing that is nice about Lincoln motors is that they are open and run cool. Mine hasn't shut down in many days and it aint 10*F more than ambient - if that.


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Think Snow Eh!
Ox

Normal reason for a hot pilot motor is phase imbalance, check the voltages between the motor terminals. The balance figures claimed on the web site certainly won't cause a hot motor.

You say you purchased an RPC panel. Does this mean you have supplied your own pilot motor? If so it may well need to be tuned to the system by adjusting the internal capacitors. Would be done at the factory for a complete system but a system supplied without motor will come with generic internals which may well not suit your motor.

(In the UK such capacitor tuning is routine for static converters to generate a third leg. An RPC is, essentially, a UK style static converter tuned to its pilot motor to provide the third leg. Devices which simply start the three phase motor and disconnect to leave it running on single phase would never be considered converters over here. All designs, however crude, at least attempt to provide some reasonable approximation to a third leg. Single phase running will eventually destroy the motor.)

Clive

Running on 3 ph will eventually destroy the motor as well for that matter.


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***When your hot'cher hot!***
Ox

On the springs wires, etc. and the fan facing the right way...I checked and double checked to make sure it was correct. It is good to go.

E

Chuckey, that is good news to hear. Thanks for the info.

E

The panel was provided by amercan rotary and I supplied the idler. it is a 5hp dayton that was once on an air compressor. It is not a TEFC and has a very open air body style. The imbalance perhaps might be the issue. I hooked up the wires and they gave this info.
These were the voltages I got measured across the legs given when the 3 pairs of wires from the idler motor were hooked up in the different combinations of the 1-7 wires from the motor, the 2-8 and 3-9.

T1-T2 T1-T3 T2-T3
244 255 258
245 255 259
244 254 259

I am assuming when people indicate that the lines should be balanced all three numbers should be the same voltage. Is this correct? The instructions from American Rotar say to hook up the T1,T2 and T3 legs in different combinations with the wires from the idler motor to find the best balance. This is a little confusing just because I thought you achieved the line balance with swithcing out the different run capacitors.

Am I missing something here and does this lend any clues to the heating up of the motor? I've never had a RPC before so I'm not sure if they should run hotor or cooler than a regular electric motor. I have a single phase 3hp motor on my tablesaw so I guess I could run it for 20 min. straight to see if it gets warm.

E