Single phase Electric Motor heat and current problem


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Old 02-28-21, 05:11 PM
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Single phase Electric Motor heat and current problem

Hi
I have a single phase electric motor. I got it from a friend that did not use it for a while. I cleaned it up and it sounds that all components are ok. I removed all dusts and add some oils to the bearings.
bearings are ok. I cleaned the connectors and checked them all and all sounds good.
I did a beep test to find the connections between coils and wires. what I find is two separated coil, one with 2.5 Ohm resistance (blue - Yellow) and second one with 3.1 ohm (Black-Red).
I far as i understood, the 3.1 ohm coil is the starter coil as it goes to starter capacitor. the motor runs well and no noise comes out from motor. it turns well and the torque sounds good.
Here is the problem:
the full load current is 6.4 A based on the motor characteristics label but when I run the Motor with No load, its current reach o 7.2 A !!!!
after 5 to 10 min operation, the motor case get hot. as it is class B motor, it can reach to 80 C. But I think there might be something wrong as it took too much current under no load test and the generated heat sounds weird.

I though it might be due to centrifugal switch mechanism and electrodes that do not well operate.I tried to check if the centrifugal switch. I can hear that it operates and due to good start, it should be fine but I can not check if the start coil well disconnect or not (should be ok)

some photos is attached to see the motor conditions. the schematic is based on what I tracked on wire management board and it sounds ok for me.

I did all I can based on my knowledge and experiences (Not too much) but I do not know what could be the problem.
any comments or idea is highly appreciated.
Waiting for your feedbacks


 
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Old 02-28-21, 05:44 PM
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The actual running current of a motor may not match exactly the nameplate current. There are many variables that will affect the running current, including voltage.
 
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Old 02-28-21, 07:04 PM
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I Also check the voltage and it is running at 115V.

Any other ideas?
 
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Old 02-28-21, 07:43 PM
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It is exactly 115 volts? Not 120? or 110?

Honestly, I do not believe there is anything really wrong with the motor.
 
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Old 02-28-21, 07:55 PM
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well it varies a bit but even with those variation, I recalculated and the current passing true the lines should be less than 6.4 A.
as far as I know, 6.4 A is full load rated current. Right?
Normally the motor should draw less current when there is no load. right?

there is only the shaft (without any load) when I measure the current and it is 7.2 A on input line. for there is something wrong.No??
 
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Old 03-01-21, 04:53 AM
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Disable the start winding; then push start the motor with only run winding live. Then verify current. Your issue could be a run winding defect, or start winding not disconnecting with rpm,
 
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Old 03-02-21, 07:24 AM
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I did some more investigation. Now I can confirm that the Red coil (Red-Black wire) is the start coil and the yellow coil, yellow-Blue wire is the running coil.
I assembled the motor and measure the Cap current when the motor was running and it gave 0.065 A.
still the No load current is around 7 to 7.2 A.
I measured the motor case temp with a direct touch sensor and after almost 10 min it reached to 65 C.
the Cap current confirms that the centrifugal switch works fine and I really can not understand why the No load current is high like this while on the nameplate it is mentioned FLA 6.4 A. is it possible that they gave wrong value?
 
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Old 03-02-21, 02:22 PM
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any way to measure rpm? What you see is consistent with a winding short.
 
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Old 03-08-21, 07:00 AM
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Hello everybody,
first, I would like to thank everybody for taking time and helping me to solve my issue.
Here is another brief of what I have done last weekend:I disassembled the Motor again, check all the mechanical issues.

1- I used multimeter beep test and ohm test to check the wires for running and starting coils. they are as before and no short between coils (run and start) and between coils and Motor case or stator.
2- I checked the Start Cap current after motor is running, normal operation and there is no current passing through the cap.
3- when the motor was disassembled, I tried to find if the centrifugal switch works fine or not and when the motor rotate and switch acts, it release the running coil and it sounds ok.
4- I visually check the centrifugal switch operation mechanism when was running (after assembling it for last test) and it was obvious that it release the contact and was able to see it when motor was running.
5- I checked the voltage when motor was running and it varies around 121 to 123 V AC.
6- Bearings and other parts sounds good to me.

Unfortunately I have no more hypothesis to check. I can not say that the nameplate gives the wrong info as it is CGE motor.
I do not want to give up but I have no more ideas.

thanks
 
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Old 03-08-21, 02:50 PM
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do not want to give up but I have no more ideas.
How about accepting that the motor just draws .8 amps higher than the nameplate and that is just the way it is. As mentioned earlier, I suspect there is nothing wrong with the motor and your troubleshooting confirms that.
 
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Old 03-09-21, 05:11 AM
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A 1/3 HP motor drawing some 800 Watts unloaded is not healthy. Your Ohm measurements, while not a bad idea to detect shorts to the frame and from start to run wires, will not be good enough to detect a turn to turn short. Turn to turn shorts are not unlikely in an older motor.
 
 

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