Single Phase electric motor problem (No load high current and heating) 2

[AR.]

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

 

[AR.]

Some more photos.

 

[waross]

First, this is a professional forum, not a DIY forum.
Second:
Find out why the starting winding is staying in the circuit.
That is the issue 98% of the time.

I can hear that it operates and due to good start,

That is trying to prove a negative.


Bill
--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[electricpete]

> as it is class B motor, it can reach to 80 C.

just as a point of clarification, class B insulation is rated for a continuous 80C temperature rise above ambient temperature of 40C...so 120C.

=====================================
(2B)+(2B)' ?

 

[AR.]

Thanks for your reply.
I am an electronic engineer and trying to change my filed. that's why I sent my post here to ask from professionals.
how can I check if that is the fault of start coil.
is it possible to disconnect the starting Capacitor and make it run by turning the shaft and then measuring the input line current?

thanks

 

[dArsonval]

Without knowing the amount of potential applied to the motor during the bench test, the measured 7.2 amps is likely insignificant.

Guessing the motor is rated somewhere around a 1/3rd horsepower and may even be an OEM device built for a specific purpose
noting the style of die-cast end-bracket barely visible off to right of the rotor in the photos.
The device vaguely appears to have a threaded shaft end as well. (It's not likely a pool pump motor for they would have a locked drive-end
bearing and photos do not show a bearing retainer behind the front bearing.)

Thank you for the very clear photos. A photo of the nameplate would have been the most useful.

I don't believe anything is wrong with the motor.

John

 

[AR.]

Hi
thanks for your replies. Actually, it is a CGE electric motor. internal condition sound good to me and based on what I have found on theories, it sounds good except the No-Load current and generated heat.
I didn't expected too much current without Load, even higher than its rated full Load current mentioned on the nameplate.
I run this motor on 115-120 V AC and I know very well the Ohm laws. but based on my knowledge it should take too much current.
based on the nameplate, it does not sounds to be an OEM motor but if it is as you said, you are right and it can take what ever it want.

I attached the nameplate photo just for more info, if it helps to clarify more issues.

 

[waross]

Measure the capacitor current.
It should drop to zero Amps if the centrifugal switch is working properly.
The second possibility is that the start and run windings are interchanged.
No load current on a small motor is often more than expected due to a poor power factor.
No load current (7.2 Amps), greater than rated FLA (6.4 Amps) is too much.

Bill
--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[AR.]

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?
for me 7.2 Amp is high for a 1/3 HP motor.

 

[zlatkodo]

Hi,AR.

Unlike three-phase motors, single-phase motors are not kind of general-purpose motors.
Each of them is designed to work on a strictly defined machine and for a specific load.
Theoretically, an ideal single-phase motor should have a different winding and capacitance for each particular value of load.
That's why it is not recommended to run the motor at no-load or at small loads at all.
In short, in your case it is perfectly normal for the NLA to be larger than the FLA.
Don't run this motor at no-load conditions.

More on Winding Design and Motor Repair

 

[waross]

In short, in your case it is perfectly normal for the NLA to be larger than the FLA.
Don't run this motor at no-load conditions.

I gotta throw the BS flag on this.
There is not that much difference between the theory of a running single phase induction motor and a running three phase induction motor.
From the pictures and the nameplate that appears to be a general purpose motor.
Despite the resistances, the start and run windings may be interchanged.
Check the windings by energizing with a small battery and testing with and a compass or hack saw blade.
The motor may be failing.

Bill
--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[AR.]

I already checked the coil and it seams that they are really separated. I did beep test and tested with a power supply.
it is a general purpose motor and based on the pulley that I founded on it, it should be used as a blower fan.
there was a kind of V-belt pulley already installed on the motor.
I have not if I can hack it with a table saw but the torque sounds ok for me while I have never tested it with load.
As I am going to use it for a belt sander (needs some modifications to adapt it to machine) I preferred to be sure about it functionality and they doing the modifications.
At this time I am nut sure if I can use it or not.
I searched almost all over the internet, consulting with you and others as experts, checked all the error sources as much as possible but still it is runs at high current with lo load.
Based on my knowledge, it is strange except if the running coil took too much current or have been changed and does not respect the nameplate (which should not be happened if I trust what I hear from the guy that bring it to me).

I am still working on it but honestly I have no more ideas what is wrong with it!!!

 

[waross]

Have you checked the applied voltage?
Your voltage may be too high.

Bill
--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[AR.]

as I live in Canada, the residential power voltage is 120 V. I will check it today but I would say it is is 120 V.

 

[waross]

120 Volts is fine but some wire service providers push the voltage up to and past the limit to maximize the KWHrs and thus their profit.
If the voltage is running much above 120 Volts, your motor may be saturating.

Bill
--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[zlatkodo]

Hi, Waross,
I am sorry for this BS flag.
I don't think I deserved it.
It seems to me that you haven’t dealt much with single-phase motors.
Otherwise you would know that the NLA of single-phase motors is very often close to or equal to or higher than the FLA. If higher than the FLA, as the load increases to the rated value, the current drops to the FLA value.
That is why it is not good for such a motor to run with no-load, because the winding can burn out.
It’s not that hard to check it.

Visit our web site

 

[AR.]

Thanks Zlatkodo for your explanation.
Would you please let me know what is the reason for such a reaction from Motor.
it does not make scene. on theory, the motor is designed for a specific RPM with some limits.
what defines the limits are the coil wiring and some other factors. increasing the load should increase the AMP to keep the motor RPM at its nominated RPM.
why should it run at such high current during no load test?
also would you please let me know how could we define the proper load for a general use motor?

I will try to add some load on shaft and see how the current changes.

 

[LittleInch]

This post seems relevant?

https://www.eng-tips.com/viewthread.cfm?qid=418737

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[electricpete]

> Otherwise you would know that the NLA of single-phase motors is very often close to or equal to or higher than the FLA.

> Would you please let me know what is the reason for such a reaction from Motor

Jumping in on that question. The ratio of NLA / FLA in general depends on speed (lower speed have higher ratio) and size (smaller motors have higher ratio) again in general. One of the reasons for the variation with size is that when you scale down motor size, the airgap does not shrink in proportion to the rest of the motor.

But how would the NLA/FLA ratio ever get above 1? That's a head scratcher. I guess if there were a run capacitor then the motor could end up with a lower power factor (leading) at no load than at full load which would be a factor to nudge the current in the direction of higher at no load... but that factor still has to overcome the increase in load component of current which seems unlikely to me (but you never know).

Are there capacitors in this motor, and how many?

=====================================
(2B)+(2B)' ?

 

[AR.]

yes, there is only one start Cap on this motor which is 400-480 MFD - 110 VAC.
I measured the current passing trough it and after running it drops to 0 A (0.06 exactly)