Single Phase Motor tripping overload

[ptonsparky]

Generally greasing the motor bearings are a bad idea. We don't do it correctly and it's too late by the time the we get called in. Time to replace them if greasing changes the sound.

 

[TwoBlocked]

Thanks again for all the tips, so the problem is solved and here is what we found.

I asked the owner if he had done any preventative maintenance and greased the bearings. He hadn't, so he did that and said it immediately sounded different. That seemed to help on amperage but only slightly.
My journeyman went out and tested the run caps, they were both bad, replaced them and now we are running around 28 amps.

So my new question is, does anyone have a good link or resource for better understanding run capacitors.
Before this point, I always just assumed that the motor wouldn't run as well (or long) as it was before tripping out the overloads if the run caps were bad.
As well as what happens if run caps aren't sized appropriately, I assume it won't run at its optimal performance. But will you get the same results if the caps are undersized verses oversized?

This link might help:

Motor capacitor - Wikipedia

en.wikipedia.org

 

[Jpflex]

Hello,
I have a customer that has a 10HP single phase 230 volt motor on a dust collector that trips out the overload that is built into the motor (reset button on the side of the motor junction box). It trips out after about a half hour of running.
The voltage is good (between phases and phase to ground), amperage is 41 amps per leg and the FLA on the nameplate is 39.
The motor is 3 or 4 years old, and we can easily spin the motor shaft by hand with everything hooked up.
This is your mission if you choose to accept it.

The motor FLC according to the NEC table will be 50 amperes.

Is the motor running 1/2 hour unloaded or is it belted running a load?

Also when you say the phase line voltage to the motor is “good” what does that mean? What exactly is the voltage?

Is this a thermal protective overload switch?

 

[Jpflex]

Are the run capacitors good?

Isn’t capacitors for capacitor start motors centrifugally switched out of the circuit once the motor reaches speed unless the capacitors are being used to create an artificial phase displacement from a single phase source?

 

[Jpflex]

This link might help:

Motor capacitor - Wikipedia

en.wikipedia.org

These capacitors create an artificial phase difference between poles just as you would have with a three phase motor without needing capacitors to do this

 

[ptonsparky]

Isn’t capacitors for capacitor start motors centrifugally switched out of the circuit once the motor reaches speed unless the capacitors are being used to create an artificial phase displacement from a single phase source?

There are capacitor start and run

 

[Jpflex]

There are capacitor start and run

Yes exactly. That’s what I was getting at. If it’s a capacitor start motor such as with dryers then the capacitors may be cut out after the motor starts, or if bad the motor would not start. Otherwise if it’s a capacitor run motor then they remain in circuit.

If the user wanted to test the capacitors he would need to put a load on the capacitors to drain their charge, use a fluke meter to check its micro farad rating and compare it to the rating marked on the capacitors

 

[ActionDave]

Yes exactly. That’s what I was getting at. If it’s a capacitor start motor such as with dryers then the capacitors may be cut out after the motor starts, or if bad the motor would not start. Otherwise if it’s a capacitor run motor then they remain in circuit.

If the user wanted to test the capacitors he would need to put a load on the capacitors to drain their charge, use a fluke meter to check its micro farad rating and compare it to the rating marked on the capacitors

There are motors that use caps to start and another set of caps to run.

 

[Galt]

the run capacitors main job is to limit the current that the start winding draws enabling it to left in the circuit taking some of load off the run winding and giving the motor a smoother running torque. If hooked directly to the line the current would be very high. when the run capacitor burns out the start winding is no longer helping so the run winding does all the work and draws more current.

 

[JB86]

the run capacitors main job is to limit the current that the start winding draws enabling it to left in the circuit taking some of load off the run winding and giving the motor a smoother running torque. If hooked directly to the line the current would be very high. when the run capacitor burns out the start winding is no longer helping so the run winding does all the work and draws more current.

Thanks for the info, that is helpful!

 

[ptonsparky]

Start windings are usually switched out of the circuit. Smaller submersible motors are an exception. Low torque requirements.

the run capacitors main job is to limit the current that the start winding draws enabling it to left in the circuit taking some of load off the run winding and giving the motor a smoother running torque. If hooked directly to the line the current would be very high. when the run capacitor burns out the start winding is no longer helping so the run winding does all the work and draws more current.

 

[JB86]

Thanks everyone, The issue was solved (see post #20), all the info has been great.

 

[kwired]

the run capacitors main job is to limit the current that the start winding draws enabling it to left in the circuit taking some of load off the run winding and giving the motor a smoother running torque. If hooked directly to the line the current would be very high. when the run capacitor burns out the start winding is no longer helping so the run winding does all the work and draws more current.

Not exactly. The run capacitor is lower microfarad value than the start capacitor.

When starting a bigger phase shift is needed to give the needed starting torque, but neither the winding or the start capacitors are intended to carry the current it will draw for very long. Capacitors usually fail first if the cut out switch isn't opening soon enough and often they rupture when doing so.

PSC motors don't have a start capacitor, but don't have the starting torque that a capacitor start motor of similar rating would have.

CSCR motors are basically same thing as a PSC motor once running.

OP's motor still had good start capacitors which allowed it to start. Once up to enough speed they switched out of the circuit and it essentially became a capacitor start induction run motor. Main motor winding was doing all the work since the aux winding likely had open circuit because of bad run capacitors. If you measured rotor speed it likely wasn't running as fast as it normally should either. Increased slip = increased current but it can't develop enough torque without a properly working aux winding to get it up to the speed it wants to run at.

Uncouple the driven load and that motor may seem to be running fine but still is only running as a CSIR motor.

 

[retirede]

Thanks everyone, The issue was solved (see post #20), all the info has been great.

You really don’t think you’re going to stop people from posting additional, mostly irrelevant stuff?

 

[ptonsparky]

You really don’t think you’re going to stop people from posting additional, mostly irrelevant stuff?

We can beat that dead horse as long as we want!!

 

[Jraef]

So my new question is, does anyone have a good link or resource for better understanding run capacitors.

Run caps in a Cap-Start / Cap-Run (CSCR) design single phase motor are used to maintain torque. Because the single phase power is crossing zero twice per cycle, the torque is basically discontinuous. It's often too subtle to be seen because the motor and load inertial carries it through. But on heavy loads it becomes more problematic, because in the discontinuous parts of each cycle, you get "negative sequence current" flowing, which is creating torque in the OPPOSITE direction, essentially fighting the motor torque you are trying to use. But because the motor WANTS to keep the load spinning, that translates into heat in the motor. The run caps help to smooth out that torque ripple effect and keep the motor running more smoothly with less heat. So if your caps were bad, the torque ripple increases, which increased HEAT made in the motor per unit of net torque. Since in this case the motor is thermally protected, the overload protection element is right there ON the motor, so it reacts to the actual heat, not just the current. So even though the current was not really enough by itself to cause a trip, the current USE was such that it was creating more HEAT than normal in the motor.

 

[JB86]

Not exactly. The run capacitor is lower microfarad value than the start capacitor.

When starting a bigger phase shift is needed to give the needed starting torque, but neither the winding or the start capacitors are intended to carry the current it will draw for very long. Capacitors usually fail first if the cut out switch isn't opening soon enough and often they rupture when doing so.

PSC motors don't have a start capacitor, but don't have the starting torque that a capacitor start motor of similar rating would have.

CSCR motors are basically same thing as a PSC motor once running.

OP's motor still had good start capacitors which allowed it to start. Once up to enough speed they switched out of the circuit and it essentially became a capacitor start induction run motor. Main motor winding was doing all the work since the aux winding likely had open circuit because of bad run capacitors. If you measured rotor speed it likely wasn't running as fast as it normally should either. Increased slip = increased current but it can't develop enough torque without a properly working aux winding to get it up to the speed it wants to run at.

Uncouple the driven load and that motor may seem to be running fine but still is only running as a CSIR motor.

Very interesting.

Run caps in a Cap-Start / Cap-Run (CSCR) design single phase motor are used to maintain torque. Because the single phase power is crossing zero twice per cycle, the torque is basically discontinuous. It's often too subtle to be seen because the motor and load inertial carries it through. But on heavy loads it becomes more problematic, because in the discontinuous parts of each cycle, you get "negative sequence current" flowing, which is creating torque in the OPPOSITE direction, essentially fighting the motor torque you are trying to use. But because the motor WANTS to keep the load spinning, that translates into heat in the motor. The run caps help to smooth out that torque ripple effect and keep the motor running more smoothly with less heat. So if your caps were bad, the torque ripple increases, which increased HEAT made in the motor per unit of net torque. Since in this case the motor is thermally protected, the overload protection element is right there ON the motor, so it reacts to the actual heat, not just the current. So even though the current was not really enough by itself to cause a trip, the current USE was such that it was creating more HEAT than normal in the motor.

Also very interesting

We can beat that dead horse as long as we want!!

LoL