110 V Motor Question

[Blackpool]

Hello everyone, I have a piece of 110V plant that is not working. The wire from plug to NVR had a partial cut (rectified). The NVR energises so assumed good. The motor has what looks like two capacitors (white and black). I am trying to run some basic checks on the windings (resistance) but wondered if the capacitors could corrupt the readings. I completely disconnected one (the black one) and I am showing low resistance on all fields. Could the white one be causing that? Or is the motor faulty? Could it be repaired? Image attached.

 

[Lucien Nunes]

It's a little hard to follow exactly what you have there. It is likely to be a capacitor start and run motor, in which the main winding is connected directly to the supply, the auxiliary winding is connected via the run (smaller value) capacitor, and the start (larger value) capacitor is paralleled to the run cap in series with a centrifugal switch that opens when the motor reaches speed.

If the capacitors are OK (and not shorted) then you should see two or three separate circuits through the leads emerging from the motor frame - the main winding, the aux winding and the centrifugal switch. The coils might be a few ohms, the switch a fraction of an ohm. There might also be a thermal cutout in series with both windings.

Capacitors are the least reliable part of the motor. A shorted cap can kill the winding, an open cap might just prevent starting. What actually happens when energised now? Does it hum? Will it start if rotated manually?

 

[Blackpool]

It's a little hard to follow exactly what you have there. It is likely to be a capacitor start and run motor, in which the main winding is connected directly to the supply, the auxiliary winding is connected via the run (smaller value) capacitor, and the start (larger value) capacitor is paralleled to the run cap in series with a centrifugal switch that opens when the motor reaches speed.

If the capacitors are OK (and not shorted) then you should see two or three separate circuits through the leads emerging from the motor frame - the main winding, the aux winding and the centrifugal switch. The coils might be a few ohms, the switch a fraction of an ohm. There might also be a thermal cutout in series with both windings.

Capacitors are the least reliable part of the motor. A shorted cap can kill the winding, an open cap might just prevent starting. What actually happens when energised now? Does it hum? Will it start if rotated manually

It's a little hard to follow exactly what you have there. It is likely to be a capacitor start and run motor, in which the main winding is connected directly to the supply, the auxiliary winding is connected via the run (smaller value) capacitor, and the start (larger value) capacitor is paralleled to the run cap in series with a centrifugal switch that opens when the motor reaches speed.

If the capacitors are OK (and not shorted) then you should see two or three separate circuits through the leads emerging from the motor frame - the main winding, the aux winding and the centrifugal switch. The coils might be a few ohms, the switch a fraction of an ohm. There might also be a thermal cutout in series with both windings.

Capacitors are the least reliable part of the motor. A shorted cap can kill the winding, an open cap might just prevent starting. What actually happens when energised now? Does it hum? Will it start if rotated manually?

It's a little hard to follow exactly what you have there. It is likely to be a capacitor start and run motor, in which the main winding is connected directly to the supply, the auxiliary winding is connected via the run (smaller value) capacitor, and the start (larger value) capacitor is paralleled to the run cap in series with a centrifugal switch that opens when the motor reaches speed.

If the capacitors are OK (and not shorted) then you should see two or three separate circuits through the leads emerging from the motor frame - the main winding, the aux winding and the centrifugal switch. The coils might be a few ohms, the switch a fraction of an ohm. There might also be a thermal cutout in series with both windings.

Capacitors are the least reliable part of the motor. A shorted cap can kill the winding, an open cap might just prevent starting. What actually happens when energised now? Does it hum? Will it start if rotated manually?

Hello Lucien

Nothing happens. No start and no humming. The problem must be the switch, capacitors or motor.

Switch energises. No wiring diagram as yet for motor (plant manufacturer is trying to get one) so only basis tests run. By way of explanation, if i take the cover off the motor electrics (as seen in photo) and probe the three terminals (closest to black capacitor) i get 'a voltage' symbol on my test probe (so some power is passing through switch) albeit i cannot confirm precise amount. All three terminals behave that way (power indicated to all of them) BUT if i switch off and try again, invariably NO power to any of them. Switch off and then try again, power to terminals restored. Sometimes this intermittent power 'restored' happens on the next power on cycle, on other occasions its the third switch on.

So not sure if the protection in the switch Kedu JD3 is interrupting power and the second or third attempt is resetting it ... albeit the JD3 its clearly letting power through the switch (not instantly cutting it) so any need to reset seems 'after the event'. But in any event, motor never turns

 

[Blackpool]

Hello Lucien

Nothing happens. No start and no humming. The problem must be the switch, capacitors or motor.

Switch energises. No wiring diagram as yet for motor (plant manufacturer is trying to get one) so only basis tests run. By way of explanation, if i take the cover off the motor electrics (as seen in photo) and probe the three terminals (closest to black capacitor) i get 'a voltage' symbol on my test probe (so some power is passing through switch) albeit i cannot confirm precise amount. All three terminals behave that way (power indicated to all of them) BUT if i switch off and try again, invariably NO power to any of them. Switch off and then try again, power to terminals restored. Sometimes this intermittent power 'restored' happens on the next power on cycle, on other occasions its the third switch on.

So not sure if the protection in the switch Kedu JD3 is interrupting power and the second or third attempt is resetting it ... albeit the JD3 its clearly letting power through the switch (not instantly cutting it) so any need to reset seems 'after the event'. But in any event, motor never turns

Just checked the capacitors. The white one is on spec 80 microfarads (spec 80 microfarads) but the black one is 184-187 microfarads which is outside the stated parameters 145-174 microfarads

 

[Lucien Nunes]

Start capacitors can have wide tolerance, that difference in value should not be a problem. Faulty caps are usually either open circuit or short circuit. The fact your motor does nothing points elsewhere. I'll reply in full later if I can

 

[Lucien Nunes]

I see what looks like a 5-core cable entering the motor - brown/black/grey/blue/earth. Obviously this is more conductors than needed simply to operate a motor in one direction and speed, so:

• Please can you confirm there is no other control functionality from the control box?
• Can you confirm the functions of the cores at the other end, so that we know where to expect continuity at the motor end?
• Can you post a pic and/or a sketch that clearly shows the connections to both capacitors?

With this info, we should then be able to make reasonable inferences about what resistances to expect across which motor terminals. It may be that the NVR coil is energised through a thermal cutout in the motor which would explain at least the 4th core of the cable.

 

[Blackpool]

Thanks Lucien. I believe the manufacturer of this plant just buys components, namely (1) switch assembly and harness and (2) complete motor from china and just swaps either out if a test rig indicates a fault on either.

Manufacturer has requested wiring diagrams from supplier. I chased them on Friday and not received yet. So will not have any definitive answers on cable and cores until then. Unless I can get the plastic fan off and have a look inside (see last paragraph below).

Will take a photo of capacitor connections tomorrow.

Just done some more testing and thinking. I am wondering whether the power to the terminals issue (mentioned in an earlier post) is actually a delay caused by the black start capacitor charging up. So to test this I hit the start button from cold (not touched for 24 hours and capacitors 100% discharged from testing and then reassembly) and the terminals did not get power for about 5 seconds. When I switched off and pressed start quickly, there was still power to terminals (presumably because start capacitor not having an opportunity to naturally dissipate its charge). But if i wait 5 seconds between switching on again, no power to terminals. So it looks like start capacitor takes 5 seconds to charge and 5 seconds to dissipate its charge when powered off.

Should there be instant power to those terminals? 5 seconds seems a long time for the plant to even think about powering up.

Regards the centrifugal switch. Not been able to take plastic fan off yet to gain access to have a look. I did try powering on and then manually spinning fan to help start (and try to engage run capacitor but nothing). Will have another attempt at gaining access tomorrow and also take photos of anything inside.

 

[Lucien Nunes]

I am wondering whether the power to the terminals issue (mentioned in an earlier post) is actually a delay caused by the black start capacitor charging up.

The capacitors charge and discharge 100 times per second (on 50Hz AC). Some residual charge might be left on a disconnected capacitor but when the motor is functioning normally, no capacitor will be left open-circuited at rest.

We don't need to play guessing games. We just need to trace systematically from the NVR through the 5-core so we know which terminal is which in the motor.

 

[Blackpool]

Start capacitors can have wide tolerance, that difference in value should not be a problem. Faulty caps are usually either open circuit or short circuit. The fact your motor does nothing points elsewhere. I'll reply in full later if I can

The capacitors charge and discharge 100 times per second (on 50Hz AC). Some residual charge might be left on a disconnected capacitor but when the motor is functioning normally, no capacitor will be left open-circuited at rest.

We don't need to play guessing games. We just need to trace systematically from the NVR through the 5-core so we know which terminal is which in the motor.

The capacitors charge and discharge 100 times per second (on 50Hz AC). Some residual charge might be left on a disconnected capacitor but when the motor is functioning normally, no capacitor will be left open-circuited at rest.

We don't need to play guessing games. We just need to trace systematically from the NVR through the 5-core so we know which terminal is which in the motor.

I have attached some more images

 

[Lucien Nunes]

OK right, so the cable from the NVR seems to be 4-core. If we number the three white terminals in a row 1 - 3 we have:
1 - brown switched line from NVR > two blacks into motor
2 - grey switched neutral from NVR > white into motor
3 - black switched line back to NVR hold coil via thermal protector > thin blue into motor

So the first circuit that we should see is zero ohms between 1 & 3 to enable the NVR coil to operate.
Then, we should see the motor main winding between 1 & 2.
The auxiliary winding and switch we have to measure by breaking into the capacitor leads but if there's nothing happening then we begin with the main winding.

What are the resistances 1-2, 1-3?