Electric motor help
Discussion
I'm trying to troubleshoot a 240v ac electric motor which isn't running. It has 4 wires coming out of the casing and a 4mF start capacitor. My DMM doesn't do capacitance but I've got zero resistance between all six combinations of any two of the four wires and infinite resistance between all of them and earth which I believe is how things are meant to be.
What I don't know is what voltage I should be getting between any of the four wires when the motor is trying to start. Can anyone tell me from the wiring diagram on figure 7.2 of the pdf below?
www.rielloburners.co.uk/lumo/upload_documents/riel...
What I don't know is what voltage I should be getting between any of the four wires when the motor is trying to start. Can anyone tell me from the wiring diagram on figure 7.2 of the pdf below?
www.rielloburners.co.uk/lumo/upload_documents/riel...
I was hoping to try starting it by giving it a shove but nothing protrudes to shove on unless I remove a bunch of oil plumbing and a casing to expose the air fan. However I might try that.
As far as voltages go, after advice from another place, I get 240v between terminals 3 and 6, 50v between 3 and 7, the same between 3 and 8 and I can't get to terminal 9 at present without running a wire into the box but I'll try that tomorrow. So to me at least it looks like voltage is getting in there, the motor seems to turn freely so my money is on the start cap.
As far as voltages go, after advice from another place, I get 240v between terminals 3 and 6, 50v between 3 and 7, the same between 3 and 8 and I can't get to terminal 9 at present without running a wire into the box but I'll try that tomorrow. So to me at least it looks like voltage is getting in there, the motor seems to turn freely so my money is on the start cap.
tbh, a basic multimeter isn't going to help you, because it's an AC machine!
The "start" capacitor is used to delay the current in one pair of windings so that when the motor is stationary, and you first apply a 50Hz AC power feed, the motor jerks onto one set of windings and starts to turn. This "Phase" delay is what you are trying to measure. However, you can't really look at the DC voltage or the RMS AC voltage, as what you really need to know is the phase current.
Assuming none of the windings are shorted to ground, you'll find that they almost certainly have too little phase to phase resistance to measure (as most of the phase winding is arranged as Reactive rather than Resistive in order to minimise losses). So without a milliohm meter, your normal DMM is going to pretty much show 0 ohms.
If there is no smell of burning from the motor (a sure sign of shorted windings) or other signs of distress, remove the start cap, and replace that, as this is the most likely fault. if that cap is bulged, leaking or discoloured it's almost certainly foo-barred. Some DMMs do have a capacitance measurement mode, and you can check the caps DC resistance between the terminals (which should be effectively infinite, once it has charged up to the test voltage the DMM puts out)
The "start" capacitor is used to delay the current in one pair of windings so that when the motor is stationary, and you first apply a 50Hz AC power feed, the motor jerks onto one set of windings and starts to turn. This "Phase" delay is what you are trying to measure. However, you can't really look at the DC voltage or the RMS AC voltage, as what you really need to know is the phase current.
Assuming none of the windings are shorted to ground, you'll find that they almost certainly have too little phase to phase resistance to measure (as most of the phase winding is arranged as Reactive rather than Resistive in order to minimise losses). So without a milliohm meter, your normal DMM is going to pretty much show 0 ohms.
If there is no smell of burning from the motor (a sure sign of shorted windings) or other signs of distress, remove the start cap, and replace that, as this is the most likely fault. if that cap is bulged, leaking or discoloured it's almost certainly foo-barred. Some DMMs do have a capacitance measurement mode, and you can check the caps DC resistance between the terminals (which should be effectively infinite, once it has charged up to the test voltage the DMM puts out)
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