why would an electric motor just stop working?
Discussion
I have an extractor in the en-suite that stopped working the other day.
Luckily, an identical unit exists in the bathroom, so I have been swapping parts today. I first swapped the control boards and took the one from the broken unit and put it in the working unit (so, if the board was dead because of say some faulty wiring before the extractor, it won't then take out the working units board as well). The extractor fired up no problem so I assume the board is fine. Next I swapped out the motor run capacitor and the working extractor still works.
That narrows it down to the motor. There is only the board, the run cap and the motor as the 3 removable pieces and while I haven't swapped the motor, I can't see how it can be anything else. The motor typically has no markings on it at all, so looking specifically for a replacement will be difficult. But I have cracked the motor open and I can't see anything untoward. It has 5 wires going into the motor and they are soldered to the stator coils rather solidly so all looks well there (red+blue, brown+purple and black). (btw does that mean its a 4 pole motor?)
There is a small ceramic looking block with 2 nylon sheathed wires, one wired into the brown wire and one soldered on its own to something. I can only assume this is a resistor or cap for something.
all the windings look fine from what I can see, no burn marks, no unmistakable smell of burnt electronics. I assume the rotor is a permanent magnet, though it doesn't seem too enthusiastic at being a magnet. Maybe you don't need much? should the rotor be obviously magnetic?
EDIT: just read, its probably a little 3 phase induction motor, so rotor isn't a magnet, the alu conductors form a magnetic field when flux lines from the stator cuts across the conductors and induces the magnetic field required. Still, no idea why its busted!
Luckily, an identical unit exists in the bathroom, so I have been swapping parts today. I first swapped the control boards and took the one from the broken unit and put it in the working unit (so, if the board was dead because of say some faulty wiring before the extractor, it won't then take out the working units board as well). The extractor fired up no problem so I assume the board is fine. Next I swapped out the motor run capacitor and the working extractor still works.
That narrows it down to the motor. There is only the board, the run cap and the motor as the 3 removable pieces and while I haven't swapped the motor, I can't see how it can be anything else. The motor typically has no markings on it at all, so looking specifically for a replacement will be difficult. But I have cracked the motor open and I can't see anything untoward. It has 5 wires going into the motor and they are soldered to the stator coils rather solidly so all looks well there (red+blue, brown+purple and black). (btw does that mean its a 4 pole motor?)
There is a small ceramic looking block with 2 nylon sheathed wires, one wired into the brown wire and one soldered on its own to something. I can only assume this is a resistor or cap for something.
all the windings look fine from what I can see, no burn marks, no unmistakable smell of burnt electronics. I assume the rotor is a permanent magnet, though it doesn't seem too enthusiastic at being a magnet. Maybe you don't need much? should the rotor be obviously magnetic?
EDIT: just read, its probably a little 3 phase induction motor, so rotor isn't a magnet, the alu conductors form a magnetic field when flux lines from the stator cuts across the conductors and induces the magnetic field required. Still, no idea why its busted!
Edited by Otispunkmeyer on Friday 3rd January 16:54
I'd be amazed if it were permanent magnet in that application. Brushless induction motor surely? Only way it can fail is knackered bearings, or burn out stator windings. Check winding continuity with a resistance meter. If it is variable speed, it may use a separately excited rotor coil, using brushes that can wear out?
Max_Torque said:
I'd be amazed if it were permanent magnet in that application. Brushless induction motor surely? Only way it can fail is knackered bearings, or burn out stator windings. Check winding continuity with a resistance meter. If it is variable speed, it may use a separately excited rotor coil, using brushes that can wear out?
yeah I just figured it won't be a permanent magnet motor. Think is a little 3 phase induction motor.The rotor spins nicely, so the bearings are good. It is a variable speed, but not in the sense it can be adjusted on the fly. If you want it to go faster, you have to re-locate a jumper wire. The rotor just pops out, it isn't attached or wired to anything, the backing plate on the motor basically sandwiches the rotor in there with a seat either end for the bearings to sit in. There are some rubber gaskets in each seat, presumably to stop crud getting in the bearings.
I don't have a multi-meter, but I will go buy one tomorrow I think. Useful item to own.
Thing is, there are 4 models in this extractor range. there is the P, which is pull cord operation the T which has a delay timer so it goes off 10 mins after you switch the lights off, (oh yeah its wired into the light circuit so that it comes on with the bathroom lights) and there is the HT (the one I have) with the delay timer or humidity detector so you can have it turn off when humidity reaches a certain level. There is a TM model but I am not sure what that does.
Anyway I am assuming that the T model at least will utilise the same motor and similar control board. I can get one new for less than £40 quid, so I can hopefully just poach the motor and fix mine.
Anyway I am assuming that the T model at least will utilise the same motor and similar control board. I can get one new for less than £40 quid, so I can hopefully just poach the motor and fix mine.
Indeed, if when you plug it in, the motor hums, and maybe vibrates a bit, but doesn't turn, then the "false phase" cap might well have failed. (as UK domestic electricity is single phase only, a lot of cheapo induction motors use a capacitor to generate a "fake" phase lagged input which makes the motor design/manufacture cheap and easy)
There is no hum, it's just dead, it won't even attempt to turn even if I help it. I think tomorrow I will actually swap the motors. See what's what. If it works then I have no idea where the issue is!
This may not make any sense, but the thing is constructed as follows:
There is a control board with various things on, but I guess the main parts are the relay (which definitely works because you can here the click) and largish square potted capacitor in yellow. There is then a similar physical size capacitor, again potted, but in black and this is separate from the main board, screwed down to the fan housing. The cables from this go into the board and one of them is in the same row as the wires exiting the board to the motor.
No idea if I am right, but I assume the yellow cap is the false phase cap and this black one is the run cap. As far as i can work out, both are working, though I did note the yellow one was still warm to the touch when I removed the board from the working extractor and this was some time after the unit had switched off, so it must get a bit toasty.
This may not make any sense, but the thing is constructed as follows:
There is a control board with various things on, but I guess the main parts are the relay (which definitely works because you can here the click) and largish square potted capacitor in yellow. There is then a similar physical size capacitor, again potted, but in black and this is separate from the main board, screwed down to the fan housing. The cables from this go into the board and one of them is in the same row as the wires exiting the board to the motor.
No idea if I am right, but I assume the yellow cap is the false phase cap and this black one is the run cap. As far as i can work out, both are working, though I did note the yellow one was still warm to the touch when I removed the board from the working extractor and this was some time after the unit had switched off, so it must get a bit toasty.
Edited by Otispunkmeyer on Friday 3rd January 23:55
Just because you hear a relay click does not always mean it is servicable, the coil may be ok and pulling the contacts together but if the contacts are worn or burned then current may not flow.
If the relay is on one of the boards you swapped and works on your other motor then ignore this post.
If the relay is on one of the boards you swapped and works on your other motor then ignore this post.
So 3 pole isolator on the wall outside. If I switch on I get a light, relay click and nothing from the fan. So power to the board is ok.
The same control board in the other extractor works fine so I assume everything on the board is fine. I have also swapped capacitors and it still works.
Today I will hook the motor up to working extractor and see what's what.
The same control board in the other extractor works fine so I assume everything on the board is fine. I have also swapped capacitors and it still works.
Today I will hook the motor up to working extractor and see what's what.
Ok swapped the motors over and I think its dead, nothing happens, it doesn't even attempt to turn nor can it be coaxed by hand starting. Quickly re-wired the known working motor and it fires straight back up so everything except the motor is good.
Inside there motor there are multiple windings and what I believe is a small capacitor wired across one of the windings. I believe, from reading around that this is normal. I haven't been able to test that cap fully, but I do know it at least isn't shorted. Ill need a large resistor if I want to see it charge up though, the windings its attached to won't have much a lot of resistance so I am not going to see anything other than OL on my multimeter.
As for the windings, well there are 5 wires entering the motor. Not sure which is which but I assume one is a common and the other 4 are wired to pairs of windings. I can measure a resistance between all except when comparing to the brown wire (there is blue, red, brown, black and purple). I have no idea if that is right or wrong but my assumption would be that I should be able to measure some kind of resistance between any two wires so whatever windings to which the brown wire is attached may be damaged.
I think the simplest thing for me to do is just buy a replacement unit and swap the motors, keep the rest for spares.
Inside there motor there are multiple windings and what I believe is a small capacitor wired across one of the windings. I believe, from reading around that this is normal. I haven't been able to test that cap fully, but I do know it at least isn't shorted. Ill need a large resistor if I want to see it charge up though, the windings its attached to won't have much a lot of resistance so I am not going to see anything other than OL on my multimeter.
As for the windings, well there are 5 wires entering the motor. Not sure which is which but I assume one is a common and the other 4 are wired to pairs of windings. I can measure a resistance between all except when comparing to the brown wire (there is blue, red, brown, black and purple). I have no idea if that is right or wrong but my assumption would be that I should be able to measure some kind of resistance between any two wires so whatever windings to which the brown wire is attached may be damaged.
I think the simplest thing for me to do is just buy a replacement unit and swap the motors, keep the rest for spares.
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