One reason motor windings fail is vibration in a loosely wound coil abrading insulation of the winding wire to create a short turn ( or turns ). This increases heating but may never lead to an escalating failure of the winding.
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New bathroom extractor fan and light switch
- Thread starter gdunbar
- Start date
Whatever - I still cannot see why a fan should ever need a 3A fuse, unless it was really so flaky that it should never be installed.
And as for
An isolation switch might be useful, but there really is no need for local fusing to try to prevent the loss of a lighting circuit in the event of a highly unlikely fault within the appliance.
And as for
despite Eric's touching faith in them, I rarely found that Ballotini fuses stopped me losing the lighting circuit when lamps failed, and life used to go on, and we lived with the behaviour, as did millions of others, I'm sure.
An isolation switch might be useful, but there really is no need for local fusing to try to prevent the loss of a lighting circuit in the event of a highly unlikely fault within the appliance.
I would not expect much vibration when the (very small) motor is stalled. Certainly in the test I did recently, with the fan motor jammed there was no audible hum and no vibration which could be felt. Nor was the motor even remotely hot after about 5 mins stalled - but I need to do a much longer-term experiment (if I can find a 'disposable' fan!).
Kind Regards, John
loosely wound coil. the vibration is in the coil and may not be detectable with or without the motor being prevented from rotating..
You really are scraping the barrel! I suppose I'm going to have to 'do the experiment'!
Kind Regards, John
I have just bought an el-cheepo axial wall fan branded steeple. I rammed some side cutters into the blades, and the current increased a little but, but nothing major. With my not very good fluke clamp meter, ( I should have used a series connected ammeter) the current was not able to be measured. I will do it properly on the next test.
After about 15 minutes that was it, the thermal fuse embedded in the motor windings opened. It is of this type and rated 115°C. The max temp measured with thermal camera was about 110°C. No thermal damage to anything, or any melting, warping or discolouration of the plastic case, the windings look ok , and no way even a 1A fuse would have done anything. I've cut out the thermal fuse so will now bypass it and see what happens then!
After about 15 minutes that was it, the thermal fuse embedded in the motor windings opened. It is of this type and rated 115°C. The max temp measured with thermal camera was about 110°C. No thermal damage to anything, or any melting, warping or discolouration of the plastic case, the windings look ok , and no way even a 1A fuse would have done anything. I've cut out the thermal fuse so will now bypass it and see what happens then!
If a motor hums in the forest and nobody hears it, does it still make a sound?
Running current 83mA
Stalled current 101mA
Stalled current 101mA
Well the casing has softened and the motor mounting screws have pulled through, smoke is starting to appear, the plastic fan blades have now softened enough that the motor is spinning again!
Pretty similar to the 91 mA / 105 mA figures I reported in post #20, then. It's good to have independent corroboration of my results.
Kind Regards, John
Was the current still around 101 mA throughout (after you had bypassed the thermal fuse) - or, per Bernards suggestion, had it crept up to high levels (high enough to blow a 3A fuse I very very much doubt!) as the windings "disintegrated and started shorting turns"??
Kind Regards, John
The windings did not, and have not failed, the smoke has stopped, and the motor is not getting any hotter, it has been stalled since my last message. I've just freed it and it still works fine. The plastic softened a lot, but has not discoloured. The insulation on the windings looks good. The free and stalled currents are almost the same as before, a couple of mA less now it is hot. It's a good job it didn't get really hot, as the plastic case burns wildly once it has ignited!
Thanks. No surprises there, then.
I would say that, between us, we have gone a long way to confirming how unnecessary/useless would be a 3A fuse.
Kind Regards, John
Echo - are you going to take back the fan and complain it got hot? 
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