davezawadi (David Stone):
Graham, I think that is wrong and misleading. The only thing which affects the slip in an induction motor is the LOAD, not the supply voltage. A fuse that lost 1V at 13A wouldn't last long, 13W is quite sufficient to blow a 100A BS88 fuse quite quickly. If the motor is electronically controlled, it is probably not an induction motor and so there is effectively no slip. This is not a mechanism of induction motor failure, mechanical overload is due to increased motor current and therefore winding resistance loss, not due to excessive rotor (squirrel cage) current which is entirely caused by the level of "slip". A normal 13A fuse dissipates around 500mW- 1W under normal maximum current, which is less than 500 mV drop. Note that supply voltage variation between 208 and 253 V (phase to neutral) does not cause failure!
My experience tells me otherwise.
The issue is actually to do with the capacitor voltage of a capacitor-run motor, and associated overheating (over time) of the start winding. We are talking about single-phase variant only here.
Unfortunately, it's [again] to do with penny-pinching in appliance manufacturer, but a problem all the same ... and not a new one, but something that appliance repair specialists have noted over a period of over 30 years.
Now, yes you are correct that most electronically controlled motors are not induction motors, but that's not always true ... the first appliance manufacturer's technical department that I am aware of noticing this problem with single-phase induction motors was actually a washing machine manufacturer, and they had speed control, but more rudimentary than now available.
I've not looked into whether it's a potential problem with some of the newer permanent magnet single-phase motors being installed on some higher-priced washing machines, because I'm pretty sure that will be addressed by far more modern control via VSD-type technology.
However, the problem remains very real for tumble dryers - particularly the cheaper ones.
davezawadi (David Stone):
Graham, I think that is wrong and misleading. The only thing which affects the slip in an induction motor is the LOAD, not the supply voltage. A fuse that lost 1V at 13A wouldn't last long, 13W is quite sufficient to blow a 100A BS88 fuse quite quickly. If the motor is electronically controlled, it is probably not an induction motor and so there is effectively no slip. This is not a mechanism of induction motor failure, mechanical overload is due to increased motor current and therefore winding resistance loss, not due to excessive rotor (squirrel cage) current which is entirely caused by the level of "slip". A normal 13A fuse dissipates around 500mW- 1W under normal maximum current, which is less than 500 mV drop. Note that supply voltage variation between 208 and 253 V (phase to neutral) does not cause failure!
My experience tells me otherwise.
The issue is actually to do with the capacitor voltage of a capacitor-run motor, and associated overheating (over time) of the start winding. We are talking about single-phase variant only here.
Unfortunately, it's [again] to do with penny-pinching in appliance manufacturer, but a problem all the same ... and not a new one, but something that appliance repair specialists have noted over a period of over 30 years.
Now, yes you are correct that most electronically controlled motors are not induction motors, but that's not always true ... the first appliance manufacturer's technical department that I am aware of noticing this problem with single-phase induction motors was actually a washing machine manufacturer, and they had speed control, but more rudimentary than now available.
I've not looked into whether it's a potential problem with some of the newer permanent magnet single-phase motors being installed on some higher-priced washing machines, because I'm pretty sure that will be addressed by far more modern control via VSD-type technology.
However, the problem remains very real for tumble dryers - particularly the cheaper ones.
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