electric motor gets very hot after switching off

message from Roy on 17 May 2004

I have a newish bandsaw that I have only used for short periods until
today when I was doing some repeat cuts and hence left it running
continuously for about 30 minutes. After I switched off I noticed a
hot electrics smell and the motor body had become too hot to touch. I
therefore investigated further and notice that when it is running the
air it blows over itself keeps it reasonably cool but on switching off
the metal casing becomes progressively hotter.
I haven't really noticed this on any of my other machines motors. Is
this normal or could there be a fault with the motor, motor
electronics or wiring.
By way of further detail the stamp on the motor says it is by
Electromotori, 250V, 7.71A, 1.1Kw. It has what I assume is a
capacitor attached (Ducati 45uF).
Any advice would be appreciated before I make a fool of myself with
the manufacturers.

Thanks

Roy

BigWallop replied to Roy on 17 May 2004

It is normal for these machines to have fan cooling while the motor is running, but
the point of it getting progressively hotter when it is switched off sounds a bit
worrying. Is it being turned off properly ? Is it wired in properly ? Is it earthed
properly ? Are the vent holes clean and clear of debris ?

It sounds as though the motor coil is still being supplied with electricity from
somewhere, not enough to run the motor, so it might be the switch or plug that has
been wired in wrong. Check them all before you plug the machine in again just to be
sure.

Pete C replied to Roy on 17 May 2004

Hi,

Some cheap tools aren't rated for continous use, eg 30 mins on and 30
mins off instead.

cheers,
Pete.

OldScrawn replied to Pete C on 18 May 2004

Well it all depends. It could be a fault as the other poster said, but you
might get a transient on the outside after switching off from the heat left
inside the windings, which will probably be hotter than the outside when in
operation. In operation, the air flow from the fan (and the rotor turning) will
cool the inside of the windings. With the motor stopped, the easiest route out
for the heat is probably outwards through the casing. For a domestic motor I
would expect the outside to "peak" in a minute or so. If it is still hotter
than the operating temperature after half an hour, then I reckon something is
drawing current. Do you have a suitable AC ammeter, and the
knowledge/confidence to use it?

Archived message: electric motor gets very hot after switching off (UK DIY House Improvement)