How does an electric motor burn out (like on a fan)?

Question

There doesn't seem to be any parts that touch each other to wear out and the magnets don't seem to break down.

The only thing I can think of is if the wiring around the stator/rotor burns out over time.

Answer 1

Put simply, most of the electrical energy supplied to a fan is normally converted to mechanical energy - by rotating the motor.

If the bearings are worn the motor will not rotate so easily.  In the worst case - a completely seized bearing - the motor won't turn at all.  

In the first case some of the applied energy will be dissipated as heat.  In the second, all of the energy will be dissipated as heat.

Either case, but particularly the second, can result in burnt out motor windings.

A more detailed explanation involves the back e.m.f., produced by a normally running motor, which limits the current through the windings.

If the motor is slowed down by faulty bearings the back e.m.f. will be reduced and the current through the windings will increase.

In a seized (stalled) motor the current will be very high indeed.

Answer 2

The windings of a motor are wrapped closely and kept separated only by a thin layer of insulating lacquer

This lacquer can deteriorate by

a) age

b) weather changes

c) heat (due to current flow)

Generally the insulation lasts a lifetime but can lose its properties faster if

a) there is dirt and dust - especially where there are oily fumes like in kitchens

b) there are water droplets - such as in shower room exhaust fans

Thirdly a motor winding can burn out by overload (excess current)

a) if the rotation of the fan is mechanically blocked (some object preventing it from turning)

b) if the AC capacitor is defective - preventing rotation

c) if the bearings are seized (stuck)

Answer 3

Are you asking in general or do you have a particular case in mind?

Bearings can wear out.

For DC motors, the brushes are always a source of failure.

The wires do flex a bit as power goes on and off, and you could argue that a poor design would allow the wires to flex enough that the insulation would eventually wear off and the wires short, causing the motor to overheat, and eventually go up in smoke.  I don't know if this is a realistic scenario or not, perhaps a motor expert may weigh in?

.

Answer 4

temperature break down or mechanical failure - failed bearing. All energy gets converted into heat which burns wiring. Motors with collector brushes can have them fail, they wear up too

Answer 5

Lets us take " Fan " as an example

Fan is a domestic appliance ... and run by standard 230V 50Hz / 220V 60Hz power supply as per National standards and designed as per these standards.

The following are the two chances of failures of an electric motor

1. The voltage fluctuates more than the prescribed value and the winding is stressed heavily and would burn out the windind.

2. Winding heats up due to continuous flow of current in it, and when the temperature rises the thrshold limit of the insulation capability, the insulation burns out which might lead to winding to winding short and some times burns out.

Hope this helped.

Murali

http://coolingtheglobe.org

Answer 6

Bearings may wear out or the  insulating lacquer on the windings deteriorates from over heating. Worn brushes also.