Broken Electric Motor? HOW TO Test If A Motor Armature With Commutator Is Damaged
The LabOtomy The LabOtomy
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 Published On Nov 30, 2017

When an electric motor is broken, one suspect is the armature with commutator of the motor. In this video, we show different tests (180 degrees test, bar-to-bar test, continuity "bar to stack" test) that can be completed to determine whether or not the problem with the motor is caused by the armature with commutator being damaged or having failed. Note that those tests apply to DC motors and universal motors that use a motor armature with commutator.

In my case, the armature, coming from an old circular saw, was found to be faulty. Was it a surprise? No. Other signs of the armature having failed included:
1) Motor not reaching full speed when using the circular saw
2) Smoke coming from the armature when using the circular saw
3) Motor not spinning at all when placing the motor brushes on A specific commutator bar (the one where the resistance drop in test #2 was observed)
4) Irregular film left by the brushes on the commutator bars

Cause of the motor failure? Short in the armature windings.
But ultimately because I'm an ass!
- Short in the armature windings was because the coils got too warm
- The coils got too warm because the tool had to draw too much power
- The tool drew too much power because I pushed an old saw (with possibly degraded winding insulation) into cutting off wood that was too thick, too fast and on a super-hot summer day, so ultimately, the tool failed because I'm an ass.

► To check the motor field coil / stator, see:
   • HOW TO Test If The Motor Field Coil /...  

► DISCLAIMER
Always make sure you operate in a safe and secure manner.
For this project this means, make sure not to eletrocute yourself, even if you find it fancy

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