[ARC5] BC-454-B Dymamotor Question

[Kenneth G. Gordon]

On 17 Jan 2013 at 20:15, J. Forster wrote:

> To me, from the downwards spike in the voltage waveform, indicates a brush
> is not making contact during part of the rotation.

Yes. Definitely. That is what I meant by "...a brush not making contact..." Thanks, John, for 
the clarification and your input.

> This could be caused by
> a stuck brush or some kind of commutator wear. It is most likely on the
> HV side.

Agreed. The brush holder can get bent, causing the brush to hang up, or the brush can get 
"sticky", or the spring can get weak or out of shape or damaged by heat so that it loses 
tension, or the brush can just plain be too worn to make contact over the full rotation of the 
armature.

Comutator insulator segments too high, caused by wear, can also cause this sort of thing.

Ken W7EKB