[ARC5] BC-454-B Dymamotor Question

[J. Forster]

I've seen a similar thing. I think it's either swelling due to oil or some
kind of stress relaxation in the graphite.

FWIW,

-John

===========


> I had a real problem with a stuck low voltage brush on one of my BC-348
> dynamotors and had to drive it out with a pin punch after disassembling
> the
> LV end of the unit.  The replacement brush fitted into the holder very
> nicely so it was the fault of the brush material, not the holder.  Can a
> brush swell all by itself?  Well, I guess they can, this one did.
>
> Clare
>
> On Fri, Jan 18, 2013 at 1:45 PM, J. Forster <jfor at quikus.com> wrote:
>
>> Ken,
>>
>> Agree on all points. However, I've never seen the commutator insulator
>> segments get too high. It probably does happen as many manuals have
>> directions for 'undercutting' the insulation after refinishing the
>> commutators.
>>
>> Best,
>>
>> -John
>>
>> =================
>>
>>
>>
>> > 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
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