The BSA A7-A10 Forum
Technical (Descriptive Topic Titles - Stay on Topic) => Lucas, Ignition, Charging, Electrical => Topic started by: alanp on 15.04. 2011 09:59
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My mag/dyno wizard has just told me that the field coils on my dynamo are unvarnished but says the coils check out ok.
Anyone know why dynamo coils are varnished?
I'm running a standard dynamo with 12V regulator/battery/bulbs/indicator electrics and tend to rev quite high plus a 20% speed up ratio on the dynamo timing belt drive. Should I worry?
Cheers
Alan
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The wire used must be varnished or the windings will short out against each other.
Most winders then add some more varnish to add another layer of electrical resistance ( compensate for scratches ) and general mechanical robustness .
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Alan,
The field coil doesn't need to be varnished after it is taped with linen or cotton tape.
I doubt whether Lucas varnished them from new judging by the amount of oil which saturates some of the coils which I have encountered.
The beauty of unvarnished coils is the ease of unwrapping them which I do to replace the leads.
I retape with cotton tape and paint the coil with varnish and let it air dry. This seals the tape and hopefully keeps oil out and maybe prolongs the life of the tape.
If the coil is dipped and baked it is a hell of a job to strip the tape.
I don't use cotton covered wire for the leads but use high temperature silicon insulated flexible wire.
I used to use V105 PVC insulated wire but find that the silicon is better.
Trev.