E3LM Dynamo brush plate fault

General electrical problems
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Joined: Tue Oct 05, 2021 8:25 pm
Location: Notts, UK

E3LM Dynamo brush plate fault

Post by dennis.t »

I have refurbished my E3LM dynamo with new bearings, armature, field coil, brush plate and brushes.
I had a few frustrating days trying to 'motor' the dynamo on the bench without success and had some suspicion of an electrical 'short'.
After the umpteenth strip-down I had a moment of inspiration. The new brush plate from India has the rivets for the brush holders protruding from the underside far enough to prevent the plate from resting level on the dynamo body and, of course as I now realised, the rivets were making electrical contact with the body! In effect the whole brush arrangement was earthed. Seeing no way rectify the problem by modifying the brush plate I made a temporary fix using a small fibre washers under each of the brush plate retaining screws to lift the plate clear of the dynamo body and insulate the plate. Hey presto it works and motors well.
I need to buy a new brush plate to make a permanent fix.
"Buy cheap, buy twice".
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