My son's A10 dynamo doesn't seem to be able to hold any residual magnetism in the field coil.
With D and F bridged it will light up a 12v 55w bulb brightly only if it's given a quick flash from the battery, it appears to work fine until you let it tick over for a few seconds then there's no output when the revs are increased again. The field coil resistance is within limits.
Any Ideas?
Commentator
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Residual magnetism?
It is accepted that the residual magnetism is lost after a few months but not while running?? The Field coil resistance being good is a very good starting point. Another area I have heard about is the field piece iron being too far from the amateur. Although there is no actual measurement for this I have heard of one person removing the field iron piece and inserting a thin piece of steel between it and the dynamo body. As the armature has already been questioned above I would say you need a decent dynamo repair man. What they normally do is completely rebuild it, in which case a new Field coil and maybe field iron piece, and new armature and all functions well, you never find the real reason for the problem as it becomes lost in fine electrical and magnetic technologies.
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Darren, My guess is the commentator has started to de solder from the coils.
Good news is new armetures are readily available and reasonably priced.
Don Anson Melbourne Australia