SOHC.co.uk Forums > The Black Bomber Board
Bomber electrics problem
royhall:
I did notice that the gaps in the commutator were totally filled with carbon from the brushes. Is that likely to be the problem? Will test the resistance on the windings tomorrow.
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Bryanj:
It could well be mate, we used to clean out the segments with a ground hacksaw blade but not too deep
If you take your multimeter probes set to ohms and check between adjacent segments all the readings should be the same, idealy you should test with a growler but that needs an old school rebuild shop.field coils will seem black and smelly if gone normally
AshimotoK0:
Also check the soldering of the armature wires to the copper segments of the armature. Sometimes the soldering looks OK but you will see a thin black burn mark line around the outside of the copper wire, which eventually creates an open-circuit
Normal multimeters will be useless other than checking continuity, as the resistance of the armature coils will probably be in the milli-OHm region. Say for example, the armature current is 100 Amps that would make the resistance of the coil typically 120 milli-Ohms. The best thing to do is pass a known current through each winding and compare the millivolt drop across that windings (which should be almost all the same value for each individual winding) . As Bryan said the old school method of testing by an auto-electrical shop. would be to test with a 'growler' . Another way is to pass the same current through each winding and get a gauge of the electromagnetism created on the steel laminations associated with that coil by holding a small screwdriver near to it. A headlamp bulb in series with the winding would give a decent current. After cleaning out the segments with a ground down piece of hacksaw blade, as Bryan suggests, I would wash it in something like isopropanol to remove any debris using an old toothbrush.
So what's this 'Growler' thingy/gizmo that Bryan is talking about? .....well I am not going to explain the facts of life to you ;D ;D but in the electrical world it's this :
https://en.wikipedia.org/wiki/Growler_(electrical_device)#:~:text=A%20growler%20is%20an%20electrical,a%20source%20of%20alternating%20current.
taysidedragon:
Well, you learn something every day. 😁
royhall:
I certainly learn something every day, usually things I knew a while ago and forgot. Thanks for all the info guys, I will rebuild the starter motor at weekend using the stupidly expensive kit from Wemoto. £118 What!!! Will keep you posted. Bye the way, resistance reading across the brush terminals shows zero ohms.
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