Erica, the Lucas test indicates that the generator is charging when spinning but it is charging before the fields are being turned on. That is why they are stating there is a short between the D and the F terminal, ie the D terminal is powering the fields without the external wire. As stated before, the short they are looking for is not the short between the armature shaft and the commutator. Assuming you have checked for the short that the test is asking you to check for, and you did not find an internal short between the D and the F terminals, then why is it charging? I have found that the residual magnetism is enough in some cases for a generator to charge somewhat as well as “motor” with a burnt out fields, which is why I do not like the “motoring” test.
Tom
Tom,
Well it turned out to be the field coil. I swapped the whole casing from my NOS unit, including coil onto my existing armature and CE bracket and it is now charging. I tested the resistance of the old coil to ground and it’s about 2 ohms. The same reading on the NOS one is about 3-4 ohms. I’m not sure if that’s indicative of anything or not.
So I’m left with three possible causes of the failure
- It was just it’s time to die
- The light rubbing from the too tall insulator strips on the rebuilt armature ( I’ve resolved that now)
- Unfortunately also correlated was the introduction of the SS regulator a couple months back. I’ve no idea if that could have caused it so don’t want to impugn that component. I removed it though and have the old points regulator installed for now.
I’ll have to unwrap that old coil one day and see if it offers any clues. I doubt it’s a fault in the wrapping as it was rewrapped in 3m glass tape 15 years ago. I guess it’s possible that the mechanical interference caused the problem although the only light contact was between the armature and the shoes which are screwed tight to the case. Too many variables here unfortunately. Thanks for the tip in the coil though!
Hard to tell if the difference you noted is significant, it is easy to get a few Ohms variation depending on how you hold the test leads on the part.
As far as to what failed there is still to much mud in the water. Changing both the frame and regulator and having it work suggests that one of those parts is defective, but doesn’t really indicate which. The field coil really is just a big coil of wire that is stationary, not much to fail, whereas the regulator has some complexity, and I’m guessing a solid state regulator for an old Lucas generator is a bit of a homebrew. I guess I’m suggesting I would be more suspicious of the regulator, and at some point you are going to have to sub one of the parts back to verify which is the failure.
David,
Oh the coil definitely went bad in some way. The first thing I subbed out was the regulator because that was the last thing I’d touched last. The generator with all the old parts still wouldn’t work with a known good points regulator. After subbing in the new coil and housing it started working. I haven’t tried putting the SS regulator back in yet.
Yeah the resistance did fluctuate wildly. I just went with the lowest possible reading.