1976 Suzuki GT550 charging problems.

[wavehog33]

Restored a 1976 GT550 and now the battery charging is causing me fits. Bike was non-running when I purchased so cant know if the charging was bad before full motor build or not. The ignition is Kokusan and I have a new AGM battery showing 12.9v at the battery posts. When the bike is running I am fluctuating around 12.6 volts with the lights off. The brushes on the stator are work close to the limit line but still within specs and the copper leads are intact. 4.5 ohms between the copper rings on the rotor, and no continuity from copper ring to the side. So that checks fine.
1. At the green wire at the brush I am reading 10.6 v, Should this be the same reading as the battery (12.9) or is the 2 volt loss normal?
2. What is the most likely cause for the loss of 2v?

[Alan H]

1. It should be close to battery voltage.
2. Bad connections. The wiring from battery to regulator to generator rotor has many and each one can have a bit more resistance than it should, so you'll really need to pull them all and clean them. Make sure the fuse and holder are good and also all battery leads/connections are ok. If you've had the frame painted, make sure the connections to earth are paint free and put a dab of copper grease on to stop further corrosion.
It sounds like you have the correct wiring in place, just bad connections. The only other thing that could be 'iffy' is the regulator, but leave that until last as it's more fiddly to mess with. (not too bad though).

[wavehog33]

1. It should be close to battery voltage.
2. Bad connections. The wiring from battery to regulator to generator rotor has many and each one can have a bit more resistance than it should, so you'll really need to pull them all and clean them. Make sure the fuse and holder are good and also all battery leads/connections are ok. If you've had the frame painted, make sure the connections to earth are paint free and put a dab of copper grease on to stop further corrosion.
It sounds like you have the correct wiring in place, just bad connections. The only other thing that could be 'iffy' is the regulator, but leave that until last as it's more fiddly to mess with. (not too bad though).

Thanks, the fuse assembly is new Suzuki assembly from the battery to the harness. The frame was powdercoated but all the the ground mounts were plugged and then re-tapped so they should be clean. I cleaned the rotor face to get nicer copper rings since this post. I will have another look at all the connector plugs. I have switched regulators and rectifiers and made no noticeable change. Thanks!!

[jabcb]

The rectifier attachment bolt needs a good ground.
Check the rectifier attachment to the electrical panel & the electrical panel attachment to the frame.

You could also run an additional ground wire from the battery to the rectifier.
If this fixes the problem then you can either fix the grounds or just use the additional ground wire.

[wavehog33]

The rectifier attachment bolt needs a good ground.
Check the rectifier attachment to the electrical panel & the electrical panel attachment to the frame.

You could also run an additional ground wire from the battery to the rectifier.
If this fixes the problem then you can either fix the grounds or just use the additional ground wire.

Thanks Bob!! You hit it on the nose. The panel was powder coated and never removed for the rectify. I noticed this again using looking at the wiring diagram. I did what you mentioned and added a ground from the mount of the rectify to the frame by battery. This also hada ground wire to the reg mount that was grounding the panel. The prefer though I feel was blocking this from rec mount...all back together and will ride it tomorrow.