Honda SL125 6v charging problems help

[MikeWa]

It's not a Venture but I am hoping someone has experience with these bikes.

 

The problem; The battery goes dead and the engine dies. It happens faster if the headlight is on.

 

The system. 1971 Honda SL125. A 6 volt balanced charging system (rectifier but no regulator). It has a four wire rectifier. Two from the stator, one battery neg and one battery pos. it has a two step 3 wire stator. White stator wire goes to headlight switch and activates second step of stator and is switched to the yellow wire when the headlight is on. The yellow wire, first step, goes to the rectifier. The pink wire goes to the rectifier and is common to the white and yellow.

 

What we have done: We resistance checked the stator. Leg 1-0.3 ohm Leg 2-1.7 ohm. No continuity to ground. AC output out of stator leg 1 7.5 to 9.5 volts AC at rectifier. Leg 2 7.5 to 9.5 volts AC at rectifier. Diode check rectifier front .350 volts to energize, back open on all 4 diodes. Disassemble selenium rectifier and clean all connections just in case. Perform voltage drop on positive and ground wires to the battery.

 

Resolution. The problem is not resolved. We have 6.3 volts 0.1 to 0.9 amp at the battery running and 5.91 volts and falling with -2.1 amp with the headlight on.

 

Questions: Is stator resistance ok? Honda does not publish a spec. Is stator AC output voltage 8-9 volts ok for a 6 volt balanced system? Can the rectifier diodes test good and it still be bad? Any ideas?

 

Plan; Our current plan is to wire in a rectifier from an automobile alternator and see what happens. Anything else we can try?

 

Thanks

Mike

[MikeWa]

Ok. Wired in two legs of an automotive rectifier and everything worked fine. So we replaced the new selenium rectifier, 100+ dollars, with an old used silicone rectifier we found this afternoon. Everything seems to be working ok now with 6.6 to 7.5 volts at the battery depending on load. I have no idea why the selenium unit tested good with a diode tester but did not function correctly on the bike.

Mike