Voltage WAY too high (17v)

[Round Dice]

This is my first post so I hope it goes well.

This is for my 1978 cb750k.

Background:

Bought motorcycle and voltage was low, 10-13. I played with the regulator and couldn't really get anything better so I just road that way for about one year. I wasn't that bad because it was mostly day riding about 20 miles a day.

I installed a solid state rect/reg off a 1981 cb750 hoping that would bring up the voltage. No luck. The voltage remained low but I still road it another year.

So after two years my voltage drops to 8ish! I open up the alternator casing to test the coils and the first thing I notice is that one of the three phase wires has been chewed up by the starter motor gear (the small one). So I repaired the wire and removed the gear (I never use that thing, I'm a kicker).

Problem:

Now my voltage is outrageously high, 12.5@1G, 17@3/4G, and I've seen it in the low 20s when I flick it (fried my LEDs).

I figured it had something to do with the 1981 solid state rect/reg so I put the old OEM stuff back in and it is still mega high.

I'm at a total loss. Any suggestions?

 

[losttravlyr]

man i would have figured someone would reply by now,i am just guess by your info. i have never run into overcharging unless it was the regulator,but it sounds suspicious being as you have tried two different ones,other than the wiring being mixed somehow or both regs being bad, i dont see how it could. so next step i would think that there should be some sort of bench test with a multimeter for the alt/stator. have you tried that yet?

 

[Round Dice]

ya my alt/stator pass that bench tests from the service manual. I leaning toward bad regulator.

 

[K2750tracy]

Check what voltage the stator is putting out test before the regulator rectifer it should be around 32v ac if thats good it has to be the reg.

 

[dirtdigger]

I have had a Ford explorer charge to 32 volt. I found that the battery had an internal short which caused to alternator to basically full field charge. Shorted and sulfated batteries can cause a lot of weird problems, especially electronic fuel injection. I spent 7 years doing automotive drive ability and one of the first tests I would do was check the battery no load voltage and do a load test on the battery....and check for AC voltage coming out of the alternator. It seems strange that you would have two bad regulators of two totally different types be bad. If it started after you repaired the wiring then look at the wiring or replace the alternator. It seems to me that there was something wrong with the wiring that you had to repair as there should be a metal bracket that keeps the wiring away from the starter gear, I just looked at a spare I have and something doesn't sound right with yours.

 

[losttravlyr]

good advice digger. you are a guru on this stuff. i didnt even think about the battery. i am leaning to the alt too though. all his probs seem to have started there with the wiring from low charge to overcharge.

 

[750kjay]

Hi,
I'm not getting 32V from the stator/rotor. I test it at around 16V before the rectifier.
Also, what should the voltage be back to the field exciter coil from the regulator? I'm getting less than 1V across the white and green wires from the regulator and from the white wire to a ground location on bike. I am assuming it's AC.
Is there electrical test specs listed somewhere on this sight? That would be a great help.
I'm new to these bikes also.

Thanks,
750kjay.