So one day, i decide to throw a meter on my battery, just to keep an eye on things. Started the bike up, 13.8 volts at idle, seems ok right? Well i revved the bike, and at anything above 2k the voltage drops to 12.4 or less (depending on battery charge.)

I have seen many bikes of this vintage ('89) with bad voltage regulators/rectifiers, so i ordered one from ebay, which was supposedly in good working order.

Fast forward to this week, when the regulator shows up. Plug it in, and the exact same behavior. 

So i followed the troubleshooting flow chart and did all the tests to rule out the stator, and the stator seems to be performing great.

What are the chances i recieved a second bad R/R?


So just to cover all the bases, i took the battery out and charged it over night. Put the battery back in the bike, and it seemed to be performing a little sub par (voltage dropping quickly from 12.8 standing to 12.00 with lights on, to 10.8~11.4 while cranking.)

A new battery is on its way (the current one is a little small for the bike, the new one is a direct stock replacement.)

Is there anything I'm missing? All my connections are clean, no resistance, etc.

Were you having problems with the bike before you checked it with a meter? If not, don't worry about it.

Quote from: comradeiggy on October 06, 2013, 06:08:21 PM
Were you having problems with the bike before you checked it with a meter? If not, don't worry about it.

I hadn't ridden the bike prior to this. I received it in pieces, and it's now finally road ready. The only time it has ran, had been mostly at idle, which would explain why i hadn't caught it sooner.

Are you sure your multimeter is accurate? Honestly, none of those numbers sound too bad, and as to the slight voltage drop above 2k rpm, I'm fairly certain that's supposed to happen.

Quote from: comradeiggy on October 06, 2013, 06:41:57 PM
Are you sure your multimeter is accurate? Honestly, none of those numbers sound too bad, and as to the slight voltage drop above 2k rpm, I'm fairly certain that's supposed to happen.

Meter is quite accurate, it is calibrated annually ( I use it for work). Everything i have read, and every other motorcycle I've ridden has sustained at least 13.4v at all rpm's.

I will see what the new battery brings. Perhaps this battery is just too far gone, and is overloading the R/R.

Sounds normal to me - don't forget your electrical system is also providing the energy for the plugs as well - higher RPM = more energy required.

My 2k7F runs similar numbers - I think the alternator on the GS500 is perhaps not as big as it should be is all.  It is one of the few bikes I have owned that would not run without a battery.

It just doesnt seem right, I guess I will just have to keep an eye on the battery state of charge.

On a different note, lessening the load of the electrical system (LED's) would result in a higher charging voltage would it not?

Using LEDs will definitely reduce the loading - and you may see a marginally higher charging voltage at the higher RPMs.  The regulator is more driven by current so the voltage increase is going to be failry small.

I have swapped out my cluster and parking lamps for LED - havent bothered with the rear / brake, but have seen some good options for a replacement at some stage.