After my bike blew both low and high beams, I decided I must have some sort of charging issue going on. Darn it, was hoping it was just a blown low beam.

Voltage measured at battery is 16-17 volts... at warm-up RPMs! Didn't bother to rev it up to check at 5000.

What are the typical things that go wrong on these bikes that lead to overcharging? Battery is a few months old, starts the bike, and measures 12.5V at rest... I assume it's good?

http://gstwins.com/gsboard/index.php?topic=38480.0

Quote from: noiseguy on February 28, 2011, 10:36:26 AM
After my bike blew both low and high beams, I decided I must have some sort of charging issue going on. Darn it, was hoping it was just a blown low beam.

Voltage measured at battery is 16-17 volts... at warm-up RPMs! Didn't bother to rev it up to check at 5000.

What are the typical things that go wrong on these bikes that lead to overcharging? Battery is a few months old, starts the bike, and measures 12.5V at rest... I assume it's good?

WTF ... you got AC over into the DC side ... regulator/rectifier is blown itself open.
If you do have AC in the charging system, you'd have a battery that heats up and swells up. Keep @ it and it will blow the tops off ...
Cool.
Buddha.

WTF was pretty much my reaction; thinking "I wonder when the battery will blow up or the wiring catch fire"

My plan was to run through the system with the bike running; once I saw the charge voltages I shut it down. With those figures I'll either bench test or shut out the battery from the system.

Is a blown rectifier the only possible cause on this? I immediately jumped to this conclusion, but want to make sure I'm being thorough.

Regulator fried. Nothing you said leads me to believe you have AC after the rectifier. 

Either way, the regulator and rectifier are in the same box, so you'll be replacing both.

Thanks. My bike's a 1990; Is this an "all years" interchange part?

All the GS rectifiers I've looked at have the same pinout.

Yeah, all the same.  I replaced one with an E-bay $35 unit.  It failed after a little over a year.  I have now installed one from a GSXR750, but that required some connector swaps.

Thanks!

Anyone tried a R/R upgrade per the following to a non-SCR based design?

http://www.triumphrat.net/speed-triple-forum/104504-charging-system-diagnostics-rectifier-regulator-upgrade.html

I did this, replacing the stock R/R with a unit off a Honda. Works great, and with a little filing, even fit the stock holes.

Thanks for the report!  I can't believe that the old, inefficient, SCR design has been in use for so long.

So Honda started putting real voltage regulators on their bikes 10 yrs ago? Well they do have a reputation to uphold.

After your story about yet another failed GS500 SCR R/R, I decided to bite the bullet and just get a good one.

The one I used cost $60 used (vs. ~$40 for a GS500 used part), with guaranty of function. I don't expect I'll need to replace it again... less heat = greater longevity. Wonder if it will keep the stator alive longer as well.