The Stovebolt Site Forums The Shop Area The Electrical Bay POSITIVE ground regulator on my Chevrolet???

I dont get it... I fried the generator, sent it out for rebuilding but the armature was toast. I bought a new one (armature), re-installed, ran the truck for an hour and fried the generator AGAIN! I instructed the mechanic to replace the Voltage Regulator, just in case. Upon inspection, it appears the VR is a positive ground unit... The truck is negative ground, always has been, and ran great for 3 years. Any insight on what could be happening here?

It sounds like it's had a GMC regulator installed at some time, which was positive ground. Your cutout relay probably stuck, which allows the battery to discharge through the armature, shorting it out. Install a new, negative ground regulator, and be sure to polarize the generator before running it, by touching the armature lead to the batery terminal for a second or so to be sure it's polarized to the correct battery polarity. If it's the original 6V system, "closing voltage" on the cutout relay should be 6.5 volts or more, to assure the cutout relay disconnects the generator from the battery when the engine stops, or armature voltage drops below battery voltage. Dirty, or sticky cutout relay points will allow the connection to stay closed, and the generator generally gets fried in the process.
Jerry

Thanks HRL! Could a positive box actually work on a negative ground system? (It obviously did, but I dont understand the specifics of 'how')...

Yes, it just doesn't work very well, and sticking the cutout relay points was one of the possible, and likely problems a wrong-polarity regulator would cause. BTW, a generator will work with either polarity. It just has to be polarized pos. or Neg. when it's installed.
Jerry

A quick update (the truck now runs as good as ever).

1 - For years it was equipped with a positive ground Voltage regulator, but it managed. The regulator's points stuck. The armature burned.

2 - We rebuilt and re-installed the generator with a brand new armature... but... at that point did not know about the VR's condition. I burned the armature... Again...

3 - We installed a rebuilt generator AND a NEW voltage regulator. No go. Negative reading upon testing.

4- We tested the NEW regulator and found it was indeed defective! Installed a new VR.
Buzzzz! = 7.3 - 7.4 volt reading. Everything is a-ok.

Thanks a LOT for your input, fellas.
Special thanks to HotRodLincoln.

Wzrick

As soon as it makes its way through the site administrators' evaluation, I've submitted the first of a series of articles on 6V DC charging systems. Keep an eyeball peeled!
Jerry

You have my vote, too, Hotrod. My '54 250 has raised a few eyebrows as I've shopped around for knowledgable techs. Fewer and fewer people I talked to wanted anything to do with something outside their last twenty years experience.

'54 GMC 250, 6 volt, positive ground.

That's the primary reason I've been in the automotive schoolteaching business either part or full time since 1970. I grew up around a top-quality independent shop in the 50's, working with oldtime mechanics from the 20's and 30's. Those guys worked on some of the very first cars, and passed along a lot of their knowledge and experience to me. Now it's my turn to keep up the tradition. Other skilled trades, carpentry, for instance, have centuries of skill and knowledge to draw upon, but auto mechanics are relative newcomers to the scene. If some of us oldtimers don't share our experience, it just dies out!
Jerry

Speaking of sharing, here's one from an old master. Dad bought regulators by the ton for the 52 pickup and the 58 4 door. His old buddy who is still a sharp mechanic told him (after both vehicles had been retired) that when you change the regulator, add a wire from the base of the regulator to the engine block to ensure good ground. We never replaced regulators a second time on any vehicle using this method.

Any regulator mounted on the body of the car needs a good ground. Some time ago, one of my students was having repeated battery failures on a Dodge pickup with an electronic regulator. The batteries would boil dry, and sulfate to the point they could not be recharged, even after adding water and cycling the charge up and down several times. We found that the charge voltage was going to over 17 volts anytime the lights were turned on. Adding a ground wire from the body to the engine solved the problem. The lights were finding a ground through the regulator wiring, and putting the alternator into full output in the process.
Jerry