Posted by David Sherman on Monday, June 11, 2007 at 16:11:17 :
In Reply to: More Electrical Woes posted by M Fanoni on Monday, June 11, 2007 at 15:45:28 :
Here's what I would do. The following assumes neg ground. 13.9 max isn't really enough to charge a battery. A float charger at 13.8 will charge a battery in a few days and hold it but in a vehicle with loads, that's just not enough. I would first check the voltage at the actual battery posts to make sure it's not a bad connection. You can also check neg post to ground, pos post to regulator and make sure you only have tenths of a volt, not volts, of drop there.
If those voltages are good (hence the wiring is okay), I would jump from pos battery terminal to field terminal on generator (like you're flashing the field) and see if it brings that battery voltage up to 14.5 or so. If it does, then the voltage regulator probably needs work. New mechanical ones are getting ridiculously expensive, but if you know what you're doing, you can clean the contacts and adjust the springs on the old one to bring it back into regulation (on a 3-coil unit, one coil adjusts the max voltage, one adjusts the max current, and one cuts out the generator when the engine is off). 3-coil ones can be adjusted for almost any application. 2-coil ones combine the current and voltage coils and are more application-specific. Anyway, a small bend in the arm on the frame of the voltage coil that the spring attaches to should up the voltage to 14.5 or so. If you have heavy loads, you might want to go a little higher, but check the electrolyte level frequently to make sure you're not overcharging.
If jumping the field to the battery pos doesn't get the charging voltage up to where it should be, then the generator is suspect. Brushes are easy to check and are usually pretty easy to replace. Shorted windings are hard to find without a "growler" and can't be repaired.
You didn't say what kind of rig it is, but if you have an alternator rather than a generator, the 3 parts of the diagnostic procedure are still the same, except it might have a built-in solid-state regulator that you can't adjust. Most "worn out" alternators really only need new brushes.
An old-fashioned generator system with a mechanical regulator won't charge its battery at idle, but it should start charging as soon as the RPMs come up a little (1000 or so). If that's the setup you have, no adjustment will make it charge at idle, but you should be able to get a solid 14.5 V at any sort of running RPMs at all.
Charging system problems aren't hard to troubleshoot, but you have to do definite tests to break it down into sections. Shotgunning it will only result in buying a new battery, a new regulator, and a new generator/alternator by the time you're done, polishing all the connections until they shine, and still wondering what the problem was (is?). It's almost certain that there's only one bad part, probably a cheap fix (brushes, dirty connection, regulator cleaning/adjustment), so the thing to do is find that part before throwing money at the problem.
Follow Ups: