The Stovebolt Site Forums The Shop Area The Electrical Bay 6v generator output fades within seconds

When I start the truck and hold the RPMs up a bit - I can see the output two marks into the positive range BUT after 5 seconds or so, even though I'm holding the pedal steady, the output slowly drops down to the near zero output.

From these symptoms does it sound like the generators fault or the voltage regulator??

Thanks!

Sounds normal to me. As the charge in the battery returns to normal the output from the generator drops. When it's fully charged the needle should be at the center mark. If you're idling and turn the lights on it should drop to the discharge side then go to charge after you turn them off, dropping back to the center as the battery regains it charge.

Oh! Well, it's possible that I never noticed it before and it really is normal. Because it's a generator, which to me means the juice produced is proportional to the rpms, therefore I expected the needle to remain as constant as the rpms. So when I saw it at zero I assumed it was failing.

the regulator controls the generator output, and what the ammeter is showing you is the current being sent to the battery - if the battery is fully charged the meter will show 'neutral', if the generator isn't keeping up with demand, such as when starting or when lights are on at a low idle, then it shows juice being drawn from the battery .... much different than the voltmeters on more modern systems

Bill

The problem isn't the charging system, it's the battery. The internal resistance of the battery determines how much voltage the generator needs to produce, and a battery that develops a surface charge quickly will cause the current flow to drop very quickly after starting. That's because the battery plates develop a coating on them called "sulfation" which makes it extremely difficult to take an effective charge. Another symptom of sulfation will be a very low reserve capacity- - - - -two or three starts in a row will deplete the battery to the point it can't produce much current.

For a quick test, run the starter for 15 seconds with the ignition shut off, then see if the engine will start. If it does, quickly go to a fast idle, and see how long it takes for the charge rate to start dropping. If the amperage drops quickly, or if the engine won't start after a 15-second cranking effort, you've probably got a sulfated battery. It's possible to reclaim it, but it takes some doing. Turn the headlights on, and run the battery down completely- - - -overnight is a good time frame. Then do a slow-rate charge, about 5-10 amps for a day or so, and check the specific gravity of the electrolyte. When it stops going up, discharge again. Recharge- - - -discharge- - - -etc. until the sulfate crystals on the plates break down. It usually takes 5-10 discharge/recharge cycles. Or, buy a new battery and don't leave it unused for very long, which causes the sulfation in the first place. Do a deep drawdown and recharge about once a month, headlights on for a couple of hours, then start and fast idle for 30 minutes. Good luck!
Jerry

Wow! My understanding was totally wrong, thanks for the education!