The Stovebolt Site Forums The Shop Area The Electrical Bay Battery Charge

I would like some opinions on a charging problem I have. My generator is overcharging my battery, causing it to boil out acid into battery box. It is an 8v battery (I know, I am going to change it out in two weeks to a 6v)I have backed off the third brush to 9.5 volts, the amp guage reads about 7 with only ignition on and the cut out air gaps are within specs. Any clue? I have got a new cutout ordered and I am going to use a 6v Optima battery in two weeks.

The battery could be shot, not taking a charge but the regulater keeps on trying.

What kind of vehicle? 3-brush generators went out of use back in the late 30's on cars. They were used on farm tractors, etc., for a little longer. The voltage must be adjusted against a fully-charged battery, with very low current flow on a 3-brush system, so it's possible the voltage adjustment is still too high. Put a small resistance, like both filaments of a 6-volt sealed-beam headlamp between the generator and the battery before adjusting the voltage. The oldtime Sun volt-ampere testers had a 1/4 ohm resistor to simulate a fully-charged battery, which was inserted into the charging circuit before making the final voltage adjustment. Current flow into the battery should be below 10 amps to get a good adjustment.
Jerry

The vehicle is a 36 GMC. I was going to go with the 6v Optima battery. I have the gen output now at 9.5 volts with around 7 amps. With head lights on it drops to around -15 amps. Once I get the fresh battery, adjust gen output to specs (around 8.5 to 9v acording to manual)?

You only need about 7.5 volts to charge a 6V battery. Some of the 3-brush systems had an auxiliary circuit through the light switch to boost the charge output with the lights on. Unless you're really stuck on an original-equipment system, a later model 3-unit regulator and a 2-brush generator will keep the battery charged much better. I'm really surprised the 3-brush setup was able to develop 9 volts!
Jerry