Alternator follow-up

[Jim Ewing]

I talked with the alternator shop and they suggested it might be a bad battery or bad cell in one of the batteries. I disassembled the bank and found one battery with no "idiot light" showing. (They're these Delco maintenance free batteries). There was a bit of growth on the + terminal. All other batteries were OK and clean terminals. Based on what the alternator guy said I think that what happened was that the alternator sensed the corrosion as a voltage drop and continued putting out amps to try and fill the battery. This didn't work and so it toasted the first battery in the bank.I'll be testing this hypothesis but right now it seems to make the best sense. I think what I also might do is put in a distribution bus so that the charge current might be distributed a little more fairly.Jim"Prospect"

 

[Bryan C.]

Bad cell = lower voltage

Each cell of the battery produces about 2.1 volts max charge. If one cell fails, the max the battery will charge to is about 10.5 (5 x 2.1). Your regulator kept pouring a charge into the battery, since the battery never read a high enough voltage to reach the trip level to cause the regulator to turn off the alternator. That caused the rest of the battery to overcharge. So I take it all back what I said earlier about the regulator.If those Delco batteries are standard car batteries, don't expect them to last long in a marine environment. First, they are probably made for cranking, not recycling. If they are standard starting batteries, they will probably only last 15-30 deep discharges before the fail. Second, car batteries may not be built with the tougher casing required for the pounding a boat takes. A standard cranking battery works fine as a starting battery, but you need deep cycle batteries for the house load.