Posted by David Sherman on Thursday, April 12, 2007 at 20:45:04 :
In Reply to: battery question for snow plowing posted by George in MI on Thursday, April 12, 2007 at 20:20:59 :
When you put the charger on it, make sure there's plenty of voltage on it (14.5 or so) when you're trying to charge it. If the battery's weak and you're putting that much voltage on it and it only draws a couple amps, then yes the battery has gone bad (gotten sulfated). Most battery chargers are roughly "constant-voltage" chargers. That's an easy and safe way to charge a lead-acid battery. You can leave it forever at 13.8 volts and it won't over-charge. The problem is, 14 volts or so isn't enough to get the charging process started in a badly-sulfated battery. In the old days, it was typical to charge a car battery by amps rather than by volts. They'd put 5 amps through it for a definite amount of time or until all the cells were bubbling, then top off the cells with water as needed. When I have a battery that's acting like yours is, since it'd be junk anyway, I put it on an ancient charger I have that lets me set whatever voltage I want. It's not really a constant-current unit, but if I keep an eye on it, it'll do a fair job. I turn it up to whatever it takes to get 5 amps flowing into the battery, watch it closely for the first half hour or so, because it'll often "kick in" and start drawing a lot more current during that time, and then let it charge all night at 5 amps or so. I had a big bus battery that would not take a charge at all from a normal battery charger, due to having been left with a load on it until long after it was completely discharged. I had to crank thee voltage way up to get it to start drawing current, and it took a full week of futzing with it to get it charged, but that was 2 years ago and it's still working fine. The only real danger of overcharging a battery is that the electrolyte will get below the top of the plates and the plates will get damaged. If you check the cells and top them off with distilled water as needed, overcharging is not a big problem. In any case, there's nothing to lose if you were about to junk thee battery anyway.
It's quite possible that your charging system isn't really up to the task. You'd like to see at least 14 volts, preferably 14.5 AT THE BATTERY TERMINALS when the engine is revved up. If you're not getting that, the truck will keep eating batteries.
A voltage regulator, even the mechanical kind, limits both the voltage (to keep the battery from overcharging) and the current (to keep the generator/alternator from burning out). The plow, when it's on, is probably sucking way more amps than the generator is putting out. It can draw those extra amps from the battery for a short while, but on the generator has to keep up with the average demand being placed on the battery. If it can't do it, you'll have a perpetually run-down battery. If this is the case, a deep-cycle battery won't help, although it may survive being run way down better. Still, if the generator can't keep it recharged, it'll eventually get sulfated and won't take a charge.
If it was mine, I'd start checking the battery voltage frequently. If you have good voltage between the genernator output terminal and ground, but not much between the battery posts, look for bad connections. If you don't have strong voltage at the generator, either the generator is too weak or the regulator is bad or needs adjusting. The reality is you might have to put on a higher-output generator.