Re: AGM batteries anyone running them ?


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Posted by Sherman in Idaho [24.32.202.166] on Tuesday, February 12, 2013 at 13:14:52 :

In Reply to: Re: AGM batteries anyone running them ? posted by Doc Dave [24.245.101.30] on Tuesday, February 12, 2013 at 10:43:48 :

I don't have much experience with the glass mat type batteries but in general, a battery that is extremely discharged will not take a charge at the voltage provided by an ordinary battery charger. Most battery chargers put out a relatively constant voltage in the range of 14-15 volts, which just isn't enough to start charging a thoroughly dead battery.

I have two continously-variable chargers that can go from 0 to 72 volts by turning a knob (variac). They are extremely handy for lots of things, but one of their main uses is restoring a bit of life to a battery that any normal charger thinks is as dead as a doornail. It commonly takes over 20 volts to get a dead battery "started", and sometimes as much as 30. The charger has amp and volt meters on it, so I crank up the voltage until the ammeter starts to show a little bit of current. At that point I stick around and watch it closely. Usually within a minute the ammeter will start climbing, at which point I turn down the voltage gradually until it's down to 15 volts or less and the battery is drawing maybe 5 amps from the charger. This whole process only takes 5 or 10 minutes. Then I let it charge at 5 amps for a few days. At least with flooded batteries, you can't over-charge them at 5 amps continuously. With a sealed battery, I'd be inclined to check it a couple times a day so as not to "boil out" any irreplaceable water. With a flooded battery, I just check the cells and top them off with water if need be. The slower and gentler the better in terms of longevity and completeness of charge.

Once any kind of lead-acid battery has been completely discharged, it's never as good as new, but I've commonly gotten another 2 years of life out of a totally dead battery by doing the treatment I just described -- high voltage to get it started, and then low amps for a long time to charge and stabilize it.

Of course it the battery is getting to the end of its free replacement warranty, you'll want to swap it out for a new one rather than squeeze a couple more years out of it and lose the warranty.

As near as I can tell, the "anti-sulfation" devices hit the battery with short high-voltage spikes. They claim the frequency and voltage of the spikes matches the resonant frequency of the sulfate molecules and breaks them apart, but I suspect all that really happens is the same thing that happens if you use a variable-voltage charger and briefly crank up the voltage like I described. The spikes ensure that even if the battery is totally discharged, it will eventually kick it into a chargeable condition.



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