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In Reply to: RE: Lead Acid Battery went dead with under voltage charges posted by wlee on December 19, 2010 at 15:22:03
...check youtube for methods.I found two sealed lead acid batteries in a recycle bin, and restored them as an experiment.
These 12 volt SLA batteries were the type found in uninterrupted power supplies or emergency exit signs.
One measured at 3 volts the other at 9 volts, which means that several cells were shorted probably due to sulfation. Reverse (burn) that sulfation away with over voltage (but controlled current) and that cell can regain continuity.
I followed some example shown on youtube: basically taking ac wall voltage through a 25w bulb and a variac (swept through 25v~130v), and lightly tapped the battery's terminals until the bulb lit. I was then able to charge both in parallel with a known good 12 volt SLA on a 13.7v float charger from Harbor freight. It was a slow charge, but at 30 hours both batteries were holding 13 volts.
Restoration can be a beautiful thing.
I've also read that a pooped pb acid battery might be reverse charged (and its polarity changed), and work perfectly well - I have yet to try that.
"Old school" is good school and always use goggles.
Edits: 12/19/10 12/19/10Follow Ups:
Great to hear your experience! I read about light bulb thing some time ago but not too serious about it, now I know it could work and I have variac so I will try and will watch you tube too!
tks a lot!
I have had some luck with this too. By using a variable voltage but very low current DC power supply. It is a somewhat delicate process that requires quite a lot of manual intervention i.e. you pretty much have to sit beside the battery and adjust the PS voltage to keep the current low as the battery gets restored. I chose to keep the current under 150mA; once the voltage got low enough (to get 150mA) I put the battery on a regular charger. Most smart chargers (like mine) will not accept a battery that's damaged.
Very recently I managed to fully restore a 6V SLA...it seems to work like new and holds a great charge. I also got a "brand new" (and not inexpensive) 12V SLA from digi-key that didn't look right to me. It did not charge like my regular 12V SLAs, and didn't seem to stay at a fully-charged voltage when unloaded. When loaded even minimally the voltage collapsed. (digi-key sent me a replacement BTW, and let me keep the bad one.) I managed to partially restore the bad battery, well enough that it's usable for some purposes, but nowhere near as good as an undamaged battery.
That's all I can remember clearly from the last couple months, but the process *does* sometimes work wonders.
I have not had good luck restoring batteries from UPSs. I think they got run right down to nothing during an extended outage...
... from the days of yore are a blessing, as my computer chipped "smart" chargers didn't cut it if a battery needed heavy duty intervention.I just got a Sears Die Hard (#28-71222) battery charger that is just smart enough not to get in the way of delivering the juice to a less than perfect AGM or SLA battery - my best 12v auto charger to date!
There's still room for battery tenders and minders, but tenders and minders are not CHARGERS.
A good DC power supply is a mighty versatile tool, even for 3v button cells.
The radio control community have some great programmable chargers as well.
Edits: 12/23/10
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