[EVDL List]

Hi, For whatever reason, a fairly new 12v/22AH Universal battery has
crapped out. It shows full charge into the 13 volts, but upon using it
with the three other (same vintage, same specs, no problems) batteries
in a 48 volt string... It works for a short time then drops to
10-something volts. I can probably take it in under warranty but I am
wondering if there are any tricks to revive it to full capacity? P.S.
I use a 6amp smart charger and it is fine.
Jeff K. Burbank, CA

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[EVDL List]

Jeffrey P. Kloth wrote:
> Hi, For whatever reason, a fairly new 12v/22AH Universal battery has
> crapped out. It shows full charge into the 13 volts, but upon using it
> with the three other (same vintage, same specs, no problems) batteries
> in a 48 volt string... It works for a short time then drops to
> 10-something volts. I can probably take it in under warranty but I am
> wondering if there are any tricks to revive it to full capacity? P.S.
> I use a 6amp smart charger and it is fine.

It may be that you haven't been charging the whole series pack quite
enough, so that one cell in that battery is much lower than the rest.
This will happen, for example, if you only use a "float" voltage charger
that takes each 12v battery up to 13.5v.

If this is the problem, you can correct it by doing an "equalizing"
charge on the offending battery. It won't hurt to do it to the whole
pack, for that matter. To equalize, take each 12v battery up to about
15v at low current (about 1-2% of its amphour rating) for an hour or
two), or until the voltage stops rising.

If this doesn't help, then it is likely that this battery just has a bad
cell, and should be returned for a replacement under warranty.
--
Ring the bells that still can ring
Forget the perfect offering
There is a crack in everything
That's how the light gets in -- Leonard Cohen
--
Lee A. Hart, 814 8th Ave N, Sartell MN 56377, leeahart_at_earthlink.net

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On 2 Nov 2007 at 14:44, Jeffrey P. Kloth wrote:

> It works for a short time then drops to
> 10-something volts.

Characteristic of a bum cell.

> I can probably take it in under warranty but I am
> wondering if there are any tricks to revive it to full capacity?

You could try a long, slow equalization charge. About 1/2 amp might be OK,
less would probably be better for a battery this small. Try not to let it
vent. Your smart charger might be TOO smart to do this. A regulated bench
supply would work.

No matter what you do, it's unlikely that you'll ever get full capacity from
it again.

David Roden - Akron, Ohio, USA
EVDL Administrator

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David Roden wrote:
> No matter what you do, it's unlikely that you'll ever get full
> capacity from it again.

I agree; this is the likely outcome.

However, if you chronically under-charge a lead-acid battery, you never
properly equalize the charge between cells. This happens if you never
charge over about 2.25v/cell (13.5v for a 12v battery). You can then
wind up with a cell that there is nothing wrong with it except that it's
at 50% SOC when the rest are at 100%. A long slow equalizing charge will
fix this, and the battery is fine again.

But more often, the user doesn't know that this condition is present. He
also has nothing to limit how deeply he discharges that battery with
the less-charged cell. So, he discharges until that 50% cell goes below
0% and reverses before he quits loading it. Now the weak cell is truly
damaged, and will never recover.

--
Ring the bells that still can ring
Forget the perfect offering
There is a crack in everything
That's how the light gets in -- Leonard Cohen
--
Lee A. Hart, 814 8th Ave N, Sartell MN 56377, leeahart_at_earthlink.net

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