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'[OT]: DOA Sealed Lead Acid Batteries. AC charging?'
2000\07\17@025848 by Robert Rolf

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David VanHorn wrote:
> >Is this a "normal" behaviour, and is it fixable?  Any references?
> >
> >Or is it a "return"?  [bought it via a friend; problematic]
>
> Feed it some AC current, limited by a lightbulb.

AC? How exactly is that supposed to work. Does the battery act
like a diode?

> If you can get it to flow 1-2A, then you're probably ok.
> Despite claims that it's permanent, it isn't always.

It depends on how badly sulfated it is, and how much effort one
is willing to expend 'monitoring' the rejuvenation process.


> My home station uses a "sulphated" 38AH gell that had zero capacity when I
> got it.
> It would run my electric lawnmower now..

Nice to hear of this success.
What -exactly- did you do to achieve this 'miracle recovery'?

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2000\07\17@031134 by David VanHorn

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>
>AC? How exactly is that supposed to work. Does the battery act
>like a diode?

No, but the reverse voltage gets some current flowing.
My initial experiments used a lab supply, current limited/voltage regulated.
With some batteries, I had to go as far up as 30V reverse, and leave this
on the cell for several minutes before I could begin to break through the
sulfation. I noticed that going back to forward voltage gave a short pulse
of normal-appearing charge current, then back to near zero. Reversing
polarity manually at 2Hz or so gave good results, but it's a major PITA.
(DPDT switch)

Finally, I tried 24VAC applied to 12V batteries, through a light bulb to
limit current, and to date, this has worked well.
I can't recover all batteries, but I can recover most.

Once you get a few hundred mA out of it, then a few normal (fixed voltage
forward only) cycles, discharging at as high a rate as practical, seem to
wake the batteries up quite well.


>Nice to hear of this success.
>What -exactly- did you do to achieve this 'miracle recovery'?

On this one, IIRC, Reverse 30VDC till current began to flow, then forward
till stop (limited to 1A for safety) several cycles, then normal fixed
charge at 2.55V/Cell (fast rate) followed by discharge in my electric
lawnmower, which is about a 30 minute run with a normal battery. It's no
precision device, but it's the only thing I have around that I can safely
dump that much energy into that fast.

I haven't checked capacity recently (somwhat of a PITA) other than running
my Igate for two days unplugged. It's a 0.35A drain when not transmitting,
and I don't get a lot of traffic here.




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2000\07\17@074845 by fernteix

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Many years ago when I had time to make experiments, I tried to recover a Pb
battery (not sealed). I exhausted the electrolyte, and filled with distilled
water. I charge the battery In the beginning the conductivity was low, but
it
increase continuously. Many days after with a small charging current the
acid had a nearly normal density: at least part of the the SO4-- was no more
in the plates, but in the electrolyte But when I was satisfied with the
result: surprise, I noticed a drop in voltage: a short in the first
element... The
classic dendrite building up across the electrodes.
As conclusion: to avoid it, is necessary to have periodic short but heavy
discharge pulses during the
charge process. So a charger with DC+AC component  can be a useful device.
Time-consuming  will be to find out the best values of AC and DC for each
type of battery.
My 0,001 cents.
Regards

Fernando


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