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In article <2225@letni.LawNet.Com> doug@letni.LawNet.Com (Doug Davis) writes:
>I Recently obtained a nice very used UPS that was broken, after repairing
>the machine I was able to get the charging and inverting circuits working
>again. My problem lies in the batteries that it uses are Gel Cells which
>a couple of them will only hold a partial charge.  But they do hold a
>charge. Two of them hold about 2/3rds normal voltage, and 2 more about
>half and one barely holds a volt. These are 6v gel cells.  My question
>is, is there any way, like shocking NiCads, to recover full capacity
>of these gel cells.

Doug,

Depending on the cell type, you may have good to moderate luck rejuvinating
a sealed lead-acid battery.  I have had very good luck with the Gates
type starved electrolyte battery and somewhat less good luck with the
true gel-cell gelled electrolyte batteries.

The technique described below should be used on batteries that are considered
a writeoff because destruction is possible.  Also note that the procedure is
rather violent to the battery.  Wear a face shield and gloves in case the 
battery ruptures.

In either case, you must work on one cell at a time.  The Gates batteries
are easy since they are assembled from individual cells.  Gel-cells are a 
bit more difficult.  The cell connections are generally sealed inside the
battery.  I usually carefully drill thru the top of the case to each cell
connector.  Then use a nail or a piece of #10 copper wire to make contact.

The failure modes seem to be either from overcharging which dries the battery
out or sulphation which results from extended periods of discharge.  And 
of course, some batteries will shed enough plate materials to short.  I
consider these to be unrecoverable.

In the case of Gates batteries, dryout is easy to treat.  If you remove
the outer metal jacket, you will find a rubber septum between the
terminals which serves as a pressure relief.  Remove the septum and
inject some distilled water to replace lost moisture.

I have yet to work with a dried-out gel-cell so I'm not sure what would be
involved in rehydrating one.  In any event, about 90% of batteries I've
worked with have suffered from sulphation.

The symptoms of sulphation are that the battery will not take charging 
current and in fact will withstand high charging voltage, often 12 
volts or more.  The treatment involves several cycles of heavy reverse
current charges, each followed by heavy forward current.

I use a high quality 15 volt, 50 amp lab power supply but most any current
limiting PX will do.  Again, this must be done one cell at a time.

First apply full reverse voltage to the cell.  It will initially withstand
the full reverse potential but as the process continues, the current draw
will rise rapidly.  I generally end this phase when the current is increasing
very rapidly.

Next reverse the polarity so charging voltage is applied in the forward 
direction.  The cell may be sluggish in the beginning but soon it will
start taking a charge.  Allow heavy current to flow for up to half a 
minute or until you detect heat from the cell.

Next short the cell thru an ammeter if possible.  The current will spike
and then decrease to zero.  At this stage, cycle through the process several
times until the current is immediate and heavy in both directions.  

At this point, a charge at a rate of about 0.1C should be started and continued
until the voltage rises to about 2.1 volts.  When this is complete, work on
that cell is complete.  Apply the treatment to the others in the battery 
and then apply a current-limited (about 0.1C) high voltage sufficient to
drive the 0.1C current across the whole battery as an equalizing charge.

Be sure and monitor the temperature of the cell while doing this procedure.
The cell will heat rapidly as soon as heavy current draw starts.  The 
temperature should not ever be allowed to rise above what is comfortable to
hold in your hand.

Using this technique, I estimate that about 90% of the gates-type batteries
are recoverable and perhaps 60% of gel-cells respond.  I have noted a 
pecularity of recovered cells that should be mentioned.  These cells re-
sulphate rapidly if allowed to sit discharged.  I use a set of recovered
Gates batteries in a homemade 2 meter rig.  If I use the radio every day
and charge the batteries promptly when discharged, they endure very well.
On the other hand, if I let them sit discharged for a week, I have to 
zap 'em again.  Strange characteristic.

Even with gel-cells, the treatment is worth the effort.  At worst, you throw
away an unrecoverable battery.  At best, you get a functioning battery for
only the cost of several hours' work.

John

-- 
John De Armond, WD4OQC                     | Manual? ... What manual ?!? 
Sales Technologies, Inc.    Atlanta, GA    | This is Unix, My son, You 
...!gatech!stiatl!john    **I am the NRA** | just GOTTA Know!!!