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In article <1989Nov14.025130.8216@oswego.Oswego.EDU> vermilye@oswego.oswego.edu (Jon R. Vermilye) writes:
>Has anyone tried to charge long dead lead acid batteries?  I
>have a batch of Gates 6v 2.5 amp hour sealed batteries made 
>up of 3 "D" sized cells.  


Depending on just HOW dead they are, I have a technique that works most of
the time.  In order to use the following technique, you must be able to access
each cell individually.  Also, very important.  This procedure is very 
stressful.  You must be careful and monitor your progress carefully.  I have
blown the vents on cells before.  Safety glasses are recommended.

The equipment you need is simple. A power supply capable of delivering
between 20 and 40 amps at about 12 volts.  It should NOT have foldback
regulation.  In other words, it should deliver the rated current even to
loads that pull the voltage down to 3 or 4 volts.  Old linear computer
power supplies are great for this.  You will also need an ammeter to monitor
progress.

The procedure is simple.  Hook the cell up to the power supply with 
REVERSE POLARITY.   The cell will initially draw a small current, dependent
on the age of the unit.  The current will rapidly increase to the limit
of the supply.  You MUST monitor the cell for heating.  The best way is to
hold it in your hand.  It will typically start heating in about 30 seconds.
Continue reverse charging until the cell is fairly warm (perhaps 110 degrees.)
Do not dally beyond this.  The heating tends to be from the center and 
the thermal conductivity is not terrific.  Therefore there will continue to
be a temperature rise after you turn off the power.

Let the cell cool for a bit and then forward charge with about 10 amps for
2 or 3 minutes.  Then short the cell.  The cell will still have a high
internal resistance so there will not be a lot of current.  When the 
discharge current is near zero, repeat the above process again. 

This time, you should see the reverse current rise almost immediately
to the limit.  The battery is in pretty good shape by this point.

Apply an equalizing charge to the cell at C/10 for at least 15 hours.
Then discharge the cell at its rated C.  Typically 5 amps for the type
cells you mention.  I use a large power resistor for the purpose.
Chage the cell at C/10 again for about 10-12 hours and you should be 
set.

You must do this procedure to each individual cell.  I usually do them
in batches.  The reverse charge procedure can be done assembly-line
style.  I have a 5 volt linear supply that I do the charging with.
It adjusts down to the ~2.5 volts needed.  I can charge several in 
parallel.  This implies, of course, breaking the pack apart.  If you
don't want to do this, then you have to do one cell at a time.

I've also had to replenish the electrolyte in very old cells.  To do 
this, you must remove the metal shell around the battery.  There is a nice
molded plastic case underneith.  There is a black rubber cap between
the terminals.  This is the vent/pressure relief.  If you remove this cap,
you can access the electrolyte.  I use a hypodermic needle to inject 
distilled water and/or battery acid into the bottom of the cell.  You 
need to do this procedure in order to get to the bottom of the dip tube
that runs the length of the cell.

If the battery has simply been float-charged to death, likely all that's
needed is distilled water.  If, on the other hand, the battery is 
heavily sulfated from sitting discharged for long periods, some acid 
will help rejuvenate the cell.

NOTE:  I've been told at various times by a friend of mine that works
for Gates that I'm {crazy, reckless, and have a death wish} for 
doing this procedure.  I suspect he is speaking for the corporate lawyers.
Nontheless, note that this procedure cranks a lot of energy very
rapidly into a small container.  If the cell pops, it COULD spew acid
around the room.  I use a lab apron and safety glasses, though the most
I've ever seen is the safety lift with a nice little fart-like sound :-)

I'm using several Gates packs around the shack here that are very old.
One set is in an old Motorola Packset radio and is well over 10 years old.
These have been shocked at least twice.

On the other hand, I've had some that simply resisted ALL treatment.  
You could slag 'em and they'd still be dead.  But you have little to 
loose in trying.

A good source of likely subjects, BTW are the alarm companies and
the emergency lighting people.  Both systems use these batteries for 
standby and are typically changed on a scheduled basis.

John


-- 
John De Armond, WD4OQC                     | Manual? ... What manual ?!? 
Radiation Systems, Inc.     Atlanta, GA    | This is Unix, My son, You 
emory!rsiatl!jgd          **I am the NRA** | just GOTTA Know!!!