🚀 go-pugleaf

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.  These are surplus batteries that 
: have probably been discharged for years.  When I try to
:  charge them, no appreciable current flows, even at 12v DC 
: input with no current limiting resistor.  Not having done 
: much with lead acid batteries, am I doing something wrong, or 
: are they beyond hope?  Any help would be appreciated.

Hm, be very, very careful with the technique I'm about to describe.  Also
use a current limiting power supply.  I once picked up an old 12V sealed LA
battery from the trash (the unit it powered was rather crushed, so I
presume it had an accident and they just threw the whole thing in.).  
Upon hooking it up I saw no voltage across it. Dusting off the labels
I saw that it was a 40 amp hour battery.  I set up a current limiting
power supply to feed it 30 volts, current limited to 100 mA.  For the
first couple days I got no significant current pumped into it (I can only
read milliamps).  After a couple days it started showing some current going
into it.  A few days after that I found it current limited to 100mA and
12 volts, bingo.  I cranked the voltage down to 14 volts and let her
charge up normally.  

First: why it does this: I'm told that when a LA battery discharges all
the way, the electrolyte becomes pure water, and supposedly cannot conduct
electricity.  This was borne out when I connected an ohm meter across the
leads (after checking for voltage presence of course :-)).  So I cranked
up the voltage higher than normal to get the first few ions to start going
through.  I limited the current to a fraction of what the battery could
handle to prevent overheating the battery once the electrolytic did start
conducting, and to limit the amount of hydrogen that might be produced.

I honestly do not know if I had damaged the battery, I've never used it
to its rated capacity so I cannot tell.  Did I do something risky?  I think
not because I periodically checked the temperature of the battery (one sure
sign of overcharging), and I limited the current to a fraction of what the
battery was rated for.  I should have kept it outside to prevent hydrogen
buildup, but I didn't think of it at the time.


Kenneth Ng: Post office: NJIT - CCCC, Newark New Jersey  07102
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Kenneth Ng: Post office: NJIT - CCCC, Newark New Jersey  07102
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