vermilye@oswego.Oswego.EDU (Jon R. Vermilye) (11/14/89)
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. Jon R. Vermilye 315 341 2138 Department of Theatre vermilye@oswego.oswego.edu SUNY Oswego ..rutgers!sunybcs!oswego!vermilye Oswego, NY 13126
ken@argus.UUCP (Kenneth Ng) (11/15/89)
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
uucp rutgers!andromeda!galaxy!argus!ken
bitnet(prefered) ken@orion.bitnet
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Kenneth Ng: Post office: NJIT - CCCC, Newark New Jersey 07102
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bitnet(prefered) ken@orion.bitnetfrankb@hpsad.HP.COM (Frank Ball) (11/15/89)
*From: vermilye@oswego.Oswego.EDU (Jon R. Vermilye) *Subject: Lead/Acid Batteries *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. If the battery is 6 V, try a charging voltage of around 7.1 volts. If they have been discharged for a long time they may or may not be beyond hope, but you need to hook up the charger and let them sit for a while. They often won't accept much current at first, but will after some number of hours. Good luck. Frank Ball frankb@hpsad.HP.COM
jgd@rsiatl.UUCP (John G. De Armond) (11/15/89)
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!!!
BHB3@PSUVM.BITNET (11/17/89)
I would help to put a little, but very dilute sulfuric acid into the dead
battery if you have access to the cells. THis will allow it to conduct. YOu
would be "chemically charging" it a bit.
Brent H. Besler