Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!rutgers!galaxy.rutgers.edu!argus!ken From: ken@argus.UUCP (Kenneth Ng) Newsgroups: sci.electronics Subject: Re: Lead/Acid Batteries Message-ID: <1349@argus.UUCP> Date: 14 Nov 89 16:31:01 GMT References: <1989Nov14.025130.8216@oswego.Oswego.EDU> Distribution: usa Organization: NJ Instit. of Tech: TEIES Project Lines: 48 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 -- Kenneth Ng: Post office: NJIT - CCCC, Newark New Jersey 07102 uucp !andromeda!argus!ken *** NOT ken@bellcore.uucp *** bitnet(prefered) ken@orion.bitnet