Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!iuvax!cica!ctrsol!emory!stiatl!rsiatl!jgd From: jgd@rsiatl.UUCP (John G. De Armond) Newsgroups: sci.electronics Subject: Re: Lead/Acid Batteries Message-ID: <581@rsiatl.UUCP> Date: 14 Nov 89 20:12:06 GMT References: <1989Nov14.025130.8216@oswego.Oswego.EDU> Reply-To: jgd@rsiatl.UUCP (John G. De Armond) Distribution: usa Organization: Radiation Systems, Inc. (a thinktank, motorcycle, car and gun works facility) Lines: 91 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!!!