New Life for Sulphated Lead-Acid Cells? Richard Perez Over the years I have tried many chemical treatments supposed to rid a cell of sulphation. None of them made any perceptible difference. A strange and devious set of circumstances has led us to the successful chemical removal of sulphation from six lead acid cells. Not only are the circumstances odd, but the chemical used, EDTA, is benign- in fact, it is used as a human food preservative. The Patients The sulphated Trojan L-16W lead-acid batteries numbered four and were the victims of a messy divorce. The pack was less than two years old when its owners had a parting of the ways. The husband took off for parts unknown. The wife left the house vowing never to return. And she left ALL the lights on when she departed. This system was sourced only by an engine/generator, with no PVs to help out. After several days the batteries were totally discharged. The batteries then sat discharged, with the lights switched on, for the next three months. The ailing pack was transported to Electron Connection for disposal as part of the whole divorce rigmarole. Upon inspecting the cells through the filler holes, we say vast amounts of white moss covering all the plate assemblies. Or at least we assumed there were plates in there somewhere because all we could see was an even blanket of moldy looking lead sulfate. Seven of the twelve cells were very low in water. Our job was to assess what these batteries were worth. In order to do this we attempted to recharge them and see how they held the charge. Open circuit voltage of the cells averaged 0.7 Volts. We placed the batteries on a four panel Kyocera J48 PV array (÷12 Amps) and the voltage immediately shot to 15 Volts where the regulator cut in. The amount of current accepted by the four L-16Ws was 0.4 Amps. We left the L-16Ws on the array for five days, but they never did accept a charge. We then tried discharging the batteries. They (all four 125 pound batteries) ran a 28 Watt car tail light for about three minutes. This gave us an electrical capacity of about 0.05 Ampere-hours per cell that originally had a capacity of 350 Ampere-hours. A classic case of sulphation ruining virtually new, high quality batteries. We pronounced the cells toxic waste and told the principals involved that the batteries were worthless. In fact, worse than worthless because someone had to responsibly dispose of them. The original owners promptly disappeared and left us holding the batteries. They sat, fore lorn and unloved, in the battery area, side by side with new cells destined for caring homes. In another reality... My friend, George Patterson-a battery techie second to none, ran into an article in an obscure British antique motorcar publication that described using a chemical called EDTA to remove sulphation from old lead-acid batteries. I related to him the story of the orphaned L-16Ws and to make a very long story short we decided to give it a try on these virtually new, but severely sulphated batteries. EDTA, what is it? It is an organic acid, a chemical cousin of vinegar. EDTA stands for the entire name of the compound which is, "ETHYLENEDIAMINE TETRAACETIC" Acid. EDTA is used for many chemical jobs, but perhaps the most amazing is as a food preservative. I noticed it on the list of ingredients of a can of Slice(r) orange pop I drank. In chemical techie terms, EDTA is a "chelating agent." which means it likes to bond to metallic ions (like lead sulfate). While EDTA is not the sort of stuff you want to eat by the teaspoon (the label carries warnings about getting it in the eyes or nose), it is relatively innocuous chemical to attack the sulphated nastiness with those L-16Ws. I admit to being skeptical. I thought we were wasting our time. How could something contained in orange pop help these severely sick cells? The Operation George Patterson located and purchased 500 grams of EDTA from a local chem lab that specializes in the chemical testing of wine. The cost was low, under $15 for the EDTA and another ten bucks for rush shipping. George then did an essential duty in this entire process. He came up to HP Central in Hornbrook and got me off my butt to actually perform this experiment. George could have shipped me the EDTA, but he knew my faith in this project was so low that I'd get it done some time next century. We decided to operate on two of the L-16Ws and leave the other two untreated as controls for the experiment. We had only sketchy information from the British motorcar pub. It described a teaspoon in every cell (hold the milk and sugar) and let sit for several hours. It neglected to mention the size of the cell, but George and I assumed that an antique motorcar would have a fairly small battery- about 70 Amp-hrs. So we upscaled the amount of EDTA to 2 Tablespoons to match the larger (350 Ampere-hour) L-16W cells. What follows is a step by step description of what we did: PLEASE NOTE: These operations involve handling sulfuric acid electrolyte. We used acid resistant Norex lab coats, rubber boots, rubber gloves, and safety glasses. If you try these operations without this safety gear, then you are risking injury. Play it safe. 1 We drained the old electrolyte from all six of the cells. Now this reads easier than it does. An L-16W battery weighs 125 pounds and contains 9 quarts of sulfuric acid in its three cells. Be careful not to drop the battery or spill the acid electrolyte. Reserve the old electrolyte in secure containers and dispose of it properly through your local battery shop. 2 We rinsed all the cells with water and drained them. 3 We added 2 Tablespoons of EDTA to each cell and refilled each cell with hot tap (÷120øF.) water. 4 We let the cells to merrily bubble (the EDTA/lead sulfate reaction is exothermic- it gives off heat) for about two hours. 5 We then drained the cells and repeated steps 2, 3, and 4 once again. We could see the sulphation disappearing, but one treatment had not got it all. Actually, two treatments didn't either because there was still some sulphation there after the second go round. 6 We rinsed each cell with distilled water and drained it. 7 We refilled each cell with new (sulphuric acid in solution with distilled water- specific gravity 1.260) lead-acid electrolyte. The Operation was a success? After spending all day lifting and draining L-16Ws, George and I were sore and ready for a few beers. This technique is not recommended to the frail. If I were to do it again, I would build a cradle to hold and invert these heavy batteries. Doing it by hand is tiresome, risky, and invites injury. Neither of us was convinced that we had accomplished much beside some heavy sweating dressed in kinky moon suits. We left the L-16Ws, disconnected and unused, in the basement battery area. Every time I passed by, I would wire the pack of two rejuvenated batteries into the PV array for some quickie recharging. I had no time to run any sustained recharging or testing at that point because we had another issue of Home Power going to press. It was not until six weeks later that Scott Hening, our summer intern, hooked up the EDTA treated L-16Ws into a working system. This system is sourced by two ancient, anemic SolaVolt PV modules. The system is simple: the PVs and the two L-16Ws. This system provides power for lighting in Bob-O's spare trailer which houses dignitaries and heads of state visiting HP Central. Here the EDTA treated batteries received about 3 to 4 amps as long as the sun was shining. Since this system is seldom used, the batteries received a constant daily overcharge for about eight weeks. Bob-O kept on top of the cells' water levels and refilled them as needed with distilled water. Since the trailer was seldom used, and no one staying there complained of dead batteries, we just left the L-16Ws alone. Since the system had no instrumentation, it was hard to tell how much improvement the EDTA treatment did. Enter a pressing need Then all of a sudden (in the space of six days) one of the L-16Ws in the main Home Power system (4@ L-16W) at Agate Flat developed a shorted cell. As distressing as it was to lose an eleven year old L-16W battery, it was fascinating to watch and record the death of one of its cells. The shorted cell dramatically unbalanced the remaining three L-16Ws in the pack. I had to do something quick. I disconnected the series string of two L-16Ws with the bad cell. Putting a new L-16W in this eleven year old pack was out of the question. I started thinking used battery and imagined the EDTA treated L-16Ws. Next day, I removed one of the EDTA treated L- 16Ws from Bob-O's trailer and inserted it the main Home Power battery. I had trouble choosing the best of the two EDTA treated batteries. I went for the one that had the least voltage variation between cells. EDTA treated L-16W performance I had no idea what to expect. The last time I tested the sulphated L-16W it wasn't able to power up a car tail light. I inserted it into the main pack as follows in the illustration below. I gave each cell a number and recorded data on the performance of the battery on a cell by cell basis. The L-16W battery containing cells 1, 2, and 3 is the EDTA treated battery. The remaining L-16Ws (cells 4 through 12) are the original, untreated, eleven year old batteries. INSERTILLO What happened? I'll cut to the chase here. The L-16W treated with EDTA had regained enough of its electrical capacity to function as an equal element with the battery. It works! What follows below is data from the all cells making up this battery under a variety of conditions. Detailed in the tables below are a variety of data, here's a score card to help tell the players: Battery Data 1. The date. 2. The battery Ampere-hour Meter reading which indicates the pack's State of Charge (minus indicates discharge amp-hrs.). 3. The discharge or charge rate in Amperes (minus indicates discharge). Individual Cell Data 4. The voltage of each cell. 5. The absolute cell voltage deviation from the average cell voltage. 6. The average battery (that's three cells in a case) voltage deviation. Note EDTA treated cells' data (Cells #1, #2, & #3) are printed in bold type. Derived Cell Data 7. Average cell voltage. 8. Cell voltage standard deviation (computed via standard statistical method). 9. Maximum cell voltage difference. INSERT CHART AND TABLE What the data means What we are looking for are differences in voltage between cells. Which is why the average cell voltage and deviations from average cell voltage are computed. A maximum cell voltage difference greater than 0.05 VDC, under light discharge (