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Text | New Life for Sulphated Lead-Acid Cells | 001
New Life for Sulphated Lead-Acid Cells? Richard Perez
©1990 by Richard Perez
ver the years I have tried many chemical treatments supposed to rid a cell of sulphation. None of Othem 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
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 rigamarole. 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, forlorn 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® orange pop I drank. In chemical techie terms, EDTA is a "chelating agent". That 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 a relatively innocuous chemical with which to attack the sulphated nastiness of 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?
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 (≈120°F.) tap water.
4 We left 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
Home Power #20 • December 1990 / January 1991
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