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Tech Notes:

Battery Safety

Richard Perez

Batteries are full of dangerous chemicals. If batteries weren't filled with reactive materials, then they wouldn't work. As long as these chemicals stay inside the cells, then everything is fine. Here's what to do if the nasty stuff inside gets out.

Experience is a hard school...

On December 27, 1991 at 10:20 in the morning, one of our lead-acid cells exploded. The battery had been recharging all night, pushed into gassing by our wind turbine and 50 mph winds. The sun rose bright that morning and the PVs added even more power to the battery. I was outside the house, about thirty yards away, pumping water for the horses. I heard what sounded like a rifle shot inside the house. I ran up and discovered that one of the lead-acid cells had exploded. The side and upper edge of the cell was blown into small bits and three quarts of fully charged sulfuric acid electrolyte were draining on the wood floor. Acid had been sprayed over the wall, over an inverter, and over two more battery packs composed of nicad cells. It was a monster mess and it caught me totally unprepared. I summoned aid from Bob-O Schultze who lives six miles away. He gathered up all the rubber gloves and baking soda in the neighborhood and rushed to help clean up the mess.

I still don't know why the cell exploded. I assume that the cell developed a short circuit, inside the cell, which sparked, and this spark ignited the hydrogen gas inside the cell causing it to explode. While no one was hurt and the only major losses are the exploded battery and a section of our floor, it made me acutely aware of battery safety. Here's what this fool learned from the hard school of experience.

Basic Equipment

We need some basic equipment to deal with any type or size of battery accident. Locate all this equipment in the entrance to the battery room, or close to the battery area. First buy a fire extinguisher for chemical and electrical fires (rated ABC). Halon gas fire extinguishers work well. Protect your body with rubber gloves and safety glasses. Use the heavy-duty industrial strength rubber gloves that come up to the elbows. Don't fool around with the lightweight kitchen models sold in supermarkets. The best type of safety glasses are actually goggles which fit

around the face firmly. For those wishing to clean up in style, wear a lab coat. We have two standard chem lab smocks for battery nerding occasions. Neither acid or caustic electrolytes will eat these lab coats.

When electrolyte spills from a cell, the primary jobs are containment and neutralization. Neutralization means adding a chemical to the electrolyte that renders it relatively harmless and stops it from eating holes in the floor. In order to tell if the electrolyte is really neutralized (pH 7), we need to have some litmus paper on hand and know how to use it. If you don't know about neutralization and litmus paper, get a high school chemistry book from your library and look it up.

Neutralizing the Electrolyte

Different types of batteries have different electrolytes. The chemicals we need to naturalize the electrolyte are different for lead-acid cells and for alkaline cells (nicads and nickel-iron). In either case, we should have on-hand, with the fire extinguisher and rubber gloves, a sufficient quantity of the neutralizing chemical to handle a large electrolyte spill.

Lead-Acid Cells

Lead-acid cells use an electrolyte that is a 25% solution of sulfuric acid in water (pH ≈ 1). The best neutralizing agent for this acid electrolyte is baking soda (sodium bicarbonate). Baking soda is cheap and available from any supermarket. The amount of baking soda you will need depends on the size of your lead-acid battery. It takes two pounds of baking soda to neutralize one quart of lead-acid electrolyte. A 12 Volt lead-acid battery with an electrical capacity of 700 Amp-hours will contain around 30 quarts of electrolyte. This mean 60 pounds of baking soda to neutralize all the electrolyte in the battery. In reality, electrolyte spills usually happen in smaller quantities, so having on hand 10 pounds or so of baking soda will handle spills up to five quarts. Baking soda has the additional advantage of being a dry powder. Adding it to the electrolyte makes a dryer mixture that doesn't spread about the area so easily. When baking soda is added to the spilled electrolyte, the entire mixture fizzes and gives off carbon dioxide. This carbon dioxide gas is also an effective fire extinguisher. So if the battery is on fire or exploded, pour baking soda all over the thing before it does any more damage.

Alkaline Cells

Alkaline cells use a 22% solution of potassium hydroxide in water (pH ≈ 13) as an electrolyte. Alkaline cells use an electrolyte that is a caustic base – the chemical opposite of the acid electrolyte used in lead-acid cells. Neutralizing the electrolyte in nickel-cadmium or nickel-iron cells is

Tech Notes

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