T-Pain Is On A Boat: [Electric Boats] How to blow up a battery

Wednesday, October 14, 2009

[Electric Boats] How to blow up a battery

I've been working on my Marco Polo conversion. 16 old US-125's (6v), an old GE 23hp motor (a heavy 170 lbs), an old Curtis PMC-25 motor controller. I started with 20 used batteries (out of an electric pickup), or 4 extras. I quickly found 4 dead cells, all in different batteries, after hooking everything up. (Voltage went from about 108v no load, to about 40volts under load.)

Then I replaced the bad with the hopefully good and was very happy for 45 minutes below 70amps (mostly 25amps). Still tied to the dock, with great volumes of water being expelled aft by the 28" three-bladed propeller. Then I poured on the power, and at around 120amps I got a really attention-grabbing explosion, almost like a shotgun.

Whoops!... forgot to water the batteries, which were all low (just barely above the plates). I forgot the secondary purpose of electrolyte: cooling. And the tertiary: spark suppression.

Just above the "plates" in a battery, usually out of sight, are the internal buss bars interconnecting the cells. Sometimes in old batteries, these are partially deteriorated, so they can't handle high amperage without heating up. Heating up how much? Too much. They start to melt, breaking the connection, creating a great spark.

In each cell is usually a marvelously explosive mixture of oxygen and hydrogen. More room for gas if there is less electrolyte. Bigger explosion if there is more gas.

This same incident also killed another battery, though not so enthusiastically. Then there were 14 (batteries). So I bought one, and am looking for another. But that didn't keep me (after watering the remaining batteries) from running 50amps for 40minutes at 90volts, trying to tow the dock.

Baking soda is good to have around. Batteries are good to keep covered. Protective eye-wear is good to wear. Insulated (or really stubby) tools are good to use around battery terminals. It was all good. Check your battery terminals for heat (under normal current drain, with latex/nitrile/rubber gloves and eye protection). Don't play with lead (poison) terminals or connectors without gloves. Around batteries, use one gloved hand when possible, or both gloved hands at the same terminal if it uses a nut and bolt fastener. Really avoid naked sweaty hands and batteries... you can off yourself (the big bye-bye) with a 12volt battery.

Stay safe,
Mark Stafford