Battery Charging and Caps

Thread 71172 has reminded me of an incident from way back. Permit me to recount it.

Years ago at the Woomera Rocket Range we used several hundred lead acid batteries to power cine cameras, missile firing circuits and the like. These were carted around as needed and recharged in the Battery Shop by a couple of electrical assistants under my charge.

The charging arrangement was several mercury vapour rectifier chargers each producing some 150 volt DC so the 12v batteries were connected in series groups of ten using short jumper leads with spring clips. The chargers had rheostats to regulate the current and these were required to be reduced to minimum current before switching off.

Before my arrival it had been the practice to remove all caps from the batteries and place them in a box until charging was complete, but it was chaotic finding the matching caps to replace on the assortment of batteries and acid was sprayed onto the battery tops so I directed that the caps be left loosely in their holes.

One day I called in my vehicle to collect the Battery Attendants at knock-off time and poked my head in the doorway. In haste, the attendant failed to reduce the current first and simply turned off the main power switch which created a current surge and caused a spark at one of the jumper clips. This in turn ignited the vented hydrogen from the charging batteries with a very bright flash!

The resulting noise from several hundred battery caps ricocheting off the steel roof and walls of the shed was like a machine gun. We simply ducked and covered our heads until it was over. Then left it until the next day to recover all the caps from inaccessible places!

It was a salutary lesson in the dangers of hydrogen gas from charging batteries.
(But it really was funny!!)