[Elecraft] ECOM scare -- FW: Soldering lesson

[Guy Olinger K2AV]

On Sun, Feb 19, 2017 at 3:37 AM, Edward R Cole <kl7uw at acsalaska.net> wrote:

> One other consideration,if using metal tools around high current sources
> (like batteries or power supplies): Shorting the terminals may cause rapid
> heating and result in explosions.  An exploding lead-acid battery can hit
> you with shrapnel and acid which can burn you, blind you, or cause death!


Back in the way-back when I was a young communications tech (still had
hair) working for AT&T in Wash DC, the long distance office I worked in had
a 10,000 ampere 12 volt DC supply which supplied entire floors of Western
Electric 310A and 311 vacuum tube filaments, plus other stuff. Was
motor-generators plus floating battery backup. Single cell low gravity lead
acid batteries, about 20x20 inches and 5 feet tall, four strings in
parallel.

The bus bar hook up leading out of the battery room to distribution panels
was four 1 inch thick, 4 inch tall solid bars in parallel for the positive
rail and the same for the negative rail. So the DC conductor was a pair of
"wires" that each had 16 square inches of copper cross section.

It was not insulated, and anyone working in there had to have all metal
jewelry, watches etc removed. Also all tools except for the tip had to be
wrapped in this gunky black cloth tape, two wraps deep. No exceptions, ever.

A contract employee was in there once, and went in there with a large
unwrapped wrench, working over the top of the bus bars. He dropped the
wrench across the plus and minus bars, which were separated by about six
inches, way more than enough to insulate for 12 volts.

Accounts said that there was a flash and both ends of the wrench vanished
into metallic vapor. The center portion dropped through the gap without
ever losing speed and bounced on the concrete floor. It was so hot it
burned leather gloves. The speculation was that the battery line could
easily have supplied a pulse of 30,000 or 40,000 amps. On one occasion I
saw the load ammeter go over 10,000 amps.

Dunno if the idiot that went in there with an unwrapped wrench got canned
or not, and don't know if he suffered eye injuries from the flash. Rumor
was that he immediately left the battery room and exited the building.

The amps that can be supplied by modern lithium batteries are so high that
it can destroy and even explode the battery.

All prior warnings of this sort in these threads are definitely
well-founded and probably understated if anything.

73, and may you never melt down any of *your* wrenches,

Guy K2AV