On Thu, 14 Jul 2005, Tim Wescott wrote:

Date: Thu, 14 Jul 2005 11:32:47 -0700
From: Tim Wescott
Newsgroups: rec.radio.amateur.homebrew
Subject: QUESTION: Fun with Svetlanas or Staying alive with kV power
supplies

Dave Platt wrote:
In article ,
Ken Scharf wrote:
snip
HV isn't the only thing that can get you. High current can give you
a nasty surprise. Like the guy replacing some batteries on a golf cart.
He was using a ratchet wrench to tighten the battery clamps and he
ended on the most positive battery terminal. The handle of the wrench hit
the chassis of the golf cart putting it between 36 volts and ground
of some VERY HEAVY DUTY batteries. Ever see a Sears ratchet wrench
glow WHITE HOT? (and melt?)


Haven't seen that myself, but I've heard of people who have had
screwdrivers, etc. literally vaporized under such circumstances.

My brother came home from a business trip once with a scar on his wrist 5/8
inches wide and all the way around -- the truck was having electrical
problems & he shorted his metal watch band through the 12V battery (there was
a wrench involved in there somehow, of course).

I felt for him, but I was very glad that _he_ was the one to learn this first
hand, rather than me...

I've got a related story to tell: I saw many years ago two guys try to
jump start another guy in the winter time. I only saw a few seconds and
surmised the following. These guys must have used the jumper cables to
connect the two twelve volt batteries in series, not parallel. Why? The
jumper cables were, themselves, literally smoking and not just a little
bit. Figure 24 volt power at, what, something like 500 amps(?) split
between heating up the interior of the two batteries and those jumper
cables (that are usually like #4 or #6 gauge?). How many seconds would it
take for on the order of 5000 watts to cause jumper cables to get up to
200-300+ degrees Farenheit? Those guys scrambled to tear those cables off
the batteries and I could tell by how they were handling the cable that it
had to be hot. They could have warped the lead plates.


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Tim Wescott
Wescott Design Services
http://www.wescottdesign.com