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Re: [Amps] Crowbars

To: <>, <>
Subject: Re: [Amps] Crowbars
From: "Jim Tonne" <>
Date: Thu, 18 Sep 2008 19:14:03 -0400
List-post: <">>
John et al:

While we are on the subject of crowbars and other ways
of "dumping" a power supply, let me share with y'all
(I am learning to speak English in Tennessee!) a true

Way back in 1987 I was working with Continental
Electronics in Dallas, Texas, USA.  I was a newcomer
to that company and was assigned to work with the
shortwave broadcasting people.  This involved working
with transmitters in the 100 to 500 kW range.  Prior to
that time the highest power I had worked with was 5 kW,
at a broadcast station (FWIW, KBIM).

I was working with the guys who were working on the
control ladder.  Turn it on, turn it off, etc.

At some point they were going to test the crowbar.  I
had never seen a crowbar before.  I had not the slightest
clue as to what a crowbar did.  They told me, with a lot
of very serious looks on their faces, that this was a device
that dumped the entire high voltage system in the blink of
an eye.  It would make a huge noise, probably shaking
the floor, dim the lights, and the testing person was at
some risk.

The testing person would take a few-inch-long piece of
#30 wire on the end of a yard-long fiberglass rod and
place that piece of wire between high voltage and ground
at a particular place in the power supply.  This would
operate the crowbar and result in the huge transient.

Since I was to be "initiated into the club" they told me
that I was chosen to do this dirty deed.  They said they
would stand behind me in case I collapsed onto the floor.
Etc.  Etc.  Etc.   Being as naive as I was (perhaps still am!), 
I took all of this at face value.  Holding the fiberglass rod 
with one hand meant that I could only cover one ear to 
block the sound of the explosion.  This alone had me 

On the scheduled day I examined the wire to be sure it
was the right size, this being verified by my immediate
supervisor.  Everyone around had this very serious look
on their faces.  3 - 2 - 1 - connect.

The wire didn't even vaporize.  The operation of the
crowbar was totally - I mean  TOTALLY -  silent.

I am sure I had turned white from stresss.  Everyone
laughed and welcomed me to the Crowbar Testing Club.

The crowbar operated as it should have.  The specs by
Eimac (remember them?) were that the crowbar must
operate in a manner such that #30 wire must survive
the test.

My boss was San Engel.  Good Guy.  I miss you, Sam, 
and I miss your delightful sense of humor!

Although I suspect some of my grey hair is due to your
crowbar joke.

- JimT

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