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From: rdsnyder@mit-amt (Ross D. Snyder)
Newsgroups: sci.electronics,sci.physics
Subject: Re: HV Cap Fun!
Message-ID: <3806@mit-amt>
Date: 29 May 89 01:40:31 GMT
References: <4924@m2c.M2C.ORG>
Organization: MIT Media Lab, Cambridge, MA
Lines: 36

A great way to have fun with HV caps is to build a project that is used as
a demo in 6.013, the Electromagnetic Fields and Energy class at MIT.
The device was invented by Prof. Harold "Doc" Edgerton, inventor of the
strobe lamp and a professor here at MIT.  The device is named the "Boomer."
It consists of a HV supply which charges 48uF's (I think) worth of caps to
2KV (I think).  A serious HV relay is used to dump the charge through a
pancake coil about 10" in diameter made of something like 4-gauge copper
wire.  I remember the resonant frequency of this LC circuit was about
2KHz, which resulted in a damped sinusoid upon discharge.  The pancake
coil converts the electrical energy into magnetic energy.  Needless to
say, the device produces a significant short-duration magnetic field.
A sheet metal disk is placed on top of the pancake coil.  The magnetic
field from the coil produces a current in the disk, which results in a
repulsive force between the coil and the disk, thus launching the disk.
The demo was done in a lecture hall with a ~30ft ceiling, and an aluminum
disk could be made to hit the ceiling.  A larger version of this device
has been used by Doc Edgerton with a metal plate about the size of a
manhole cover to create underwater sonar impulses.  The professor let
students come up after the lecture and put their hands over the pancake
coil.  I did it and could feel the current induced in my hand because of
its conductivity and the presence of the magnetic pulse.

A videotape of the demo was shown with Doc Edgerton doing the demo himself in
a room with a ~10ft ceiling.  Another professor suggested in the tape that
doing the demo in that room would likely punch a hole in the ceiling tiles,
but suggested that MIT might not care too much since it was Doc's company,
EG&G, that had donated the entire building to MIT.  :-)

A word of caution:  The HV supply and caps were in a steel cabinet with safety
interlocks on the access panels.  The relay was in another steel box within
the cabinet and had an interlock on its door.  Don't just throw together a
kludge.  If you're going to build one of these, do a good job and insulate
everything and use HV wire, lots on silicone sealant, and bleeder resistors
across your caps.

-Ross