[Lowfer] Here's another good one!

[WE0H]

Damn John, you have all the fun.

Mike>WE0H


-----Original Message-----
From: lowfer-admin@mailman.qth.net [mailto:lowfer-admin@mailman.qth.net]
On Behalf Of John Davis
Sent: Friday, October 17, 2003 9:23 PM
To: lowfer@mailman.qth.net
Subject: [Lowfer] Here's another good one!

Ed Phillips observes:
>
> I haven't heard about this specific occurance but if you'll look at old
>sources on electrostatic generation you'll find references to generators
>that using anything from STEAM[!!!] to moving particles of various kind;
>all involve some form of flowing material so this one also sounds
>reasonable.
>


And would you believe, plain air?

Picture this:  a box fan with metal body, sitting on plastic feet on a
concrete floor, one corner of the box within an inch of a grounded, metallic
trough cover.  It's plugged into a properly grounded electrical outlet and
running well.  But every minute or two...SNAP!  The fan discharges to the
trough cover.

Now, in the interest of full disclosure, here's the rest of the picture:
the fan is sitting five or six feet from an open HV compartment of a
transmitter, providing cooling for some components under test with 32kV DC
on them.  There is a partial barrier of non-conducting materials allowing
air flow, but preventing accidental human contact.  Does it make sense now?

As near as I can figure it, my staff had created a sort of reverse Van de
Graaf generator using a highly amorphous and (probably) very inefficient
"belt"--the flowing air itself.  The fan blew air into the compartment, a
percentage of the gas molecules picked up an extra electron or two, and
eventually some of those molecules made their way back around the room and
through the box fan.  Charges intercepted by the housing built up on the
outside of the metal case (a highly incomplete substitute for a sphere, but
good enough for Gauss) until there was enough potential to jump the air gap.

Replacing the barrier of insulating materials with a well grounded metal
mesh reduced the number of ions roaming loose, and grounding the fan body
took care of the rest.

And then, of course, there's all the fun you can have with an AM radio tower
on a windy day if the static drain choke has opened up....

John



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