MOTs Rule Again!

To: tesla-at-pupman-dot-com
Subject: MOTs Rule Again!
From: "Gregory R. Hunter" <ghunter-at-accucomm-dot-net> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)
Date: Sun, 12 Mar 2000 08:13:21 -0700
Approved: twftesla-at-uswest-dot-net
Delivered-To: fixup-tesla-at-pupman-dot-com-at-fixme

Fellow Coilers,

I've just made a few short runs with my improved 4"x24" coil energized by a
dual MOT power supply with two half-wave voltage doublers.  Coil
improvements include a new secondary using 22AWG magnet wire and doubled
MMC from .023uF to .047uF.  I also added a bigger, 4"x20" toroid. At first,
results were pretty spectacular.  With approximately 1700VA of AC input, I
got multiple branching 36" to 48" streamers, with constant hits to the
strike rail.  Very exciting show!  However, after a few short runs,
performance began to fall off until I could barely get breakout.  I
suspected a failed MMC, but found that my MOT power supply could barely
jump the spark gap, even with the tank circuit disconnected.  Hmmm.

I figured I had a blown doubler diode, so I slipped on a brand new set.  No
improvement.  I thought maybe I had a shorted MOT, so I tested them
individually by allowing them to fire a spark gap.  Plenty of flaming arc
from both.  Hmmm again.  All that left was a failed doubler capacitor.  I'm
using four .9uF/2300WVAC units wired in series in two sets of two.  I moved
jumper wires around so as to use only one pair of caps.  By this process I
hoped to isolate the bad cap.  Of course, this new configuration greatly
increased MOT current, because I'd increased the doubler capacitance to
.45uF up from about .225uF.  I hit the switch and...LORDY!  Sparks
literally hit the ceiling!  1700VA was great, but >2000VA is simply
heart-stopping!  I got multiple, insane, chaotic branching sparks of 48 to
60 inches!  The thing actually scares me.  I had no idea a 4" coil could be
pushed so hard.  I'll need to put some grounded chicken wire or something
on the ceiling to catch the sparks.  I guess I had a punctured doubler cap
after all.  All my MOT stuff was salvaged from dead ovens, so I should have
expected a faulty part or two.

Oddly, the MMC and spark gap faces both stay cool--as if they're loafing.
I see no racing sparks or even any corona anywhere on the secondary
winding.  In other words, no signs of stress.  Could the improved 4" coil
process even more power?  I'd have to move it out doors to find out!  Not
enough head space--what a cool problem to have!

I can't wait to get started on my planned 6" coil.  Moved out doors and
driven with the ~2KW MOT supply, it will be a threat to low-flying
aircraft.  MOTs rule again!

Best Regards,

Greg Hunter
Cochran, GA