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Experiments with a MOT tank supply
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From: Marco Denicolai [SMTP:marco-at-vistacom.fi]
Sent: Thursday, June 11, 1998 1:53 AM
To: tesla-at-pupman-dot-com
Subject: Experiments with a MOT tank supply
My tank supply is made of 2 microwave oven transformers and voltage doubler
that make up a 12KV DC pulsed at 50 Hz. The MOTs are capable of outputting
up to 0.5 A.
When I first connected a simple steel bolt spark gap (no primary cap, primary,
nor compressed air quench) I got about 1 cm spark and could keep it on as long
as I liked (1-2 minutes). Never blown a fuse.
Then I built a RQ static gap, used 7 gaps (the max number I could get a spark
with) and in each run I ALWAYS blew a 10A fuse in about 5 seconds. Again,
note that I have no primary cap, no primary coil but I do have 3 mH and
550 pF filters between the gap and the tank supply.
Why this?
I explain it like this: the bolt gap was quenching poorly and the supply
(almost shorted) current limiting stabilized on about 0.5 A current. Almost
no current spikes. The RQ gap quenches better, the supply is pulsed shorted,
I get higher current spikes (the current limiting cannot be so fast to
avoid them) that in a matter of seconds warm and blow my 10A fuse.
This makes me to believe that in the complete TC (using the primary
capacitor) I MUST disconnect the tank supply before discharging the primary
cap through the primary, otherwise again I'll blow a fuse.
MY IDEA:
========
Build a rotary spark gap where the rotating sections will FIRST connect the
primary capacitor to the tank supply and THEN connect it to the primary.
--------------
rotating metal section ---> | | ---> movement direction
--------------
|| || || 3 electrodes
|| || ||
| | |
to tank to cap to primary
So I'll get first a spark between the tank and the cap, that will charge it.
Then, when the rotating section moves forward, I'll get a second spark
between the cap and the primary coil, that will discharge the cap and will
not short the tank supply.
By having N metal sections on a rotating disk I can have N discharges for a
50 Hz cycle (supposing a 3000 RPM motor). The distance between the electrodes
and the rotating disk will set the minimum trip voltage.
For instance, with a 7 cm diameter disk, supposing a usable electrod-section-
electrod lenght of 1 cm (that is, the lenght the two electrods are shorted)
and 3000 rpm I can get 1 msec available time for the charge and 1 msec
available for the discharge (roughly).
Has anybody tried this before? Comments and/or suggestions?
________________________________________________________________________
Marco Denicolai Vista Communication Instruments, Inc.
Hardware Development Manager www.vistacom.fi
marco-at-vistacom.fi Kaisaniemenkatu 13 A
fax: +358-9-622-5610 SF-00100 HELSINKI
phone: +358-9-622-623-15 Finland
Remember, Murphy was an optimist! I am not...
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