RE: [TCML] 6 MOT stack?

["S&JY" <youngs@xxxxxxxxx>]

Jeremy,

Yes, there is no substitute for more power for longer streamers.  But with a
23 inch secondary, 2 KVA is probably about all it can take.  You will need a
longer (& wider) secondary to handle 5 KVA.

I run a 6 MOT stack, centrally grounded, with all 6 MOTs immersed in
transformer oil.  The oil is the key to survival of the outer two MOTs at
the high primary to core voltages, and all of them by helping get rid of the
heat.

The archives are full of ballasting ideas, ranging from using a welder in
series with your stack, to using a reel of #10 wire, to winding your own
iron core inductor, to using more MOTs with the secondaries shorted.

Personally I prefer not using any ballast and instead rectifying and
filtering the output of a MOT stack, then using DC resonant charging with a
variable speed rotary spark gap.

You might also consider eventually going solid state, e.g. DRSSTC, which
avoids the need for high voltages completely.

Steve Y.

-----Original Message-----
From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] On Behalf
Of Jeremy Chan
Sent: Tuesday, June 02, 2009 7:08 AM
To: TCML
Subject: [TCML] 6 MOT stack?


Greetings to all,
I have recently completed the construction of my first coil. It has a 3ft by
3ft primary with 17.5 turns, a 4.5'' by 23'' secondary wound with 22.5 AWG
wire, and a 6.5'' by 16'' torroid. The primary and secondary is supported on
a 4ft by 4ft 12mm plywood board, supported over a second lower deck by 8
threaded rods, which houses my circuitry. The whole set-up is mounted on 6
3'' diameter castor wheels so the thing is mobile.
There is no problem with this set-up, in fact it is an over-kill where it
comes to most aspects such as the supporting structures and wires etc. The
problem is that i am currently running the whole thing off a 15/30 NST (the
best thing i could find in the pathetic island country of Singapore), which
effectively supplies 225W to a coil which I believe is more than capable of
handling 5kW. Thus far, I have only maxed out 20cm sparks no matter what I
tried (save for increasing the safety and master gaps, cos i can't afford to
kill my only precious 15/30 NST). Angling the primary to 45 degrees to
increase coupling seems to offer no appreciable advantage over a flat
Archimedes spiral, and the optimal primary turn has been tapped at turn 12.5
I have thus come to the conclusion that I simply need more power. Since,
once again, over-head power lines are non-existent in the wonderful island
country of Singapore, pole pigs are non-existent as well; and there's no way
I will be able to draw enough power to supply a 200kVA pad mount transformer
in my neighbourhood since my neighbourhood is probably powered by 1 of those
in the first place... The next best thing would be MOTs, a.k.a. the 'mini
pole pigs'. I have a dozen of them aching to be used, 6 of them appearing to
be of the same model, which is a good thing. The bad thing is that I have no
idea whatsoever how ballasting works. I am a Chemistry major in university,
and the coil construction was already stretching the bounds of my electrical
engineering experience. I do know that an unballasted MOT puts out about
3500W of power before burning out after 5 minutes, and a ballasted MOT puts
out about 1kW. But I need to know how to ballast a MOT stack for about 5kW,
whether capacitively or inductively. Programmes for calculating circulating
currents as well as trans/cap matches would be much appreciated. 
I considered a 4 MOT stack initially, but am concerned if it can handle the
full 5kW for prolonged periods, and the 8400V supplied seems low for a 5kW
coil. Then again, with a 6 MOT stack I am worried that the MOTs at the
extremities might not be able to handle the 6300V even with the stack
centrally earthed. Does anyone have any experience or advice on these
matters?
Any advice would be much appreciated.Merci Beacoup,Jeremy
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