Hurray! 6 Pack MOT supply success

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Dave Hartwick by way of Terry Fritz <twftesla-at-qwest-dot-net>" <ddhartwick-at-earthlink-dot-net>

In honor of my dead T&R PDT (Pole Distro transformer--Ariel), I've
endeavored to get sparking again with an MOT supply. I have MOTs coming out
of me arse--may as well put them to work.

Making these cooperate  has been a difficult road. This  is surprising
because this is not my first time trying to tame these beasties; but over
the last some days I made a series of retched blunders that doomed success.
For one thing, I did not take into account the inherent difficulty in trying
to drive an MOT pack with reference to mains center ground (or neutral) and
a 240 v variac feeding the outer primary legs. Now I understand why Ted does
not drive all MOTs with a variac(s).

In addition, unnoticed by me, one of my final output MOTs---ones with max
voltage--was missing its shunts. I had pulled them during the '99 sessions.
Coupled with the above mentioned error and some other errors too
embarrassing to mention, I ended up arcing (core to winding) some INNER
MOTs--those units  carrying minimum potential!  Some sort of imbalance I did
not foresee.

The above errors were manifest in a 4 pack arrangement with only the outer 2
MOTs oil immersed. After discovering my wiring and shunt error, I endeavored
to immerse all MOTs in oil and correct those errors. (Thanks Tim Johnson for
the sage counsel!)

All MOTs in oil is probably the way to go--at least from a heat dissipation
point of view. Oil--in this case taken from my dead PDT (Ariel)--makes a
very significant thermal difference. I've not quantified it; but in an
effort to accelerate oil permeation of the MOTs by reducing the oil's
viscosity, I shorted the secondaries and drove each with 60-80 volts  while
monitoring the oil temperature with a deep fat fryer thermometer. About 2
hours were required to reach 200 deg F. Observing the current draw,
convective flow within the oil, and accessing my experience data base, it is
clear that oil immersion provides significant thermal system property
benefits. In other words, these MOTs would have  long before been smoking
without the oil.
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Well--the bottom line is the output, and I'm guessing most of us "test" our
supplies by drawing an arc. With MOT supplies, the failure fear is
core/winding arcing on the outer most xfmrs, but not  a problem tonight--I
was able to drive the  6 pack at max voltage and pull off some very
satisfying arcs with no sign of problems. Pulling those flaming/growling
angry arcs may be as satisfying as producing big coil discharges!

I should note that I installed a conservatively set safety gap on each MOT
and during initial testing, many of them fired. I gradually increased the
gap and input voltage in increments during the test process. Each MOT is
placed in a virgin paint can (Lowe's). A piece of masonite bolted to each
core serves as a mounting structure for a more salutary connection platform,
properly bringing the leads vertically up and out of the oil. (pics are
coming, if interested)

This MOT experience is hardly ground-breaking  in light of Tim's and other's
work, but I thought I would share the experience. What may of interest is
that these MOTs  are not the brands recommended by Tim J. I'm using  YEC,
Utrad-Triad, and Advance transformers--brands with lesser Core winding
clearance.  This is not to say that I doubt Tim's recommendations--I'm
currently looking for just those brands recommended by him: Zebra, Tabuchi,
etc. What may of interest is that MOTs with less than max core/winding
spacing can be made to work. Caveat--I've not yet fired a coil with this
6-pack, but I've a hunch it will perform in Tesla Coil duty without
problems. Installing individual safety gaps on each MOT may not be a bad
idea.

I'm sure spark gap is soon in the offing.

A bit long here...
Dave Hartwick