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Re: First light
In general, I think the impulse to make a TC with fairly little
expenditure is a good one. Being a poor college student, I need to save
all the cash I can. I've spent probably two summers collecting scrap
materials for a tesla coil-- I have decided recently to start building a
magnifier with what I have: about 20 lb. of 18 gauge solid copper wire
(insulated) which will be the driver secondary--- a large poly barrel, and
some 1/2 inch hardline aluminum coax for the driver primary.
I also have 8 microwave oven transformers which I have experimented
extensively with, and I have concluded that in order to make a suitable
power supply with them I would need to arrange them in a center-tapped,
staged, series/parallel configuration, submerged in insulating oil or
wax. I intend to acquire (hopefully with no expenditure) four or more of
the heavy duty, large core type. These usually have a polished appearance,
have little transformer hum when connected, and will arc continuously
without burning up. Avoid transformers built by "Advance" transformer co
(these are 4kv instead of 2, and handle less power, despite their large
appearance) or any that have different voltage and current ratings. The 12
transformers will be arranged with six on either side of the center tap,
with matched pairs of two, bottom fed for a maximum voltage of 12 kv from
both sides of the array. To do this several things are required: detach
the lowest turn of the high voltage coil from the core on all of the 4 and
6kv stages. The 2kv stages won't need detachment, since they will be
grounded anyway. The output of the 2kv stage is tied together, fed into
the 4kv ground, and the 4kv output is fed into the 6kv ground. I have
found that the 6kv stage is really the only one that needs insulation-- any
un-insulated transformer being fed 4kv that is dishing out more than 2kva
will burn up from core to coil breakdown. To prevent this, the whole array
will be bolted to a large hardwood board and placed upside down into a box
of similarly heavy construction, and then backfilled with wax-- I think
here I will use mineral oil with poly dissolved in it-- thanks to whoever
came up with this idea. Any comments would be appreciated about the
configuration-- I'm not sure whether connecting the stages in parallel will
result in stress on any of the Mots that aren't uniform.
Brian-- to go back to your problem-- I think it is entirely possible to
make an un-insulated MOT supply (under 2kva) that will put out anywhere
from 60 to 120 ma at 12kv-- with no expenditure, if you can find the
transformers for free. All you need is six transformers, three for each
leg, and a current limiter. All that is needed for the current limiter is
a seventh MOT, connected in series with the array, with the output
shorted. I have tried this in the last week, and after continuous arcing,
none of the transformers were warm.