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Re: MOT to NST "extra transformer"
Original Poster: Terry Fritz <terryf-at-verinet-dot-com>
My comments are below. I didnīt want to SNIP this mail yet.
Hi All,
I am going to get a MOT to play with and a thought occurred to me today.
Most MOTs (microwave oven transformers) put out about 2000 volts at 300 mA.
The voltage is too low and current too high for most TC applications.
However, how hard would it be to make a transformer to bring it to a nice
level? Perhaps a 2000V/300mA primary and a 12000V/50mA secondary. Since
the turns ratio would only be six to one, there should be room to use
insulated 24 gauge wire on the secondary which would make it almost burnout
proof (in oil). In fact, two or more MOTs could be used to drive this
"extra transformer". The current protection in the original MOT should
function normally (I think).Since the number of secondary turns is much less
than say a 120v to 15000v transformer, such an extra transformer would be much
easier for the average person to wind. With 24 gauge insulated wire in oil
with poly between
layers, It would be burnout proof no matter how hard it was hit. It would
still need to be rated for 900VA and one would have to do a little design work
but this may solve the problem of not being able to get HV transformers in
certain countries and all that.
TF
Hi Terry, ALL
This is a very, very interesting thought. Why didnīt I think of this? I have a
good iron core from a welder and three Gardner type MOTS (2.3kv-at-700mA).
They are virtually indestructable. I hard tested them. They ran a Jacobīs
Ladder for ten minutes and didnīt even get warm. The only thing that got warm
was my power cord !
At almost 7kV I would need a step up ratio of only 1:2.2 for 15kv and 320 mA.
This would pretty much fill my bill for the transformer and it would be easier
to wind than a 230V to 15kV transformer (Iīm almost ready to do this !!).
Please do experiment with this and keep us posted. There would be a lot of
Teslaphiles out there, that would be grateful till deathīs end.
The only "fault" I can see in your thoughts would be your given 100% input =
100% output (i.e 600W in and 600W out). Transformers arenīt perfect V & I
convertors.
Well, I couldnīt resist trying: I used a 2kv 500mA MOT (non Gardner type, just
in case something goes wrong) as my first step up transformer. (in: 230V
out:2kV)
1 Test.)
A Gardner MOT hooked up backwards 230 (in this case 2kv)in / 2.3kv out: Step
up Ratio 1:10
(230 v side was connected to the 2kV from above)
Results: This did not work at all. A string of 10 neon lamps (series)
connected to the 2.3 kv output barely lit. My guess is the primary side of the
Gardner type had too little inductance/resistance so my 2kv "input" probably
didnīt put very much voltage.
2 nd Test)
A step up transformer from an old tig arc starter setup (also 1:10 ratio 230V
in 2300 out) was connected the same way as test one.
Results #2: Amazing. The output of this transformer really had guts. The
output was at least 20kV. The transformer held up quite a while. I attached it
to my small tc (being originally powered by a 10kV 20mA OBIT). The spark
length didnīt change, but the sparks were a lot hotter (crisp, snappy white).
I didnīt retune the setup, tho, so it might have made longer sparks. After
about 3 minutes the second step transformer died. The secondary arced over
internally (no wonder, I was running it at 10 (!) times the rated limit.
1st Conclusions:
1.) The primary of the second step up transformer has to have a pretty high
inductance, otherwise your MOT wonīt be able to drive it.
2.) The primary to secondary step up (using magnet wire) ratio cannot be very
high as the insulation wonīt hold up. I would suggest something around 1:5, no
more. It would be interesting to find out how high you can go running it
under oil and using enameled wire, tho.
3.) The MOT (non Gardner type) and the second step up transformer get very,
very hot, after only a few minutes of running. This wonīt result in a very
long life. I noticed the same effect as I was hard testing MOTs on the Jacobīs
Ladder. The only type that stayed cool (cold !!) were the Gardner type. These
MOTīs seem to be able to supply real brute power. The insulation of these MOTS
let you string 4 of em (dry, in series, w/o a center tap) w/o any corona or
arc overs (i.e: they seem to be very desirable). I would guess 6 of these
would hold up quit well if ctīd and run under oil.
They are not current limited (no shunts), so you would need an
inductive/resistive type ballast on these.
4.) We should continue to investigate this type of setup. Over here in Germany
(Europe? ) you canīt get hold of decient NSTīs.
Real (iron core) NSTīs are starting to die out. They are being replaced by
solid state stuff.
These PSUs are dimmable and have only about 650-900 volts output. The neon is
started by a small thyristor/trigger transformer that gives the ionizing kick.
These are of course useless for TC work. I would suspect that America is going
the same way, at least for smaller signs. The tubing diameter, etc. of the
neons is also decreasing, which lets the manufacturers make smaller and
smaller transformers. This makes it hard for beginners to find suitable
transformers. Bigger coils will probably continue to run on PTīs or pole pigs
(in the US at least)
Given second thoughts, should our experiments fail, it shouldnīt be too
difficult to wind your own HV transformer I will probably try this anyway,
even if I find a suitable transformer, just to find out. I will try it as soon
as I have the time.
Comments, Suggestions, and Experiments are welcome,
Coiler greets from germany,
Reinhard