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Enhanced NST
Hey Guys,
Last week I decided that I was tired of dragging around my coil with the 4
NSTs and 2 rolled LDPE caps bolted to the base. The 150+lb coil assembly
was just too annoying. In order to lighten things up a bit, I decided to
build a MMC and enhance one of my NSTs by depotting and removing some of the
current shunts. Here is the progress that I have made on the NST so far. I
will report on the MMC as soon as I get it all soldered up.
The first step involved finding my very best Franceformer 12/60 and then
attacking it with a chisel and ball peen hammer. I managed to overcome the
case and then I put the tar-laden core in the freezer. The next few
evenings involved chipping at the tar while trying to avoid destroying the
wires. Then came the days of soaking NST in gasoline and digging through
the soft tar with various tools. Finally, I managed to completely
disassemble the core and get the primary off. The secondaries still
wouldn't come off so I put the 2 halves of E core with secondaries still
attached in the oven and baked them at about 225 for an hour. The
secondaries slid off nicely this time! Since I finally had all of the wire
off the core, I worked on it with some aggressive solvent to remove
virtually all traces of tar. Both secondaries and the primary went back
into the bucket of gasoline, then to the gasoline soaked toothbrush, then
soapy water, and finally back in the oven to be dried. The components were
so clean at this point that you can hardly tell that it was ever potted.
BTW, this cleaning procedure was a terrible pain, next time I will simply
use heat from the start!
Anyway, I replaced all secondary leads with Teflon coated wire and wrapped
the secondaries and sides of the E core with several layers of Kapton tape.
Now for the fun part, testing, muhahaha!
I just couldn't resist trying the Enhanced NST (ENST?) without any shunts in
the core. Here are the results. (Output current meters were Triplett 1A
and 200ma AC panel meters, input current meter was the cheap I meter on my
NST controller)
------------
* No shunts
Vin ~ 135-140 VAC
Iout = 0.6A, yes, that's 600ma. BTW, that's after the needle quit
oscillating on the Triplett!
Iin = slammed the 30A meter on my control panel! Core was "humming" quite
violently. Lights dimmed.
Needless to say, I didn't run it very long here, maybe 3 runs of 2 seconds
each. It caused so much interference on the cable TV that my roommate
walked out to the garage and asked what the hell I was doing <g>
------------
* 10 shunts in each of the 4 spaces
Vin ~ 135-140 VAC
Iout = 170ma
Iin = 19A
------------
* 14 shunts in each of the 4 spaces
Vin ~ 135-140 VAC
Iout = 135ma
Iin = 13.5A
The input current seemed to vary linearly with the output current of the NST
for both the 10 & 14 shunt runs. I don't think that the core is saturated
in either of the last 2 runs. I will probably use 12 shunts and aim for an
output current of 150ma for initial TC tests.
While I was at it, I had some PFC caps laying around (thanks Jeff & Brian)
so I decided to play with 'em. I was able to drop the input from 13.5A down
to 7A(!) by adding a large 140uF cap in parallel with the NST primary. The
same test with a 10.4uF cap only reduced the current to 13A. I haven't
calculated or researched what value PFC cap that I need, but the 140uF
seemed to work wonders.
Photos and more details will be on my page in a week or so.
Hot-rodding NSTs in Huntington Beach, CA
Ross