RE: SSTC page updated

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

Original poster: "Jan Wagner by way of Terry Fritz <teslalist-at-qwest-dot-net>" <jwagner-at-cc.hut.fi>

Hi,

On Fri, 21 Feb 2003, Tesla list wrote:
 > Original poster: "Mccauley, Daniel H by way of Terry Fritz
 > <teslalist-at-qwest-dot-net>" <daniel.h.mccauley-at-lmco-dot-com>
 >
 > Chris,
 >
 > One thing that I am concerned with is the fact your primary is directly
 > ontop of your secondary.  You also state that
 > you have some corona occuring around the primary.  Two things here.  One,
 > this is the reason you are getting only a 1-2 inch
 > output.  You are probably getting a lot of arcing, albeit very small corona,
 > between primary and secondary.  Secondly, you are slowly destroying your
 > secondary coil like this especially since you are seeing corona between the
 > two already.
 > I'd try to separate the primary and secondary by at least another PVC pipe
 > (at least 0.5" spacing).  I think you'll see the
 > output go up drastically.

Another option is of course to make the primary flatter ("less high").
Although this makes the coupling less, it doesn't give any too drastic
performance decrease. Well, if you don't overdo it... :-) And it
helps well against corona. Alternatively, a slightly more complicated
magnifier arrangement might do.


 > Also, i think if you try building a new secondary / primary coil, for
 > example maybe using 4" PVC for secondary and 5" PVC
 > for primary, you'll probably get better results and run at a much higher
 > frequency as well.  But you do need that primary / secondary spacing or it
 > will be too closely coupled and at high risk for flashovers.

Uhh, VC doesn't sound good at all - in my experience it is one of the
lousiest materials for solid state coils. Ignoring that it costs $0.

Drying it in the oven, sauna or some other hot place, for one day or so
could help to make it perform better. Never bothered to try, tho.
Why go through that trouble when you can get large polypropylene buckets,
readily available, and much cheaper than new large-dia PVC pipes? PP/PE
buckets have considerably better RF properties and don't need any curing.
With a small 400kHz coil, PP vs non-dried-PVC gave about ~20..30%
improvement. I ain't never gonna touch PVC again, PP rulez... ;-)


 > Also, play with the number of turns on the primary.  20 Turns does sound a
 > bit high.  I think I only have about 8-12 turns I think.

True. Btw, blowing 3A fuses at 70VAC => a fuse upgrade would be a good
idea as well ;-)


Chris wrote:
 > I've been doign a few more test with my SSTC and posting my findings and
 > results as I do them. I don't know much about it so some of it is
 > speculation based on current findings. I will keep updating the pages as I
 > do more work. If anyone has anything to add , comments or suggestions then
 > please let me know. The pages are history of the work as I do it, and I will
 > add my thoughs on various things and try to prove or disprove them as I
 > think up more tests. I hope some of you will find the pages interesting. The
 > clever people can sit and grin while I try to make sence of it all :)
 >
 > Chris
 >
 > http://www.cps-games.co.uk/sstc/sstc.htm

About the current measuring method - from your page:
"The smoothing caps work out to a value of 0.5F. These are of course
pretty beefy caps. Off hand I think I worked out this value to give a 2amp
supply for 1 second with a voltage drop of 10volts"


dV/dt = I/C   <=>   I = C*dV/dt
I ~= 0.5F * 10V/1s = 5A

The above approximation works out ok for small dV/dt changes vs
capacitor voltage, dV/V ~= 10% or thereabouts. T.ex. 100V discharging
down to 90V. It could be calc'ed more accurately but that requires
working out the full math, maybe too bothersome.

If you run CW, without the interrupter, the AMM will be able to measure
the drawn mains current accurately (full sine, only little "mess"). The
value it shows is about equal to the peak current drawn if the SSTC runs
with the interruptor. If you know the interruptor duty cycle, you can
figure out the average current from the peak current.

Btw a fuse isn't reliable for <=1s measurements. A fast 3 amp fuse which
doesn't blow during that time could still mean 6A average or more was
conducted (which t.ex. might be the constant current drawn if running from
a _constant_ 100VDC supply - unlike the lower average current of the cap
discharge, exponential voltage decay, setup).

cheers,
  - jfw

--
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  high voltage at http://www.hut.fi/~jwagner/tesla
  Jan OH2GHR