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Re: 20 joules at 100 bps vs 4 joules at 500 bps

Original poster: Greg Leyh <lod@xxxxxxxxxxx>



Original poster: "Dmitry (father dest)" <dest@xxxxxxxxxxx>

[snip]

Tl>  > b.t.w. - how i must take into
Tl>  > account flashover voltage? imagine i`m building 4" coil, secondary
Tl>  > height 20", frequency at around 220khz - how could i know that
Tl>  > voltage? or - i`ve calculated the toroid voltage (70 cm diameter) -
Tl>  > 1.2 MV - what height should be the secondary to prevent flashovers?

Tl> There's a bit of suck and see.

oh no no no - i`ve no time, so i prefer to "read & see" :-)

Tl>  Mileage varies depending on
Tl> atmospheric conditions. Surface tracking also plays a part. I think
Tl> Greg Leyh's Electrum coil may have shown a tendency to flashover at
Tl> odd times and has an output approaching 1.5MV.

let`s see:
http://www.lod.org/Projects/electrum/techdata/electrumspecs.html

"SECONDARY COIL TOWER STRUCTURE
Lsec = 0.130H
Fsec = 37.92kHz (w/7' spherical electrode), 52.60kHz (no electrode)
Isec (pk) = 61A, with full primary voltage at 38kHz
Total tower height - 38' 8"

61 a means that bang energy = 241.86 joules - real "big bang", i love
this guy %-) total capacitance of discharger and the coil would be 135
pf, then secondary voltage is 1.9 MV. and 38' is not enough for such
voltage? i don`t believe - maybe some construction feature are
involved, maybe lack of thick coats of poly ^___^
and it seems that sphere protects the secondary worse than toroid:
http://www.lod.org/Projects/electrum/testing/pages/electrumeric.html


You're correct -- a toroidal electrode would have provided far better field control than the spherical electrode used on Electrum. The spherical electrode geometry was part of the overall aesthetic requirement however, and had to be accommodated. As a result, the operating instructions for the machine specify to immediately remove power for 5 seconds if a tower strike is observed.

Based on experience, 5kV/inch seems to be a reasonable surface gradient to maintain on the outside of a secondary form. Electrum has to run at almost double that, but uses an external coating of quartz-loaded fiberglass, which is periodically washed and electrically tested. So far, there has been no permanent surface tracking observed in Electrum's outer casing. The 2x4's supporting the secondary windings in the expeirmental coil
http://www.lod.org/Projects/120L50K/bisectedprimary.jpg withstand an average surface field of about 4500V/in, in normal use.

The next secondary coil that I'm working on will have convolutes on the outer casing, like this: http://www.lod.org/Status/90L10KPhotos.htm The intention here is to support higher surface fields than a standard external winding, without requiring significant amounts of transport care or maintenence.


-GL