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Re: Solid-state t.c.'s
-----Original Message-----
From: Tesla List <tesla-at-pupman-dot-com>
To: tesla-at-pupman-dot-com <tesla-at-pupman-dot-com>
Date: Tuesday, March 14, 2000 6:35 PM
Subject: Solid-state t.c.'s
>Original Poster: "Kennan C Herrick" <kcha1-at-juno-dot-com>
>
>The List apparently enjoys precious few solid-state t.c.-ers so I paid
>particular attention to Gary Johnson's recent posting.
I posted a bunch of stuff several years ago. I got discouraged and decided
to wait until IGBT's got cheap and powerfull enough. Why?
Impulse coils perform better than CW or CW-burst coils. Arc length and bang
just aren't there.
FET's are too fragile. Paying a lot for FET's, only to see VSWR (that is,
high unabsorbed, primary back-emf) destroy them doesn't sound like much fun.
Lots of grief paralleling devices; FET's may share current better than
bipolars, but they are not perfect.
Need of significant protection- transorbs, thermal and active overvoltage
shutdown.
>4. Thus, I reasoned, I need to minimize the quantity of turns in order
>to minimize the voltage, so as to allow me to use power-MOSFETs of
>reasonable voltage capability. At one time I looked into driving the
>secondary directly, at its bottom end, but I concluded that the impedance
>there was way too high to get a decent current from reasonably-rated
>transistors. So, I have chosen a primary configuration incorporating
>just 1 equivalent turn--the absolute minimum.
>e) allow for all power sources (typically, electrolytic capacitors
I realy hope you checked into the construction technique and loss factors
for your electrolytic capacitors! They will undergo horrible abuse. Many
people think electronic components store an ephemeral electric and magnetic
field. Electric and magnetic fields mean energy density, mean FORCE stored
in magnetic and dielectric materials. High MU and E materials are frequently
lossy, and suffer from hysterisis and other loss mechanisms, espiecialy
acoustic losses. Good luck.
>But my system does have the advantages of a) no instantly-lethal high
>voltage in the primary, b) no noisy/unreliable spark gap and c) being
>always and instantaneously in tune.
I wish you the best of luck. I hate spark gaps. My plan (after toasting my
.5uF capacitor/MOT, that I thought was poly but was realy mylar) is to
maximize voltage, minimize capacitance and suffer with insulation woes. What
I would realy like are giant avalanche-breakdown transistors or diodes.
There are devices like these intended for radar service, but I would want
them for much lower frequency use. There are also trigger diodes used for
HPS lighting, but these aren't realy suitable for use either.
Scott