Re: Off-Line Tesla coils (OLTC)

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

Original poster: "Jim Lux by way of Terry Fritz <twftesla-at-qwest-dot-net>" <jimlux-at-earthlink-dot-net>

This starts to look like a high rep rate xenon strobe circuit.  There are a
number of flash tubes that can take this kind of load (several hundred
watts).  I'd definitely look into photoflash type capacitors for this..

For the secondary, you might want those tapewound air core inductors about
which there were some postings a few months back in an oil tank.  Fair
amount of inductance in a small package at reasonable price.  I'll look for
the link.


Having built a few strobe circuits, i'd say you definitely want resonant
charging here (without the "constant current" effect of a NST output, you'll
dissipate as much power in the ballast resistors as you put into the TC).
An offline voltage doubler (a 110:110 transformer could get you 240V into
the doubler without having to wire 240V supply.. or if you live in the rest
of the world, just plug it in) feeding a BIG reservoir cap (several tens of
thousand uF, so the voltage doesn't sag much during the charging cycle (450V
electrolytic caps turn up surplus all the time)) and a conventional
choke/diode charging circuit.  Then, you're not constrained to 60 Hz rep
rate. (actually, maybe a double doubler might work off 110V (a quadrupler..)
normally terrible performance, but in this application you don't care about
regulation, and you can have a ton of stored energy to smooth the ripple.

Actually.. Say you use a offline multiplier to get the primary voltage up a
bit (a x10?), then you might be able to make your primary C smaller, raising
your frequency a bit.



----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Saturday, July 20, 2002 2:33 PM
Subject: Off-Line Tesla coils (OLTC)


> Original poster: "Terry Fritz" <twftesla-at-qwest-dot-net>
>
> Hi All,
>
> I have been doing some studying of off-line Tesla coils.  These are (would
> be) Tesla coils that have "no" HV transformers but run directly off line
> voltages.  What I found so far (purely by computer modeling) is somewhat
> encouraging.  While a far cry from a 38 foot streamer unit, it may easily
> approach an NST powered coil in power.  The only real new components would
> be an IGBT solid state spark gap and rather odd MMC caps.  Everything else
> is quite conventional.  So far, the design would run off 240VAC at around
> 700 watts.  This is the schematic as it now stands:
> >
> The questions I have for those that may know:
>
> 1. Does anyone have any data on Tesla coils running at near 16kHz and
their
> streamers?  Do streamer still form ok?
>
> 2. Does the human body "feel" 16kHz (nice sine wave) high voltage signals?
> Not that I am planning on finding out the hard way ;-)
>
> 3. Does anyone know of a reliable source for say 1000V 2500Apeak IGBTs
with
> built in reverse diode.  Quantity one or two...  Affordable...  IGBT
arrays
> may be the way to go here too...  MMIGBT (sorry ;-))
>
> 4. Any ideas on a better charging circuit?  Note that the diodes are
> conducting during the firing of the gap at the negative part of the cycle
> and only the 20 ohms of resistance provides isolation (but pretty good).
>
>
> If all seems well I will try to make it.  The caps and IGBTs will cost
real
> money but not too bad.  Since it is low voltage, I have a much better
> chance of not blowing up a lot of IGBTs.  Of course, those big ones don't
> blow up easy...
>
> Hope this is of interest and at least amusing ;-))
>
> Cheers,
>
> Terry
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