Re: Simulation of a conventional Tesla coil

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

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

There is some time-related dynamic effect in sparkgap voltage though.  I use
100V as a rough and ready number for the breakdown and for low currents, but
consider that the Open Circuit voltage on an arc welder is in the 20-30 V
range, and clearly that supports an arc in the tens of amps range (and, once
struck, the arc probably has a lower voltage drop because of the inductively
ballasted V/I curve of the welder)...

In my recollection, though, such low arc voltages depend on there being a
very hot "cathode spot" to give lots of thermionic emission.  Maybe in the
typical Marx/TC application, the spark doesn't dwell long enough in one
place to form a cathode spot, so the "on voltage" (usually the "cathode
voltage drop) never has time to drop?


Maybe some sort of 4layer diode (DIAC) as a model?


----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Monday, May 19, 2003 6:44 AM
Subject: Re: Simulation of a conventional Tesla coil


 > Original poster: "Bert Hickman by way of Terry Fritz
<teslalist-at-qwest-dot-net>" <bert.hickman-at-aquila-dot-net>
 >
 > Hi Terry and Ken,
 >
 > Don't give up on the spark gap idea just yet. You may be able to use a
back
 > to back Zener diode as a first order approximation as a model for a
 > conducting spark gap. A ballpark estimate for the voltage drop across a
 > firing gap is of the order of 100 volts in either direction, and this
 > voltage drop will be pretty much independent of current flow as long as
the
 > arc channel is open and unconstrained. A 5,000 amp discharge with a 100
 > volt drop would imply a dynamic gap resistance of around 20 milliohms at
 > peak current, and around 2 ohms at 50 amps...
 >
 > Best regards,
 >
 > -- Bert --
 > --
 > -----------------------------------------------------------
 > Unique Offerings - Scarce Technical Books, Coins Crushed by
 > Ultrastrong Magnetic Fields, and Captured Lightning Bolts!
 > All from Stoneridge Engineering - http://www.teslamania-dot-com
 > -----------------------------------------------------------
 >
 > Tesla list wrote:
 > >Original poster: "Terry Fritz" <teslalist-at-qwest-dot-net>
 > >Hi Ken,
 > >At 02:30 PM 5/18/2003 -0700, you wrote:
 > >
 > >>Tell me more about the ohms per gap.  Is that ohms per 1/4"-or-so arc,
or
 > >>ohms per arc + hardware, or... what?  And what, I wonder, would be the
 > >>resistance of a 0.03" gap--with negligible hardware resistance?  That
 > >>might well be a lot better.
 > >
 > >I just looked at the ring down of my spark gap coil primaries with no
 > >secondary in place, and that is the resistance I get.  The 2-3 ohms
things
 > >seems to always work well and predict the gap losses close enough.
 > >It would be interesting to revisit spark gap voltages and currents now
 > >that the equipment is so much better...
 > >Cheers,
 > >         Terry
 > >
 > >.
 >
 >
 >
 >
 >
 >