Re: Simulation of a conventional Tesla coil

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

Original poster: "K. C. Herrick by way of Terry Fritz <teslalist-at-qwest-dot-net>" <kchdlh-at-juno-dot-com>

Bert, Terry (& all)-

In my most complex Marx-like simulation so far, I incorporate 8
capacitor/gap sections with the capacitors charged resonantly using the
switched mains sine wave I'd started out with.  I use 5 m-ohms for each
gap resistance and 10 m-ohms for the rest of the 2-turn primary
resistance--wildly optimistic, no doubt.  I get 375 KV output,
diminishing to 20% in ~ 4 cycles (with 0.2 coupling).  Rms mains current
is ~12 A at 115 V.

So I raised the gap resistance to 20 m-ohms each but didn't incorporate
any gap voltage-drop.

I then got a wimpy 225 KV output but lasting somewhat longer.  There's an
odd anomaly, though, in that at the 4th cycle the primary current
reverses phase & opposes the output voltage-phase for a while.  Until
then, primary current is in phase with output voltage.  Can anyone
explain that?

Perhaps Triacs paralleled by MOVs might be used instead of gaps.  The
MOVs would protect the slower Triacs until they fired.  Peak primary
current occurs in the 1st 1/2 cycle and is 4 KA with the 50 m-ohm total
primary resistance.  (So my prior surmise as to when the peak current
occurs was not correct.)  Any thoughts on Triacs, anyone?  The first half
cycle at 125 KHz occupies only 4 us so one would want speedy Triacs.

Ken


On Mon, 19 May 2003 07:44:20 -0600 "Tesla list" <tesla-at-pupman-dot-com>
writes:
 > 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
 > >
 > >.
 >
 >
 >
 >
 >
 >
 >
 >