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Re: [TCML] Spark gap Resistance
David,
I agree with what you say, annoying isn't it ;-)
During my simulation, I had to place a 50R resistor in the circuit in order
for any sensible figures to come out... I had something like a 500W TEsla
coil simulation and it would output 1,600,000volts, the tank current was
like 50KA... the only way I could get it to behave was to class the spark
gap as a 50R loss. then I would get 200KV output and tank current maybe
200amps.
Not sure what you get with XL figures ?
The only place I can find like 50 ohms is the impedence of the primary.
Which shifts just about all the losses into the primary coil. Even though
the primary maybe only 10uH, with the secodnary in situ it could be 100uH...
I get 100uH with 100khz = 62ohms. 62 ohms is 161amps in the tank..
everything makes perfect sense then!
The voltage gain formulas also worked out the same as my simulation
1,600,000volts... though it is in general accepted that 500W power gives
200KV.. well something like that!
To be honest I am convinced that with 500W input power there is only
100watts actually "getting" to the secondary coil. 500W input is not 1.6MV,
but if you fiddle with 100W input then you just about get 200KV.. again all
figures tally up!
In general it seems anything over 200nF tank is bad, but if you have 62ohms
in the primary circuit then you gain nothing at all extra current wise after
200nF.. again figures all tally up!
I think most blame the spark gap for losses, though I feel it works better
with higher currents.. I can't backup my claim though! I think also the
primary resistance accounts for some losses, though It may only be a few
watts per second... But on tank wattage terms, 161amps at 10KV,
1,610,000watt pulse for what, 10uS ? losses over 62ohms ?? losses over 1
second just a few watts! I have no idea on actual figures, so hopefully
people will not shoot me down for that!
I think primary resistance is very important, 100amps over 0.100R primary =
1KW heat loss. 1,000amps is 100KW heat loss. Our primary coils do not melt
as the duration is very small. I did work it out the other day more exact,
was like 100KW pulse and only 10 watts loss per second. 10watts will not
heat the primary coil up one bit but we are loosing KW's of power!
Inductance is the next problem, limits the current flow from the tank cap,
reducing peek current. 100uH primary as a normal figure, 161 amps. Reduce
coupling to give 50uH ...30ohms...more amps! take 400amps as the new figure,
can your tank cap pulse at 400amps in the first place ? If not then you are
forced to use more primary turns so you do not fry your cap bank!
I try to look at things one part at a time, but when you start adding in
everything, it is once big balance act! For such a simple circuit of just a
few parts the considerations are almost beyond me. Like I said before, if
you can rule out the spark gap then everything is easy, everything adds up
in the simulation and in real working coils!
Thats my simple life for you!
Chris
----- Original Message -----
From: "David N. Van Doren" <DNVanDoren@xxxxxxxxxxx>
To: "Tesla Coil Mailing List" <tesla@xxxxxxxxxx>
Sent: Tuesday, November 20, 2007 5:26 PM
Subject: Re: [TCML] Spark gap Resistance
I believe it's the ratio of XL to R. The discharge current of C1 is limited
by XL+R. XL is the useful part and R is thrown away. So the smaller R is to
XL the less gets wasted. In addition to that there is an R-L decay going on
that defines the time it takes the current to decay. So one needs to get
the energy transferred before the end of this decay cycle and the smaller
percentage of that time the less wasted energy. The Higher the ratio of XL
to R the longer the ringdown time and more time to transfer energy hence
the need for lower k's.
Low ratio XL to R, as in High current designs need higher confident of
couplings to transfer the energy before R-L decay takes to much away. (I
think?)
It's a F*****g Balancing act.
A Tesla Coil has too many knobs to turn simultaneously. It seems to help
me to reduce the circuit to as simple as possible for study, just 6
components and a k, L1, C1, R1 "k" L2, C2 and R2. C2 is fixed by the
charging supply (one less knob). If we could settle on a spark gap R, that
would be another knob fixed. --- That would be down to 4 knobs and a "k".
Now if we could fix R2 (streamer R) then we would have just 3 three knobs
and a "k" left to twiddle with. How difficult can it be? (=^P)
Dave
----- Original Message -----
From: "David N. Van Doren" <DNVanDoren@xxxxxxxxxxx>
To: <tesla@xxxxxxxxxx>
Sent: Monday, November 19, 2007 10:43 AM
Subject: [TCML] Spark gap Resistance
Does anyone have any data on spark gap resistance?
and for that matter Streamer impedance?
I've been doing some simulations, and for the lack of any better number
I've been using 4 ohms for spark gap R's and have tried using
220kohm+1.5pf'/ft for streamers, but doesn't always seem to look right in
the sims. Trying to characterize plasma is always difficult at best.
Thanks
Dave
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