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Re: [TCML] Question on Dummyload-Testing in DC Resonant Chargingcircuit, similar pursuit

Hi Stefan,

Thanks for the details about your system - very impressive, indeed! Getting back to your original question about having a high resistance dummy load...

As long as the the spark gap's dwell time is more than about 2-3X the RC time constant of the tank cap and dummy load, the residual voltage remaining in your tank cap will be between 14% (2*Tau) and 5% (3*Tau) of your fully-charged voltage, and the residual energy left in the tank cap will be between 2% and 0.2% of the original bang energy --> i.e., negligible. With your load, and with the filaments hot, the RC time constant is only 25 uSec, and considerably shorter when the filaments are cooler. So even with higher load impedance, > 98% of the tank cap's initial energy is transferred to the load after about 75 usec.

Let's compare this with normal operation (with the primary and secondary windings in place). Depending on your system's coupling coefficient, a single Primary-to-Secondary energy transfer, or vice-versa, will take 2.5-4 RF cycles (for k in the range of .22 - .13). I'll also assume that you have an efficient spark gap that provides 2nd-notch quenching. Thus, the initial tank energy is transferred to the secondary, back from the secondary to the primary, and finally back to the secondary, after which quenching occurs. Based on the assumed coupling, the total process should take between 7.5 - 16 RF cycles. I'm guessing that your coil may have an operating frequency in the range or 60 - 80 kHz, making RF cycle in the range of 12.5 - 16.6 usec. With 2nd-notch quenching, the total active energy transfer time will thus be in the range of 94 to 200 usec.

So, even though your load bank has higher resistance (than the surge impedance of your tank), because the lamp load is almost purely resistive, it removes tank cap energy significantly FASTER than your proposed (highly-reactive) tank circuit and secondary will. Not entirely obvious until you bend the numbers... :)

Bert Hickman
Stoneridge Engineering
World's source for "Captured Lightning" Lichtenberg Figure sculptures,
magnetically "shrunken" coins, and scarce/out of print technical books

Teslalabor wrote:
Hi Jim,

you can not run such a circuit only with a primary in place without a
secondary. The result would be extreme currents through your transformers,
spark gap and capacitor, which would mean total failure of this components.
So I did some calculations concerning the dummyload with the result, that
the halogen dummyload testing is absolutely okay and the very best method
for testing such a circuit without messing arround with sparks... ! In my
case it consists of 20 halogen bulbs, each is 240V 500W.
10 of them are connected in series and 2 of this groups in parallel, giving
a 10kW Dummyload. The resistance of one bulb is 100Ohm when glowing, so 10
of them in series is 1kOhm, 2 groups in parallel giving 500Ohm total of my
The dwell time of the spark gap is arround 500us, so this is enough time to
empty my 50nF capacitor during each bang.

Jim, I think you need another charging reactor, the Burnett-Equations will
show you. This 150H inductor, built into your HVDC Supply, is not suitable.
It's inductance is much to high, I think it is not possible to build a
properly resonant charger with this. Also 24kV could mean some trouble,
remember that the tank cap is charged to twice that voltage, in your
case 48kV !

Some short facts about my coil: The system is designed (by using the
Burnett-Equations) for running 7kW full power @ 400bps. I am actually
testing it with my 3000rpm Schraner-Style SRSG (Hello Kurt :-) ), running @
only 300bps fixed (it is not variable in speed). The variable speed rotary
is still in progress...  System is 3-phase powered, with a 6-pulse
rectifier, DC Charging voltage is 13,3kV. The tank cap is 2 Maxwell Caps in
series, each 40kV/100nF, giving me 80kV / 50nF. My charging reactor is 12,4
Henries. The energy is fired into the 10kW dummyload, mentioned above. The
performance seems to be amazing. Primary and Secondary coils will be build


----- Original Message ----- From: "Jim Mora" <wavetuner@xxxxxxxxx>
To: "'Tesla Coil Mailing List'" <tesla@xxxxxxxxxx>
Sent: Sunday, June 08, 2014 4:18 AM
Subject: Re: [TCML] Question on Dummyload-Testing in DC Resonant
Chargingcircuit, similar pursuit

Hello Stefan,

Why not get some heavy gauge wire and simulate the calculated turns?
Now you
have introduced the inductance albeit the R is off rather than purely
resistive load which seems reasonable to me as R is so small anyway. I
people have tuned traditional coils ahead of time this way. That was a
Resonance trick I believe.

I too am starting on a DC resonate coil. I have a huge Choke in my
circuit which can not reasonably be altered. I have the ability to add a
de-queing diode easily enough, but there is not one in the old charger
the military. This one outputs 24KV and is full-wave 3P tube circuitry
6x GL
8020's. The inductor says it is 150H ! Plugging in Richie Burnent's
equations, if I performed the math correctly, I am limited to 116 BPS
with a
.05UF Tank cap (I have 2 .1uf's) It drops to 82 BPS @ .1 uf. So that's
too ideal and I wonder about quenching and Tungsten size in the rotor.

The equations also reveal my max power will be 6.7KW at 116BPS which is
probably fine. Comments anyone?

Jim Mora

Sorry to hijack your thread Stefan, we may be talking more ;-^) What
size is
your coil going to be?

-----Original Message-----
From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] On
Of Teslalabor
Sent: Friday, June 06, 2014 10:14 AM
To: tesla@xxxxxxxxxx
Subject: [TCML] Question on Dummyload-Testing in DC Resonant Charging

Hello all,

I just finished the DC resonant charging circuit for a planned medium
coil project. It is 3-phase powered and today I started testing it with
reduced power and a dummyload in place of the primary coil, which will be
installed later. The dummyload consists of several 240V 500W halogen
which are glowing very nice and smoothly :-) So on the first glance, it
seems to work well for testing.
But the question is, how does such a dummyload with a high resistance

say 500-1000Ohms when glowing) influence the behavior of the charging
circuit? My guess is, that the capacitor never can discharge
completely into

this dummyload during each bang and still have much of its charge
after each

bang... So the drawn power should be much higher, when using the real
setup later, instead of this dummyload?


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