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Re: [TCML] SISG PSU problem
The Piranha primary circuit is resonant. It will ring the transformer
voltage higher than normal.
See this file that has all the waveforms and such:
Once the coil fires, the voltage will increase just like LTR coils do.
That is why you have to turn the variac down further to get it to stop
firing. The normal peak voltage from the transformer is multiplied three
times in the diodes and caps once the coil is firing. I have the
MicroSim files somewhere.
The medical transformer should not have failed. It is not a terribly
hard load. That might have just been a defect.
Herwig Roscher wrote:
Hello silicon coilers,
I've copied Terrys genial Piranha II-system. After replacing my
previous capacitors with the CD 940 series - thank you, Terry - the
strike distance increased from 35" to 40". As "longer is better" I
then replaced the 2232 Vrms-MOT with a 2880 Vrms-tranni from a
diathermy machine. This increased the strike distance to 45", but
suddenly the tranni died (still stone cold). I found out that the
reason was a short in its secondary winding and I was very surprised,
because I always assumed components for medical applications to be
more robust than those for microwave ovens.
So I rewired the MOT and soldered 4 MOVs S20K625 in series directly
across its secondary winding in order to protect it from kickbacks.
To my surprise they got so hot within seconds that the became
Strange: The MOT puts out 2232 Vrms and the maximum permissible
voltage of the 4 MOVs is 4 x 625 V = 2500 Vrms. So I disconnected the
diodes from the tranni and repeated the test: no heating at all!!
Conclusion: There must be a voltage that heats up the MOVs when the
diodes and the rest of the circuitry are connected. To find out the
amplitude of this voltage I added MOVs in series until they stayed
cold: 3675 Vrms!! I didn't dare to connect my scope in the
neighborhood of a running Tesla machine. Therefore I choose this
Looking at Terrys description of Piranha II I found that he used a
2000 Vrms MOT which - after the voltage doubler - should provide a
little less than 5600 Vpeak. He set the firing voltage of the SISG to
6300 V and the system works, but where did the necessary additional
voltage come from? In one of his MicroSim models he attributed 65 H
to the secondary winding of the MOT. Could switching this large
inductance cause high kickback voltages, not only enabling the SISG
but also causing the voltage breakdown of a maybe not so good
insulated tranni? This kickback voltage would also contribute to the
"chaotic" = unpredictable behavior of the Tesla machine surely.
Unfortunately I do not see any method to protect the secondary
winding of the tranni except of using a model 240/4000 V and to run
its primary winding from 120 V. Hopefully the secondary winding is
designed to withstand much more than 4000 V and this would provide a
larger safety margin. And MOTs with potted secondary windings should
Any critics, comments and proposals are very welcome.
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