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[TCML] SISG PSU problem
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
unsoldered.
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
method.
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
be preferred.
Any critics, comments and proposals are very welcome.
Herwig
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