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Re: Beginner's Tesla coil -First Light!
At 05:57 PM 11/16/98 -0800, you wrote:
snip>>
>
>Terry:
>
> Two points. First, I could never get more than about 3-1/2 inches
>spark out of the coil, due to internal arcing even in oil. Can 't tell
>if your 10" sparks are directly from the coil or from a TC with the
>primary capacitor charged from the coil, but if you got 10" directly out
>of the coil you are very lucky. Second, the insulation between the
>inside of the secondary and the primary will break down at a thousand
>volts or so, so make sure not to exceed that voltage.
The 10 inches was from a rod conected to the coil's output and going upward
through an oil filled PVC pipe. The arcs were from the top exposed rod
back down to the tray the coil was in. I cut the coil open and the
internal insulation is very well done. A HV terminal to ground arc inside
the coil will have to go through 1/4 inch of epoxy and many layers of
insulating sheet. The coils secondary is wound with different insulation
thicknesses. Just like some old induction coil designs. I am quite
confident that a good coil will stand up to at least 100Kv and probably
twice that. Of course, without oil the output will just arc a few inches
to the input wires across the outside surface of the coil. The oil gets
the output far enough away so that the sparks can reach their real length.
>
> I am able to get 5"+ sparks from two coils (in oil) hooked in series
>(low end of secondaries connected together and to the AC line through
>600V MOV varistors in parallel with 4700 uufd 7 kV bypass capacitors.
>Primary is driven by a quadrac working from a voltage-doubling DC supply
>directly connected to the line, and using resonant charging to get about
>600 volts across the capacitor. This is the same driver I have posted
>here from time to time.
>
>Ed
>
The problem is the core!! When you pump 600 volts into the primary the
core saturates and just acts as a short to all that input power. Sam
Barros (and I in the distant past) as well as many of us have all tried the
high voltage input thing. The problem is that the high voltage induces
high flux in the steel core and it just saturates and eats up all the
power. After reading Sam's earlier post, I kept wondering where all the
power was going and why it didn't work. The recent transformer posts gave
me the clue about saturation which was the problem all along. Cut the
cores off and tune them like tesla coils. You will then get "real" spark
finally out of these coils. Trust me, I know what I'm doing! :-))
Terry
Holder of the coveted GMHEICSLR :-))
References: