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Re: Several questions about coil.
In a message dated 12/27/99 11:46:29 AM Pacific Standard Time,
tesla-at-pupman-dot-com writes:
> Original Poster: Kamil Kompa <czlonek-at-polbox-dot-com>
>
> I have made a tesla coil which is powered by 10kV 150mA transformer.
> I have a static gap (im still trying various gaps - any suggestions),
> 4in secondary (770 turns made with 0.7mm wire),my primary is
> flat archimedes spiral (it's12 turns ,but of course I can adjust number
> of turns from 1 to 12). I have 23nF capacitor made of 20 beer bottles
> and salt water. My grounding is home water pipe system. My home
> installation is 10A 220V 50Hz.
> This is characteristic of my coil , and i have some questions about it.
>
> My first problem is that I connect my transformer with 1800W water
> heating device (i don't have variable transformer :-( and without
> ballast,my 10A fuse burns when the spark gap is on.
> What is real output in this connection?
> Is it much worse than with variac.
>
> Second question is about capacitors. I have made a 25nF rolled capacitor
> , and it worked, but much worse than beer bottle capacitor. What can be
> wrong with it ?
>
> I have also problem with toroid. I have made a 17pF toroid but it
> doesn't work properly. It's not making any sparks into the air. I can
> make only about 4-5in spark to grounded rod. I noticed that when im not
> using a toroid , but small, one inch diam. ball,
> my coil produces 3-4 in sparks into the air and also 4-5 in sparks to
> the grounded rod. Of course i want to do something to make my coil
> working properly with toroid. Which part of my coil may cause this
> problem ? Is the toroid too big, to use in my coil, or something is
> wrong?
> Of course i remamber about changing resonant frequency.
>
> My last question is about configuration of my coil. If you have any
> suggestions, what to change in my coil please share your knowledge.
>
> Great thanks for all answers.
>
> Kamil Kompa
> czlonek-at-polbox-dot-com
Kamil,
I ran some calculations on your coil - after making several assumptions. The
secondary should be approximately 9.4 mh. The primary, I assumed to have an
internal diameter of 6.0", with .25" dia tubing and .25" spacing between
turns. This would produce an inductance of about 45 uh. With a 17 pf
toroid, you would need .005 uf of primary capacitance for proper tuning.
This would be tapped at turn #12. Proper tuning at turn #11 would require
about .006 uf. I believe your coil is way out of tune. I haven't built salt
water caps before but I remember someone saying that beer bottle caps produce
about 100 pf each. If I have this correct, your 20 bottles would only
produce about .002 uf of capacitance - which would be way too low. You could
probably tune this coil by using two .025 uf caps in series. This would be
equal to about .0125 uf and would tune at about turn #8 on the primary.
Actually, the coil should work with the .025 uf cap when the primary is tuned
to turn # 5 or 6 on the primary. Are you sure the .025uf cap is good - and
not failing (shorting internally) when in the circuit?
Good luck.
Ed Sonderman