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A tragic coil




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From:  Bert Hickman [SMTP:bert.hickman-at-aquila-dot-com]
Sent:  Thursday, February 19, 1998 8:51 AM
To:  Tesla List
Subject:  Re: A tragic coil

Tesla List wrote:
> 
> ----------
> From:  mark [SMTP:moyson-at-tig-dot-com.au]
> Sent:  Thursday, February 19, 1998 5:17 AM
> To:  Tesla List
> Subject:  Re: A tragic coil
> 
> Thankyou everyone for responding!
>  1. I have used banks of 630V caps before with no problems.
> 
>  2. The wire on the secondary is a marone/red colour. Does this mean it is
> enammeled?
> 
> Does that also meam that the turns can touch??
> 
> The turns on this coil are separated so if it was uninsulated wire, then
> would it still work or should I trash this coil and build one myself??????
> 
>  3. I replaced the 630V caps with a bank of 3KV caps and then a strange thin
> happened. When I turned it on....no sparks but absolutly MASSIVE RF
> interference. The tv in another room lost the reception (I was told) and the
> auto garage door opened up by itself and went "haywire" till I turned the
> coil off. It also lit up a neon light at about 10cm from the coil.
> 
> What is going on here?????? I am totally lost now!!!!

Mark,

Your primary tank circuit must be tuned to oscillate at the same
frequency as your secondary for optimal operation. When you changed the
tank cap did you retune the system?

If the secondary doesn't "break out" (start throwing streamers), you
will generate large amounts of RFI, much to the consternation of your
equipment and possibly your neighbors. Place a small sharp object (a
nail, short piece of wire, or a thumb tack, point up, on top of the
discharge terminal and carefully tune for maximum spark at lower power
levels. Once you're in tune, you can then bump the power level upwards.

>From your description, it sounds like you DO have insulated wire on your
secondary. You want the turns to touch to maximize inductance (and the
Q) of your secondary. Do you have a good RF ground connected to the base
of your secondary? If you have relatively few turns on the secondary,
this may be one of the major reasons why the coil is a poor performer. A
tight-wound secondary, with moderate gauge (#22-26 AWG) wire will give
you better performance.

BTW, I'd also bet that the 630 volt caps you used were oil-immersed
mylar filter caps. The dielectric heats up quite rapidly under RF
conditions, and since they are sealed, the pressure builds up internally
until they blow, showering you with hot oil (sometimes PCB's) and
capacitor fragments. What kind of caps are you using now?

Check out the archives on Chip's website or on Funet for LOTS of solid
information on caps, coils, tuning, etc...

Safe, unexplosive, coilin' to you!

-- Bert --