RE: First coil - questions

To: tesla-at-pupman-dot-com
Subject: RE: First coil - questions
From: "Coiler" <mycroft-at-access1-dot-net> (by way of Terry Fritz <terryf-at-verinet-dot-com>)
Date: Sat, 28 Nov 1998 19:00:40 -0700
Approved: terryf-at-verinet-dot-com
See comments inserted below.

Michael Baumann
Coiler, Homebrewer, Nerd. mycroft-at-access1-dot-net

> The specs follow:
>   6" secondary wound to 21.125" in length
It would help to know what gauge wire you wound this with. We can compute
the inductance then. (I assumed 24AWG for some of my other comments below)

>   Unused toroid (4" by 16")
>     (can't get break out or tuned so I am not using it)
I'll get to this later, I use a 6x22 on the same basic size coil,
but I cannot get breakout yet either. In my case, I belive my cap is
too small, but you should be able to break this out once you get tuned.

>   .250" refer tubing spaced at 2.50" at 19" angle
>     6.75 turns
Unusual spacing on the primary, most prefer a much tighter wind.
What is the diameter of the inner turn? I assume you mean a 19 degree
rise?

>   12KV -at- .060A
Good enough.
>   approximately .1875" spark gap (Four 2" copper couplings)
Are you cooling this in any way? Suggest a fan blowing across.
>   .01uf rolled poly cap (25KV)  72 mil (12 6 mill sheets)
Here is part of the problem, I think. Cap is too small. Also, unless
you split this into at least 2, preferably 3 in series, this cap
will fail eventually from corona damage. Try to keep the voltage across
any one cap below about 5KV if you can. Even under oil, at 10KV things
start to go south.

> First problem:
> 1) The only way I can get it to work well is if I connect
> the inside turn of my primary to the secondary, otherwise
> I get about 5" arcs jumping between the secondary and
> primary coils an no output.
This is a bad plan. Two things are in effect here.
1) You are not correctly tuned - at all. You need either a bigger cap,
or more inductance (I'd go for the inductance first) Add more turns to
your primary. And DISCONNECT FROM THE PRIMARY!
2) You may be overcoupled. Try raising the secondary out of the primary
a bit. However, I really suspect that the problem is the tune.

If you really meant 2.25 inch spacing on your primary - with no topload
I estimate you'd need between 7-8 turns of your primary to work.
If you relly meant 0.25" spacing, then the number is around around 9-10
turns
[Hint, get a 50' roll of tubing, not 25, and I assumed 24AWG wire on the
secondary]

>
> 2) If I connect my toroid, I get no arcs, even with a bump.
No surprise here, you cannot tune even without the toroid, add the topload
and you need:
Assming your 2.5" spacing you'd need 11 turns (said coil would also use
almost 100ft of tubing, and be 5 ft in diameter, suggest you rewind if this
is true)
with 0.25 spacing, tune is around 14 turns (but you only need 50ft, and its
about
2ft in diameter)

>
> 3) I am not connecting any ground to the primary.  I thought
> it was not 100% necessary, can anyone correct me? (Its
> under construction.)
Primary? No. Secondary? Absolutely. The top end must work against something.
without the ground on your scondary, you will produce all kinds of RF hash
and other undesireable stuff. oh.. and your coil won't work worth a darn
either :)

>
> 4) Is the arc output sound right? Should I be able to get
> more or less output?
More. Much More.  My 6x25" coil did up to 30" with 12KV-at-60ma


Please note, I had to make a bunch of assumptions here - if you could
repost to clarify, it would help us to help you.
items that need to be cleared up:
1) Secondary wire?
2) Inner Diamater of your primary
3) Possible typo on spacing of primary
4) Is the 0.1uf cap the measured value, or calculated?