What next for longer sparks?

From:  FutureT-at-aol-dot-com [SMTP:FutureT-at-aol-dot-com]
Sent:  Friday, July 03, 1998 8:30 AM
To:  tesla-at-pupman-dot-com
Subject:  Re: What next for longer sparks?

In a message dated 98-07-02 01:41:36 EDT, you write:

<< snip
> - is 20" the best I can get for my tank and my secondary size?
> - what should I do to increase the streamer length?
> I ask this because I feel (primary capacitor size, MOT max current, etc.) I
> have got plenty of power to get longer strikes. What is the best way to go:
> - bigger toroid?
> - bigger secondary?
> - more coupling (I didn't go lower than 1.5", I didn't reach overcoupling
> yet)?
> - different spark gap?


I think you have a good idea in using the voltage doubler circuit.  I
agree that your coil can give longer sparks...at least 35 or 40".

I don't think a bigger secondary or tighter coupling will help much. 
A big secondary would probably add only about 3" more spark length. 
But it's worth playing some with the coupling.   I'm not saying that
coupling is not important...it is very important, but I think the 
coupling is probably about right in your coil.  Be sure to try not 
only tighter coupling, but looser also, if you haven't already.  It is
that the quench is failing in the gap.  If you turn up the variac power and 
the power input goes up, but the spark length stays the same, the 
quenching may be failing.  Once the main problems are solved, you
can benefit from a larger toroid.  Since your spark is only about twice
as long as the toroid's diameter, this tells me that the main limitation
is elsewhere at the moment, unless you have numerous simultaneous,
very bright streamers coming from the toroid.  In that case, a larger
toroid will reduce the number of streamers, and better utilize the
energy.  But if there are only one or two weak streamers, then a 
larger toroid won't help much.  My point is, the toroid won't help
unless sufficient energy is available to drive it.  

BTW, I use a 4 1/4" diameter by 23" high secondary wound with
# 28 wire, with a 6" by 26" toroid and I get 65"  sparks at 1760 watts,
which shows that small coil forms can perform well.

I suspect the main problems are the gap and/or the amount
of input ballasting.  You may have to adjust the amount of
inductive ballast you're using to give best results with the amount
of power you have available.  Am I correct that you are using 220V
at 10Amps maximum?

Low voltage, high current, large cap, limited power, static gap
systems can be tricky to optimize because the low voltage limits
the number of series static gaps you can use.  You may be getting
some power arcing and poor quenching in your gap, and may benefit
from the use of a few more series gaps if you have enough voltage.
You may have to reduce the gap spacings to make this possible.  

Have you tried putting the gaps in series rather than series parallel?
You may have to decrease the gap spacing.

Without the ballast MOT, the gap may be power arcing.  It may
be power-arcing somewhat also even with the ballast MOT is place.
Another possibility; the ballast MOT may be limiting the current *too*
much and reducing the output sparks?  You may need an adjustable
ballast.  The coil may be current-starved using the ballast MOT.

A rotary gap may help, but it should be possible to get good results
using the static gap I suppose.  The small number of turns in the
primary may be making it harder to quench the gap.

In any case, it seems a fine balancing act between ballasting
and gap adjustment/type will be needed to optimize this coil within
the power input constraints.

Can you safely use a 20amp fuse?   :)     I think you'd get 50" sparks
with more power input and a larger toroid to match the greater power
input, (provided that quenching and ballasting are correct).

I tried to cover a number of possibilities, because it's hard to give
good advice sometimes without actually seeing the coil in operation.

Good luck and safe coiling to you,

John Freau