What next for longer sparks?

From:  D.C. Cox [SMTP:DR.RESONANCE-at-next-wave-dot-net]
Sent:  Thursday, July 02, 1998 11:17 AM
To:  Tesla List
Subject:  Re: What next for longer sparks?

to: Marco

The main limiting factor here Marco is the diameter of your secondary coil.
 If you step you to a 6 or 8 inch dia secondary coil your spark length at
this power level with this cap should increase to at least 48 inches.  We
run a 20 inch dia. coilform running the same .05 MFD cap at 500-600 ma
drive current and it delivers a 9 ft. long spark.  Two important factors to
consider for any design are:

1) Make the secondary inductor as large as practical for your intended use.

2) Tesla coils love current.  9-15 kV drive is all that is required but
most systems see substantial improvement by increasing available current
from the power xmfr.

Your system has plenty of current -- now you need to run a much larger dia
sec coil with this power level.


> -----Original Message-----
> From: Marco Denicolai <marco-at-vistacom.fi>
> To: tesla-at-pupman-dot-com <tesla-at-pupman-dot-com>
> Date: Wednesday, July 01, 1998 12:29 AM
> Subject: What next for longer sparks?
> After 3 hours of running my TC I got a strike from toroid to the primary
> that
> killed one of my doubler diodes. I had no strike rail that time. I
> now the single diodes with two diode pairs (two diode in series). In
> parallel with each of the 9000KV 350mA diodes a 33Mohm 3.5KV resistor
> and a series of two 1.5nF 3KV capacitors. Guys, that was the best I could
> get from the local store! I also grounded back my strike rail.
> In a few days I'll be testing this new setup.
> Anyway, after initial excitement, I was able to precisely measure strike
> length to a grounded rod and that was 20" (not 1 meter as I wrote same
> ago). That means that the primary-secondary rises my tank HV roughly by a
> factor of 60 (from 6.5 KV to 400 KV).
> The voltage drop in my tank (from 8KV to 6.5KV) is due to the third MOT
> which
> works as a reactor in series with the MOT primary windings. Without that
> always blow my 10A fuse.
> My questions are:
> - 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.)
> have got plenty of power to get longer strikes. What is the best way to
> - bigger toroid?
> - bigger secondary?
> - more coupling (I didn't go lower than 1.5", I didn't reach overcoupling
> yet)?
> - different spark gap?
> *************************************************************************
> My coil data:
> Secondary 4.33" diameter, 19.7" wind with AWG 26 enamel wire, 7 layers of
> epoxy paint. Toroid 3.15" diameter tube, 11.4" outer diameter, 12.7 pF.
> Mounted 1.6" over the secondary top. The pair resonates at 240 KHz.
> Primary 7 turns of 3/16" copper tube, inner diameter 5.3", turn spacing
> 0.3". Flat pancake. Clearance from inner turn to secondary 0.5".
> Secondary capacitor 0.05uF 50KV. Set to resonate also at 240 KHz.
> Secondary first turns 1.5" higher than primary first turn.
> Tank supply made of two MOTs and two voltage doublers, output 6.5 KVAC,
> almost 0.5A (I believe). A third MOT primary (with shorted secondary)
> is in series with the 2 MOT primaries on the 220V side to work as a
> Spark gap is a RQ static gap with blower and two series of 2 of 0.275"
> connected in parallel.
> ________________________________________________________________________
> Marco Denicolai                   Vista Communication Instruments, Inc.
> Hardware Development Manager      www.vistacom.fi
> marco-at-vistacom.fi                 Kaisaniemenkatu 13 A
> fax:    +358-9-622-5610           SF-00100 HELSINKI
> phone:  +358-9-622-623-15         Finland
>    Remember, Murphy was an optimist! I am not...
> ________________________________________________________________________