Re: My new coil

To: tesla-at-pupman-dot-com
Subject: Re: My new coil
From: Bert Hickman <bert.hickman-at-aquila-dot-com>
Date: Thu, 13 Feb 1997 06:53:46 -0800
Subscriber: bert.hickman-at-aquila-dot-com Thu Feb 13 22:11:58 1997
Tesla List wrote:
> 
> Subscriber: greenj-at-swlogica.demon.co.uk Wed Feb 12 23:07:37 1997
> Date: Wed, 12 Feb 1997 12:30:00 -0500
> From: Julian Green <greenj-at-swlogica.demon.co.uk>
> To: tesla-at-pupman-dot-com
> Subject: My new coil
> 
<SNIP>

> Powered by 11KV 5KVA single phase pole transformer using a home made
> rotary spark gap based on a brush type motor with top speed of 15,000
> rpm.
> 
> The toroid is pathetic, being the same diameter as the coil, I
> could'nt wait to try the coil out so last week end I fired her up.
> 

<SNIP>

> 
> With more power being applied to the pole transformer large bangs and
> rough
> coil running the variac began to smoke and fuses blew.   12" sparks for
> the
> top of the coil - went to bed.
> 
> Using a pole transformer for the first time was scarey!   Good job I had
> practiced on a neon transformer first.   I always unplug HV supply when
> making
> adjustments even if the variac is at 0%.   I got a nasty shock from my
> neon
> when supply still connected and variac at 0%.  I later measured the
> output
> of the variac - it was 2 volts, stepped up through the neon made
> 150volts.
> 
> With a fresh mind the next morning I repaired the variac (stuck brushes)
> replaced the fuses, and used a 100 meter extension lead as resistive
> balast.
> 
> This time I ran the spark gap at
> about 40% and coil at 40%.   Things ran much smoother, no banging, and
> no
> blowen fuses.   Getting 2' arcs.   Increced power to coil to 100%.
> Sparks
> now up to 3'.    Increaced power to spark gap to 80%.   The spark length
> increaced significantly 4-5' the color of sparks changed from purple to
> white/blue, noise increaced (need ear protection) - must be getting
> better
> quenching from the gap as speed increases.
> 
> Then desaster!  Vibrations on the spark gap cause the electrodes to
> strike
> shatering the rotor and bent the stationary electrodes.   Pieces of
> spark gap
> shot across the garage.
> 
> After re-building the sparkgap (better desgn this time) I can not get
> longer
> sparks than 4-5'.   Partly because the ceiling of the garage is in the
> way.
> Everything is being run at 100% power now.
> 
> Things I plan to do to increase spark length:
> 
> 1)      More electrodes on the rotary spark gap.   Currently 2 increase
> to 4
> 2)      Build a toroid
> 3)      Add more capacitance to the tank circuit in order to match new
>         secondary resonance when new toroid fitted.
> 4)      Connect second pole transformer (5KVA)
> 
> Any tips on getting better/longer sparks are very welcome
> 
> Julian Green

Julian,

1. You need to add inductance into your ballast circuit. Resistive
ballast alone is not as effective. The lack of ballast on your first try
overloaded your rotary and almost fried your variac (it became the
ballast!)

2. Your toroid needs to be at least 2-4X your coilform diameter, and
you're right - it'll probably require more tank capacitance. However,
increasing the tank capacitance may now overload your rotary gap, since
peak primary energy will now increase. Think about larger diameter gap
electrodes, running vacuum-coooled static gaps in series with your
rotary, and/or providing force-air cooling to the static electrodes on
your rotary.

3. Make sure you have a GOOD RF ground solidly tied to the base of your
secondary. With pole-pig powere level you'll need it!!

4. For the life of your caps, and potentially for YOUR life, never come
close to running the rotary to the 15000 RPM max speed. I'd permanently
limit speed somehow (mechanically or electrically). Plan to max out at
around 600-700 BPS.

Safe coilin' to you!

-- Bert --