Re: Rotary Spark Gap Design

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: "Gregory Hunter" <tesla_39560@xxxxxxxxx>

Hello Rajesh,

--- Tesla list <tesla@xxxxxxxxxx> wrote:

> Original poster: "Rajesh Seenivasan"
> <rajeshkvs@xxxxxxxxxxx>
>
> Dear forum members,
>
> I'm planning to build a rotary spark gap:
> 8 spinning electrodes mounted on a wooden disc,

I don't like wood for this duty. A wooden disk may be
difficult to balance, and wood is a poor insulator at
high voltage and high frequency. If you are trying to
do this cheaply using materials at-hand, try cutting
your rotor from a plastic kitchen cutting board. I
suspect these are cheap and plentiful virtually world
wide. They are usually made of thick polyethylene or
polycarbonate plastic. This material is far more
uniform than wood and should make for easier
balancing. Plastic is a much better high voltage
insulator. Careful though--a plastic rotor may soften
from heat and release the flying electrodes like
little bullets! With proper tuning and careful
management of duty cycle, the heating problem may be
mitigated. You should also surround the rotor with a
tough plywood safety shield--just in case. Another
idea--I made a very sturdy rotor by stacking four
layers of unclad fiberglass circuit card stock and
then cutting out a circle. I ended up with a 6"
(150mm)diameter rotor about 1/4" (6mm) thick. It is
immune to heat and apparently indestructible. I've
been spinning it for years at 10,000rpm with no sign
of distress. The price was right too--I salvaged the
scrap circuit card stock from a dumpster at work.

> 2 stationary electrodes,
> brass bolts used as electrodes.
>
> I have seen in some Tesla coil designs that the AC
> input voltage is stepped
> up to few kilo volts
> (using NSTs/PolePigs), rectified and then fed to the
> tesla coil circuit
> that is using the spark gap.
> Can I run the tesla coil without stepping up the AC
> input voltage ? I'm
> planning to use
> 440VAC input, rectify it and then feed this DC

No way. That voltage is way too low to reliably
trigger a spark gap. If you want to avoid the high
voltage transformer, then I suggested you adopt a
solid-state design using IGBTs. These work well at a
few hundred volts. If you really want a spark gap
coil, then try to find a suitable transformer. Even a
single MOT can be made to work if you follow it with a
voltage multiplier. I saw one guy's design which used
a single 2200vac MOT, followed by a solid-state
voltage quadrupler, followed by a DC charging choke.
He was charging his tank cap to 17,000vdc! His Tesla
coil made pretty big sparks too.

> voltage to the tesla coil
> circuit which uses a
> rotary spark gap. Any advice ?
>
> Thanks in advance,
> Rajesh.
>
>
Cheers,


=====
Gregory R. Hunter

http:\\hot-streamer.com/greg