Re: A 20 kV DC tank supply
With a coil of this design 450-480 pps (bks/sec) usually provide optimum
energy levels for powerful and bright discharges. I was wondering why you
prefer to go to 800 pps as the sparks will be much thinner and
streamer-like? ---- certainly not as appealing to the eye.
If you are restrained to 3 phase power to operate at the desired power
level then the DC supply sounds fine, otherwise a 60 Hz supply will work
great if you have single phase power available. 60 Hz straight xmfr with
variable current limiting inductor will work excellent without all the
trouble of going to DC. Also, DC is somewhat more difficult to quench
properly and those who have gone this route before usually fry a few
hundred $$$$ worth of diodes before getting the tuning right.
> From: Tesla List <tesla-at-pupman-dot-com>
> To: tesla-at-pupman-dot-com
> Subject: A 20 kV DC tank supply
> Date: Monday, December 07, 1998 6:31 AM
> Original Poster: "Marco Denicolai" <Marco.Denicolai-at-tellabs.fi>
> I would like to built a 20 kV DC supply for my big coil. These are the
> tentative specs:
> - 20 kV DC output
> - primary capacitor 0.1 uF, charged at 20kV --> 20 Joules
> - maximum DC deviation: 1%
> - maximum BPS: 800 Hz
> If I use a 3-phase 14 kV pole pig and 6 diodes I get a ripple of 50*6 =
> Hz. Voltage varies between 14 kV * 1.41 = 19.8 kV and
> 14 kV * 1.41 * 0.866 = 17.1 kV.
> I need a flywheel capacitor to provide, roughly, enough energy for 3
> primary capacitor chargings (at BPS = 800 Hz, I get almost 3 bangs
> each ripple top), that is 20 * 3 = 60 Joules allowing the top voltage to
> drop down only 1%. That is:
> maximum voltage drop = 20kV * 0.01 = 200V
> Cflywheel = dQ/dV = 3 * Cprimary * 20kV/200 = 30 uF.
> And this without taking care of losses!
> I have still to protect the flywheel capacitor from discharging when the
> rotary gap conducts: what about using a current limiting inductor for
> feeding primarty capacitor and rotary gap?
> Has anybody got some good idea or hints how to build such a DC power
> P.S. Another solution would be to go with a stabilized 17,1 kV, but how
> "cut away" the ripple?