# Re: A 20 kV DC tank supply

```Marco,

I believe you are on exactly the right track to have controlled TC
experiments:  a stiff DC HV supply!

As to how to transfer energy to your primary capacitor from your "flywheel"
capacitor, consider using an H-Bridge configuration, depicted below.  Larry
Robertson  uses such an arrangement, apparently with good success.  You can

+ ----|------------------|-------------------|
|                  o                   o
|                gap A1              gap B2
| 30 uf            o  pri C   pri L    o
===                 |----||---OOOOOO----|
| 20 KV            o                   o
| filter         gap B1              gap A2
| cap              o                   o
- ----|------------------|-------------------|

Gaps A1 and A2 simultaneously fire, then Gaps B1 and B2 fire, repeating ad
finitum.  This can be done with a (more complicated) RSG, or you could
consider using triggered spark gaps.  The H-bridge avoids a spark gap
directly across the flywheel cap.

Your idea of using a current limiting inductance works also and is what
Greg Leyh uses.  But the above may be better for controlled experiments.

--Steve
----------
> 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
> <snip>
> I need a flywheel capacitor to provide, roughly, enough energy for 3
> primary capacitor chargings (at BPS = 800 Hz, I get almost 3 bangs
between
> 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
> supply?
>
> <snip>

```