[Amps] big capacitor in HV PS

[John Lyles]

The stored energy in that capacitance at 3.6 KVDC is 8.1 kilojoules. 
This is a tremendous amount to deal with for a power supply. Roughly 
equivalent to the mechanical force of a part of a stick of dynamite when 
it lets loose. I would not want to have to deal with the safety aspects 
of this design. For instance, if there was an internal arc in the power 
supply, before the series resistor (mandatory) to the load, it would do 
a lot of damage, such as rupture capacitors, blow holes in metal. This 
is just from the stored energy. An active crowbar might be needed if a series resistor 
isn't enough to prevent more than a few Joules of energy to be dissipated 
in a thin wire shorted across the power supply output, to simulate a tubes grid wires.
Then there is the inrush current. Rectifiers would need to be designed for high peak currents, 500 amps or more.
Step start would need to be carefully designed to prevent taking out the diodes. 

Seems like a lot of trouble to get stiffer high voltage that isn't really needed for am amateur
amplifier for SSB, CW, AM. I would not recommend going above 1/10 of that capacitance, unless prepared
to deal with the effects mentioned above. I have a 250 uF capacitor at 28,000 volts at work, and 
it took months to design the inrush and crowbar protection, to prevent blowing a 30 AWG wire when shorted across the output. 
This bank of capacitance is in a steel vault with chicken-wire reinforced glass in the windows. Of course, this
is far more stored energy than 8.1 k, about 10X this amount, needed to prevent more than a kilovolt of droop 
during the pulses of an RF amplifier. 

73
John K5PRO

> I am curious. I see some 10,000uf 450volt electrolytic caps for sale on
> Ebay. 8 of these would give you 3600volt capability at more or less
> 1250uF total capacitance. Is this too much?. Are there any dangers using
> this much C in a filter for a PS? In the past I have used eight 560uF
> caps and other values similar to this. Just curious, thank you. Lane
> Ku7i