[Amps] Filtering capacitor in a HV PS: How low can you get away with?

[Harold B. Mandel]

Sr. Vilaseca,

Immediately scrap all plans to use the 2.5KV capacitor.  If your final DC
voltage is
targeted at 2500 volts your filter capacitor voltage should be at around
5KV
so that the peaks of the rectified waveforms do not approach the puncture
limit of the filter capacitor's dielectric medium.

The 25 microfarad, 4KV capacitor is excellent as far as capacity, but 
marginal as far as a voltage rating.

In addition, you should carefully examine the filter capacitor to
determine if it
is a photo-flash (strobe) energy storage device or a true power supply 
capacitor.

A true power supply capacitor will exhibit markings that tell you
the working voltage, i.e., 4KVWVDC. A photo-flash capacitor
might read 4KVPWV to show 4KV peak volts, and this type
of unit is not meant for ICAS or CCS transmitter service.

Again, the design of your power supply filter is crucial. Do you plan
on using a capacitor-input filter or will you be employing a choke
or chokes for a multi-part filter. 

Respectfully,

Hal Mandel
KA1XO

On Mon, 16 Aug 2004 18:12:57 +0200 Angel Vilaseca <avilaseca at bluewin.ch>
writes:
> Hi,
> 
> I am building a 2500 V power supply for a one-KW transmitter. It 
> will
> use 2 4CX20Bs.
> 
> I have two oil-filled capacitors: 2.5 KV 40 uF  and a 4 KV 25 uF.
> 
> I feel quite uncomfortable using the 40 uF 2.5 Kv one, because it 
> would
> work very close to its voltage limit.
> 
> On the other hand, the 4 KV 25 uF would be OK as far as voltage is
> concerned, but would not 25 uF be too low?
> 
> Is there a rule of thumb ?  How low can you get away with 
> capacitance in
> a HV power supply feeding two tetrodes?
> 
> Vy 73
> 
> Angel Vilaseca HB9SLV
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