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

[R.Measures]

On Aug 16, 2004, at 10:13 AM, Harold B. Mandel wrote:

> 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

Oil-filled filter-service  capacitors have a conservative V-rating.  
For instance, Sprague's Vitamin-Q line of filter capacitors:  at 25ºC, 
a 4uF, 600WV unit typically has a breakdown potential of 3500V.

> 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.

Excellent advice.
>
> 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.

However, by de-rating a flash-C to 60%, it will usually be OK in 
transmitter PS 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
>
Richard L. Measures, AG6K, 805.386.3734.  www.somis.org