Re: [CAD_CAM_EDM_DRO] Help on big caps / sources please

In a message dated 22-Jun-02 12:14:24 Central Daylight Time,
mfraser@... writes:

> 2. Have some rated 50v, can I safely series these and expect them to be
> exposed to only about 1/2 the total voltage each, without need for the
> Lexan housing? (since these are surplus, I did my 30v trials with the
> power supply outside, and me behind the metal garage door < grin >)
>

Mark: If you SERIES electrolytics to increase the "working voltage", you
must put a RESISTOR in parallel with each capacitor. This effectively
"forces" a voltage-dividing so that each gets only "its fraction" of the
total voltage. If you do NOT install these resistors, the tiny variation in
"leakage chemistry" (that's "electrical leakage", not "chemical leakage"!)
will cause a difference in "voltage sharing", and some capacitors might
therefore "see" more than their max-rated DC voltage.

Some educated person like Mariss should explain how to calculate the
resistance for this application, but I suspect something like 4K7 across each
20 millifarad cap would be about right. Maybe even 10K. I don't know from
my own actual "breadboarding experience", only "academically", and, as I have
never USED that in practice, I have long forgotten how to figure or "guess"
the R. Sorry! Duh...

Jan Rowland, Ignernt ol' troll.


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