Re: [CAD_CAM_EDM_DRO] Re: Capacitor safety questions

****Moderator Note: You guys are starting to wander out in the weeds with this one. Please post some links to useful info or provide useful calculations for people building CNC supplies. -L

On Saturday 27 December 2003 15:15, ballendo wrote:
> Safety organisations like UL set requirements for the voltage level
> remaining after 3 time constants. (That is, it must be to a "safe"
> value within this time.) Bleeder resistor calcs should bear this in
> mind.

Thats just plain wrong.

after 1 time constant [1] the voltage will be 1/e, after 2 it will be 1/e^2
and after 3 it will be 1/e^3 or roughly 1/20th ... this will always be the
case regardless of what value of R or C you choose, after 3 tc has elapsed
the voltage will be 1/20 of its initial value

so if safe voltage is, for example, 50V according to your version of the
rules that means that no capacitor can ever have more than 1000V on it ...
because it will always be at more than 50V after 3 lots of time constants
have elapsed...

I suspect that the time to safe voltage is specified in terms of seconds, and
probably takes account of how long from power off it takes to get the covers
off too.

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