Don K wrote:
wrote in message oups.com...
wrote:
Don K wrote:
wrote:
There's nothing to limit the current when capacitors fail, so that failure
will cause a fire.
X rated capacitors use fusible coatings, so a short causes a burn out
of the conductor around the short. The overall capacitance is not
noticeably affectde, IOW its self healing.
I doubt that. The diodes will probably open, and I used really skinny wire.
Very fine wire sounds like effective fusing to me.
You only need 20mA of AC current to cause ventricular fibrillation.
If the capacitor fails, someone could get killed touching whatever
your circuit connects to.
Don
It would be a foolish designer that enabled users to touch the output
of one of these, so thats a non issue in a competent design. If for
some reason they did, Y rated caps would be more appropriate than X -
but still, liability like that isnt something I'd want to take on
unnecessarily.
As far as fusing, if a cap shorts, enough i will flow to pop a fine
wire, assuming it really is fine. A single strand of a thin stranded
equipment wire etc. So the fuse concept is good.
I suppose if one wanted to improve the safety of an unsafe device (ie
nonisolated supply with outputs touchable) one could put a cap in both
poles and earth the supply output. Would need to ensure R is
significant to avoid RCD problems.
NT