Gary Coffman wrote:
On 30 Dec 2003 23:09:40 -0800, (William J. Beaty) wrote:
(John Albers) wrote in message
om...
I took a couple of old HP deskjet 40V DC wall warts and wired them in
series to produce 80V DC. I checked this with a DVOM and I am getting
80V DC output. According to various sources the break down voltage of
air is around 20V per .001 inch.
Nope. The breakdown for short gaps in air (Paschen's Law) is:
Volts = 30,000(cm) + 1,350
Paschen's Law only holds for uniform fields. In other words it
is valid when the electrodes have a large radius with respect
to the gap distance. But if one or both of the electrodes is
sharply pointed, or other shape which produces a nonuniform field, ie
is hollow, has complex features, etc, the field strength is much higher
at points in the gap than the simple potential
divided by distance between the electrodes would indicate.
Ratios here go up to about 4:1 for actual E over uniform for a point
source- like a needle perpendular to a flat surface but a bit away from it.
^
|
________|_______
A protruding somewhat rounded source is about 3.
So as Gary says you get a corresponding reduction in V.
Lets try my 4
V =~ 1350/4= 338 volts (not bad eh!)
but as Gary points out Paschen's Lay only true when gas present.
Paul