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| Metalworking (rec.crafts.metalworking) Discuss various aspects of working with metal, such as machining, welding, metal joining, screwing, casting, hardening/tempering, blacksmithing/forging, spinning and hammer work, sheet metal work. |
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Where's the spark ??
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 |
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