Re: Lowered Expectations

Tesla List wrote:
> Original Poster: "JimmyD" <jim_del-at-email.msn-dot-com>
> Is there any reason one couldn' build a Spark Gap Tesla Coil setup using
> 120v line voltage?
> I know everybody's trying to have the biggest, but what are the limitations
> of going smaller?
> << Jim >>
The real problem is that 120V won't jump an air gap, no matter how
small. The minimum sparking voltage for air at atmospheric
pressure/temperature is about 320 volts. All gases (and mixtures) have a
minimum sparking voltage, below which, you cannot get a spark, no matter
how high the field (volts/meter) is.

For instance, in arc welding (which typically uses about 30-50Volts open
circuit) , you have to "strike" the arc by touching the electrodes then
pulling them apart. The touch creates a localized heating, vaporizing a
bit of metal, which then can be "stretched" to form the arc. The skill
in arc welding is mostly in knowing how to do this, and to control the
arc current (and hence the heating rate) by varying the distance from
the electrode to the workpiece (and, it IS a skilled craft, much more
difficult than soldering, for instance).

Fancy TIG welders and plasma cutters use a small High Frequency HV
supply ( a mini TC) to generate a few kV across the gap to cause the arc
to form without actually touching the electrodes. This gets around the
minimum sparking voltage issue.

I have more data on this at:

Jim Lux                               Jet Propulsion Laboratory
ofc: 818/354-2075     114-B16         Mail Stop 161-213
lab: 818/354-2954     161-110         4800 Oak Grove Drive
fax: 818/393-6875                     Pasadena CA 91109