# Re: Output

```Determining output voltage accurately (say to 10%) is quite a challenge for
hundreds of kV, particularly when it is a pulsed RF signal.  You can't just
hook up a voltmeter, because the meter will change the characteristics of
the coil.

Many folks attempt to relate spark length to voltage, but this is doomed to
failure.  Why?  because the equations work for uniform electric field, and
the field around a tesla coil is far from uniform.  Probably the best way
to guess at the voltage is to look at the radius of curvature of the top
load, which will provide an upper bound for the voltage. For a perfect
sphere in infinite space, 1 meter radius = 3 Megavolts.  But consider that
for lightning, the E field is perhaps 10 kV/meter (1/300th that necessary
for breakdown in a uniform field), over a 1000-2000 meter path, only 10 MV
total...

Particularly for long sparks, the source impedance driving the spark is
probably more important than the actual voltage.  Once you get the leader
started, you've got to keep the electrons flowing into the spark.

Terry Fritz (our esteemed moderator) has done some work with Efield probes,
which, with a bit of calibration, could probably answer the voltage
question with some accuracy. (i.e. put known voltages on the top load and
measure the calibration constant of the efield probe in the test
environment).

As a practical matter, I'd say most TC's run around 500 kV to 1 MV peak
voltage, judging from the top load sizes and the look of the arcs.

----------
> From: Tesla list <tesla-at-pupman-dot-com>
> To: tesla-at-pupman-dot-com
> Subject: Output
> Date: Saturday, August 26, 2000 9:54 PM
>
> Original poster: "Dan Kunkel" <dankunkel-at-hotmail-dot-com>
>
> Coilers,
>
> why is it that we have no way of determining secondary voltage in these
> modern times? how was Tesla always able to quote his output voltage? was
it
> an educated guess (arc length). i think his bold claim was 135 million
> volts. did Golka or the brothers Corum ever state their output?
>
> Dan
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>
>

```