# Re: Voltage/Length (fwd)

```

---------- Forwarded message ----------
Date: Mon, 19 Jan 1998 19:17:09 +0000
From: "John H. Couture" <couturejh-at-worldnet.att-dot-net>
To: Tesla List <tesla-at-pupman-dot-com>
Subject: Re: Voltage/Length (fwd)

Jeff, All -

Several engineering HV labs have researched and published tables on
voltage per length of spark. These tables are based on spark conditions and
using apparatus that is very different compared to Tesla coils. For this
reason these tables cannot be used for Tesla coils.

There are, however, other possibilities. For example the equation

KV = 65 x S^.07

where S equals the spark length in inches and KV is the approximate
kilovolts of the Tesla secondary circuit.

This equation is non linear because the Tesla coil varies in overall
efficiency. Small coils with short sparks are more efficient than large
coils with long sparks. Also, the equation is based on benchmarks that have
been used by coilers in the past, such as 60 inches represents one million
volts for Tesla coils.

A graph showing the voltage per length of spark for the TC secondary is in
the Tesla Coil Construction Guide and the efficiency graph is shown in the
Tesla Coil Notebook. A third graph is shown in the Tesla Coil Design Manual
showing the wattage per spark length. These three graphs tie in four of the
major parameters of the Tesla coil design.

The equation assumes standard air conditions so spark length may be
slightly different for non standard air conditions. However, the spark
length is only an approximation so non standard air probably would change
the spark length only for extreme non standard air differences. I have not
heard of anyone who has built and tested enough Tesla coils to make a table
for non standard conditions.

It should be noted that the Tesla coil secondary voltage can only be
approximated because connecting any metering instrumentation to the
secondary circuit would decrease the voltage by an indeterminate amount.

John Couture

------------------------------------------------------------

At 05:29 PM 1/17/98 +0000, you wrote:
>
>
>---------- Forwarded message ----------
>Date: Sat, 17 Jan 1998 11:05:59 -0600
>From: Jeff Larson <jflarson-at-starnetinc-dot-com>
>To: Tesla List <tesla-at-pupman-dot-com>
>Subject: Voltage/Length
>
>Does any one have the voltage per length approximation formula?  This
>would be used to approximate the voltage of a coil output based on the
>measured spark length.  I imagine the spark length would be dependent on
>the humidity regardless of the voltage?
>
>--
>	Jeff Larson		jflarson-at-starnetinc-dot-com
>	Design Engineer		Home phone 847-934-1877
>	Propheteer INT		Work phone 847-359-8988
>	Palatine IL
>
>

```