Re: TC Secondary Voltage vs Spark Length (was - 12 MV 100 years ago)

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "by way of Terry Fritz <teslalist-at-qwest-dot-net>" <FutureT-at-aol-dot-com>

In a message dated 5/22/03 2:37:50 PM Eastern Daylight Time, 
tesla-at-pupman-dot-com writes:

John C,

I find it surprising that you consider ~120 bps to be the typical break rate
for a coil.  Many coils with async rotaries, or static gaps with small
value caps run at much higher breakrates.  This will make the voltage
vary a lot between different coils for a given spark length.  More below.

>John F. -
>
>In my previous post I forgot to give the TC details for which the graph was
>designed. The Voltage vs Spark Length graph is for the typical classical TC
>operating at about 120 BPS. The spark length is a controlled spark length
>and not the streamers that coilers normally use to rate their coils. It
>should be noted that there are many other possible graphs of this type
>depending on the parameters, such as break rates, etc. Some of these graphs
>are shown in the Tesla Coil Design Manual.
>
>It is interesting to note that the Voltage vs Spark Length graph can be used
>as a  "KVoltmeter".  Only the controlled spark length is required to
>determine the secondary voltage of any typical Tesla coil.


I'm not sure how sensitive the controlled spark length is to breakrate.
I would think the controlled spark length would be roughly proportional
to the free-air max spark length for various breakrates.  In other words,
although the controlled spark lengths will be shorter than the max
free-air sparks, I'd think the controlled spark lengths would vary with
breakrate much as the max free-air lengths do.  The concept of a "typical"
tesla coil is hard for me to accept.  Folks seem to build a great variety
of coil designs, with widely varying break-rates, gap spacings, etc.
For those who are not familiar with phrase "controlled spark lengths",
John C. is refering to the the longest sparks when can be drawn out
to a ground while remaining continuous.

    After you measure

>the controlled spark length the graph will tell you the secondary voltage,
>the same information you would get from a KVoltmeter. You do not need to
>know the power input, the coil size, the capacitor sizes, the type of
>operating gap, TOROID SIZE, etc, etc, to determine the secondary voltage of
>your coil.


Some of those those factors can affect the breakrate.  If the breakrate
is changed, then the voltage for a given spark length is changed.  For
example, if the input power is increased, but the static gap spacing
is not changed, then the breakrate will increase (with a properly quenching
gap), and the spark length will increase although the output voltage
remains constant.  This is just one example of behavior which
invalidates the use of a standard voltage-versus-spark-length chart
for Tesla coils.

John F.



For example if you reduce the input power to your TC and measure

>the spark length the graph will give you the new secondary voltage just like
>a KVoltmeter!
>
>John Couture