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

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

Original poster: "John H. Couture by way of Terry Fritz <teslalist-at-qwest-dot-net>" <couturejh-at-mgte-dot-com>


John F. -

The reason I used 120 BPS is because that is the BPS where most of the test
data is presently available. There is very little data for other BPS. When
more data is available with other BPS then other graphs can be made. It
appears that several coilers are researching the effect of BPS on spark
length so it may be possible to make new graphs in the near future.

The problem with making spark length graphs for Tesla coils is that so many
variables are involved. This means that a particular graph can represent
only a small group of TCs. The secondary voltage also presents problems
because it cannot be accurately measured. Connecting any instrumentation to
the secondary will load the circuit enough to make the measurement
inaccurate. This voltage therefore has to be estimated using other
information. This brings in more variables which would require more graphs.

What you are talking about (other BPS) requires much more TC testing to
provide enough data for making the proper graphs and this will take many
years before this data becomes available.

John Couture

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


-----Original Message-----
From: Tesla list [mailto:tesla-at-pupman-dot-com]
Sent: Thursday, May 22, 2003 7:43 PM
To: tesla-at-pupman-dot-com
Subject: Re: TC Secondary Voltage vs Spark Length (was - 12 MV 100 years
ago)


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