Re: [TCML] Measuring Voltage?

[DC Cox <resonance@xxxxxxxxxxxx>]

Spark gap tables work great for standard 1/2 dia rod gaps, which are
commonly used to measure peak DC and AC potentials.  As long as you are only
making 1 spark every 15-20 sec, and not 200 pulses/sec, then the peak
potential as measured with a rod gap is independent of the waveform.  That's
why Tesla coil measurements have to be taken in a pulsed mode.  I use a
large rectifier in series with a 30 meg power resistor in series with the
pri cap.  This provides a nice spark every 20 to 30 sec depending on the
size of your cap.

A common mistake many experimenters make is to assume the Vpri is the peak
voltage of the neon transformer.  Example would be a 12 kV neon xmfr with a
peak potential of 16.9 kV.  The true Vpri used in these calculations is
dependent on the spark gap setting, not the peak potential of the xmfr.  I
published accurate measurements of these potentials in the archives using a
calibrated power supply and taking measurements accurate to 1 mil (.001
inches).  In most cases the usual Vpri is around 12-14 kV and not the full
16.9 kV, but again this depends on your exact total spark gap setting.

You can have a 100 kV power supply, but if the pri gap is set to breakdown
at 14 kV, then 14 kV is the max peak voltage the primary will see, and the
equation Vsec = Vpri x 70% x SQR (Lsec/Lpri) is every accurate.

Dr. Resonance




On Tue, May 25, 2010 at 6:00 AM, jimlux <jimlux@xxxxxxxxxxxxx> wrote:

> Neal Namowicz wrote:
>
>> Yeah, you know, it just seemed too easy when I first put it together.
>> Okay, so someone mentioned "guesstimating" the voltage, that works for
>> someone like myself who is math-challenged. So, ballpark figures, what might
>> my secondary output voltage be from a 4" coil, 9kv power supply? The
>> streamers run about 25 to 30". Also, how would that change for a bi-pole
>> coil with a secondary gap of only a few inches?
>> I ask these questions partly for my own curiosity, but also when people
>> see my stuff in operation, I can give a fairly decent answer to when they
>> ask, how much voltage IS that?
>> Thanks everyone for your input!
>>
>> Neal N.
>>
>>
>
> there's a very, very loose relationship between spark length and voltage.
>  (spark gap tables only work for short sparks in an essentially uniform
> field, neither of which is the case for a TC)
>
> The voltage is limited, for the most part, by the radius of curvature of
> your topload.  For a smooth sphere, the maximum voltage is about 30kV/cm  of
> radius.  That is, a 12" sphere (15 cm radius) can have about 450kV on it
> before it starts to make sparks.
>
> And that's a maximum, surface imperfections and bumps will reduce it.
>
> Most small coils probably run in the several hundred kV range.  There's no
> way that a small coil is a megavolt or more (as you sometimes see in ads or
> such).
>
>
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