Measuring secondary voltage (fwd)

From:  Malcolm Watts [SMTP:MALCOLM-at-directorate.wnp.ac.nz]
Sent:  Thursday, January 22, 1998 2:22 PM
To:  Tesla List
Subject:  Re: Measuring secondary voltage (fwd)

Hi all,
        I've been following the discussion on Vout with much 
interest. There are a couple of parameters directly involved in long 
sparks from TCs which only one or two have mentioned:

- First is break rate. The voltage doesn't increases but the sparks 
sure do as break rate is upped

- The second is Tbeat. This directly influences the time energy is 
left sloshing around in the secondary and presented to the air. Quite 
modest k's around the 0.1 to 0.2 mark work extremely well contrary 
perhaps to expectation. Since beat time involves a number of cycles 
rather than a fixed period, it is axiomatic that low frequency 
running can only improve the situation for a given value of k.

    I've mused on the repetitve element in long sparks lately. It is 
the belief of some very experienced coilers that the only requirement 
is hot air, given short ion lifetimes. Suppose that's true. There is 
one characteristic of hot air that could aid conduction: due to 
expansion, the air channel would be more rarified than the 
surrounding cold air.

    Lastly, a word on measuring Vout:

> From:  John H. Couture [SMTP:couturejh-at-worldnet.att-dot-net]
> Sent:  Wednesday, January 21, 1998 1:16 AM
> To:  Tesla List
> Subject:  Re: Measuring secondary voltage (fwd)
> At 01:19 AM 1/20/98 +0000, you wrote:
> >
> >
> >---------- Forwarded message ----------
> >Date: Mon, 19 Jan 98 18:51:58 EST
> >From: Jim Monte <JDM95003-at-UCONNVM.UCONN.EDU>
> >To: tesla-at-pupman-dot-com
> >Subject: Measuring secondary voltage
> >
> >
> ><from John Couture's post of Mon, 19 Jan 1998 19:17:09 +0000>
> >
> >>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.
> >
> >  If you really wanted to know the voltage and were willing to spend
> >  some time to find it, how about taking a series of measurements,
> >  using a voltage divider with a different impedance for each
> >  measurement?  By plotting measured voltage against voltage divider
> >  impedance magnitude and extrapolating to infinite impedance, it
> >  seems that a reasonably accurate value for the secondary voltage
> >  can be measured.
> >
> >  Jim Monte
> >
> --------------------------------------------------
>   Jim -
>   Wouldn't "extrapolating to infinite impedance" give you infinite voltage?
>   However, I believe your idea could be used by extrapolating to a very high
> impedance where the reduction in voltage could be negligible.
>   Maybe Robert Stephens would want to try this. It certainly could be used
> for small coils.
>   John Couture

I think the last system that one should attempt to extract an 
accurate figure from is a small one. IMHO, a large system (one with a 
large Cself) running at much reduced Ep to bring it into the measuring 
range of test equipment would be the best option. For one thing, 
large Cself minimizes the influence of divider probes and the like. 
Is there any reason why the result could not be extrapolated to 
high values of Ep if an accurate measurement at low Ep could be made?