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Measuring secondary voltage (fwd)
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From: D.C. Cox [SMTP:DR.RESONANCE-at-next-wave-dot-net]
Sent: Thursday, January 22, 1998 10:06 PM
To: Tesla List
Subject Measuring secondary voltage (fwd)
to: Malcolm
You are absolutely correct in saying that the output potential is
independent of the break rate. Our potential measuring tests were
conducted with a pulsed ignitron tube with an external trigger (the same
trigger used to trigger the scope sweep). The peak potential is determined
essentially by the inductance, resistance, and capacitance of the system.
These values are all determined by the geometric proportions of the system
components. A pulsed system will accurately determine the exact output
potential of the system while increasing the break rate will produce much
longer sparks due to the previous ionization and residual ions from the
pulses that existed a few fractions of a second earlier. We operated our 1
MEV test system in both high break rate (400 pps) and static firing. The
static firing was used to determine max potential while the normal
operation determined the max spark length possible with the same potential
at a higher break rate. Give or take a few inches the value of a 20 inch
dia system operating at 6.5 kva and 400 pps was a true one million volts
with 9 ft spark discharges between two 1/2 inch dia rods. System was
running with a 34 x 8 1/2 inch dia torus. The static firing produced spark
discharges only 34 inches long between the torus and a 24 inch dia ground
oblate.
Hope this information is of assistance.
DR.RESONANCE-at-next-wave-dot-net
>
> ----------
> 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?
>
> ?
> Malcolm
>