Re: Coil Efficiency (and true wattmeter)

From: 	David E. Sharpe[SMTP:sccr4us-at-erols-dot-com]
Reply To: 	sccr4us-at-erols-dot-com
Sent: 	Monday, July 28, 1997 10:25 PM
To: 	Tesla List
Subject: 	Re: Coil Efficiency (and true wattmeter)

Tesla List wrote:
> From:   John H. Couture[SMTP:couturejh-at-worldnet.att-dot-net]
> Sent:   Saturday, July 26, 1997 11:38 PM
> To:     Tesla List
> Subject:        Re: Coil Efficiency (and true wattmeter)
> At 05:27 AM 6/30/97 +0000, you wrote:
> >
> >From:  David E. Sharpe[SMTP:sccr4us-at-erols-dot-com]
> >Sent:  Thursday, June 26, 1997 11:40 PM
> >To:    Tesla List
> >Subject:       Re: Coil Efficiency (and true wattmeter)
> >
> >Tesla List wrote:
> >>
> >
> >-------------------
> >Chip, Malcolm, ALL
> >
> >Attached is the latest schematic of the opto-isolated wattmeter.
> >The document is drawn in WORD6.  If you can't download and
> >translate, contact privately, can provide CAD drawing, text, and
> >board layout with a SASE.
> >
> >
> >
> >
> >Attachment Converted: C:\WORLDNET\EUDORA\WMETER.DOC
> >
> ---------------------------------------------------
>   Dave -
>   I finally have gotten around to printing out your opto wattmeter circuit.
> Many thanks. I had no trouble in downloading and printing the file.
>   How does this circuit work? I note that you are measuring voltage and
> current and integrating it with the 2.2 uf feedback cap. The 741 appears to
> be summing the voltage and current instead of multiplying. Is this correct?
> Are you getting a linear output at the 0-15 volt DC meter?
>   I note you did some testing with this circuit a while back, have you done
> testing with your coils? What inputs, outputs, efficiencies did you get?
>   For coilers interested in building this circuit the NEC PS2501-04 is
> available from Digi-Key for less than two dollars.
>   Thanks for the information.
>   John Couture


The differential voltages (Vshunt) and (Vload) are in fact
MULTIPLIED to the form:

   39 X Rshunt/Rmultipler * Vload * I load

which is the instanteous load power multiplied by the term
39 X Rshunt/Rmultiplier.  Because of the low level signals
involved, a precision op amp, as a OP27 or MAX427CPA should
be used in place of the 741, although the 741 implementation
worked well for experimental use.

The wattmeter output is reasonably linear over the span of
the meter, with values given will measure from 0-1.4kW.

I have previously posted preliminary information on measured
streamer lengths (MAX) to a ground target versus input power.
I agree with Malcolm that efficiencies from AC line to coupled
power into resonator is very low (typically less than 20%).
I furthermore agree with the original post by Greg Leyh (HI) 
that the power into the tank circuit really drives the system,
but I suggest that the COUPLED POWER into the base of the
secondary (regardless of magnifier or standard coil) be the
metric that determines ULTIMATE SPARK LENGTH OF_ANY_SYSTEM!!!

My spin is therefore:

Power efficiency = .5 * Vcap^2 / C * BPS * k / PacIN

	Vcap = Adjusted RMS voltage based on permitted firing
 	       window on AC wave (kV)
	C    = Tank capacitance (uF)
	k    = Coupling coefficient (Primary to secondary)
	Pacin= TRUE AVERAGE INPUT AC POWER, measured via
	       true wattmeter (optoisolated or otherwise)

The ONLY assumption in the above equation is that the
predominant coupling mechanism by FARADAY's LAW is magnetic.
I will, however, admit that a significant amount of power
transfer occurs CAPACTIVELY between the primary and secondary.
Measuring that contribution would be difficult.