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Re: Coil Efficiency (and true wattmeter)




From: 	David E. Sharpe[SMTP:sccr4us-at-erols-dot-com]
Sent: 	Thursday, June 26, 1997 12:45 AM
To: 	Tesla List
Subject: 	Re: Coil Efficiency (and true wattmeter)

Tesla List wrote:
> 
> From:   FutureT-at-aol-dot-com[SMTP:FutureT-at-aol-dot-com]
> Sent:   Tuesday, June 24, 1997 2:39 PM
> To:     tesla-at-pupman-dot-com
> Subject:        Re: Coil Efficiency (and true wattmeter)
> 
> In a message dated 97-06-21 07:13:23 EDT, you write:
> 
> << Hi all,
> >          I think we could be on the verge of making some real
> > progress in nailing down the merits of actual coil parameters. There
> > is much to be done in the wall socket -> coil efficiency stakes. But
> > if we look at the raw E x BPS vs spark length figures, we can start
> >to see where the coils themselves might be improved. I think there is
> > now a most fruitful area of research open to us. We might at last
> > have a platform from which to examine L/C ratios and the like. It
>  >seems obvious now that when using current efficiency measurements we
> > are floundering around in the dark (with an arc to light the way :)
> 
> > Malcolm
>   >>
> 
> Malcolm, All,
> 
> I agree.  Can you suggest a simple way to measure the capacitor voltage?
> 
<SNIP>   The max power input for the circuit is 1300 watts,
but maybe this can be "upped" using appropriate shunts.  I haven't built
one yet, but I don't really think there's any choice, unless someone can
suggest something simpler of comparable accuracy.

Maybe Dave will add some more info here about his unit.

John Freau
-----------------
Chip, John, Malcolm, ALL

The wattmeter that I have previously posted can be upgraded
easily to at least 10,000 W by simply increasing the Vmultiplier
resistor from 100k, 1/2W to 220K, 1W (115 to 230VAC input),
and changing the Rshunt from 4.6" of #14 AWG THHN copper wire
(1.00 milli-ohm) to 3.8" #8 AWG THHN wire (250 micro-ohm).
The 0 and span of op-amp is adjusted for 0-10V = 0-10kW.  Full
scale up to +rail of op-amp (about 14kW) is possible with
this arrangement.  Higher current capability is possible,
Rshunt should provide 15 millivolts FS at IFS. The above 250 micro-ohm
shunt would be suitable to currents up to 60A.  Large shunt wire should
use mechanical lugs, and sense wires tapped off lug to optocoupler
as a standard Kelvin voltage sense connection.

The 741 opamp can be replaced by a MAXIM MAX427CPA instrumentation
grade precision op amp (cost less than $5.00, Digikey, Jamesco,
MCM other in USA). This upgrade will improve accuracy to significantly
better than 1% across full span, and pin-outs are identical (direct
one-for-one swap).

Several indicating meter options are available, I like the Yokogawa
hybrid digital/baragraph analog 51 segment panel meter.  Even though
pricey (about $200 through outlets for 0-10VDC input), can be scaled
at no cost to engineering units (0-10.00KW), is specifically designed
for switchgear service, and is a very professional indicator.

The only concern I have with this design is there is minimal circuit
board clearance through the optocoupler (0.1 and 0.3 inches).  Fusing
of the V multiplier with 250V fast blow fuses (1/16A) is probably
a prudent thing to do.  The optocoupler and opamp should be carefully
shielded from air currents, and should be allowed 5-10 minutes warm-up
(actually thermal equilibration) for max accuracy.  Info for the
op-amp is available for download at the MAXIM WWW website.  Several
multichannel optoisolators with up to 5kV isolation have recently
become available from several suppliers (Hewlett-Packard) which have
significantly wider clearances than above mentioned.  I can not
infer performance of these HV devices as an analog pass-thru device
as the NEC 4 channel optocoupler part is used.

I will keep list informed as a large unit is built and tested.

DAVE SHARPE, TCBOR