Re: Coil Efficiency (and true wattmeter)

From: 	Malcolm Watts[SMTP:MALCOLM-at-directorate.wnp.ac.nz]
Sent: 	Wednesday, June 25, 1997 3:23 PM
To: 	tesla-at-pupman-dot-com
Subject: 	Re: Coil Efficiency (and true wattmeter)

Hi John, all,

> I agree.  Can you suggest a simple way to measure the capacitor voltage?

Best is an EHT probe for the scope (and a storage scope if one has 
that luxury) to capture a large number of breaks. Second best is 
using an accurately metered supply to measure gap fire voltage, then 
letting the coil rip while scoping BPS remotely. Not as good, but 
gives a reasonable indication of gap firing voltage.

> Regarding wall plug power; who knows how the distorted and pulsed
> waveforms are affecting our ammeters and wattmeters.  To solve the
> problem, I suggest that we all build the optical isolator wattmeter
> suggested by Dave Sharpe of the TCBOR.  Dave has I believe posted
> info on the results of the project...and I believe accuracy was within
> 5% which is a lot better than any typical meter, because this optical
> isolator device gives an accurate representation of the true 
> instantaneous power delivered to the load even  with a wandering 
> input voltage and a non-linear, reactive load.   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.

Agreed. I think that's where a lot of false figures are coming from. 
In many cases the waveforms are terrible. However, I have scoped 
transformer primary currents using a very low value resistor in series
and probing across it with an isolated scope which not only shows 
waveform but peak current as well. For an RMS figure, a bit of 
calculus can be used. A valve scope is a must for a running coil.
   I like your idea better though. The thought of a blown up scope 
makes me blanch.