RE: [TCML] 3000W Halogen Dummy Load WAS: Coil V4 fail (additional)

["Phil Tuck" <phil@xxxxxxxxxxx>]

Steve,
Yes I'm a daft so & so. I had the less than unity figure in my mind's eye
and just applied the same thinking to the meter output. 

Also my coil figures, now that I look into it with some proper thought, are
different as well. I can get 260v out of the variac at home, but the last
teslathon only saw about 235v from the mains and 240v from the variac, as I
measured it when wiring up a 3 phase to single plug for the coil. This fact,
which I hadn't allowed for,  would make the new VA mains draw on my coil
(PSpice simulation) equal to 5470VA with a supposed (and optimistic) 0.9 PF.
So at 240v = 23.9 amps  My meter (cheapo Chinese Ebay) was showing 25+ amps,
so things are not so far adrift for me after all.

Re, the other:  I only have an analogue scope, but I'll play with the
current transformer idea sometime.

Phil


-----Original Message-----
From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] On Behalf
Of Steve Ward
Sent: 22 December 2010 15:30
To: Tesla Coil Mailing List
Subject: Re: [TCML] 3000W Halogen Dummy Load WAS: Coil V4 fail (additional)

Phil,

Power factor is always less than 1, meaning the the current readings are
always *higher* than the true power consumed (V*A > W).

The real issue is more likely that you have some un-accounted impedance in
your charging supply which is indeed limiting the current to something less
than expected.

Current transformers (the 50/60hz variety) appear to have bandwidth usable
to a few khz and work very well for measuring line currents that are
unusually shaped (not just a sine wave).  There is the added benefit that
you can add your own external shunt resistor (something like 1 ohm is
usually a good start) and hook it up to a voltage meter instead of a current
meter.  Ive also used this to look at current on an oscilloscope when
designing various power supplies.  If you have access to a nice digital
scope, they almost always have a RMS (or cycle RMS) function built in, so
not only can you see the shape of the current (which can give some
indication of whats going on), but you can get a good RMS measurement of
waveforms that will often fool other types of meters (ones that cant do the
number crunching).

Steve

On Wed, Dec 22, 2010 at 6:20 AM, Phil Tuck <phil@xxxxxxxxxxx> wrote:

> Stephan et al
> As I understand because of power factor issues, unless you have a true 
> power meter, it means the readings are always low. I #think# a moving 
> iron meter reads correct, not sure though. On mine I just read the 
> variacs input current with a moving coil meter but that always reads 
> low compared to his PSpice file for a simulation. I base all my power 
> estimates on what PSpice gives me. The current drawn by a shorted 
> transformer with just the ballast to limit the current is always 
> different when you add in the tank circuit if you have a SRSG.
> This all assumes you have followed his method and allowed what he 
> calls his 'ballast correction  factor' .
> The charging method only really laying  down the foundations of the coil.
> The actual performance being dependant on lots of other things, but 
> you say that part is good.
>
> Estimating the power and actually measuring are a thing I've long 
> meant to look into more. I wonder on the suitability of current 
> transformers for this matter - anyone?
>
> Regards
> Phil
>
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