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

[Steve Ward <steve.ward@xxxxxxxxx>]

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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