RE: Input power measurement

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Lau, Gary by way of Terry Fritz <teslalist-at-qwest-dot-net>" <Gary.Lau-at-hp-dot-com>

John, from your original post it appeared that you were suggesting that a 
lamp-based RMS current monitor and little else could be used to calculate 
the true power drawn by a Tesla coil.  I don't have your Tesla Coil 
Construction Guide, so I don't know if this is an accurate interpretation.

Beyond that, it's not clear that a standard ammeter offers any accurate 
correlation to the true RMS current and phase angle, given the complex, 
non-periodic waveforms that are involved.  I think that trying to measure 
the phase angle between voltage & current waveforms on a scope would be 
challenging and inaccurate, if that's what you're suggesting.

Wouldn't inserting an incandescent bulb in series with a Tesla coil power 
supply primary cause a significant voltage drop, resulting in less power 
being drawn by the power supply than if no bulb was present?

A standard ammeter current measurement will be accurate regardless of power 
factor for sinusoid waveforms; it's non-sinusoidal waveforms that 
necessitate hot wire ammeters or other true-RMS measurement techniques.

Gary Lau
MA, USA

Original poster: "John H. Couture by way of Terry Fritz 
<teslalist-at-qwest-dot-net>" <couturejh-at-mgte-dot-com>
Gary -

On the contrary that incandescent lamp current is a very special current
(Active). With the Active current and the Total current you can find the
power factor or phase angle and much more including the Active,  Reactive,
and Total power as I showed in a previous post on this subject.

The electrical current triangle consists of the Active (Incan Lamp), Total
(Std Ammeter), and Reactive (Calcs) currents. The power factor is found from
the cosine of the angle between the Active and Total currents. The power
triangle consists of the Active, Total, and Reactive powers. The Total power
(VA) is easily found with the standard voltmeter and ammeter.

We have found the power factor above so the true wattage is found by
multiplying the VA by the cosine of the power factor angle. The reactive
power is found by multiplying the VA by the sine of the power factor angle.
You can also find the active and reactive voltages in this way.

That incandescent lamp test gives you a very special current (Active) that
the standard ammeter (Total) can not supply except of course at 100 percent
power factor.  A hot wire ammeter can also do the job but would be more
expensive even if you can find one. However, as I said before when you use
the incandescent lamp method you have to do a little research to find the
correct lamps, etc. You also have to study the circuitry.

John Couture

---------------------------

Original poster: "Lau, Gary by way of Terry Fritz <teslalist-at-qwest-dot-net>"
<Gary.Lau-at-hp-dot-com>

Using an incandescent lamp to gauge RMS current is fine, but I don't think
it has any application towards measuring power or Watts, the topic of this
thread.  To measure Watts, the phase angle between the current and the
voltage must be considered.

Gary Lau
MA, USA

=======================================================

Original poster: "John H. Couture by way of Terry Fritz
<teslalist-at-qwest-dot-net>" <couturejh-at-mgte-dot-com>


Steve -

There is only one way to measure TC currents or watts that is cheap and
accurate. However, it requires a little more research and on your part and a
little more understanding of what is going on in the circuits.

The solution is shown in the Tesla Coil Construction Guide. This shows how
the proper incandescent lamp can be used as a sensor to detect currents and
wattages under the harsh enviroment of Tesla coil operation. The lamp gives
you true RMS values and is not affected by waveform, frequency, power
factor, or current pulses. The non linearity problems of the lamp are
avoided by calibrating the lamp for each measurement.

There are other possibilities but all are more expensive than this method
and are usually less accurate.

John Couture

<snip>