Simple to build isolation transformer that consumes less power than it gives out

[poynt99]

Steve,

Unless I am mistaken, it appears from your photo that the clamp meter has BOTH conductors of the line cord going through it. You must have only ONE conductor going through.

I suggest you move the meter over to where the wiring breaks out to the transformer leads, then you can clamp around ONE of the leads.

[JouleSeeker]

Steve,

Unless I am mistaken, it appears from your photo that the clamp meter has BOTH conductors of the line cord going through it. You must have only ONE conductor going through.

I suggest you move the meter over to where the wiring breaks out to the transformer leads, then you can clamp around ONE of the leads.

You are mistaken in this case, Poynt -- there was only ONE conductor going through the clamp-on meter. 
The single conductor going through is a brown wire from the cord going to the P3 meter.
And when I used two clamp-on meters for comparison, each had ONE of the brown wires from this cord going through it.  Both clamp-on meters then agreed on the input current (and disagreed with the P3 meter).

Thanks for the diagram, Wattsup.

[poynt99]

OK Steve, that's good. The point needed to be raised though.

It's difficult to see that on the photo. It really does appear as though the whole cord goes through the clamp meter, surely you agree at least that it appears that way?

[JouleSeeker]

Poynt: " It really does appear as though the whole cord goes through the clamp meter..."
   It may appear that way, but then the clamp meter would show zero amps.

Anyway, I've taken another photo showing two clamp meters -- each shows 0.14A (AC) while the P3 meter shows 0.25A (demonstrating the discrepancy and the reason I question things).

   Hopefully one can clearly see in this photo that one wire goes through each clamp meter.

I also looked at the power fact P.F. -- for the input, it shows as approx. 0.6  -- and it varies, 0.5 to about 0.7.  (The input power comes from a dimmer, which is connected to the mains.)
Could this be why the P3 meter is having difficulty getting the AC amps (and the power)?  Also, are the clamp meters accurate when PF is NOT unity?  How does one measure the current accurately -- or better, the power -- when the PF is not 1.0?

[JouleSeeker]

To further explore the question of how to measure Pinput when PF is not 1, I connected the input plug directly to the mains; see photo which now shows the clamp meters at 0.17 A while P3 shows 0.19A.  This is much better agreement than with the dimmer, where the PF was approx 0.6.  With the mains for this circuit, the input PF is shown on the P3 meter to be 0.99-1.0. 

   It thus appears that the P3 meter performs reasonably when the Power Factor is 1.0, but not reliable otherwise -- either the P3 or the clamp meters are not reliable when PF < 0.7 anyway. 

The question comes again -- how does one reliably measure the power (say, around 20 watts) when PF < 1?