Hi

My AC theory is pretty bad and I need to be able to simulate an AC mains supply at varying power factors. What I am after is a circuit that I can take 2 voltage values from, with the second voltage being out of phase -+45deg.

Does this make sense and is this possible?

Thanks for any help

 

anything is possible... if you are going to try and run a load off of it it is extremely impractical.

 

Power Factor is usually caused by the load, not by the source of the AC power. In other words, if the current drawn by your load is not in phase with the voltage applied to it, then it exhibits an "undesirable power factor".

 

I was thinking of using a capacitor as a load to shift it. I was hoping that I could either switch in different capacitors or have a variable one so that I can change the phase in real time.

I'm needing something like this so I can show a power monitor I have made works correctly. (they don't let us touch mains wiring so need another option)

I have been using jsut s signal generator to give same in phase voltage to current and voltage channels.

 

well then an RC filter will work, though it will also reduce the voltage to the current input. since you are not using the actual current sensor there should not be a problem

Dan

 

How do I calculate values to give certain phase shifts?

 

You need to use vector algebra.
I did this; the output resistance is high and the voltage output changes with the phase shift but is does work (on paper).
The component values might be unwieldy so you might also want to build one of these
Gyrator - Wikipedia, the free encyclopedia

Post your specs for shift, voltage and current input and output.

 

For voltage channel I need 'zero phase'(reference phase) with 0-500mVpp preferbly stepped down from 5V input supply. For the current channel also need 0-500mVpp with phase difference of 45deg if only a single phase change is possible or 0deg - 45deg if variable phase. Current input will be low as signal generator will be used, noy sure of max output current, the chip(CS5463) I'm using doesn't give maximum value but I'm assuming its very low.

Does that make sense?

 

So for a 45 deg. phase shift you need an R and a C such that Xc = R at the freq. of interest.
The choice of R and C depends on the source impedance you want and the freq..

E.g., 1 uf at 60 Hz = ~2650 Ω.

 

Ok I will have a look and see if I can get it.
Cheers

 

An allpass network is perfect for getting 45 deg phase shift with no loss in amplitude. Variable phase shift is easy.

__________________
Ron

 

You da' man!
All-pass filter - Wikipedia, the free encyclopedia

 

Well today made a quick RC circuit with 1K4 resistor and 2.2uF cap. Did the job but had the decreased amplitude on output, which I could of lived with but the all-pass filter will be perfect for the job.

Cheers for your help

 

You can change from lead to lag by swapping R and C in the Wikipedia op amp-based circuit.

__________________
Ron

 

I was messing around with a Fluke 41 Power analyzer and found a regular Switching power supply Is highly Capacitive and an Iron core Transformer is highly reactive. The Fluke displays phase angle and power factor. You could
have each type of supply give you an approximation. Just a guess.