Is this following on from Measuring AC current output from a VFD?
What sort of motor does the pump have, is it an induction motor, is it 3-phase or single? What voltage and power rating?
My first comment (after the above) is I think you’re getting a bit confused between power factor and phase. It’s true that in some circumstances p.f. = cos(φ) ; but those circumstances generally only exist in labs and text books. In the real world, it can be a decent approximation if you know when it’s safe to use it.
There are two ways out of that:
- You can use a 415 V : 9 V transformer instead of our a.c. adapter (AKA a 240 V : 9 V transformer in a case with a plug), or
- Make yourself a star point and connect the a.c. adapter to this. I’d use 3 identical high power resistors (250 W electric heaters - if your VFD can supply that, otherwise size to suit the drive).
If there’s no a.c. input detected, it only measures current, multiplies it by a fixed constant of 230 and calls the result watts. But it isn’t, it isn’t even VA, but an estimated apparent power using the assumed voltage. So it’s really amps times 230.
You definitely mean power factor there.
Have you checked with the manuals/the manufacturer? It’s possible that there’s a neutral, just not readily available.
Or have you measured the output voltages to earth?
What is the input to the VFD - 3-phase or single? If it’s single, measure the output voltages to the input neutral. If they’re all 240 V, there’s a good chance you can use that - at least for measurements with the a.c. adapter.
The way the emonTx software works is it takes alternate samples of voltage and current. Then it processes the numbers in 3 ways:
- It squares the voltage, averages it, takes the square root to give the rms voltage,
- It does the same with the current,
- If multiplies each pair of voltage and current samples together to give the instantaneous power, then averages those to give the average real power.
From those you get Vrms & Irms, multiply those two together and get apparent power, then it uses the definition of power factor = real power ÷ apparent power to give the power factor. Angles don’t come into it. (And so it can’t tell you whether the p.f. is leading or lagging from that.)
So yes, if you measure the line current and line-neutral voltage, the software will give you the power factor directly.