Ct clip reading from emontx different from emonpi

Hello I have trouble figuring out what is happening, I clamped a CT sensor connected to emontx v3.4 on battery power, to the neutral of my heat pump located outside. The reading seemed a bit high with a Standby power consumption ok 88-92 Wh. So I decided to put another ct sensor on the neutral directly on the general interruptor for the heat pump. That reads 5w,
Very odd then when load of the heat pump tends to lower due to modulation, the reading steps abruptly up reading circa 250Wh more and more than the whole house consumption which, in normal conditions, everything off just fridge router, switch and Ventilation running, is around 250-300 Wh

, that is how it looks like, and that is the strange behaviour happening At lower loads.
Can anybody help me troubleshooting that?

Do you really mean that? You put the c.t. on the D.C. cable from the battery? A c.t. will ONLY work on a.c. cables.

“Wh” is a unit of energy, not power. Do you really mean “kW” - it looks as if you do?

I suggest you put both c.t’s next to one another on the same cable. Then you can make a direct comparison. Do you have a.c. adapters for your emonPi and emonTx? Are both set to the same voltage (i.e. not “USA”)? The values you must compare are power.

thanks for your comment, no I put the ct clamp around the wire going to the heat pump. I wanted to say that the emontx is battery powered. I have ac-ac adapter but just on the emonpi on the main breaker. I corrected voltage in the script thought and they are matching at 224V.
apart from the unit I used, sorry for the confusion, I wanted to point out that the reading of the two clamps are similar under higher load, at lower loads the emontx looks inconsistent, I’m checking the power consumption with the main power counter and it looks like the emonpi is right with the lower reading and the emontx is the uncorrect one.
how could I solve that and making the two reading similar? do you think it is a Phase error or does the Ct clamp pick up some other load? I don’t know…

If your emonTx is battery powered, then it is estimating apparent power based on the measured current and the voltage you’ve told it. All other things being equal, apparent power can never be less than real power. The ratio (real power) ÷ (apparent power) is the power factor. The power factor for a pure resistance load is 1.0, for a small induction motor it can be around 0.6, meaning the apparent power is 1.67 × the real power.

So, what is happening, I think, is that as the load on the heat pump gets smaller, the power factor gets worse and the current falls more slowly than the real power. The result is the apparent power - as shown by the emonTx - falls more slowly than real power, which is what the emonPi with its a.c. adapter reads.

So that answer is, both could be reading correctly, but they are reading different quantities.

Thanks Sir for the hint and for your time, assuming it is a power factor error, do you have any suggestions on how to solve it? I could try to put an ac ac adapter on the Emontx outside, do you think it would improve the readings?

If that is indeed the problem, then yes, it should make the readings closer.

One way you could test this is by removing the a.c. adapter from your emonPi, powering down, powering up again. That will force the emonPi to also calculate apparent power, rather than real power. If it and the emonTx now agree, it has proven that the heat pump’s power factor is the reason for the difference.

Remember, when you put the a.c. adapter back, you must power down and power up before the emonPi will recognise it and use it again. Likewise, if you add the a.c. adapter to the emonTx, you must reset or cycle the power on that for it to recognise and use the a.c. voltage, and convert to calculating real power.

Thanks Sir,
You were indeed right, I ordered another Ac-Ac transformer and The readings look ok now!

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