# 3x AC Sensor and 1x Voltage Sensor

Now that I skipped my ADS1115 idea, and used an Arduino that sends data over softserial to the Wemos, I found another limitation.
I only got ONE voltage sensor, but 3 phases. I could add two more voltage sensors, but there is not a lot space in my wallbox, and I have to order the sensors first.
As i expect the voltage on the 3 phases more or less similar, I’d like see how it works with one sensor, but for calculation of power etc I need voltage values for the 2 other phases as well.
Will something like this work?

``````  emon1.voltage(0, VOLT_CAL, 1.7);  // Voltage: input pin, calibration, phase_shift
emon1.current(1, CURRENT_CAL);    // Current1: input pin, calibration.
emon2.voltage(0, VOLT_CAL, 1.7);  // Voltage: input pin, calibration, phase_shift
emon2.current(2, CURRENT_CAL);    // Current2: input pin, calibration.
emon3.voltage(0, VOLT_CAL, 1.7);  // Voltage: input pin, calibration, phase_shift
emon3.current(3, CURRENT_CAL);    // Current3: input pin, calibration.``````

It will work for phase 1, and if you only want apparent power on phases 2 & 3, that would be fine. But if you want the real power on all three phases, no.

EmonLib was designed for the UK single phase system. In Austria, I believe you have a 3-phase, 4-wire system. In that, the voltages of phases 2 & 3 are shifted (ideally) 120 and 240 degrees behind the phase 1 voltage. If you try to compute real power using the phase 1 voltage, you will have a serious error.

You need the 3-phase sketch. Although that only measures the phase 1 voltage, it saves a little over 240 degrees worth of samples and uses those to synthesize what it hopes will be a reasonably accurate representation of what the phase 2 and phase 3 voltages would be; and it uses those to calculate the real power in those two phases.

I’m getting closer, and what you say makes sense to me (university is already decades ago). Yes, we have 3 phase & neutral here in Austria. 120 degrees shifted. So the voltage can only be correct for the first phase, and needs to be shifted by 120 degrees for the others. Got it.
As I want to know how much I have to pay for electricity, I’m not interested in “real power” or “true power” - whatever the correct term for “Wirkleistung” (what the German term) is. Afaik the electrical company charges me for “apparent power” (“Scheinleistung”) so ALL power consumed over the wires. Correct?
May I ask one more favor: If you say 3-phase sketch, you mean this? GitHub - openenergymonitor/emontx-3phase: emonTx 'approximate' 3-phase firmware - This is for complete hardware, but where can I find the source?
Any one more: How would I know which of the other phases is phase #2 (120° shift) and which one is phase #3 (240° shift)? - But maybe I just concentrate on “apparent power” and call it a day!

I think you should check what exactly you pay for. In most countries, real or active power (Wirkleistung) is what you pay for, often (but for industrial users only) with an extra charge for reactive power (Blindleistung). If it really is apparent power (Scheinleistung) that you pay for, then what you proposed with emonLib will work.

EmonLib does calculate the rms average values for voltage and current, and it does calculate apparent power for you. So

`TotalPower = emon1.apparentPower + emon2.apparentPower + emon3.apparentPower;`

Yes, and that IS the source. If you look in the documentation (English only, sorry - but your English is very much better than my German ), you will find in the ‘Installation’ section a method to identify the phase sequence (Phasenfolge).
It should be marked on your energy meter, or by the wire colours (1 = brown, 2 = black, 3 = grey)