Hardware recommendations

Hi all. Long time user of the emon platform.
My old system consisted of 2 emontx v2 radio sensors each with 3 ct sensors and 1 ac sensor.
I’m now in a new location which has 3phase power and a 10kw solar pv array.

I’m looking to build a new system for this located in Australia.

From my current research. I can’t use a single phase ac measurement due to the phases being quite different in voltage.

So I’ve arrived at 2 options
3x emontx V3… On each unit measure an ac phase plus the pv side and the grid power via ct

3x emontx arduino shields setup in the same method as the emontx V3 and transmit radio back to a raspberry pi shield

Am I missing any options?
Is my line of reasoning sound?

Any responses would be greatly appreciated


I think your line of reasoning is sound. Having only one a.c. input, the emonTx must “guess” the voltages of the other two phases. If they’re different, your power readings will be wrong. Therefore, you must treat what you have as three single-phase systems.

You don’t say what you’re doing with the data?
What radio frequency is your old system?
How is your PV connected - star or delta? (i.e. is it really 3 × single-phase inverters in one box, or a genuine 3-phase? My bet is on 3 × single-phase.)

A few suggestions:

  1. One emonTx V3 plus your old emonTx V2s. (RF freq’s permitting)
  2. an emonPi plus your old emonTx V2s. (RF freq’s permitting)
  3. an emonPi plus two V3s
  4. Convert your old emonTx V2s with a DIY “outboard” extender pcb carrying two voltage inputs, using the spare ADC channels.
  5. A DIY emonTx or emonTx Shield with 3 voltage, 6 current inputs?
  6. Talk to Robin Emley (mk2pvrouter.co.uk :wink:)

Did you mean 3 emonTx Shields all on one Arduino? I don’t think you can do that.
But you can stack 3 emonTx V2s (if you can source a third one) - Full-fat 3-phase monitor | Archived Forum

My 3-phase PCB supports 3 voltage measurements (one on each phase) and three measurements of current. This “uses up” all of the analog IO ports on the Almel 328 processor.

This hardware is primarily indended for diverting surplus power to one or more dump loads. It can equally well be used to monitor power in a 3-phase environment. A kit of parts is available via my Shop page (£50 including the RF module, plus postage).

I should clarify. My old system both the old emon tx v2s are dead. Look like element exposure finally got them. They weren’t in the greatest case.

With the arduino shield no I was referring to one shield per arduino

Tbh I’m looking at the shields as it’s a far cheaper option than 3 emontx v3s with currency conversion to australia

Specifically im looking to compare:
3x emontx v3
3x arduino shield + arduino nano + either radio/wifi

Then obviously a collector if radio option (which im thinking about just adding the radio chip to a standard wifi connected raspberry pi3

Have you seen this: 3-phase board 3 voltages and the BluePill - #2 by Robert.Wall

Can you clarify when you say, “phases being quite different in voltage,” you mean that each phase has a different Vrms? Or are the Vrms amplitudes actually the same, it’s just that they are not aligned in phase?

If the latter, you can try my firmware listed here with a single emontx3:
Emontx3-continuous - New continuous monitoring firmware

The calibration constants in cal.h can be set to IPH1=-120 and IPH2=-240 degrees , to rotate two of the phases into alignment with IPH0. As long as Vrms for phases 0,1,2 are equal, it should be fine.


Sorry thats starting to go over my head,
What i mean is that phase1, phase2 and phase3 at one point may be:
240, 230, 235



OK, yeah, if your desire is high precision then you will have to measure each phase independently with multiple emonTxes.