3-phase independent voltage measurement - unbalanced load - minor emontx_v3 hardware mod or exposed pins

I need to monitor a 3 phase PV system where the appliance side if quite often unbalanced. So having indipendent voltage sensing for every phase would be the better solution I think.

So l was wondering if you think it would be possible to use ADC6 and ADC7 to sense the voltage replicating the measuring part connected to ADC0. It should be possible with “minor” hardware modification. I see ADC6 is used on the RJ45 port but I don’t need it so… And ADC7 seems to be unused.

Did you think it could be a viable way?

Thank’s for you advice

It is possible to measure 3 voltages and 3 currents with an ATmega328p, I’ve done it before now with a custom built board and I believe @calypso_rae has a 3phase front end for his mk2pvdiverter that does this but I have not heard of it being done with an emonTx.

It may be possible if you use adc5 and adc6 for the additional Vac inputs, adc7 is hardwired to be a battery voltage sensor. adc5(d19) is intended to power any 1-wire temp sensors wired via the 6way terms but they can be constantly powered directly from the 5v rail rather than switched via d19 to conserve power.

And you must be careful to use the correct methods from emonLib so that you can specify the pins for the voltage inputs, i.e. voltage(…), NOT voltageTX(…) .

Good, I will investigate a little bit more on the mk2 pv 3-phase router before to take any decision.

Thank’s for you help

The 3-phase version of my Mk2 PV Router is described at


Contact email addresses are on my Shop page

Yes you’re right, Mk2 PV Router could be the straight line solution. But at the same time this mean keeping a quite different board and firmware. I would like to investigate if and how we could bring “native” 3-phase sensing on the emonTX in such a way of having a more modular system that we could adapt to our PV situation that is quite frequent in Italy when we don’t need to divert the energy or anyway in any 3-phase monitoring situation.

About emonTX, it seems we could just use ADC5 on J3 and ADC6 on the RJ45 to explore the solution.

I don’t know if the path for ADC5 and ADC6 would be clean enough, but that will permit to experiment native 3-phase sensing with a few external component. And in case think about a more “adaptable” emonTX with really marginal change to the board keeping it on a default 1-phase configuration but letting using the board also on 3-phase situation without having to use N redundant board that make no real sense.

@calypso_rae In the mean time I will probably contact you to resolv my immediate situation with your board.

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