Monitoring 13 circuits over three phases

Hi all,

Having recently bought the emonPi to test it with one circuit, I am very happy with it and I would like to extend it. In total, there are 13 circuits that I want to monitor, but they are distributed over 3 phases (4 on phase L1, 5 on L2 and 4 on L3, this is a 3-phase system with neutral connection). I was thinking of getting 3 emonTx stations, one connected with an AC-AC adapter to each phase and leave the emonPi on L2 to monitor the extra phase (since there are only 4 inputs in each emonTx). Is that a viable setup, or are there better options?

One extra complication is that one of the systems I want to monitor is a 3-phase heat pump. Is it possible to combine the readings from the 3 phases into one power reading?



Hi Bart,
You might want to take a look at IoTaWatt. One device could monitor 12 three phase circuits, with individual voltage references on each phase. The output and EmonCMS (.org or Pi) supports adding the total heat pump. You can keep using the Pi for that 13th channel and IoTaWatt can send the data to EmonCMS on the Pi. IoTaWatt also retains up to 15 years of historical data with the most recent year in 5 second resolution.

You would need a couple of VT adapters which I can provide gratis. Let me know if you are interested. Im anxious to have some three phase users.


Hi Bart

Yep what you propose will work exactly as you suggest and powers across multiple phases can be summed in emoncms

Thanks, the IoTaWatt seems to be exactly what I need. Is it more accurate to use the 20 A CTs? I would be interested in the adapters, could these just be shipped with the main unit when I order it?

Practically speaking vs the sct013 - no, but they are smaller and cost less, so if some of your circuits are under 20A they are a good choice.

CThat would depend on when you order.
I’ll make some up and send them right out to the UK, but I’m in the US so might take a week or more. I have no problem with shipping to Belgium, but you would have to deal with any import duties, etc. The other option is to order and drop OEM a note to wait for adapters to ship.

OK, I’m in no rush, so I’ll indicate that I need the adapters when ordering from OEM. Thanks a lot!

Bart, adapters shipped today to OEM. Typically - two weeks. Contact me when you have all the gear. Thanks.

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Alright, I just placed my order :slight_smile:

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Hi Bob,

I’ve been following your work on the iotawatt device with great attention. I’m aiming for exactly the same as written above: I need to monitor a 3-phase network. I checked the demo site and I understood I can just configure any two inputs as additional voltage references besides the default. But where do I get the additional two AC-AC adapters from? Would it be the same type as the default VT (and same plug)? Do I just plug them in and that’s it?

Szenti Ga

Yes, you can use the same VTs, but you will need a simple adapter to connect them to the current inputs. It’s Thanksgiving here today, so I’ll publish how to make the adapters in a day or so. It’s very simple, requires a single resistor and a couple of connectors. I’ll try and publish the source for the parts.

That’s great but I’m afraid I won’t have the time for manual tweaks. Can I somehow purchase the specialized VTs along with the rest of the stuff? I would aim at purchasing the complete stuff (along with the CTs) on line tomorrow.

Hi Bob,

if I place an order today, can I somehow indicate the need of the specialized VTs as well? I just read you were anxious to have some 3-phase users, you can count me in :slight_smile: BTW, I would order from Europe, does it make a difference?

Not sure the status of those adapters. I sent them out last week without tracking. There was an extra set in the package, but I don’t know if they are committed to anyone else. If they are available, you are welcome to them. If not, you would have to wait for me to make more and send them from the US to UK.
@glyn.hudson, or @Gwil can you connect the dots here?

Europe is fine.

Hi @szentiga,

As Bob mentioned, we have a spare set of these adapters. Just leave a comment with your order - the option to do this will appear at checkout - and we’ll include them free of charge.

That’s what I did, when I just placed the order. Thanks!

Hi Bob,

I got all the gear today, with the two adapters, many thanks! I’ll try to install everything this weekend.



My recommendation would be to install the first VT and calibrate it as per the wiki, then install the other two on any two input channels and calibrate them.

Once you have more than one VT configured, a new drop down to Specify the associated VT will appear as you configure the CTs.

When all is done, you can configure an output channel that adds the three phases of your heat pump. You can also configure an input to EmonCMS that adds those together.

Should all go smoothly.

And it did! I still need to configure emoncms a bit, but on the IoTaWatt everything is working perfectly!

Congratulations. You have just performed the first production IoTaWatt true three phase installation (that I’m aware of). I’ll be interested in details when you get some running time and experience with it.

I just got all the stuff I ordered, thanks! I got one adapter (for the CT’s), but instead of the the extra VTs I got two special cables with built-in resistors. Can I just use two regular 9V adapters to use with the cables to act as voltage reference for the other two phases? What output power is needed?