Couple quick questions before my purchase

Hi from Australia

I was initially looking at a EmonPI Solar PV but because my intention is to monitor multiple lines (hot water, ducted air conditioning, input, solar generation) I need more sensors. It appears it’s cheaper to just buy a emonTX + emonBase than an Emon PI Solar and a second EmonTX.

  1. What NodeID should I buy the EmonTX pre-configured to?
  2. How do I power the emonBase? Just standard 5v micro USB?
  3. My Ducted air conditioning is a large unit (15kw), will I need the large 100A monitor? How do I confirm this?
  4. I need to buy 3x “1 x high sensitivity single-phase CT current sensor input channel (18.8A / 4.5KW @ 240V max)” but I can’t find these on the shop. Can I still buy them?
  5. Lastly, I’ll be using a simple UK to AU adapter on the AC-AC for the EmonTX. Will this be okay?

Thanks so much

The NodeID only matters when you have more than one on the system. The emonTx comes with a choice of two, so you can have two emonTx’s with the default firmware, the third onwards will need a small change to the firmware.

It is a Raspberry Pi, so the standard Pi power supply is fine.

The definitive source of information is the rating plate on the aircon unit, or the manual. Failing that, you need to contact the supplier or manufacturer.
You are on 240 V mains, single phase, or is it a 3-phase supply? 15 kW @ 240 V single phase is rather less than 100 A, unless the power factor is particularly bad. But it is a very large motor for a single-phase supply. And the emonTx might not record the starting (inrush) current correctly. (This depends to the type of starter - if it is DOL, then there might be problems, if it is a soft-start, then it will probably be OK. If your lights dip noticeably when the aircon starts, then there is a big inrush current.)
The 100 A c.t. is the standard. If it turns out to be not suitable, there are other options, see the “Use in N.America” page.

Erm – What’s one of those? I think you’ve misread / misunderstood the emonTx specification. Input 4 on the emonTx has a higher resistance burden than inputs 1 - 3, which is what makes that input the high sensitivity one. Using the standard 100 A c.t., inputs 1 - 3 read up to 100 A, input 4 reads up to 18.8 A.

Yes, if your mains supply is a nominal 240 V.

That’s exactly what I have been doing for the last 3 years. Just make sure it is in a secure location/position so it does not get disturbed. Also in Australia.

Robert, thank you so much!

Arr, so it’s the device not the actual sensor. Thank you And yes, I definitely misunderstood.

I also just stumbled upon the WiFi adapter for the emonTX. Awesome feature, looks like I can have all my sensor inputs and connect the emonTX directly to without an emonbase. Nice one!

Does this help? Looks like it’s rated at 28.2A so I’ll need to ensure it’s on the 100A circuit?

Thank you Gary

Where can I buy the UART cable for the Wifi adapter?

They are just individual socket to socket leads like this P1017 Mixed Prototyping Wire Pack 60pcs - Altronics

If you look closely at the photo you can see the strands are not joined. Also you only need 4 not all six. +ve grd rx tx if I recall correctly.

If you have that, you will definitely need a 5 V USB power supply for your emonTx (as well as the ac adapter), because the current that WiFi requires puts too big a dent in the ac adapter output, making it useless for accurately measuring the voltage.

(Can I just point out that, if you stayed with the emonBase, you’d have your own local emoncms running inside your own LAN, and that’s totally under your control and more customizable than You can still add emoncms running on a Raspberry Pi - or anything else on your LAN - later.)

The rating plate of your aircon seems to say that there are two units in there, a heat pump which is 28.2 A single phase, and a compressor which is 3-phase and 23.4 A (per phase).
I’m suspicious. Can you look at you main distribution board and tell me whether you have a 3 phase or a single phase supply? 23.4 A per phase agrees with your 15 kW, so I think you have a 3 phase installation.

The reason for questioning this is, the emonTx was designed for the UK market and a single phase. Although with fiddles it can work well on a 3-phase supply, you rapidly run out of inputs and without the right sketch, you might well end up getting the wrong numbers out.


This was the route I was hoping to go down. Start via but maybe move locally if I need (I have tonnes of Linux boxes around the house).

This is the distribution board. The MCB Is a “Hager MSN132” which according to their website is:

Technical Characteristics
Number of modules: 1
Number of poles: 1 P
Rated short circuit breaking capacity: 6 kA
Curve: C
Rated current: 32 A
Frequency: 50/60 Hz
Rated insulation voltage: 500 V
Operating temperature: -25 to 60 °C
Electric endurance in number of cycles: 4000
Number of mechanical operations: 20000
Top and bottom screw terminals connection capacity with rigid cable: 1/25 mm²
Top and bottom screw terminals connection capacity with flexible cable: 1/16 mm²
Tightening torque: 2,8Nm
Height of installed product: 83 mm
Width of installed product: 17,5 mm
Depth of installed product: 70 mm

Does this help?

That definitely looks like and says it is a single pole MCB, so it must be single phase. So the problem I thought you might have doesn’t exist. Presumably, the plate on the aircon unit means that they use the same plate on single-phase and 3-phase versions, which doesn’t help when I’m on the opposite side of the planet to you.


Thank you so much, I’ve gone ahead and ordered. Really appreciate your help.