Expansion of system, and 'Virtual' Sharing of an EmonVS

[glen_m (Glen McGeachen)]

I currently have a EmonTXv4 installed in my meter box, along with a 3 Phase EmonVS, and just want to confirm a few things before I purchase any expansions to the system.

Existing Setup
The HL existing schematic is as follows, with all existing components mounted inside the Meter Box:

More details around the existing installation are available in the following post:

3 Phase Monitoring with EmonTXv4 WiFi

Hi @TrystanLea - Just want to say thanks for sorting us out with the extra components to convert this unit to a 3 phase. They have arrived, and I dusted off my soldering skills to complete the upgrade, and the electrician has been today to hook it all up. Yes - It ended up as unplanned cost for me (the additional circuit protection, and requirement for a electrician), but with the benefit of hindsight, probably ended up being a better solution than what I originally had intended, so all good. I…

Requirement:
I want to expand the system to get some more granular power measurements on specific circuits within the house (e.g. water pumps, heat pumps, and a bunch of other things).

I am therefore looking to install a further 12 channel setup inside the house switchboard (Also 3 phase), which will also send data back to my local EmonCMS installation.

There are no physical paths available for routing additional cables from Meter Box to House Switchboard, which would preclude the use of sharing an EmonVS between two devices via the splitter available in the shop.

For the sake of these questions, you can assume that the voltages will be near-identical between the meter-box and house switchboard (16mm2 cable per phase), and not a huge distance between the two.

Maybe in future, I will also look to monitor more individual circuits within the Shed as well (more water pumps etc), which also cannot have a physical connection back to the existing EmonVS

Questions

• Firstly, after reading other posts on this forum, with the demise of the EmonTX v4, it appears that the replacement option would be to use the EmonPi2 (with the Pi Zero option) if I want to transmit directly over WiFi back to my local EmonCMS installation, the same as the existing EmonTXv4?
• I would prefer to avoid purchasing (and paying an electrician to install) another EmonVS 3 phase for the house switchboard - The installation and balance-of-system components push the cost through the roof. Even worse if I want to install a further monitor in the shed in future. So the related questions are:
  • I assume I can power a EmonPi2 with just a USB power supply, and no EmonVS?
  • If I get current-only reading feeds from the new EmonPi2, and then calculate power within EmonCMS by also using voltage feeds sent from the existing EmonTXv4? (Basically the ‘virtual’ EmonVS approach)?
  • What am I loosing from this ‘virtual’ approach in terms of accuracy etc, vs. locally calculated power reading within the EmonTX/EmonPi2 when paired with a EmonVS?
  • Lastly - I see there is no ‘Current Only’ firmware for the EmonPi2 with 12 ports? Is this planned, and if so, roughly when?

Cheers

[Robert.Wall]

@glen_m

I assume I can power a EmonPi2 with just a USB power supply,

I don’t have an emonPi2, so I can’t answer definitively, but this certainly appears to be the case from the PCB layout and schematic diagram, and it’s true for the emonTx4 (which is effectively what the emonPi2 is).

@glen_m

If I get current-only reading feeds from the new EmonPi2, and then calculate power within EmonCMS by also using voltage feeds sent from the existing EmonTXv4?

Your problem - if it is a problem, you might not think so - is you need the actual voltage wave to calculate real power in the emonTx4/emonPi2. If you measure the rms current in your house (with a 12-channel emonPi2, and the existing software does that, it just doesn’t send the values anywhere) and then multiply those currents by the rms voltage, all you have is apparent power, which might be the same some of the time, but generally it will be a larger quantity, depending on the power factor of the working appliances/load you have at any moment. And a further consideration - the current and voltage stand to be out of syc by up to 10 s, so if you have pulsating loads such as an induction hob, your bet is as good as anybody’s for what you’ll read.

@glen_m

I see there is no ‘Current Only’ firmware for the EmonPi2 with 12 ports? Is this planned, and if so, roughly when?

I’m not aware of a plan to publish this, however it’s a trivial task and one of the demonstration sketches that come with the emonLibDB library shows how to do it, and puts the currents in the serial output to be viewed on a monitor.

Would I be right in thinking that the need for an electrician is down to your local regulations? And you don’t have an “industrial” 3-phase socket you could use just for the emonVs – like this?
https://www.screwfix.com/p/mk-16a-3p-n-e-connector-380-415v/140jr

[glen_m (Glen McGeachen)]

Thanks for the great explanations Robert.
Probably not the answer I wanted to hear, but none-the-less, the right answer

For the house switchboard, I guess I am just going to have to get the VS/EmonPI combo so I can get accurate readings. May just need to wait a short while. Between the device costs going up, and the NZD/UKP exchange cross dropping, just a bit harder to get past the domestic financial controller !!

Perhaps for the shed (future project), I might look at a cheaper current-only monitoring solution for the individual circuits, as its mostly just Irrigation Pumps, and I already have overall shed per-phase monitoring via my existing VS/TX4 combo in the MeterBox.
Cheers - Glen