emonTx V4 vs Shelly 3EM


I was in the process of upgrading our 3-phase monitoring using V3 emonTX systems and adding an additional burden resistor to the 4th CT for additional capacity. From here each emonTX was going to be dedicated to a phase to resolve the lack of voltage reference on each phase when using the 3-phase firmware.

Part way through the emonTX V3 went out of stock and I’ve been eagerly watching the V4 discussions. I now don’t have enough V3s to complete my work but in the mean time I also took a look at the Shelly 3EM

On a like-for-like basis, the 3EM appears considerably cheaper. It has a voltage reference for each phase (3-phase emonVs not yet available, and presumably will be more expensive than the £50 single phase option) and comes packaged with three CTs. £120 vs. £208.

I’m hoping that I’ve missed something or whether anyone has done any analysis on the two systems. Having followed the V4 thread, I have no doubt that it’s been exquisitely engineered, but is there any performance data which makes it stand out from the 3EM.

Also, is it possible for multiple emonTX V4 units to share a single emonVs? If this was the case I could wait for a single 3-phase emonVs and reduce this aspect of the expenditure.

I really like the emon hardware and have been genuinely impressed so please don’t take my questions as criticism!

Many thanks,


I use no emonTX only 2 Shelly 3EM, but here are some facts to know about Shelly and emonCMS (local).

With a 3EM

  • you will not see some power peaks, like the inrush of a 3-phase motor (heatpump compressor in my case)
  • you have to have a “translator” e.g. NodeRed to convert the measured data to a format emonCMS accepts (but it works reliable if you are OK with it)
  • the automatic configuration of the emonCMS is not working. You have to configure the feeds/processing manually
  • configuration gets more complicated if you have PV

I don’t know when the 3-phase version of emonTX V4 will be available and if there will be an easier setup for that configuration or not.
I am using the first since 1,5 years, the second 3EM since 1 years an am actually satisfied with it, i can live with above mentioned restrictions. At the time I bought them, there was no real 3-phase system at OEM and buying 3 (or 6) single phase emonTX would have cost me significantly more, then the Shellys.

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Hello @element2202 The shelly 3EM certainly looks like a nice bit of kit. I cant speak to what is inside it as I’ve only seen the product brochure. The main difference on the surface at least seems to be 3CT sensor inputs on the shelly vs 6CT sensor inputs on the emonTx4. So we might be closer to being competitive if 2x shelly 3M’s were required… and of course when the 3 phase version of our kit is available :slight_smile:

Thank you @TrystanLea!

How will the emonVs work for the 3-phase firmware? Is it 1:1 for voltage reference to Tx?

Cost is not the main driver but it’s naturally a factor!! I’m invested and love the current setup but whatever I do is going to be expensive so I want to get it right :+1: