EmonTx and Solar Diverter

Good Afternoon Everyone.

I have recently purchased a EmonTx and connected it to 4 circuits to monitor. So far finding a great piece of kit and very interesting.

I was looking at purchasing a solar diverter but after reading some material on the OEM website you can actually run the EmonTx as a solar diverter. Coool :slight_smile:

I do have a question regarding running it a diveter. Their are sketches online that you can upload to run the EmonTx as a solar diverter but can it be used as a monitor and diverter? Does the device have enough processing power?

Kind Regards


I have a SSR that can use to switch the immersion heater its

Welcome, Gareth, to the OEM Forum.

I’m not sure that the emonTx can handle 4 inputs and divert, but both Robin’s and MartinR’s sketches will certainly handle two inputs. It wouldn’t be difficult to convert either sketch to 4 inputs to test it, though.

One reservation about using an SSR - will your SSR work on a 3.3 V input signal? Many only work on 5 V (and is it the zero-crossing type or fully proportional phase control?).

Thank you for the prompt reply.

I’m not sure that the emonTx can handle 4 inputs and divert, but both Robin’s and MartinR’s sketches will certainly handle two inputs. It wouldn’t be difficult to convert either sketch to 4 inputs to test it, though.
Ok so both of Robin’s and MartinR’s sketch will log data to emonCMS and divert with 2 inputs?

Yes my SSR is zero crossing with a control voltage of 3-13V.

Am I rightly thinking that if I remove jumper JP2 and connect a 5Vdc usb connector into the emon TX shield its better than relying on the AC/AC adaptor to power the unit- if I am think of using as a diverter?



IIRC both will actually work fine with 4 CT’s.

I have been running my own variant of MartinR’s PLL for 6 years now on a emonTx v2 with just 3 CT’s without issue, the monitoring is plenty accurate for purpose despite me not really spending much time calibrating and as for the diverting, it is absolutely spot on, it is more accurate at tracking the export than a commercial unit that was installed by the PV installers, the emonTx+Mk2 still squeezes out a little more even after the commercial unit has taken what it wants. The LED on our supply meter is on solid for hours and hours (it registers both import and export with flashes). I have also had MartinR’s PLL working on a emonTx v3 whilst helping convert it to 4CT for another user years ago on the old forum.

For examples of Robins code for emonTx v3 + diverter (with 4 CT’s) see



Robin has used the high sensitivity input (ct4) for the diverter and therefore recommends using a 2nd CT on the same cable for monitoring above the 4kW(ish) limit of the high sensitivity input so whilst it uses 4CT’s it might only offer 3 values. Personally I would just use a std (ct1-3) input, it works well enough on my emonTx v2 and some of the accuracy of the high sensitivity input is lost due to the potential phase error of the higher value burden resistor. What you gain on one front you can lose on another, especially when dealing with the lower currents like appliances in standby and electronic chargers etc which is where the diverter kicks in, not when you have a nice 4kW oven running (for example) so i would rather have the extra input myself.

I’ve had a quick search but cannot find any 4 ct examples for the PLL, but I will post here if I find something.

I think there would be good demand for a proper OEM emonTx+diverter firmware, I would certainly be on-board, the only reason I haven’t swapped out my emonTx v2 (aside from it working perfectly well) is because there is no focused development in this area, just links to very old FW, I know from Robert’s work on the emonLibCM there have been improvements made in the way things are done but I’m not able to reverse engineer those changes out and apply them to the old FW, so I’m sticking with the Tx v2 for now as the emonLibCM doesn’t do diverting (yet?).

Maybe one day i will try and tackle it but since my v2 works so well, it isn’t high on my to do list.

This is true of any emonTx, but yes especially if using as a diverter with 2 or more CT’s. The continuous sampling will be more accurate with a separate PSU and you will have more power available for the diverter triac/ssr. I believe it is possible to run a emontx diverter from a single ac adopter but it is tight especially if you start thinking about pulse counting or temp sensors and/or your emonTx or PSU is at the wrong end of component tolerances.

Good question - I was pondering that one. emonLibCM came originally from Robin’s code, I’ve speeded it up a little in critical places so I don’t see why it’s not possible to make it divert by grafting parts of the original code back in. But it won’t be a 5-minute job.

and if the mains suffers a dip.
I can check the numbers for that, but if your SSR takes more current than the high sensitivity opto-coupler that’s specified, it will fail.

IIRC, the recommended max load for an AC-AC powered emonTX v3 is 10 mA,
and the absolute maximum load spec is 60 mA.


Important note regarding powering with AC: powering via AC is recommended only for standard emonTx operation without auxiliary sensors (apart from a maximum of 4 DS18B20 temperature sensors) or equipment (e.g. relay modules) connected. Correct operation via the AC supply is critically dependent upon using the correct AC-AC adapter. If you are using the recommended AC-AC adapter and the current draw exceeds 10 mA and the mains supply is below the minimum allowable, then circuit operation will be impaired, adversely affecting the accuracy of the emonTx. To avoid damage to the emonTx V3 circuits, the current drawn from the AC circuit should never exceed 60mA - see the technical wiki for more info. If more than 10 mA of current is required, it is recommended to remove jumper 2 (JP2) and power the emonTx via the 5V mini-USB connector. When JP2 is removed, the AC-AC adapter (if connected) will be used only to provide an AC voltage sample, i.e. it will not power the emonTx.