Three Phase PV monitoring with single emon TxV3

Continuing the thread “Three Phase PV and Grid-In Monitoring” on the old forum that is here:

So, I have now:

  • bought the little UART board and USB cable
  • installed the Arduino software on my Windows 7 PC
  • powered up and connected my emon Tx 3.4 with standard 433MHz module
  • verified the programming environment can see the Tx
  • copied the content of emonTxV3_4_3Phase_Voltage.ino to the Arduino software
  • commented out the line #define CT4LINE 1 as I cannot put a clamp where I need to for that
  • clicked Compile
  • crossed fingers
  • clicked Upload

Noting that comments in the sketch say things like “These need to be set in order to obtain accurate results”, I’m afraid I’m simply unable to do what’s required. Our electrician is not going to want me in the relevant “fuse box” for any longer than necessary - in fact he might insist on connecting the current clamps himself and I won’t get a chance to measure anything. Will this mean my measurements are going to be meaningless?


Do you mean split-core current transformers when you write “clamps”?

Where is your emonTx located? It should be outside the fusebox and your installer should bring the 3 C.T. leads out and plug them into the emonTx before he livens the circuits. Although the YHDC CT’s that are sold in the shop have protection, you should never open-circuit a CT on a current-carrying conductor. Your installer should be aware of this.

If your CT is accessible, and given that you’re using the a.c. adapter for the voltage signal, it’s perfectly safe to connect your computer to the emonTx and reprogram it after installation. You don’t need to unplug the CTs (nor the ac adapter) for setting up and calibrating the sketch.

If you’re using the recommended CTs and ac adapter, the default values in the sketch should be close, but given that you appear to have everything needed to set the unit up, perhaps you could explain why you think you can’t? There may be alternative methods that you can use.

Sorry about my repeated CT/clamp naming issue - its from long ago when you could buy a hand-held multimeter that had a built-in current transformer that they called a “current clamp”.

Yes, the emon hardware will be outside the big steel “fusebox” - the electrician will have to find a way to route the CT cables in from the Tx. I’m aware of the open circuit issue - not quite sure how we’ll get around that but we’ll try.

Yes, I can change parameters in the software if I take a laptop with me but what I can’t do is jab a multimeter into the wiring to check voltages.

Well, you can measure the voltage anywhere in the installation, as long as you bear in mind that a high current load at the end of a long wire could be seeing a voltage drop of 5% before it is out of specification.
You can probably also measure the current in an appliance provided that it is the only item on that phase energised at the time.
Or you can of course calibrate the voltage and current ‘on the bench’ prior to installation, leaving only the phase correction calibration to be done in situ.

If I’m testing a CT, I use a 6.3 V 8 A transformer, a high-power resistor and multiple turns through the CT - low power, and perfectly safe to handle. (Make sure each CT stays with its respective input once you have got the calibration constant.)

As for the open-circuit CTs, 3 sockets with tip-sleeve shorted? - Swap them for the emonTx when it’s all off-load.