I have two solar production sites within 100m of each other, can I use put two ct clamps, on the same phase but on different Inverters to add the outputs of the two?
Welcome @Lmm_Cams to the OEM forum.
I presume you mean current transformers, and using an emonTx or emonPi and taking the voltage reference from or near to one of the inverters? What exactly do you mean by “add the inputs of the two”, because you can either use the two inputs of an emonPi, or two of the four inputs of an emonTx, and add the powers in software in emonCMS, or (especially if you have only one current input available) wire the two c.t’s in parallel and connect to one input, physically adding the secondary currents of the two c.t’s. In this case, the c.t’s must be identical, and the total current must not exceed the 100 A that the input is rated for (using our standard c.t., that’s 50 mA of secondary current in total).
Your principal problem might be pickup and interference on a 100 m long cable, but otherwise you can have as many c.t’s as you have inputs for, as long as they are all on the same phase.
A second-order problem might be the voltage drop between the inverter and the point of use, arising from that 100 m cable run, meaning that the power you measure won’t be the power out of the inverter. I’m referring to the inverter output, not the c.t’s extension cable.
Thanks for the reply, in this case I am not using emoncs, I am actually asking ask i fitting at my house a Zappi electric vehicle charger, and it has 6 CT clamps. 3 monitor what is going out to the grid from my solar production, and 3 monitor the solar production. My problem is I have 2 solar production facilities onsite, about 50m away from each other. Both are 3 phase. I presume other than interference issues I may have, it’s possible to add the two together as one input. I maybe able to buy some shielded twisted 2 core. So they need to be in parallel not series, and on the same phases? Any other recommendations welcomed:-)
Thanks again for your help.
Yes, because a true current transformer is a current source, so the currents add when wired in parallel. If your c.t’s have internal burdens, i.e. a voltage output, they are voltage sources and you wire them in series and the voltages add.
Yes - otherwise, what are you measuring? Look at a 3-phase waveform and add two of the waves together - the answer is not the sum of the individual waves, because of the time difference between them. Or think of it this way: the voltage line-neutral is 230 V. The voltage line-line is 398 V, not 460 V.
Where do the cables from the two inverters come together? Or do they feed into separate distribution boards?