Continuing the discussion from North America, CTs and Calibration:
I also recently acquired an emonpi and have it running monitoring 2 circuits on my electrical panel. As far as that goes, it is working fine. But, I neglected to check that the standard CT’s would fit over the supply wires when I ordered. They are AWG 4/0 aluminium rather than the AWG 0 copper. I had my service upgraded two years ago and was visulaizing the old wiring. So I need to purchase replacement CT’s.
I too was considering Wattcore CTs, WC3-100-RV001, which have a 1V output. I have seen these recommended elsewhere and some people seem to have insisted that it be the 1V model, not some other value. I don’t understand why. These must have their own internal burden resistor that will effectively be in parallel with the emonPi’s internal burden resistor of 22 ohms. The original CTs provided are unburdened. So, the calibration must be incorrect with these alternate CTs. Where are the calibration factors located? In my emonhub config file, viewable in the emoncms utility in my browser, the only possible entry is the ‘scale’ factors. Are these the calibration factors?
Is it necessary to remove the burden resistor with the above alternate CT? I believe that they are surface mount devices. I am unsure how to do that safely. What about using Wattcore CTs, WC-100-MA100, that are unburdened devices with an output of 100ma at 100A input? I believe that these would require an additional 22ohm resistor in parallel with the existing burden in the emonPi. I think there are existing through holes in the PC board for that purpose. This would ensure 1.1V at 100A. In this case are the exisitng calibration factors nearly correct?
I have only begun to understand how this system operates, so please excuse me for my ignorance. I need clarification. I think the 2nd option is easier, but I could be wrong.