I had a new ac coupled battery system installed and one of the features it has is a CT on the other inverters on the circuit. The issue is it can only have 1 and my inverters are in different locations so the installer chose the easiest one.
I contemplated having 2 separate Modbus CT power meters and then emulating the Modbus RTU CT unit with the summed total, but though I would try the cheaper option of putting a second CT coil in parallel with the first.
I purchased a CT with the same turn/current ratio of 1000:1, installed it in the remote inverter location then ran a 4 core shielded cable to the new AC coupled inverter. This was a 12m run. From the inverter there were 2 spare pairs on the CAT5 cable running from it to the meter box where the power meters are located. The other 2 pairs are Modbus RTU and a DRED signal to inhibit inverter operation. I used 1 pair for the CT signal and the other pair I connected to the grounded shield to try to help with any interference.
It is good to point out that I did not install the CT on the AC cables in the remote inverter location, as that would have made some lethal voltages, me being a cheap skate and buying CTs that did not have any over voltage protection for an unloaded CT. I also took the CT off the cable being monitored by the power meter even though it probably actually had dome dirt of protection.
The power meter closely matched what the inverter said it was producing so it was matching its specs of being +-0.5% accurate. After I wired the second CT to the power meter (still not on the remote inverters) and reattached the original CT it was only reading about 60% of what the inverter did it was producing. I found I had not clipped the CT together fully and was excited to see it read 4189W when the inverter said 4400W, a 211W or 4.8% under reading. I then disconnected a lead of the remote CT to see what just the cable loading was and it came to 3.7%
As luck would have it I clipped the remote CT on backwards (or had the wiring swapped) so had to fix that, but now I can have a reading of I’ll my solar production on the one platform.
