improving CT accuracy on emonPi

I am looking to monitor a compact system (balanced ventilation with heat recuperation) using the emonPi. The system is connected with two 16A, 230V lines. When using the standard 100A CT’s on the Pi, the current measurements will be often towards the lower limit (< 10A) of the sensor input, hence less accurate. AC to AC converter will be installed. What would be recommended to improve the CT readings:

- multiply the current, by routing the power line multiple times (say 5x) through the core of the CT 
- modding “high precision” inputs on the emonPi like at the emonTx V3 line 4, by replacing the standard burden resistor of 22 ohm by a 120 ohm version?

Finally, where exactly should the calibration be adjusted (it is a bit of a puzzle in which file on the SD card) for the emonPi? Would welcome advice and insights!

Robert Wall's picture

Re: improving CT accuracy on emonPi

The best way would be to first multiply the primary turns, then if necessary remove the burden resistor and replace it with a higher values one. You can choose the resistor value to give whatever input sensitivity you want - it doesn't have to be 120 Ω.

To update the sketch, you either need to recompile and transfer the executable file to your SD card, or install the IDE on the Pi. I can't tell you offhand where the file is, but there' a fairly recent post about this, which a search should find. Failing that, you can calibrate the current/power in emonCMS.

marcneelen's picture

Re: improving CT accuracy on emonPi

Thanks, all clear - I'll first try with multiplying the turns through the CT core.

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