Li-Ion current clamp sensor

  • I have a simple consumer whole house, single current clamp monitor. As I was looking into getting it to talk to Domoticz, I came across MySensors, this is great! So now I want to make a few battery powered MySensors to monitor various power loads, I have done a lot of reading, and want to make sure what I am thinking is correct before I order parts.

    Because of where the sensors will be located, they must be battery powered. I plan to use the NodeMCU+NRF23L01 as a WIFI gateway, think this will plug and play with Domoticz, and this will be mains powered.

    The sensors:
    Arduino Pro Mini atmega328 3.3V - Modified remove power LED and regulator
    100A SCT-013-000 CT Clamp
    18650 Lithium Ion (one or maybe two in parallel depending on size, extremely cheap/free from old laptop batteries, 4.2v->Discharge->3.6v)
    MCP1702 TO-92 regulator

    Assumptions I am making, that I want to check before ordering parts:

    • The MCP1702 regulator be efficient from a Lithium Ion battery
    • The MCP1702 produce clean enough power to run the NRF24L01+ (I have read noisy power will cause issues)
    • I should use a 22Ohm Burden resistor, and will give me about 26 Watt (10bit ADC) accuracy using 3.3v
    • If I use a larger resistance 2 * 22Ohm = 44Ohm total, I will get twice the accuracy, but only half the max load reading of 50Amps
    • The voltage divider resistors for the CT Clamp should be rather high, say 470k, to reduce current draw
    • The capacitor in the CT clamp circuit should be 10uF electrolytic
    • Also if I find myself needing better accuracy, I can ad-on a 16 bit ADS1115, giving up to 1/2W accuracy with the 22Ohm burden resistor / 100A range.
    • Cell voltage can be measured with a simple voltage divider and 3.3v reference, everything is running constant 3.3v from the MCP1702
    • With this setup I should get many months of operation

  • Did you get anywhere with this in the end? This is something I would like to do also!


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