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I have a basic 12V solar panel system set up with a basic (non-PPT) charge controller(anode/cathode for Panels-Battery-Output). I would like to monitor/control the system with an arduino-based external controller.

Specs on the panel system (let me know if I left anything out)

12V DC - 20A Max current - 12V 35Ah lead-acid - Panel output: 100W

I am looking for Wh left in the battery and W currently being used.

To achieve this:

  • Voltage divider on battery
  • Shunt on charge controller output line.

Can I combine these circuits into one?

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    \$\begingroup\$ You also need a current measurement (shunt or other) to monitor battery discharge. Most applications just use a single shunt/hall effect transducer in series with the battery to resolve both positive and negative currents (discharge and charge). \$\endgroup\$
    – HikeOnPast
    Dec 2 '12 at 5:15
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No, you can't - the current shunt has to be in line with the current flow and very low value, while the voltage divider is high resistance and out of the main current path.

There are a number of devices like the very neat INA226 that support both current and voltage monitoring in a single device, however. The INA226 has an I2C interface, is extremely accurate, and will even calculate power usage for you.

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