Im trying to design a circuit that the load will get power from solar panel or a battery (in case the solar panel will not deliver enough current\voltage)

Also wanted to mention that this is a hobby, so I dont have deep knowledge in electronics..

So the question is about connecting charge controller and BMS-2S to load

1. 12v solar panel connected to charge controller as input
2. 2S (3.7 each) Li-Ion batteries
3. RPI Zero as load. will draw about 150~200mA

about the BMS, it says that pins P+ connected to charger+ and load+. And P- connected to charge- and load-.

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Connecting that way, that the BMS and the load are parallel to charge controller, will not interrupt the charge controller main goal? Im wandering how it will affect the Constant Current and Constant Voltage mechanism.

Im not sure that the load supposed to be connected that way, ill be happy for guidance.


  • \$\begingroup\$ Did you find your answer? I'm also wondering if load and BMS in parallel impacts charging. \$\endgroup\$
    – rrmoelker
    Mar 14, 2021 at 19:12
  • \$\begingroup\$ The charge controller will probably never finish its charge cycle because the RPi will draw a significant amount of current. This will confuse the charge controller into thinking the batteries are not yet full. The LiIon batteries will therefore be under constant charge, which will kill them in a short amount of time. \$\endgroup\$
    – StarCat
    Jan 7 at 9:16

1 Answer 1


When your energy source is a solar panel, the constant current is not constant, as it depends on how much current your panel delivers.

This way, the "constant current - constant voltage" charging algorithm transforms into "limited current - limited voltage" charging. Batteries are generally OK with this, as long as your BMS behaves.

The load will subtract from the available charging current and it is up to you to get large enough solar panel if you want the batteries to be fully charged at the end of the day.


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