Solar Lipo charger



  • Can someone confirm if the solar Lipo charger (Adafruit) will work with the LoPy and expansion board?

    https://www.adafruit.com/product/390

    Thank you



  • @JimT Sorry, I could have told you. You may use a 1N4001 model (or any of the 1N400x series). You have to put that in series to the solar module, Anode of the diode at the + pin of the solar module, Kathode (the side with the ring on the diode case) to the charger module's + input. Doing that, the voltage of the solar panel will be reduced by about 0.7 V. I would add a small load too behind the diode, to cap the no-load case, like by a 1 k resistor at the chargers module input between + and GND. You can use the additional power in lead pads of the charger module for that.
    I see that the module has already a built in diode, but that is a MPB120 Schottky type and reduces the Voltage only by 0.3 V.



  • Is it too much to ask for the diode specifications as I'm not an EE. Thank you for your help.



  • @JimT I would recommend it, even if the voltage of the Panel never exceeds 6V. That's because the input voltage of LoPy is specified at 3.3-5.5V. It will withstand 6V but then there is not safety margin at all. But before that, test the solar panel' s output voltage at bright sunlight and with low load. Then you would get the highest possible Voltage.
    The data sheet of the cell says:
    Output:
    Open Circuit Voltage: 7.7V
    Peak Voltage: 6.5V
    That sounds like you will need some protection against overvoltage.



  • Thank you for the response. I was planning to use a 6V 2W Solar panel. Do I still need the diode?

    https://www.adafruit.com/product/200



  • @JimT That should work, if you connect the LiPo to the charger and Vin/GND of the LoPy to the load output.

    RISK: Since in charging mode the input is connected to the output, be careful that the Input voltage from the solar cell does not exceed the maximum input voltage of the LoPy. I do not know if the output voltage of the solar cell is internally limited. If not, you have to add extra protection. And even if, I would add a silicon diode in series reducing the voltage from the cell to 5.3 V. So do not use it before you know the properties of the solar cell.



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