USB solar panel to charge Boron

I’m curious if a USB solar panel like this one would work to power the on board LiPo charger on the Boron?

Weatherproof Solar Panel https://www.amazon.com/dp/B07SR6BCMR/ref=cm_sw_r_cp_api_i_p7fJFbGF9MGJG

Hi,
It’s a little dependent of your LiPo and you have to confirm that with LiPo manual. e.g you have LiPo which is 2000mAh so the answer is “easy” :slight_smile:

The best way is to check with LiPo manufacter, and check for charging requirements.

Best regards

From reading the comments, I would hesitate to use that panel. It looks like it does not regulate the output and one commenter reported getting 6V at 300 mA in partly cloud conditions. While the VIN/VUSB on the Boron can take up to 17V (with some limitations), the actual micro USB power input has a limit of 5.8V because it’s connected to both the bq24195 PMIC and the nRF52840 MCU. The MCU is what’s imposing the 5.8V limit in this case. Using the VUSB pin to power does not have this limitation as it’s only connected to the PMIC and up to 17V is acceptable.

I would use a 5W or 10W 6V or 12V bare panel and connect the + line to VUSB instead of using the micro USB connector.

Dear @rickkas7,

  1. So the physical USB input power is not the same as the “VUSB” pin despite the naming?
  2. Are you confirming it is safe to apply 6+ volts to VUSB, even applying a 12V solar panel which can output 14 volts? There has been plenty of contradictory information about the maximum allowable voltage for Boron. Thanks.

The micro USB connector 5V power line (VBUS_NRF in the schematic) is connected to both the bq24195 (with a diode) and also to the nRF52 MCU. The reason is that the MCU powers down the USB block to save battery power when there is no power on the USB port. However, the nRF52 has a lower maximum voltage of 5.8V on VBUS (what the signal is called on the nRF52).

The VUSB pin is what the Adafruit Feather spec calls the pin. The schematic shows it as VIN, which is what the signal is internally named.

The Feather spec requires that the signal be approximately 5V, and if you are using other FeatherWings on a doubler or tripler you need to be careful about applying a higher voltage on the VUSB pin.

However, if you are using the Boron in your own board, not with other FeatherWings, the VUSB pin is really the same as VIN on the Electron and E Series.

The Electron and E Series datasheet have always listed 12V as the maximum voltage. However, it’s actually 17V. On the Tracker SoM, which has the same bq24195 PMIC, it’s listed as 17V.

A 12V solar panel should always be safe. However, in vehicle situations, surge voltages can exceed 17V so that should be taken into account in vehicles.

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I’ve used a solar panel that can do up to 18v, but put it through a L7805c voltage regulator first, and a diode to stop discharge through the panel.

I did put in an INA219 module too, to measure incoming power, but that is not needed, just curiosity.