I recently bought the Photon 2 and the Adafruit solar charger Adafruit Universal USB / DC / Solar Lithium Ion/Polymer charger [bq24074] : ID 4755 : Adafruit Industries, Unique & fun DIY electronics and kits
I had planned on going out of the solar charger load output to the photon 2 battery connector but it looks like this is connected to the Li+ pin which has a max voltage of 4.2v while the the load out of the solar charger has a max voltage output of 4.4v.
Will this be an issue? Should I take the load out to VUSB instead?
Thanks!
That will not work with the Photon 2. On the Photon 2 (also Argon), the Li+ is only intended to be used for a battery, as there is no way to disable the charging circuit. Also, the 4.2V maximum voltage input is less than that board's output of 4.4V.
You can't use VUSB, because that board has a maximum output of 4.4V, and the minimum for VUSB is 4.5V.
Generally the cellular devices such as the Boron have an onboard PMIC, which allows the VIN pin to have a much wider input voltage range. You can connect it directly do a 12V solar panel without the need for a separate charge controller.
Another option is to use a solar USB charger with battery. You can just plug the Photon 2 in via the Photon 2 Micro USB B connector. One caveat: Some USB power packs (solar or not) will turn off if the load is very low to conserve battery. This can prevent being able to use sleep mode on the Photon 2.
Thanks for the help! I already have the hardware so I'll probably just put a diode in series and drop the voltage by ~.7v. that would put the max V at the Li+ pin to 3.7v. If that isn't reliable I'll find a solar USB charger.