M0 solar LiPo charger breakout/shield

[i670]

It would be great to have a shield to allow a small pv panel to charge a lipo battery and supply power to the M0.  A JST connector for each and a switch to disconnect the battery would be icing on the cake.  I reckon there would be a reasonable demand for this one.  Thoughts?

dave

[Tirititelu]

Solar panel+TP4056+LiPO+MT3608

[Uncle Buzz]

I wonder how a constant current / constant voltage charger will deal with a solar panel (current source) as power supply...

[mlewus]

The Moteino M0 already supports charging of a lipo battery with its MCP73831 onboard charger. While the Moteino's regulator can handle 16v on Vin, the MCP73831 charger has a recommended supply voltage (Vdd) limit of 6v on VUSB. This limit is reduced to 5 V if USB is connected to another dvice.

One way to get around the strict input voltage limitations of the MCP73831 is to power the M0 from a solar panel and pre-regulate it to 5.0 volts with a switching regulator. For my outdoor M0 projects I use 12v panels because they are cheap and readily available, but any panel with a working voltage over 6 V will work. The regulator is more than 90% efficient converting the panel output to 5 V. I use a low-cost potted switching regulator module CUI V7805-1000 and a switch in series with the positive battery cable.

The regulator costs around $7 qty 1 and is available from Digikey: https://www.digikey.com/product-detail/en/cui-inc/V7805-1000/102-1715-ND/1828608.  if you decide to go this route I suggest a 10uF/25v X7R or X5R ceramic capacitor on the regulator input, and 1uF/25v X7R or X5R ceramic in parallel with 10uF/6.3v aluminum electrolytic on the output.

[Felix]

Soar charging a LiPo is a little more tricky than just straight using a charger like the MCP73831 (or the suggested TP4056) which require a steady current supply and is not a MPPT or dedicated solar charger. A 5-6V solar cell cannot supply 1A (or configured charging current) all the time, in fact it's usually going to be at rated voltage only in full sunlight.
One possible solution is what mlewus suggested - using a higher voltage panel, and regulate it down to 5V for charging.