RE: Solar SPEC - Design Concept

genebren — Sat, 04 Aug 2018 21:27:44 GMT

Very interesting update to your solar powered devices project. You mention MPP (maximum power point), but I don't think that you can get the 'thing' board to control the charge rate for your battery. On periods of partial sunlight, the charger will load your solar panel down to the point were the voltage drops below the charging threshold and no charge will occur. The trick with simple Li-ion charger chips (like the MCP73831) is that you have to be able to control the charge rate to match the solar panel's available energy (MPP). There are a couple of ways to do this. One is to use a programmable resistor (or digital potentiometer) in place of the fixed (2K) resistor (increasing resistance as the solar panel's voltage drops). It is also possible (and a bit trickier) to create a closed loop system to trim the charge setting, inject current into the 'PROG' proportionally to the voltage on the solar panel (as the voltage drops, inject current to effectively lower the charge rate), to decrease the charge charge so the solar panel's voltage increases (to stay about the charge threshold voltage).

Good luck,

Gene

RE: Solar SPEC - Design Concept

DAB — Sat, 04 Aug 2018 17:49:30 GMT

Nice update.

I am curious, why did you not just use the solar cell as your indicator for sunlight?

DAB