Datasheet

the CHRG light is on but really its doing a poor job of it!

Solar Optimization!

OK so how do we fix this problem? The issue we have here is that the voltage collapses

during high current draw. We need to find a way to keep the lipo charger from drawing too

much current, and backing off when the voltage starts to droop. We looked high and low

and finally found a chip that has something like this built in. The MCP73871 calls it Voltage

Proportional Charge Control (VPCC) and basically, it does precisely what we want. We can

set the voltage to a point just above the battery charge voltage point (say 4.5V) and then

instruct the charger to draw as much current as possible. It will automatically

increase/reduce the charge rate to keep the voltage higher than 4.5V!

In this case, we set the voltage using two resistors, the voltage divider ends up stabilizing it

at ~4.5V. Because the voltage collapse of a panel is really sudden, we still end up needing

a little more help stabilizing the panel. We do that by adding a BFC (Big Freaking

Capacitor).