I think I almost understand what I need to try ;)

solar panel -> Cap -> LC pi filter -> boost (or buck) FET
and inductor -> Cap -> shunt I sense -> battery

12V/1.26W Solar panel , OC V on a bright day = 18V, SC I 160mA
1st Capacitor ?? 47uF
LC filter values ?? no idea ;)
P-channel mosfet wired as a switch (NDT456)
2nd capacitor ?? 47uF
Shunt I sense 1R (enough that I can measure current)
Battery - 3.6V 600mAh

How does that sound?
I am running 10bit ADC so can measure reasonable resolution, I
also have a 2V reference chip that I measure to calibrate all the
AD inputs to help cope with changes in supply voltage.

Note on the battery.. SLA is to big for me, and I am actually
going to go to 2xC size cells soon with a boost SMPS.

Basic software flow...
FET off - check solar voltage
If solar volt enough (ie daytime), start PWM at low level.
Measure shunt V drop
if lower than target V drop increase PWM
repeat till target is met.

other checks to add in..
- solar volts fall to low (cell can't provide the current?)
- battery charge conditions (target current might change for
a trickle condition.

In my quick calculations a 1.26W cell at 100% eff could
give me 350mA @3.6V


Hows all that sound?
Should have time to put something together later this week
unless sunshine or other less interesting jobs get in the
way..

Oh, what target goals are we looking to achieve other than
a good consistent charge current?

Cheers
Peter Mcalpine

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