Here's a little controller I got for my lithium batteries. It's pretty limited, only supporting a maximum of
28 volts on the panel side, and 10 amps on the battery side. But it should work with a 100 watt 36 cell panel.
If you connect two standard 100W-rated panels to this in parallel, that should roughly max out this controller's
voltage, current, and watts. And for $22, that's a pretty good deal for MPPT lithium charging. Standby current
is under 1mA.
I've recently discovered this controller uses a BQ24650 which is not an MPP tracker, it's a panel voltage regulator. It adjusts power delivery into the buck regulator so that the panels maintain a fixed voltage, which
on these boards is usually set to 18v, making this controller only suited for 36 cell panels. Both the battery
and panel voltage are set by configuration resistors on the board.
The schematic below is for the 75w version, this one has doubled up all three mosfets to handle more power,
but is otherwise the same.
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