I realized a solar battery charger circuit based on LT3652. Actually it doesn't work well, but I think I made some project error. In fact it doesn't reach the end of charge status. But first of all I need some theoretic suggestions.

Panel: Voc = 20V; Vp = 16.5V; P = 5W; Ip = 0.31A;

Battery: Lead-Acid; 12V; C = 4Ah;

The questions are:

What is the maximum charging current reachable? Icharge < Ipeak * (efficiency *Vpanel ) / Vbat is correct?

What happens if I set a charging current too high, for example 1A?


1 Answer 1


Most of the time the panel current in the datasheet is measured as a short-circuit. I would suggest connecting the panel directly to the battery and measuring the current to at least get a baseline.

Next, measure the voltage at the panel terminals while charging. You might be surprised as it might be below the minimum voltage the regulator requires. You also have to consider the diode drop.

Maximum current reachable is not easily calculated by a formula, you have to measure it using a load or getting the manufacturer graphs.

Last but not least, without a schematic it's really hard to figure if everything is wired correctly.

Also, take a look at http://learn.adafruit.com/usb-dc-and-solar-lipoly-charger/design-notes it describes various solar panel limitations and charging approaches.


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