# Simple Solar Circuit

I had a very cheap solar panel + controller where the controller died. To cheaply replace it I was going to build my own using some parts I had laying around and use a step-down (LM2596) to limit voltage from the solar panel into a battery and out to a XL6009E1 to boost battery voltage up to 5 volts to an esp cam. Super simple circuit diagram as follows:

Solar panel == LM2596 == battery == XL6009E1 == ESPcam

while testing this circuit out on my bench power supply, before hooking the ESPcam up or battery, I noticed that at about 3.9 volts input on the LM2596 I am seeing 19 volts output on the XL6009E1! Checking on the output of the LM2596 I am seeing 3.2 volts.

testing circuit

Bench Power Supply == LM2596 == battery holder (no battery) == XL6009E1 == multimeter

Is this some limitation of the XL6009E1?

http://www.datasheetcafe.com/xl6009e1-datasheet-converter-xlsemi/

When I increase the voltage to >5V everything seems to smooth out, but will a dying battery fry my espcam?

• the actual xl6009e1 board I got from amzn.to/34SVLNl Sep 18 '19 at 17:58

## 1 Answer

A solar cell has a point at which it supplies maximum power. While you can get away with a switching regulator, it is not optimal for drawing power from the cell.

One problem is you are using a switching regulator connected directly to the solar cell. To use sufficient power from the cell, an switching regulator with Maximum Peak Power Tracking (MPPT) needs to be used.

The last problem is you might not have enough power that is sourced from the cell in the first place. Calculate the max power by using 300W/m^2 (equator on a sunny day is 1000W/m^2) and the area of your panel. Then multiply that power number by the efficiency of the panel, that will give you the amount of watts the panel can supply.

• Ya I'm not certain the solar panel can't supply enough, but at the moment it's a bench power supply hooked as input not a solar panel. The data sheet I posted does say the XL bottoms out at 5V, but the amazon page said 3V which is what I had thought. Perhaps, this is just undefined behavior at 3.2V? Sep 19 '19 at 1:29
• Are you measuring current with the multimeter? because that is a direct short unless a resistor is in series Sep 19 '19 at 2:18