# lock output solar panel if too few current

I use a solar panel which provide 12v-3W. I convert that to 5V using this converter.

This 5V is used as input of a card which to charge a lipo battery and as a power supply for a raspberry zero.

The problem when the power of the panel is under the nominal power of the raspberry Pi. The lipo chager don't work properly.

So my question : how to cut power line from solar panel if current is under 400mA ? Ref of a module or CI which do that?

• How do you imagine knowing if the supportable current is under $400\:\textrm{mA}$ if you aren't loading the solar panel in order to find out? So would this be some kind of SPDT relay that locks in place so long as there is at least $400\:\textrm{mA}$, but drop out as soon as it goes below, requiring you to re-enable it manually? Or do you expect some kind of magic circuit that knows when to re-engage? What are your thoughts? – jonk Oct 19 '17 at 20:48
• Measure the amps with a current sensing module (arduino) and switch to a dummy load (resistor) if your amperage is too low. Keep measuring and switch back when amps are okay again. – ctrl-d Oct 19 '17 at 22:12
• Measure the voltage output from the buck converter. If it is less than 4.5V then cut power to the raspberry and lipo charger. Add in a 5 minute startup delay, since even a little sunlight will cause the voltage to jump up once the load is gone. – Daniel Cormode Jan 22 '18 at 2:59