Solar controller

[mosfet123]

Hi;

I have 4W-12V solar panel and 6,4V-40W lifepo4 battery. and my load 3W led modul. and ı want to controle fixture with PIR sensor and time. What kind of controller should i chose or which parts should i use ?

 

[d123]

Hi,

A PV buck converter-based Li-ion charger IC is a place to start researching.

 

[BradtheRad]

Lithium ferrophosphate. Wikipedia states it's suitable for solar applications...

provided the charging systems are adapted not to damage the LFP cells through excessive charging voltages (beyond 3.6 volts DC per cell while under charge), temperature-based voltage compensation, equalisation attempts or continuous trickle charging

And:

a protection system also needs to be implemented to ensure no cell can be discharged below a voltage of 2.5 V or severe damage will occur in most instances

Tentatively at best efficiency your PV panel provides 12V @ 1/3 A. (4W divided by 12v).
The aim is to draw this continually.

For charging your 6V battery a buck converter is a good recommendation (as in post #2).

It should have some kind of input filter that draws a continual smooth Ampere waveform from the PV panel. Internally a switched-coil converter generates current peaks and troughs.

It must be adjusted so output doesn't go above 7.2V (that is, 3.6V per cell).

A converter probably is needed to drive your LED safely. Automatic shut-off should be built-in to prevent batteries from dropping below 2.5V per cell.