PV to LiFePo4 1-2cells charger

[viktor_au]

Hello

I need some advice.
I work on a project: a few PIR sensor(s) + LED security light power supply from PV solar panel.

Thought at first to use 12v PV panel but later changed my mind for a 6v panel (to drop down the heat loss).
From www: For example, if Vin – Vout is only 300 mV, then even with 3 A of load current the power dissipation is only 0.9 W which is low enough power to be handled by most regulators.

Linear regulator looks like a choice.
On www plenty of projects to charge one cell (3.2v for LiFePo4 or more for LiOn) based on LM315,LM317(adj,1-1.5A).

I have two choices.
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Use one cell LiFePo4 battery with a boost regulator 3.3v -> 5v. 10AH cell can cost up to $20Au.
This will simplify the charging circuit by using one LM317. LM317 provides the CC mode as the charging stage 1 and CV mode at the charging stage 2.
As I have to power Arduino Nano or Mega 24/7, three PIRs (4.5v each) 24/7 and at night only the one LED light.
Uno takes apprx 50mA. LED light will take more power. It depends how many times it will be triggered at night. 0.5A ? 1A? 3A?
Should I power the LED light from a separate boost regulator to lower it power consumption? I can cut the Time-On duration down as well.
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Use 2cells LiFePo4 battery with LM338. Two cells can supply up to 20AH. Should be enough even if security light will be on many times.
I can use 5A LM338 or 3A LM350. LM338 is obsolete. I am not sure what has replaced it.
LM338 can handle up to 5A (7A max for short time).
It provides the CC and CV mode. The current can increase by paralleling LM338.
Datasheet: LM138 to be used with heavy transient loads and speeds start-up under full-load conditions.
However a single 6v 6w PV solar panel can provide apprx up to 3A (?) current. One LM338 should be enough for one PV.

Would be great if anybody did similar project and can direct me in right direction.
Thanks.

[chipfryer27]

Hi Viktor

I'm no expert on battery charging and usually use 3rd party supplies that incorporate.

My goto for battery info is

https://batteryuniversity.com/

They may not give you a design but you will definitely know what to do and what not to do for pretty much any battery type.

Regards

[viktor_au]

thank you