Continue to Site

Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

Charging 2s Li Ion with solar panel

I14R10

Full Member level 3
Joined
May 31, 2015
Messages
182
Helped
0
Reputation
0
Reaction score
0
Trophy points
1,296
Activity points
2,711
I have a small self made wireless weather station that I want to be powered by two 18650 Li Ion batteries. It uses around 10-20mA.
EDIT: I need 3.3V for my circuit. I could use single 18650, but then I would need to use very low dropout linear regulator for when battery is at let's say 3.7. So I'm using 2 in series.

I have a CN3722 based solar charger (MPPT) for 2s batteries. Right now I have the batteries connected in series. I read a lot about how it's not a good solution and that I need balanced charger which CN3722 is not. I'm checking every day the voltages of each battery and so far they are staying close together. My solar panel is 10W 12V panel (about 18-20V open circuit voltage).

So, batteries are charged in series right now. But I'm concerned they might suddenly start charging differently and have different voltages.

Then I started reading about connecting them in parallel which has its own set of problems. They need to be at the exactly same voltage and if not I should use schottky diode. Then they say they shouldn't be charged in parallel together, instead each should have its own charger.

I'd rather not have them in parallel. So I read about BMS for 2 in series. There are boards like this one on Aliexpress https://www.aliexpress.com/item/1005003648953550.html but they are not made for solar panel. Now I don't know what to do.

Maybe I'm blind but I haven't seen solar charge controller (with balancing) for 2s Li Ion batteries. Any advice?
 
Last edited:

BradtheRad

Super Moderator
Staff member
Joined
Apr 1, 2011
Messages
14,688
Helped
2,867
Reputation
5,744
Reaction score
2,876
Trophy points
1,393
Location
Minneapolis, Minnesota, USA
Activity points
109,735
uses around 10-20mA.
EDIT: I need 3.3V for my circuit. I could use single 18650, but then I would need to use very low dropout linear regulator for when battery is at let's say 3.7.

You may find you can get by simply installing a low-ohm resistor inline. Say 10 to 15 ohms. At 15mA you drop 0.2 volt.

Thus when the battery is 3.7 V it becomes 3.5 V seen by your device.
 

LaTeX Commands Quick-Menu:

Similar threads

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Top