# Charging Lithium - Ion Battery With Solar Cell

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## Introduction: Charging Lithium - Ion Battery With Solar Cell

This is project about charging Lithium - Ion battery with sollar cell.

## Step 1: Material

1 x Solar cell 5V - 6V, 360 mA or 1.2 W (or similar solar cell )

1 x Li - Ion charger board TP4056 TP4056

1 x diode 1N4148 1N4148

1 x Lithium - Ion battery (18650), I buy 1 poor, you can choose better with capacity around 2000 mAh, Samsung

1 x Lithium - Ion battery holder holder

1 x cables, I use internet cables with 6 wires inside

1 x solder tools (station, tin, rosin etc.)

## Step 2: Right Solar Cell

For Li - Ion battery I choose solar cell with 5V and 160 mA. For choosing solar cell, you must choose:

1. voltage of solar cell 1.5 x voltage of battery, so 3.7V to 4.2 V of Li-Ion is equivalent of 5.55 V to 6.3 V of solar cell.

2. current of solar cell should have 1/10th of capacity battery diveded by 1 hour (for Ni Mh batteries). I use same rule for Li - Ion battery. It is called C - rate rule. So If I have 500 mAh battery, I should choose 50 mA sollar cell. Good Li- Ion batteries have 2000 mAh, so current should be around 200 mAh or 1.2 W.

I use bad Li - Ion battery with measured around 600 mAh. For that, I should choose solar cell with 60 mA peak, or 0.360 W (POWER = CURRENT X VOLTAGE).

## Step 3: Lithium - Ion Batteries 18650

I find good website with tests lithium - ion batteries. Mostly there are 3400 mAh maximum.

Here is some theory of charging them:

https://www.instructables.com/id/Li-ion-battery-charging/

https://www.instructables.com/id/SOLAR-POWERED-ARDUINO-WEATHER-STATION/

## Step 4: Circuit

Circuit is simple, but I describe it here.

Connect positive terminal of solar cell to anode of diode. Connect negative terminal of diode to IN+ (input positive) of TP4056. I use diode because of reverse current.

Also connect negative terminal of solar cell to IN- (input negative) of TP4056. Finally connect battery, positive terminal of battery to BAT + of TP4056, similar negative terminal.

## Step 5: LED Diodes on TP Board

On board, there are 2 diodes, which also consupt some power. I remove them with knife. Check picture.

## Step 6: Calculation of Efficiency

Test you charging, you can connect your multimeter to solar cell, or battery.

Test:

cloudy, with a little sunny 10 mA (output current from TP4056), 24 mA (from solar cell)

cloudy, not direct to sun 0.87 mA (TP4056), 5.1 mA (solar cell)

sunny, direct sun 26 mA (TP4056), 89 mA (solar cell)

According pveducation.org website, you can calculate direct solar radiation in kW. Just fill your home lattitude and longtitude. And remember time, because radiation during day vary. I got around 1 kW/m2.

So, solar cell give me 89 mA, and 5V, so it gives 445 mW, or 0.445 W. Surface of solar cell is around 70 cm2 (basically only small lines make energy, so around 30 cm2).

Solar cell output = 0.089A x 5 V = 0.445 W

TP4056 output = 0.026 A x 4 V = 0.104 W.

To calculate how much solar radiation fall on 30 cm2 according pv education website, we must convert surface to m2, it is 0. 00 30 m2. Incident radiation is 1000 x 0.003 = 3 W.

Efficiency of solar cell = 0.445 W / 3 W = 0.1483 = 14.8 %.

Efficiency of TP4056 = 0.104 W / 0.445 W = 23.37 %

Total efficiency of system = 0.104 W / 3W = 0.034666 = 3.46 %.

So total efficiency is not much, but helps. Do you remember C-rate? For this project, the bigger solar cell is necessary. I test on september, which is average between winter and summer. I use battery for my esp logger, which must survive during winter, summer is good. I will test others solar cells, in future, and show my results.

## Step 7: Extra: Thingspeak Graph

I test battery voltage with my esp logger. I got graph on thingspeak. Results are in ADC values, not in voltage. Values 720 is equivalent of battery with 4.07 V. I use bad 600 mA Lithium - Ion battery.

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## 2 Questions

0

hi why not use scotty diode? example 1N5819 5819 1A 40V SCHOTTKY DIODE?
voltage drop not 0,6-0,8V only 0,1-0,2 V ?

0

Hi

Could you give me some further explanation why you choose solar panel voltage to be 1/5 of battery voltage and solar panel current to be 1/10 of battery current divided by 1 hour.

Regards

sam

0

voltage - input of TP4056 must be higher then 4,2 V so I choose 1.5 times bigger voltage.

Current - C-rate law. I just check what usually is charging current for lions battery - it is around 500 mA, but smaller currents are good , too. Also, during summer, the battery is charge fully + as temperature increase, the voltage of battery is higher. I dont want bake battery.