4s 18650 li-ion battery cell charger powered by sun

The motivation to undertake this project is to create my own 18650 battery charging station, which will be an important part of my future wireless network (power wise)projects.
I chose the wireless line because it made the electronics project move and smaller and I had a bunch of recycled 18650 batteries around me.
For my project, I chose to charge 4 18650 Li
The ion battery is connected in series at one time, which makes this a 4S battery layout.
For fun, I decided to install four solar panels on my device, which almost didn\'t charge the battery . . . . . . But it looks cool.
The project is powered by a spare laptop charger, but any other power supply is more than 16.
8 volts can also be.
Other Additional features include li-
Ion battery charging indicator that tracks the charging process and USB 2.
Port 0 for charging your smartphone.
Electronics: Architecture: Before I start this project, I\'m on li-
I found that I can tell BMS (
Also called battery management system)
Is the main solution to this problem (
I\'m not saying it\'s the best and the only one).
This is a sure 18560 li-
Ion batteries work in safe and stable conditions.
It has the following protection functions: various BMS circuits are designed for different purposes.
They have different protection circuits and are built for different battery configurations.
I used the 4S configuration in my case, which means four batteries are connected in series (4S).
Depending on the quality of the battery, this generates about the total voltage of 16, 8 volts and 2 Ah.
In addition, you can connect as many battery series as you need in parallel.
This will increase the battery capacity.
To charge this battery, you need to supply the BMS with a voltage of about 16, 8 volts.
The connection circuit of BMS is in the picture.
Please note that to charge the battery you will need to connect the necessary supply voltage to both P and P-pins.
To use a rechargeable battery, connect the components to B and B-pins.
The power for my 18650 battery is the HP 19 volt and 4,74 amp laptop charger I have placed.
Since its voltage output is a bit too high, I added a step-down converter to lower the voltage to 16, 8 volts.
When everything has been built, I tested the device to see how it works.
I put it on the windowsill and charged it with solar energy.
When I got home, I noticed that my battery was not charged at all.
In fact, they are fully discharged and when I try to charge them with a laptop charger, the buck converter chip starts to make a strange hissing sound and gets very hot.
When I measured the current of the BMS, my reading exceeded 3. 8 amperes!
This is much higher than the maximum rating of my buck converter.
BMS has a lot of current because the battery is completely dead.
First, I reconnected all the connections between the BMS and the external components, and then I handled the discharge issues that occurred when charging with solar energy.
I think this problem happened because there is not enough sunlight for the buck converter to turn on.
When this happens, I think the charger is starting to move in the opposite direction-from the battery to the buck converter (
Buck converter light on).
All of this is solved by adding a Schottky diode between the BMS and the buck converter.
In this way, the current will certainly not return to the buck converter.
The maximum DC blocking voltage of the diode is 40 volts and the maximum forward current is 3 amps.
To solve the huge load current problem, I decided to replace my buck converter with a current limiting function.
This step-down converter is twice as bulky as it is, but luckily I have enough space in my case to accommodate it.
It guarantees that the load current will never exceed 2 amps.
For the sake of this project, I decided to incorporate the solar panels into the mixture.
By doing so, I want to have a better understanding of how they work and how they can be used.
I chose to connect four 6 V and 100 mA solar panels in series, which in turn provided me with 24 V and 100 mA in the best sun conditions.
This adds up to no more than 2.
The power of 4 Watts is not much.
From a practical point of view, this addition is very useless and can hardly charge 18650 batteries, so it is more of a decoration than a function.
In my test run on this part, I found that this series of solar panels only charge 18650 batteries under perfect conditions.
On cloudy days, it may not even turn on the buck converter that follows the array of solar panels.
Usually, you will connect a blocking diode after the PV4 panel (
Take a look at the schematic).
When there is no sunlight and the panel does not generate any power, this will prevent the current from returning to the solar panel.
The battery pack will then start discharging to the solar panel array, which can cause potential damage to them.
Since I have added a d3 diode between the buck converter and the 18650 battery pack to prevent current reflow, I don\'t need to add another one.
For this reason, it is recommended to use Schottky diodes because their voltage drop is lower than that of ordinary diodes.
Another precaution for solar panels ispass diodes.
When solar panels are connected in series, they are required.
They help when one or more connected solar panels are blocked.
When this happens, the shaded solar panel will not generate any electricity and its resistance will become high, thus blocking the current flow of the unshaded solar panel. Here’s were by-
Come in through the diode.
For example, when the PV2 solar panel is obscured, the current generated by the PV1 solar panel will go up the path with the least resistance, which means that it will flow through the diode d2.
This will lead to a reduction in total power (
Because of the shadow panel)
But at least not all the current is blocked together.
When no solar panel is blocked, the current ignores the diode and flows through the solar panel because it is the path with the least resistance.
In my project, I used a BAT45 diode in parallel with each solar panel.
Schottky diodes are recommended because they have a lower voltage drop, which in turn increases the efficiency of the entire solar panel array (
In the case of some solar panels being blocked).
In some cases,
By being integrated into solar panels with a barrier diode, this makes the design of the device easier.
The entire solar panel array is connected to the A1 step-down converter (
Reduce the voltage to 16. 8 volts)
Switch via SPDT.
In this way, users can choose how they should power 18650 batteries.
For convenience, I added a 4S battery charge indicator connected via a tactile switch to show if the 18650 battery pack is already charged.
Another feature I added is USB 2.
Port 0 for device charging.
This may come in handy when I bring my 18650 battery charger outside.
Due to the 5 V voltage required for smartphone charging, I added a step
The lower buck converter takes the voltage from 16.
8 V to 5 V.
Also, I added the SPDT switch so the A2 step-down converter doesn\'t waste extra power when not using a USB port.
As the base of the shell, I used a transparent organic glass plate that I cut with a hand saw.
The materials are relatively cheap and easy to use.
To fix everything in one place, I used metal pointed brackets and bolts and nuts.
This way, you can quickly assemble and disassemble the housing if needed.
On the other hand, this method adds unnecessary weight to the equipment because of the use of metal.
I used an electric drill to make the holes needed for the nut.
Solar panels are glued to organic glass with hot glue.
When everything is put together, I realize that the look of this device is not perfect, because you can see all the electronic mess through transparent glass.
To solve this problem, I covered the plexiglass with tape of different colors.
While this is a relatively easy project, I have the opportunity to gain experience with electronics, build the shell for my electronics and be introduced to the new one (to me)
Electronic components.
I hope the instructions are interesting and useful for you.
Please feel free to comment if you have any questions or suggestions?
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