Li-ion batteries of the 18650 type of various capacities are now very widespread. With their acquisition, the problem of charging arises and must comply with the technical requirements for the charging process. Here are some of these requirements:
- charging with stable current;
- voltage stabilization mode;
- indication of the end of charging;
- not exceeding the permissible temperature during battery charging.

We present to your attention a Li-ion battery charger circuit that is easy to manufacture and set up and has proven itself in operation.

The circuit is a current and voltage stabilizer. Until the voltage on the battery during charging reaches the level Ustabil.=(R7/R5+1)*Uref (Uref-reference voltage TL431=2.5V), TL431 is in the closed state, and the circuit works as a current stabilizer. Ist.=0.6/R2 (0.6 is the opening voltage of the KT816V transistor). As soon as the voltage on the battery reaches Ustabil., the circuit goes into voltage stabilization mode. For a Li-ion battery, this value is 4.2V. When the battery voltage reaches 4.2V, the yellow LED starts to light up, indicating that the battery is 80-90% charged. The charging current decreases to 7...8mA. Leave the battery in this state for 10-15 hours until it reaches its full capacity.

A little about the purpose of the circuit elements.
LED1 - blue, lights up when the battery (AC) is installed in the charging box and the charger power is not connected. When the voltage across the battery is less than 3V, LED1 does not light up.
LED2 - yellow. Serves to indicate the end of the battery charging process. When an uncharged AK is placed in the box, LED2 does not light up. If it lights up, then this indicates that a charged AK is inserted into the box (with the charger power not connected).
R2 - limits the charging current of the AK.
R5, R7 - serve to set the voltage to 4.2V on the contacts of the charging box before installing the battery in it (any one can be used).

All charger parts, except the transistor, are installed on the printed circuit board on the side of the printed conductors:

Board option for those who are not lazy to drill holes in fiberglass:

The transistor is equipped with a small heatsink. During charging, the transistor heats up to 40°C. Resistor R2 also heats up, so it is better to install two 10 Ohm resistors in parallel to reduce heating.
The power supply voltage for charging one battery is approximately 5V DC. If it is necessary to charge several batteries at once, the power supply voltage is selected so that it is 4.2V on each unit. The power of the power supply is selected from the charging current for each battery. You can use a switching power supply. The dimensions of the charger will be smaller.
The process of setting up the charger is simple. Without inserting the battery, we supply power to the circuit. Both LEDs should light up. Next, we measure the voltage at the contacts of the charging box. If it is 4.2V, you are in luck and the setup is almost complete. If the voltage is more or less than 4.2V, turn off the power, instead of resistor R5 or R7, solder in a variable multi-turn resistor 10k and precisely set the voltage to 4.2V on the contacts of the box. Having measured the value of the resulting resistance of the adjustable resistor, we select the same constant and solder it into the circuit. Once again, check the voltage at the contacts of the charging box. We check the amount of charging current with an ammeter at the contacts of the charging box without inserting the battery. By selecting the value of resistor R2, you can set the desired charging current. We don’t get carried away with high currents; the battery may heat up, which is absolutely unacceptable. Overheating causes the capacity of Li-ion batteries to decrease and not be restored.
It is best to charge batteries one at a time. If you need to charge several batteries simultaneously, you can connect the blocks in series according to this scheme.

In this scheme, each battery is charged separately. The voltage at the end of charging on each battery will be 4.2V, and the charging current will be 0.5A. When charging, for example, seven batteries simultaneously, the power source voltage should be 4.2V*7=29.5V. The power of the power source is determined by the charging current of 0.5A for each battery, i.e. approximately 40W.

Photo of the finished device.

I discovered that I have a number of quite serviceable lithium batteries lying around from dead mobile phones, laptops, etc., which can be used in various crafts. They need to be charged with something. Suitable parts were found in the deposits, and away we go...

Charger circuit

We draw a diagram, keeping an eye on the presence of parts in the desk drawer. I’m too lazy to run to the store for such a simple product.

limits current, TL431+IRF limits voltage. Nothing special, probably dozens of exactly the same diagrams have already been drawn. The current limit is set to 125 mA based on the capabilities of the transformer used and the heat dissipation limitation in the small plastic housing. In fact, even small cell phone batteries hold a much higher charging current without overheating.
The board was made compact enough to fit into the existing plastic case.

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Thank you for your attention!
Igor Kotov, editor-in-chief of Datagor magazine

Thank you for your attention!

Amazing lithium batteries, 6 pieces, free shipping.
6Pcs 18650 3.7V 5000mAh Rechargeable Lithium Battery

Lithium-ion batteries are very popular nowadays; they are used in various gadgets, such as phones, smart watches, players, flashlights, and laptops. For the first time, a battery of this type (Li-ion) was produced by the famous Japanese company Sony. The schematic diagram of a simple battery is shown in the picture below; by assembling it, you will have the opportunity to restore the charge in the batteries yourself.

Homemade lithium battery charging - electrical diagram

The basis for this device are two stabilizer microcircuits 317 and 431 (). In this case, the LM317 integrated stabilizer serves as a current source; we take this part in the TO-220 housing and must install it on the heat sink using thermal paste. The TL431 voltage regulator manufactured by Texas Instruments is also available in SOT-89, TO-92, SOP-8, SOT-23, SOT-25 and other packages.

Light emitting diodes (LED) D1 and D2 of any color you like. I chose the following: LED1 red rectangular 2.5 mm (2.5 miles Candel) and LED2 green diffuse 3 mm (40-80 miles Candel). It is convenient to use smd LEDs if you do not install the finished board in the case.

The minimum power of resistor R2 (22 Ohm) is 2 Watts, and R5 (11 Ohm) is 1 Watt. All other ones are 0.125-0.25W.

A 22 kilo-ohm variable resistor must be of the SP5-2 type (imported 3296W). Such variable resistors have a very precise resistance adjustment, which can be smoothly adjusted by twisting a worm pair that looks like a bronze bolt.

Photo of measuring the voltage of a li-ion battery from a cell phone before charging (3.7V) and after (4.2V), capacity 1100 mA*h.

PCB for lithium charger

The printed circuit board (PCB) exists in two formats for different programs - the archive is located. The dimensions of the finished printed circuit board in my case are 5 by 2.5 cm. I left space for fasteners on the sides.

How does charging work?

How does the finished circuit of such a charger work? First, the battery is charged with direct current, which is determined by the resistance of the resistor R5, with a standard value of 11 ohms, it will be approximately 100 mA. Further, when the rechargeable energy source has a voltage of 4.15-4.2 volts, constant voltage charging will begin. When the charging current drops to small values, LED D1 will turn off.

As you know, the standard voltage for charging Li-ion is 4.2V, this figure must be set at the output of the circuit without load, using a voltmeter, so the battery will be fully charged. If you lower the voltage a little, somewhere by 0.05-0.10 Volts, then your battery will not be fully charged, but this way it will last longer. Author of the article EGOR.

Discuss the article CHARGER FOR LITHIUM BATTERIES

Sergey Nikitin

Charger for Li-ion batteries.

The simple charger discussed in this article allows you to charge Li-ion batteries that do not have a charge controller.
This charger does not allow them to be overcharged or charged with a current that exceeds the permissible current for these batteries, which greatly extends their service life.

It all started as always.
The fact is that when at least one battery in a laptop battery fails, the controller blocks it, and replacing the faulty battery with a new one usually does not restore the battery’s functionality. The battery needs to be unlocked, but it's not that easy. You need something like a programmer and a program that costs a lot of money. And there is no complete guarantee that by replacing one battery in a battery, another one will not fail in a month or two, and new ones also cost a lot of money.

And so, as a consequence of the above, batteries from laptop batteries of different capacities and years of manufacture appeared in households, and these batteries began to migrate to flashlights and other devices.
The capacity of these batteries is on average 3 A/H, and while charging them we had to control the charging process every time, which was quite annoying. Laziness inspired creativity, and in connection with this, the following scheme was developed.

This memory was planned to be powered mainly from the USB connector of a computer or laptop, and in connection with this, a mini-USB connector and a regular USB connector were installed at the input of the memory, for versatility.

Then two chargers were assembled in one case to simultaneously charge two Li-ion batteries, but as it turned out, not all devices with a USB output can charge two batteries at the same time.
In this case, a regular connector was also installed in the memory for connecting a power supply (charging from a phone) with an output voltage of 5 Volts and a permissible current of 3A.

As I said above, I assembled two chargers in one case to charge two batteries at once. As an output transistor, VT1 installed a MOSFET from the motherboard.
Here you can use any suitable MOSFET, only with a P-channel. There are a lot of powerful MOSFETs on motherboards, but mostly they have an N-channel, but on some motherboards there are one or two transistors with a P-channel. They all have a low operating voltage of up to 20 volts usually, but very high currents, over 20 amperes, and this is in the SMD version.

Now how does this all work;
When an input voltage of 5 Volts is applied to the charger, the green LED lights up, and when a battery is installed in the charger, charging begins, this is indicated by the red LED.
VT2 opens, and it opens VT1 (the MOSFET has a very small resistance in the open state, hundredths or thousandths of an Ohm).

When the voltage on the battery reaches 4.1 Volts, VD3 opens, which closes VT2, and it in turn allows VT1 to close (to be very precise, everything does not close completely, a small current is supplied and 4.1 V is retained on the battery, this is normal mode for lithium batteries).
When the battery is charged, the red LED goes out.

With the indicated ratings of elements R10 and R8, the final charge voltage is 4.1 Volts, which slightly does not correspond to the full charge of Li-ion batteries (4.2 Volts), but significantly extends their service life.

Instead of TL431, you can install KA431, or any other 431 so-called “integrated adjustable voltage stabilizer” (they are used in almost any switching power supply).
The board was made for two channels in SMD design, although not all installed parts are SMD.
This is how it looks in its working version.

I lost my original digital camera charger on a business trip. Buy a new "frog" type. The toad crushed me, because I am a radio amateur and therefore I can solder the charging of lithium batteries with my own hands, and besides, it is very easy to do. The charger of absolutely any lithium battery is a 5-volt constant voltage source that delivers a charge current equal to 0.5-1.0 of the battery capacity. For example, if the battery capacity 1000 mAh, the charger must produce a current of at least 500 mA.

If you don’t believe me, try it and we will help.

The charging process is shown in the graph. At the initial moment, the charging current is constant; when the voltage level Umax on the battery is reached, the charger switches to a mode where the voltage is constant and the current asymptotically tends to zero.

Charging lithium batteries process diagram

The output voltage of lithium batteries is typically 4.2V, and the nominal voltage is about 3.7V. It is not recommended to charge these batteries to the full 4.2V as this will reduce their life. If you reduce the output voltage to 4.1V, the capacity will drop by almost 10%, but at the same time the number of charge-discharge cycles will almost double. When using these batteries, it is extremely undesirable to bring the rated voltage below the level of 3.4...3.3V.

Charging lithium batteries circuit on LM317

As you can see, the scheme is quite simple. Built on stabilizers LM317 and TL431. Another radio component includes a pair of diodes, resistors and capacitors. The device requires almost no adjustment; just use the trimmer resistance R8 to set the voltage at the device output to a nominal value of 4.2 volts without a connected battery. Using resistances R4 and R6 we set the charging current. To indicate the operation of the structure, there is a “charge” LED, which lights up when an empty battery is connected, and goes out as it charges.

Let's start assembling the structure for charging lithium batteries. We find a suitable case; it can accommodate a simple five-volt transformer power supply, and the circuit discussed above.

To connect the rechargeable battery, I cut out two brass strips and installed them on the sockets. The nut adjusts the distance between the contacts that are connected to the battery being charged.

I made something like a clothespin. You can also install a switch to change the polarity on the charger sockets - in some cases this can be a big help. I propose to make a printed circuit board using the LUT method; we can get the drawing in Sprint Layout format from the link above.

Despite a huge number of positive characteristics, lithium batteries also have significant disadvantages, such as high sensitivity to excess charge voltage, which can lead to heating and intense gas formation. And since the battery has a sealed design, excessive gas release can lead to swelling or explosion. In addition, lithium batteries do not tolerate overcharging.

Thanks to the use of specialized microcircuits in branded chargers that control voltage, this problem is not familiar to many users, but this does not mean that it does not exist. Therefore, to charge lithium batteries we need just such a device, and the circuit discussed above is only its prototype.

Charging lithium batteries universal circuit

The device allows you to charge lithium batteries with a voltage of 3.6V or 3.7V. At the first stage, the charge is carried out with a stable current of 245mA or 490mA (set manually), when the voltage on the batteries increases to the level of 4.1V or 4.2V, the charge continues while maintaining a stable voltage and a decreasing value of the charging current, as soon as the latter drops to a threshold value (set manually from 20mA to 350mA) battery charging automatically stops.

The LM317 stabilizer maintains the voltage across resistance R9 at a level of about 1.25V, thereby maintaining a stable value of the current flowing through it, and therefore through the battery being charged. The output voltage is limited by the TL431 regulator connected to the control input of LM317. The limiting voltage value is selected using a divider across resistances R12…R14. Resistance R11 limits the supply current to the TL431.

A current-voltage converter is built using an operational amplifier DA2.2 LM358, resistances R5...R8 and a bipolar transistor VT2. The voltage at its output is proportional to the current flowing through resistance R9 and is calculated by the formula:

With the values ​​shown in the diagram, the current-to-voltage conversion coefficient is 10, i.e. with a current through resistance R9 of 245 mA, the voltage across R5 is 2.45 V.

From R5, the voltage goes to the non-inverting input of op-amp DA2.1. The inverting input of the comparator receives voltage from an adjustable divider across resistances R2…R4. The divider supply voltage is stabilized by LM78L05. The switching threshold of the comparator is set by the nominal value of the variable resistance R3.

Charging lithium batteries circuit setup.

Instead of toggle switch SB1, place a jumper and apply voltage to the circuit, selecting resistances R12...R14 to make the output voltage 4.1V and 4.2V for the open and closed states of toggle switch SA2.

Using toggle switch SA1 we set the value of the charge current (245mA or 490mA). Using the SA2 toggle switch, select the maximum voltage value; for 3.6V batteries, select 4.1V; for 3.7V batteries, select 4.2V. Using the variable resistance motor R3, we set the current value at which the battery charge should be completed (approximately 0.07...0.1 C), connect the battery and press the SB1 toggle switch. The process of charging the lithium battery should start and the indicator on the VD2 LED lights up. When the charge current decreases below the threshold, the high level at output DA2.1 changes to low, field-effect transistor VT1 closes and relay coil K1 turns off, breaking the battery from the charger with its front contact K1.

I provide a drawing of the printed circuit board for the charger and recommend making it yourself using

To allow charging lithium batteries from mobile phones and smartphones, a universal adapter was made:

All batteries of this type must be used in accordance with certain recommendations. These rules can be divided into two groups: User-independent and user-dependent.

The first group includes the fundamental rules for charging and discharging batteries, which are controlled by a special charger controller:

The lithium battery must be in a condition where its voltage should not be more than 4.2 volts and not fall below 2.7 Volt. These limits are the maximum and minimum charge levels. The minimum level of 2.7 volts is relevant for batteries with coke electrodes, however, modern lithium batteries are made with graphite electrodes. For them, the minimum limit is 3 volts.
The amount of energy supplied by the battery when the charge changes from 100% to 0% is Battery capacity. A number of manufacturers limit the maximum voltage to 4.1 volts, while a lithium battery will last much longer, but will lose about 10% in capacity. Sometimes the lower limit rises to 3.0 and even 3.3 volts, but also with a decrease in capacitance level.
The longest service life of batteries occurs at 45% charge, and with an increase or decrease the service life is reduced. If the charge is in the above range, the change in service life is not significant.
If the battery voltage goes beyond the limits specified above, even for a short time, its service life will drop sharply.
Battery charger controllers never allow the battery voltage to rise above 4.2 volts during charging, but may limit the minimum level in different ways when discharging.

The second group of user-dependent rules includes the following rules:

Try not to discharge the battery to a minimum charge level and, especially, to a state where the device turns itself off, but if this happens, it is advisable to charge the battery as quickly as possible.
Don’t be afraid of frequent recharging, including partial recharging; a lithium battery doesn’t care at all.
Battery capacity depends on temperature. So, at a 100% charge level at room temperature, when going out into the cold, the battery charge will drop to 80%, which in principle is not dangerous or critical. But it can also be the other way around: if a 100% charged battery is placed on a battery, its charge level will increase to 110%, and this is very dangerous for it and can sharply shorten its life.
The ideal condition for long-term battery storage is to be outside the device with a charge of about 50%
If, after purchasing a high-capacity battery, after a few days of use. If the device with the battery starts to glitch and freeze, or the battery charging turns off, then most likely your charger, which worked perfectly on the old battery, is simply not able to provide the necessary charging current for a large capacity.

A selection of original phone chargers consisting only of simple and interesting amateur radio ideas and developments

This amateur radio design is designed to charge lithium batteries from mobile phones and 18650 type, and most importantly ensures that the battery is properly charged. The device has an LED charge indicator. Red indicates that the battery is charging, green indicates that the battery is fully charged. Smart charging is achieved through the use of a specialized charge controller on the BQ2057CSN chip.

Modern lithium batteries do not use pure lithium. Therefore, three main types of lithium batteries have become widespread: Lithium-ion (Li-ion) Unom. - 3.6V; Lithium polymer(Li-Po, Li-polymer or "lipo"). Unom. - 3.7V; Lithium iron phosphate(Li-Fe or LFP). Unom - 3.3V.

Flaws

The main disadvantage of Li-ion batteries, I would highlight them fire hazard due to overvoltage or overheating. But lithium iron phosphate batteries do not have such a big drawback - they are completely fireproof.
Lithium batteries are very sensitive to cold and quickly lose their capacity and stop charging.
Requires a charge controller
At deep discharge lithium batteries lose their initial properties.
If the battery does not “work” for a long time, then first the voltage on it will drop to a threshold level, and then a deep discharge will begin as soon as the voltage drops to 2.5V, this will lead to its failure. Therefore, from time to time we recharge the batteries of laptops, cell phones, and mp3 players.