I am fulfilling another request from one of the site visitors, who is not a radio amateur, but wants to make a simple charger for LI-Ion batteries with his own hands, which he installed instead of failed batteries for a screwdriver. To obtain 12 volts, three LI-Ion batteries were required, and the charger would have to have three charging channels. But, in order to fully utilize the capabilities of the transformers and, so to speak, just in case, I added a fourth, spare one. The device diagram is shown in Figure 1.

All circuit components are purchased. Step-down pulse stabilizers and charging modules were purchased from the Eliexpess online store. Below are screenshots from the pages of this store.

Rectifier filter capacitor C1 consists of four 2200 microfarad capacitors at 16 volts. The capacitance value was chosen from the generally accepted rule, 2000 microfarads per ampere of load current. Any rectifier bridge VD1 can be used for a current of at least 8A. Anything is possible during the operation of the charger, so there must be a margin of parameters. Imported bridges, for example, RS801, KBU8A, BR805... are well suited for these purposes.

All of these bridges are rated for 8 amps. When charging three batteries simultaneously, based on the data for the LTC4056 module, which indicates a charge current of one ampere, a current of three amperes will flow through the bridge. With such a current, power will be released on the bridge: P = Ud In 4 = 1 1.5 4 = 6 W. Where Ud is the voltage drop across the diode in the forward direction (V), In is the average current flowing through the diode in the bridge rectifier (A), and there are 4 diodes. Thus, we are convinced that with a released thermal power of 6 W, . The network transformer used is a unified incandescent TN-36. All its secondary windings are designed for a current of up to one ampere, therefore, to obtain the required current value - 4A, all windings are connected in parallel.

The diagram provides a fuse only in the primary network, but I would recommend installing 1.5A fuses in all channels of the charger.

And the most important thing! The microcircuit used in the LTC4056 charging module, if the battery being charged is connected incorrectly, overheats very quickly and fails!

Today, many users have accumulated several working and unused lithium batteries that appear when replacing mobile phones with smartphones.

When using batteries in phones with their own charger, thanks to the use of specialized chips for charge control, there are practically no problems with charging. But when using lithium batteries in various homemade products, the question arises of how and with what to charge such batteries. Some people think that lithium batteries already contain built-in charge controllers, but in fact they have built-in protection circuits, such batteries are called protected batteries. The protection circuits in them are designed mainly to protect against deep discharge and overvoltage when charging above 4.25V, i.e. This is an emergency protection, not a charge controller.

Some “do-it-yourselfers” on the site will immediately write that for little money you can order a special board from China, with which you can charge lithium batteries. But this is only for “shopping” lovers. There is no point in buying something that can be easily assembled in a few minutes from cheap and common parts. We must not forget that you will have to wait about a month for the ordered board. And a purchased device does not bring as much satisfaction as a home-made one.

The proposed charger can be replicated by almost anyone. This scheme is very primitive, but completely copes with its task. All that is required for high-quality charging of Li-Ion batteries is to stabilize the output voltage of the charger and limit the charge current.

The charger is reliable, compact and highly stable output voltage, and, as you know, for lithium-ion batteries this is a very important characteristic when charging.

Charger circuit for li-ion battery

The charger circuit is made using an adjustable voltage stabilizer TL431 and a medium power bipolar NPN transistor. The circuit allows you to limit the battery charging current and stabilizes the output voltage.

Transistor T1 acts as a regulating element. Resistor R2 limits the charging current, the value of which depends only on the battery parameters. It is recommended to use a 1 W resistor. Other resistors may be 125 or 250 mW.

The choice of transistor is determined by the required charging current set to charge the battery. For the case under consideration, charging batteries from mobile phones, you can use domestic or imported NPN transistors of medium power (for example, KT815, KT817, KT819). If the input voltage is high or a low power transistor is used, the transistor must be installed on a radiator.

LED1 (highlighted in red in the diagram) serves to visually indicate battery charge. When you turn on a discharged battery, the indicator glows brightly and dims as it charges. The indicator light is proportional to the battery charge current. But it should be taken into account that if the LED is completely extinguished, the battery will still be charged with a current of less than 50 mA, which requires periodic monitoring of the device to prevent overcharging.

To increase the accuracy of monitoring the end of the charge, an additional option for indicating the battery charge (highlighted in green) on the LED2, low-power PNP transistor KT361 and current sensor R5 has been added to the charger circuit. The device can use any type of indicator depending on the required accuracy of battery charge monitoring.

The presented circuit is intended to charge only one Li-ion battery. But this charger can also be used to charge other types of batteries. You only need to set the required output voltage and charging current.

Making a charger

1. We purchase or select from those available, components for assembly in accordance with the diagram.

2. Assembling the circuit.
To check the functionality of the circuit and its settings, we assemble the charger on the circuit board.

The diode in the battery power circuit (negative bus - blue wire) is designed to prevent the lithium-ion battery from discharging in the absence of voltage at the charger input.

3. Setting the output voltage of the circuit.
We connect the circuit to a power source with a voltage of 5...9 volts. Using trimmer resistance R3, we set the output voltage of the charger within 4.18 - 4.20 volts (if necessary, at the end of the adjustment we measure its resistance and install a resistor with the required resistance).

4. Setting the charging current of the circuit.
Having connected a discharged battery to the circuit (as indicated by the LED turning on), we use resistor R2 to set the charging current value using the tester (100…300 mA). If the resistance R2 is less than 3 ohms, the LED may not light up.

5. Prepare the board for mounting and soldering parts.
We cut the required size from the universal board, carefully process the edges of the board with a file, clean and tin the contact tracks.

6. Installation of the debugged circuit on the working board
We transfer the parts from the circuit board to the working one, solder the parts, and make the missing connections using a thin mounting wire. Upon completion of assembly, we thoroughly check the installation.

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.

Batteries

What current should I use to charge a li ion 18650 battery? How to properly use such a battery. What should lithium-ion power sources be afraid of and how can such a battery extend its service life? Similar questions can arise in a wide variety of electronics industries.

And if you decide to assemble your first flashlight or electronic cigarette with your own hands, then you definitely need to familiarize yourself with the rules for working with such current sources.

A lithium-ion battery is a type of electric battery that has become widespread in modern household and electronic equipment since 1991, after it was introduced to the market by SONY. As a power source, such batteries are used in cell phones, laptops and video cameras, as a current source for electronic cigarettes and electric cars.

The disadvantages of this type of battery start with the fact that the first generation lithium-ion batteries were a blast in the market. Not only literally, but also figuratively. These batteries exploded.

This was explained by the fact that a lithium metal anode was used inside. During the process of numerous charging and discharging of such a battery, spatial formations appeared on the anode, which led to the short circuit of the electrodes, and as a result, to a fire or explosion.

After this material was replaced by graphite, this problem was eliminated, but problems could still arise on the cathode, which was made of cobalt oxide. If operating conditions are violated, or rather recharging, the problem could recur. This was corrected with the introduction of lithium ferrophosphate batteries.

All modern lithium-ion batteries prevent overheating and overcharging, but the problem of loss of charge remains at low temperatures when using devices.

Among the undeniable advantages of lithium-ion batteries, I would like to note the following:

• high battery capacity;
• low self-discharge;
• no need for maintenance.

Original chargers

The charger for lithium-ion batteries is quite similar to the charger for lead-acid batteries. The only difference is that the lithium-ion battery has very high voltages on each bank and more stringent voltage tolerance requirements.

This type of battery is called a can because of its external similarity to aluminum beverage cans. The most common battery of this shape is 18650. The battery received this designation due to its dimensions: 18 millimeters in diameter and 65 millimeters in height.

If for lead-acid batteries some inaccuracies in indicating the limit voltages during charging are acceptable, with lithium-ion cells everything is much more specific. During the charging process, when the voltage increases to 4.2 Volts, the supply of voltage to the element should stop. The permissible error is only 0.05 Volt.

Chinese chargers that can be found on the market can be designed for batteries made from different materials. Li-ion, without compromising its performance, can be charged with a current of 0.8 A. In this case, you need to very carefully control the voltage on the bank. It is advisable not to allow values ​​above 4.2 Volts. If the assembly with the battery includes a controller, then you don’t need to worry about anything, the controller will do everything for you.

The most ideal charger for lithium-ion batteries will be a voltage stabilizer and current limiter at the beginning of the charge.

Lithium must be charged with a stable voltage and limited current at the beginning of the charge.

Homemade charger

To charge the 18650, you can buy a universal charger, and not worry about how to check the necessary parameters with a multimeter. But such a purchase will cost you a pretty penny.

The price for such a device will vary around $45. But you can still spend 2-3 hours and assemble the charger with your own hands. Moreover, this charger will be cheap, reliable and will automatically turn off your battery.

The parts that we will use today to create our charger are available to every radio amateur. If there is no radio amateur with the necessary parts at hand, then on the radio market you can buy all the parts for no more than 2-4 dollars. A circuit that is assembled correctly and installed carefully starts working immediately and does not require any additional debugging.

Electrical circuit for charging a 18650 battery.

In addition to everything, when you install the stabilizer on a suitable radiator, you can safely charge your batteries without fear that the charger will overheat and catch fire. The same cannot be said about Chinese chargers.

The scheme works quite simply. First, the battery must be charged with a constant current, which is determined by the resistance of resistor R4. After the battery has a voltage of 4.2 Volts, constant voltage charging begins. When the charging current drops to very small values, the LED in the circuit will stop lighting.

The currents recommended for charging lithium-ion batteries should not exceed 10% of the battery capacity. This will increase the life of your battery. If the value of resistor R4 is 11 Ohms, the current in the circuit will be 100 mA. If you use a 5 Ohm resistance, the charging current will be 230 mA.

How to extend the life of your 18650

Disassembled battery.

If you have to leave your lithium-ion battery unused for some time, it is better to store the batteries separately from the device they power. A fully charged element will lose some of its charge over time.

An element that is charged very little, or discharged completely, may permanently lose its functionality after a long period of hibernation. It would be optimal to store the 18650 at a charge level of about 50 percent.

You should not allow the element to be completely discharged and overcharged. Lithium-ion batteries have no memory effect at all. It is advisable to charge such batteries until their charge is completely exhausted. This can also extend the life of the battery.

Lithium-ion batteries do not like either heat or cold. The optimal temperature conditions for these batteries will be in the range from +10 to +25 degrees Celsius.

Cold can not only reduce the operating time of the element, but also destroy its chemical system. I think each of us has noticed how the charge level in a mobile phone quickly drops in the cold.

Conclusion

Summarizing all of the above, I would like to note that if you are going to charge a lithium-ion battery using a store-made charger, pay attention to the fact that it is not made in China. Very often, these chargers are made from cheap materials and do not always follow the required technology, which can lead to undesirable consequences in the form of fires.

If you want to assemble the device yourself, then you need to charge the lithium-ion battery with a current that will be 10% of the battery capacity. The maximum figure may be 20 percent, but this value is no longer desirable.

When using such batteries, you should follow the rules of operation and storage in order to exclude the possibility of an explosion, for example, from overheating, or failure.

Compliance with the operating conditions and rules will extend the life of the lithium-ion battery, and as a result, save you from unnecessary financial costs. The battery is your assistant. Take care of her!

Progress is moving forward, and lithium batteries are increasingly replacing the traditionally used NiCd (nickel-cadmium) and NiMh (nickel-metal hydride) batteries.
With a comparable weight of one element, lithium has a higher capacity, in addition, the element voltage is three times higher - 3.6 V per element, instead of 1.2 V.
The cost of lithium batteries has begun to approach that of conventional alkaline batteries, their weight and size are much smaller, and besides, they can and should be charged. The manufacturer says they can withstand 300-600 cycles.
There are different sizes and choosing the right one is not difficult.
The self-discharge is so low that they sit for years and remain charged, i.e. The device remains operational when needed.

"C" stands for Capacity

You can make a simple or not very simple charger yourself, depending on your experience and capabilities.

Circuit diagram of a simple LM317 charger

Rice. 5.

The required charging current for a particular lithium-ion (Li-Ion) and lithium-polymer (Li-Pol) battery is selected by changing the Rx resistance.
The resistance Rx approximately corresponds to the following ratio: 0.95/Imax.
The value of resistor Rx indicated in the diagram corresponds to a current of 200 mA, this is an approximate value, it also depends on the transistor.

It is necessary to provide a radiator depending on the charging current and input voltage.
The input voltage must be at least 3 Volts higher than the battery voltage for normal operation of the stabilizer, which for one can is 7-9 V.

Circuit diagram of a simple charger on LTC4054

Rice. 6.

Rice. 7. This small 5-legged chip is labeled "LTH7" or "LTADY"

I won’t go into the smallest details of working with the microcircuit; everything is in the datasheet. I will describe only the most necessary features.
Charge current up to 800 mA.
The optimal supply voltage is from 4.3 to 6 Volts.
Charge indication.
Output short circuit protection.
Overheating protection (reduction of charge current at temperatures above 120°).
Does not charge the battery when its voltage is below 2.9 V.

The charge current is set by a resistor between the fifth terminal of the microcircuit and ground according to the formula

I=1000/R,
where I is the charge current in Amperes, R is the resistor resistance in Ohms.

Lithium battery low indicator

Rice. 8.

The nuance of durability

Operation and Precautions

Failure to comply with the first three points leads to a fire, the rest - to complete or partial loss of capacity.

From the experience of many years of use, I can say that the capacity of batteries changes little, but the internal resistance increases and the battery begins to work less time at high current consumption - it seems that the capacity has dropped.
For this reason, I usually install a larger container, as the dimensions of the device allow, and even old cans that are ten years old work quite well.

For not very high currents, old cell phone batteries are suitable.

Where do I use lithium batteries?

I put small batteries in children's toys, watches, etc., where 2-3 “button” cells were installed from the factory. Where exactly 3V is needed, I add one diode in series and it works just right.

I put them in LED flashlights.

Instead of the expensive and low-capacity Krona 9V, I installed 2 cans in the tester and forgot all the problems and extra costs.

In general, I put it wherever I can, instead of batteries.

Where do I buy lithium and related utilities

The Chinese usually lie about the capacity and it is less than what is written.

Honest Sanyo 18650