Smart charging for lithium-ion batteries. Charger circuit for lithium Li-Ion batteries

Today, many users have accumulated several working and unused lithium batteries appearing when replacing mobile phones to smartphones.

When using batteries in phones with their own charger, thanks to the use specialized chips to control the charge, 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 primarily to protect against deep discharge and excess voltage 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. Everything you need for high-quality charging Li-Ion batteries, this is to stabilize output voltage charger and limit the charging current.

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

Charger circuit for li-ion battery

The charger circuit is made on adjustable stabilizer voltage 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.

In the previous article, I considered the issue of replacing nickel-cadmium (nickel-manganese) NiCd (NiMn) screwdriver batteries with lithium ones. It is necessary to consider several rules for charging batteries.

18650 size Li-ion batteries can generally charge up to 4.20V per cell with permissible deviation no more than 50 mV because increasing the voltage can damage the battery structure. The battery charge current can be 0.1xC to 1xC (here C-capacity). It is better to select these values ​​from the datasheet. I used brand batteries in remaking the screwdriver. We look at the datasheet - charging current -1.5A.

The first stage should provide D.C. charge. The current value is 0.2-0.5C. I used a battery with a capacity of 3000 mAh, which means the nominal charge current will be 600-1500 mA. After the can is charged at a constant voltage, the current constantly decreases.

The battery voltage is maintained within 4.15-4.25V. The battery is charged if the current decreases to 0.05-0.01C. Taking into account the above, we use electronic boards from Aliexpress. Step-down CC/CV board with current limiting on the XL4015E1 chip or on the LM2596. A board like this is preferable as it is more convenient to configure.

List of tools and materials.

Adapter 220\12 V, 3 A - 1 piece;
-standard screwdriver charger (or power supply);
-CC/CV charge board on or -1pc;
- connecting wires - soldering iron;
-tester;
- plastic box for charge board - 1 piece;
- minivoltmeter - 1 piece;
-variable resistor (potentiometer) for 10-20 kOhm - 1 piece;
- power connector for the battery compartment of the screwdriver - 1 pc.

Step one. Assembling a screwdriver battery charger on an adapter.

We have already chosen the cccv board above. As a power source, you can use any one with the following parameters - output voltage not lower than 18 V (for a 4S circuit), current 3 A. In the first example of making a charger for lithium-ion batteries of a screwdriver, I used a 12 V, 3 A adapter.

First, I checked what current it can produce at the rated load. I connected a car lamp to the output and waited half an hour. It produces 1.9 A freely without overload. I also measured the temperature on the transistor radiator - 40°C. Quite normal mode.

But in this case there is not enough tension. This can be easily fixed using just one cheap radio component - a variable resistor (potentiometer) of 10-20 kOhm. Let's look at a typical adapter circuit.

Next, we connect the charge control board to the adapter. We exhibit trimmer resistor the voltage on the board is 16.8 V. Using another trimming resistor, we set the current to 1.5 A, and first connect the tester in ammeter mode to the output of the board. Now you can connect the lithium-ion screwdriver assembly. Charging went well, the current dropped to a minimum at the end of the charge, and the battery was charged. The temperature on the adapter was between 40-43°C, which is quite normal. In the future, you can drill holes in the adapter body to improve ventilation (especially in the summer).

The end of the battery charge can be seen by the LED on the board on the XL4015E1 turning on. In this example, I used another LM2596 board in the same way that I accidentally burned the XL4015E1 during experiments. I advise you to do better charging on the XL4015E1 board.

Step two. Assembling a screwdriver battery charger circuit using a standard charger.

I had a standard charger from another screwdriver. It is designed to charge nickel-manganese batteries. The task was to charge both nickel-manganese and lithium-ion batteries.

This was solved simply - I soldered the wires to the CC/CV board to the output wires (red plus, black minus).
The no-load voltage at the output of the standard charger was 27 V, this is quite suitable for our charging board. Further everything is the same as in the version with the adapter.

The invention and use of tools with autonomous power sources has become one of the hallmarks of our time. New active components are being developed and introduced to improve the performance of battery assemblies. Unfortunately, batteries cannot work without recharging. And if on devices that have constant access to the power grid, the issue is solved by built-in sources, then for powerful power sources, for example, a screwdriver, separate chargers for lithium batteries are necessary, taking into account the characteristics of different types of batteries.

In recent years, products based on lithium-ion active components have been increasingly used. And this is quite understandable, since these power supplies have proven themselves to be very good:

• they have no memory effect;
• Self-discharge has been almost completely eliminated;
• can work at sub-zero temperatures;
• hold the discharge well.
• the number was increased to 700 cycles.

But, each type of battery has its own characteristics. Thus, the lithium-ion component requires the design of elementary batteries with a voltage of 3.6V, which requires some individual features for such products.

Recovery Features

With all the advantages of lithium-ion batteries, they have their drawbacks - this is the possibility of internal short-circuiting of elements during charging overvoltage due to active crystallization of lithium in the active component. There is also a limitation on the minimum voltage value, which makes it impossible for the active component to accept electrons. To eliminate the consequences, the battery is equipped with an internal controller that breaks the circuit of elements with the load when critical values ​​are reached. Such elements are stored best when charged to 50% at +5 - 15 ° C. Another feature of lithium-ion batteries is that the operating time of the battery depends on the time of its manufacture, regardless of whether it has been in use or not, or in other words, it is subject to the “aging effect”, which limits its service life to five years.

Charging lithium-ion batteries

The simplest single cell charging device

In order to understand more complex circuits charging lithium-ion batteries, consider a simple charger for lithium batteries, more precisely for one battery.

The basis of the circuit is control: a TL 431 microcircuit (acts as an adjustable zener diode) and one reverse conduction transistor.
As can be seen from the diagram, the control electrode TL431 is included in the base of the transistor. Setting up the device comes down to the following: you need to set the voltage at the output of the device to 4.2V - this is set by adjusting the zener diode by connecting resistance R4 - R3 with a nominal value of 2.2 kOhm and 3 kOhm to the first leg. This circuit is responsible for adjusting the output voltage, the voltage adjustment is only set once and is stable.

Next, the charge current is regulated, the adjustment is made by resistance R1 (in the diagram with a nominal value of 3 Ohms) if the emitter of the transistor is turned on without resistance, then the input voltage will also be at the charging terminals, that is, it is 5V, which may not meet the requirements.

Also, in this case, the LED will not light up, but it signals the current saturation process. The resistor can be rated from 3 to 8 ohms.
To quickly adjust the voltage across the load, resistance R3 can be set adjustable (potentiometer). The voltage is adjusted without load, that is, without element resistance, with a nominal value of 4.2 - 4.5V. After reaching the required value, it is enough to measure the resistance value of the variable resistor and install the main part of the required value in its place. If the required value is not available, it can be assembled from several pieces using a parallel or serial connection.

Resistance R4 is designed to open the base of the transistor, its nominal value should be 220 Ohms. As the battery charge increases, the voltage will increase, the control electrode of the transistor base will increase the emitter-collector contact resistance, reducing the charging current.

The transistor can be used KT819, KT817 or KT815, but then you will have to install a radiator for cooling. Also, a radiator will be required if currents exceed 1000mA. In general, this classic charging scheme is the simplest.

Improvement of the charger for lithium li-ion batteries

When it becomes necessary to charge lithium ion batteries, connected from several soldered elementary cells, it is best to charge the cells separately using a control circuit that will monitor the charging of each individual battery individually. Without this circuit, a significant deviation in the characteristics of one element in a series-soldered battery will lead to a malfunction of all batteries, and the unit itself will even be dangerous due to its possible overheating or even fire.

Charger for 12 volt lithium batteries. Balancer device

The term balancing in electrical engineering means a charging mode that controls each individual element involved in the process, preventing the voltage from increasing or decreasing below the required level. The need for such solutions arises from the features of assemblies with li-ion. If, due to the internal design, one of the elements charges faster than the others, which is very dangerous for the condition of the remaining elements, and as a result of the entire battery. The balancer circuit design is designed in such a way that the circuit elements absorb excess energy, thereby regulating the charging process of an individual cell.

If we compare the principles of charging nickel-cadmium batteries, they differ from lithium-ion batteries, primarily for Ca - Ni, the end of the process is indicated by an increase in the voltage of the polar electrodes and a decrease in the current to 0.01 mA. Also, before charging, this source must be discharged to at least 30% of the original capacity; if this condition is not maintained, a “memory effect” occurs in the battery, which reduces the battery capacity.

With the Li-Ion active component the opposite is true. Completely discharging these cells can lead to irreversible consequences and dramatically reduce the ability to charge. Often, low-quality controllers may not provide control over the level of battery discharge, which can lead to malfunctions of the entire assembly due to one cell.

A way out of the situation may be to use the above discussed scheme on adjustable zener diode TL431. A load of 1000 mA or more can be achieved by installing more powerful transistor. Such cells connected directly to each cell will protect against incorrect charging.

The transistor should be selected based on power. Power is calculated using the formula P = U*I, where U is voltage, I is charging current.

For example, with a charging current of 0.45 A, the transistor must have a power dissipation of at least 3.65 V * 0.45 A = 1.8 W. and this is a large current load for internal transitions, so it is better to install the output transistors in radiators.

Below is an approximate calculation of the values ​​of resistors R1 and R2 for different charge voltages:

22.1k + 33k => 4.16 V

15.1k + 22k => 4.20 V

47.1k + 68k => 4.22 V

27.1k + 39k => 4.23 V

39.1k + 56k => 4.24 V

33k + 47k => 4.25 V

Resistance R3 is the load based on the transistor. Its resistance can be 471 Ohm - 1.1 kOhm.

But, when implementing these circuit solutions, a problem arose: how to charge a separate cell in a battery pack? And such a solution was found. If you look at the contacts on the charging leg, then on the recently produced cases with lithium-ion batteries there are as many contacts as there are individual cells in the battery; naturally, on the charger, each such element is connected to a separate controller circuit.

In terms of cost, such a charger is slightly more expensive than a linear device with two contacts, but it is worth it, especially when you consider that assemblies with high-quality lithium-ion components cost up to half the cost of the product itself.

Pulse charger for lithium li-ion batteries

Recently, many leading manufacturers of self-powered hand tools have been widely advertising fast chargers. For these purposes, pulse converters based on pulse-width modulated signals (PWM) were developed to restore power supplies for screwdrivers based on a PWM generator on a UC3842 chip; a flyback AS-DS converter was assembled with a load on a pulse transformer.

Next, we will consider the operation of the circuit of the most common source (see the attached circuit): mains voltage 220V is supplied to the diode assembly D1-D4, for these purposes any diodes with a power of up to 2A are used. Ripple smoothing occurs on capacitor C1, where a voltage of about 300V is concentrated. This voltage is the power supply for a pulse generator with transformer T1 at the output.

The initial power to start the integrated circuit A1 is supplied through resistor R1, after which the pulse generator of the microcircuit is turned on, which outputs them to pin 6. Next, the pulses are supplied to the gate of the powerful field effect transistor VT1 opening it. The drain circuit of the transistor supplies power to the primary winding of the pulse transformer T1. After which the transformer is switched on and the transmission of pulses to the secondary winding begins. The pulses of the secondary winding 7 - 11 after rectification by the VT6 diode are used to stabilize the operation of the A1 microcircuit, which in full generation mode consumes much more current than it receives through the circuit from resistor R1.

In the event of a malfunction of the D6 diodes, the source switches to pulsation mode, alternately starting the transformer and stopping it, while a characteristic pulsating “squeak” is heard; let’s see how the circuit works in this mode.

Power through R1 and capacitor C4 start the chip's oscillator. After launch, for normal operation more is required increased current. If D6 malfunctions, no additional power is supplied to the microcircuit and generation stops, then the process is repeated. If diode D6 is working, it immediately turns on the pulse transformer under full load. During normal startup of the generator, a pulse current of 12 - 14V appears on winding 14-18 (at Idling 15V). After rectification by diode V7 and smoothing of the pulses by capacitor C7, the pulse current is supplied to the battery terminals.

A current of 100 mA does not harm the active component, but increases the recovery time by 3-4 times, reducing its time from 30 minutes to 1 hour. ( source - magazine online edition Radioconstructor 03-2013)

Fast charger G4-1H RYOBI ONE+ BCL14181H

Pulse device for 18 volt lithium batteries produced by the German company Ryobi, manufactured in the People's Republic of China. The pulse device is suitable for lithium-ion, nickel-cadmium 18V. Designed for normal operation at temperatures from 0 to 50 C. The circuit design provides two power supply modes for voltage and current stabilization. Pulse current supply ensures optimal recharge of each individual battery.

The device is made in an original case made of impact-resistant plastic. Forced cooling from a built-in fan is used, with automatic switching on when reaching 40° C.

Characteristics:

• Minimum charge time 18V at 1.5 A/h - 60 minutes, weight 0.9 kg, dimensions: 210 x 86 x 174 mm. The charging process is indicated by a blue LED; when completed, the red LED lights up. There is a fault diagnosis, which lights up when there is a fault in the assembly with a separate light on the case.
• Power supply single phase 50Hz. 220V. The length of the network cable is 1.5 meters.

Charging station repair

If it happens that the product has ceased to perform its functions, it is best to contact specialized workshops, but basic faults can be eliminated with your own hands. What to do if the power indicator is not on, let’s look at some simple faults using the station as an example.

This product is designed to operate with 12V, 1.8A lithium-ion batteries. The product is made with a step-down transformer, transforming the reduced alternating current A four diode bridge circuit is performed. An electrolytic capacitor is installed to smooth out the pulsation. Indication includes LEDs mains power, beginning and end of saturation.

So, if the network indicator does not light up. First of all, you need to check the integrity of the circuit through the power plug primary winding transformer. To do this, you need to test the integrity of the primary winding of the transformer through the pins of the mains power plug with an ohmmeter by touching the probes of the device to the pins of the mains plug; if the circuit shows an open circuit, then you need to inspect the parts inside the housing.

The fuse may break; usually it is a thin wire, stretched in a porcelain or glass case, which burns out when overloaded. But some companies, for example, Interskol, in order to protect the transformer windings from overheating, install a thermal fuse between the turns of the primary winding, the purpose of which, when the temperature reaches 120 - 130 ° C, is to break the power supply circuit of the network and, unfortunately, after the break does not restore.

Usually the fuse is located under the cover paper insulation of the primary winding, after opening which, this part can be easily found. To bring the circuit back into working condition, you can simply solder the ends of the winding into one whole, but you need to remember that the transformer remains without short circuit protection and it is best to install a regular mains fuse instead of a thermal fuse.

If the primary winding circuit is intact, the secondary winding and bridge diodes ring. To check the continuity of the diodes, it is better to unsolder one end from the circuit and check the diode with an ohmmeter. When connecting the ends to the terminals of the probes alternately in one direction, the diode should show an open circuit, in the other, a short circuit.

Thus, it is necessary to check all four diodes. And, if, indeed, we got into the circuit, then it is best to immediately change the capacitor, because diodes are usually overloaded due to high electrolyte in the capacitor.

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It's simple charger for lithium-ion batteries, as well as lithium polymer batteries built on the well-known LM317.

The charging process is shown in the graph below. At the first moment of the charging process, the charge current is constant; when the target voltage level (Umax) is reached on the battery, the charger switches to a mode where the voltage remains constant and the current asymptotically tends to zero.

The output voltage of lithium-ion and lithium-polymer batteries is typically 4.2V (4.1V for some types). Usually, the output voltage does not match the nominal voltage which is 3.7V (sometimes 3.6V).

It is not recommended to charge this type of battery to the full 4.2V as this will reduce battery life. If you reduce the output voltage to 4.1V, the capacity drops by 10%, but at the same time the service life (number of cycles) will almost double. When using batteries, the rated voltage cannot be lower than 3.4...3.3V.

Description of the charger

As already mentioned, charging is based on the LM317 stabilizer. Li-Ion and Li-Pol are quite demanding in terms of accuracy charging voltage. If you want to charge to full voltage (usually 4.2V), then you need to set this voltage with an accuracy of plus/minus 1%. After charging to 90% capacity (4.1V), the accuracy may be slightly less (about 3%).

The circuit using LM317 provides fairly accurate voltage stabilization. The target voltage is set by R2. Current stabilization is not as critical as voltage stabilization, so it is enough to stabilize it using a shunt resistor Rx and an NPN transistor (VT1).

If the voltage drop across resistor Rx reaches approximately 0.95V, then the transistor begins to open. This reduces the voltage at the “Common” contact of the Lm317 stabilizer and thereby stabilizes the current.

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 Rx resistor value indicated on the diagram corresponds to a current of 200 mA.

The charger's input voltage must be between 9 and 24 volts. Exceeding this level increases power losses in the LM317 circuit; decreasing it will disrupt correct work(you need to recalculate the voltage drop across the shunt and minimum voltage on the “General” contact). Transistor VT1 can be replaced with BC237, KC507, C945 or domestic

I made myself a charger for four lithium-ion batteries. Someone will now think: well, he did it and did it, there are plenty of them on the Internet. And I want to say right away that my design is capable of charging both one battery and four at once. All batteries are charged independently of each other.
This makes it possible to simultaneously charge batteries from different devices and with different initial charges.
I made a charger for 18650 batteries, which I use in a flashlight, powerbanks, laptop, etc.
The circuit consists of ready-made modules and is assembled very quickly and simply.

Will need

• - 4 things.
• - 4 things.
• Paper clips.

Manufacturing a charger for different numbers of batteries