Modern electronic devices (such as cell phones, laptops or tablets) are powered by lithium-ion batteries, which have replaced their alkaline counterparts. Nickel-cadmium and nickel-metal hydride batteries have given way to Li─Ion batteries due to the better technical and consumer qualities of the latter. The available charge in such batteries from the moment of production ranges from four to six percent, after which it begins to decrease with use. During the first 12 months, battery capacity decreases by 10 to 20%.

Original chargers

Chargers for ion batteries are very similar to similar devices for lead-acid batteries, however, their batteries, called “banks” for their external similarity, have a higher voltage, so there are more stringent tolerance requirements (for example, the permissible voltage difference is only 0. 05 c). The most common format of a 18650 ion battery bank is that it has a diameter of 1.8 cm and a height of 6.5 cm.

Just a note. A standard lithium-ion battery requires up to three hours to charge, and the more precise time is determined by its original capacity.

Manufacturers of Li-ion batteries recommend using only original chargers for charging, which are guaranteed to provide the required voltage for the battery and will not destroy part of its capacity by overcharging the element and disrupting the chemical system; it is also undesirable to fully charge the battery.

Pay attention! During long-term storage, lithium batteries should optimally have a small (no more than 50%) charge, and it is also necessary to remove them from the units.

If lithium batteries have a protection board, then they are not in danger of being overcharged.

The built-in protection board cuts off excessive voltage (more than 3.7 volts per cell) during charging and turns off the battery if the charge level drops to a minimum, usually 2.4 volts. The charge controller detects the moment when the voltage on the bank reaches 3.7 volts and disconnects the charger from the battery. This essential device also monitors the temperature of the battery to prevent overheating and overcurrent. The protection is based on the DV01-P microcircuit. After the circuit is interrupted by the controller, its restoration is carried out automatically when the parameters are normalized.

On the chip, a red indicator means charge, and green or blue indicates that the battery is charged.

How to properly charge lithium batteries

Well-known manufacturers of li-ion batteries (for example, Sony) use a two- or three-stage charging principle in their chargers, which can significantly extend the battery life.

At the output, the charger has a voltage of five volts, and the current value ranges from 0.5 to 1.0 of the nominal capacity of the battery (for example, for an element with a capacity of 2200 milliamp-hours, the charger current should be from 1.1 amperes.)

At the initial stage, after connecting the charger for lithium batteries, the current value is from 0.2 to 1.0 of the nominal capacity, while the voltage is 4.1 volts (per cell). Under these conditions, the batteries charge in 40 to 50 minutes.

To achieve constant current, the charger circuit must be able to raise the voltage at the battery terminals, at which time the charger for most lithium-ion batteries acts as a conventional voltage regulator.

Important! If it is necessary to charge lithium-ion batteries that have a built-in protection board, then the open circuit voltage should not be more than six to seven volts, otherwise it will deteriorate.

When the voltage reaches 4.2 volts, the battery capacity will be between 70 and 80 percent capacity, which will signal the end of the initial charging phase.

The next stage is carried out in the presence of constant voltage.

Additional information. Some units use a pulse method for faster charging. If the lithium-ion battery has a graphite system, then they must comply with the voltage limit of 4.1 volts per cell. If this parameter is exceeded, the energy density of the battery will increase and trigger oxidation reactions, shortening the life of the battery. In modern battery models, special additives are used that allow the voltage to be increased when connecting a charger for li ion batteries to 4.2 volts plus/minus 0.05 volts.

In simple lithium batteries, chargers maintain a voltage level of 3.9 volts, which for them is a reliable guarantee of long service life.

When delivering a current of 1 battery capacity, the time to obtain an optimally charged battery will be from 2 to 3 hours. As soon as the charge becomes full, the voltage reaches the cutoff norm, the current value rapidly drops and remains at the level of a couple of percent of the initial value.

If the charging current is artificially increased, the time of use of the charger to power lithium-ion batteries will hardly decrease. In this case, the voltage initially increases faster, but at the same time the duration of the second stage increases.

Some chargers can fully charge the battery in 60-70 minutes; during such charging, the second stage is eliminated, and the battery can be used after the initial stage (the charging level will also be at 70 percent capacity).

At the third and final charging stage, a compensating charge is carried out. It is not carried out every time, but only once every 3 weeks, when storing (not using) batteries. In battery storage conditions, it is impossible to use jet charging, because in this case lithium metallization occurs. However, short-term recharging with constant voltage current helps to avoid charge losses. Charging stops when the voltage reaches 4.2 volts.

Lithium metallization is dangerous due to the release of oxygen and a sudden increase in pressure, which can lead to ignition and even explosion.

DIY battery charger

A charger for lithium-ion batteries is inexpensive, but if you have a little knowledge of electronics, you can make one yourself. If there is no accurate information about the origin of the battery elements, and there are doubts about the accuracy of the measuring instruments, you should set the charge threshold in the region from 4.1 to 4.15 volts. This is especially true if the battery does not have a protective board.

To assemble a charger for lithium batteries with your own hands, one simplified circuit is enough, of which there are many freely available on the Internet.

For the indicator, you can use a charging-type LED, which lights up when the battery charge is significantly reduced and goes out when discharged to “zero”.

The charger is assembled in the following order:

• a suitable housing is located;
• a five-volt power supply and other circuit parts are mounted (strictly follow the sequence!);
• a pair of brass strips is cut out and attached to the socket holes;
• using a nut, the distance between the contacts and the connected battery is determined;
• A switch is installed to change the polarity (optional).

If the task is to assemble a charger for 18650 batteries with your own hands, then a more complex circuit and more technical skills will be required.

All lithium-ion batteries require recharging from time to time, however, overcharging as well as completely discharging should be avoided. Maintaining the functionality of batteries and maintaining their working capacity for a long time is possible with the help of special chargers. It is advisable to use original chargers, but you can assemble them yourself.

Video

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 constant voltage source of 5 volts, delivering 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 operating 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. We set the charging current with resistances R4 and R6. 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.

Lithium batteries (Li-Io, Li-Po) are currently the most popular rechargeable sources of electrical energy. The lithium battery has a nominal voltage of 3.7 Volts, which is indicated on the case. However, a 100% charged battery has a voltage of 4.2 V, and a discharged one “to zero” has a voltage of 2.5 V. There is no point in discharging the battery below 3 V, firstly, it will deteriorate, and secondly, in the range from 3 to 2.5 It only supplies a couple of percent of energy to the battery. Thus, the operating voltage range is 3 – 4.2 Volts. You can watch my selection of tips for using and storing lithium batteries in this video

There are two options for connecting batteries, series and parallel.

With a series connection, the voltage on all batteries is summed up, when a load is connected, a current flows from each battery equal to the total current in the circuit; in general, the load resistance sets the discharge current. You should remember this from school. Now comes the fun part, capacity. The capacity of the assembly with this connection is fairly equal to the capacity of the battery with the smallest capacity. Let's imagine that all batteries are 100% charged. Look, the discharge current is the same everywhere, and the battery with the smallest capacity will be discharged first, this is at least logical. And as soon as it is discharged, it will no longer be possible to load this assembly. Yes, the remaining batteries are still charged. But if we continue to remove current, our weak battery will begin to overdischarge and fail. That is, it is correct to assume that the capacity of a series-connected assembly is equal to the capacity of the smallest or most discharged battery. From here we conclude: to assemble a series battery, firstly, you need to use batteries of equal capacity, and secondly, before assembly, they all must be charged equally, in other words, 100%. There is such a thing called BMS (Battery Monitoring System), it can monitor each battery in the battery, and as soon as one of them is discharged, it disconnects the entire battery from the load, this will be discussed below. Now as for charging such a battery. It must be charged with a voltage equal to the sum of the maximum voltages on all batteries. For lithium it is 4.2 volts. That is, we charge a battery of three with a voltage of 12.6 V. See what happens if the batteries are not the same. The battery with the smallest capacity will charge the fastest. But the rest have not yet charged. And our poor battery will fry and recharge until the rest are charged. Let me remind you that lithium also does not like overdischarge very much and deteriorates. To avoid this, recall the previous conclusion.

Let's move on to parallel connection. The capacity of such a battery is equal to the sum of the capacities of all batteries included in it. The discharge current for each cell is equal to the total load current divided by the number of cells. That is, the more Akum in such an assembly, the more current it can deliver. But an interesting thing happens with tension. If we collect batteries that have different voltages, that is, roughly speaking, charged to different percentages, then after connecting they will begin to exchange energy until the voltage on all cells becomes the same. We conclude: before assembly, the batteries must again be charged equally, otherwise large currents will flow during connection, and the discharged battery will be damaged, and most likely may even catch fire. During the discharge process, the batteries also exchange energy, that is, if one of the cans has a lower capacity, the others will not allow it to discharge faster than themselves, that is, in a parallel assembly you can use batteries with different capacities. The only exception is operation at high currents. On different batteries under load, the voltage drops differently, and current will start flowing between the “strong” and “weak” batteries, and we don’t need this at all. And the same goes for charging. You can absolutely safely charge batteries of different capacities in parallel, that is, balancing is not needed, the assembly will balance itself.

In both cases considered, the charging current and discharge current must be observed. The charging current for Li-Io should not exceed half the battery capacity in amperes (1000 mah battery - charge 0.5 A, 2 Ah battery, charge 1 A). The maximum discharge current is usually indicated in the datasheet (TTX) of the battery. For example: 18650 laptops and smartphone batteries cannot be loaded with a current exceeding 2 battery capacities in Amperes (example: a 2500 mah battery, which means the maximum you need to take from it is 2.5 * 2 = 5 Amperes). But there are high-current batteries, where the discharge current is clearly indicated in the characteristics.

Features of charging batteries using Chinese modules

Standard purchased charging and protection module for 20 rubles for lithium battery ( link to Aliexpress)
(positioned by the seller as a module for one 18650 can) can and will charge any lithium battery, regardless of shape, size and capacity to the correct voltage of 4.2 volts (the voltage of a fully charged battery, to capacity). Even if it is a huge 8000mah lithium package (of course we are talking about one 3.6-3.7v cell). The module provides a charging current of 1 ampere, this means that they can safely charge any battery with a capacity of 2000mAh and above (2Ah, which means the charging current is half the capacity, 1A) and, accordingly, the charging time in hours will be equal to the battery capacity in amperes (in fact, a little more, one and a half to two hours for every 1000mah). By the way, the battery can be connected to the load while charging.

Important! If you want to charge a smaller capacity battery (for example, one old 900mAh can or a tiny 230mAh lithium pack), then the charging current of 1A is too much and should be reduced. This is done by replacing resistor R3 on the module according to the attached table. The resistor is not necessarily smd, the most ordinary one will do. Let me remind you that the charging current should be half the battery capacity (or less, no big deal).

But if the seller says that this module is for one 18650 can, can it charge two cans? Or three? What if you need to assemble a capacious power bank from several batteries?
CAN! All lithium batteries can be connected in parallel (all pluses to pluses, all minuses to minuses) REGARDLESS OF CAPACITY. Batteries soldered in parallel maintain an operating voltage of 4.2v and their capacity is added up. Even if you take one can at 3400mah and the second at 900, you will get 4300. The batteries will work as one unit and will discharge in proportion to their capacity.
The voltage in a PARALLEL assembly is ALWAYS THE SAME ON ALL BATTERIES! And not a single battery can physically discharge in the assembly before the others; the principle of communicating vessels works here. Those who claim the opposite and say that batteries with a lower capacity will discharge faster and die are confused with SERIES assembly, spit in their faces.
Important! Before connecting to each other, all batteries must have approximately the same voltage, so that at the time of soldering, equalizing currents do not flow between them; they can be very large. Therefore, it is best to simply charge each battery separately before assembly. Of course, the charging time of the entire assembly will increase, since you are using the same 1A module. But you can parallel two modules, obtaining a charging current of up to 2A (if your charger can provide that much). To do this, you need to connect all similar terminals of the modules with jumpers (except for Out- and B+, they are duplicated on the boards with other nickels and will already be connected anyway). Or you can buy a module ( link to Aliexpress), on which the microcircuits are already in parallel. This module is capable of charging with a current of 3 Amps.

Sorry for the obvious stuff, but people still get confused, so we'll have to discuss the difference between parallel and serial connections.
PARALLEL connection (all pluses to pluses, all minuses to minuses) maintains the battery voltage of 4.2 volts, but increases the capacity by adding all the capacities together. All power banks use parallel connection of several batteries. Such an assembly can still be charged from USB and the voltage is raised to an output of 5v by a boost converter.
CONSISTENT connection (each plus to minus of the subsequent battery) gives a multiple increase in the voltage of one charged bank 4.2V (2s - 8.4V, 3s - 12.6V and so on), but the capacity remains the same. If three 2000mah batteries are used, then the assembly capacity is 2000mah.
Important! It is believed that for sequential assembly it is strictly necessary to use only batteries of the same capacity. Actually this is not true. You can use different ones, but then the battery capacity will be determined by the SMALLEST capacity in the assembly. Add 3000+3000+800 and you get an 800mah assembly. Then the specialists begin to crow that the less capacious battery will then discharge faster and die. But it doesn’t matter! The main and truly sacred rule is that for sequential assembly it is always necessary to use a BMS protection board for the required number of cans. It will detect the voltage on each cell and turn off the entire assembly if one discharges first. In the case of an 800 bank, it will discharge, the BMS will disconnect the load from the battery, the discharge will stop and the residual charge of 2200mah on the remaining banks will no longer matter - you need to charge.

The BMS board, unlike a single charging module, IS NOT A sequential charger. Needed for charging configured source of the required voltage and current. Guyver made a video about this, so don’t waste time, watch it, it’s about this in as much detail as possible.

Is it possible to charge a daisy chain assembly by connecting several single charging modules?
In fact, under certain assumptions, it is possible. For some homemade products, a scheme using single modules, also connected in series, has proven itself, but EACH module needs its own SEPARATE POWER SOURCE. If you charge 3s, take three phone chargers and connect each to one module. When using one source - power short circuit, nothing works. This system also works as protection for the assembly (but the modules are capable of delivering no more than 3 amperes). Or, simply charge the assembly one by one, connecting the module to each battery until fully charged.

Battery charge indicator

Another pressing problem is to at least know approximately how much charge remains on the battery so that it does not run out at the most crucial moment.
For parallel 4.2-volt assemblies, the most obvious solution would be to immediately purchase a ready-made power bank board, which already has a display showing charge percentages. These percentages aren't super accurate, but they still help. The issue price is approximately 150-200 rubles, all are presented on the Guyver website. Even if you are not building a power bank but something else, this board is quite cheap and small to fit into a homemade product. Plus, it already has the function of charging and protecting batteries.
There are ready-made miniature indicators for one or several cans, 90-100 rubles
Well, the cheapest and most popular method is to use an MT3608 boost converter (30 rubles), set to 5-5.1v. Actually, if you make a power bank using any 5-volt converter, then you don’t even need to buy anything additional. The modification consists of installing a red or green LED (other colors will work at a different output voltage, from 6V and higher) through a 200-500 ohm current-limiting resistor between the output positive terminal (this will be a plus) and the input positive terminal (for an LED this will be a minus). You read that right, between two pluses! The fact is that when the converter operates, a voltage difference is created between the pluses; +4.2 and +5V give each other a voltage of 0.8V. When the battery is discharged, its voltage will drop, but the output from the converter is always stable, which means the difference will increase. And when the voltage on the bank is 3.2-3.4V, the difference will reach the required value to light the LED - it begins to show that it is time to charge.

How to measure battery capacity?

We are already accustomed to the idea that for measurements you need an Imax b6, but it costs money and is redundant for most radio amateurs. But there is a way to measure the capacity of a 1-2-3 can battery with sufficient accuracy and cheaply - a simple USB tester.

Most modern gadgets receive power in two ways: from the mains or from batteries. Which one will you choose? Probably the second one, as the most convenient. But then you will have to take care of charging them regularly. There is special equipment for this – a charger for lithium-ion batteries. When choosing it, they are usually interested in the charging speed and the number of batteries that can be restored at the same time.

But we should not forget that it must be optimized to work with specific batteries. Most foreign battery manufacturers also produce their own chargers, which saves you from the tedious search for a suitable model. What is their difference and how to navigate this sea of ​​products? Now we will tell you in more detail.

Charging for AA batteries

This device is a necessary item for people who prefer an active lifestyle and have switched the maximum number of gadgets they use to battery power. One of the most common of these devices is the mobile phone.

All of them are equipped with lithium-based batteries. Therefore, it is recommended for them to purchase a charger for a 18650 lithium battery. Since an attempt to restore the battery capacity using a device of the wrong model will lead to its damage.

Typically, devices labeled EP are used to charge lithium-based batteries. In a mobile phone, the battery is considered the most vulnerable point. And if you use the wrong charger, its service life may be shortened, it will begin to discharge quickly, which will cause a lot of inconvenient moments. To avoid this, it is necessary to select the correct recovery equipment. Moreover, it is not necessary to purchase a ready-made model; you can make a charger for lithium batteries with your own hands. Such a device will cost less than an industrial product.

Design features of the charger

The classic 18650 lithium battery charger circuit includes two main parts:

• Transformer;
• Rectifier.

It is used to generate direct current with a voltage of 14.4V. This parameter value was not chosen by chance. It is necessary so that current can pass through a discharged battery. And since at this time the battery voltage is about 12V, it is impossible to charge it with a device whose output has the same value. That is why the value of 14.4V was chosen.

Operating principle of the charger

Restoring battery capacity begins when the charger is plugged into the network. At the same time, the internal resistance of the battery increases and the current decreases. As soon as the voltage on the battery reaches 12V, the current will approach zero. These parameters indicate that the battery has been charged successfully and the device can be turned off.

In addition to the usual process, which takes quite a long time, there is also an accelerated one. Rapid charging significantly reduces the time, but at the same time negatively affects battery performance, so experts do not recommend using this method.

Criteria for choosing a charging device

You can determine how high quality the purchased device will be by the following points:

• Availability of independent charging channels;
• Toku;
• Discharge functions.

Let's look at each of them in detail. Let's start with the most important thing - independent charge channels. The presence of them in the selected model indicates that its electronic filling is capable of separately controlling the charging process and stopping it as soon as the battery capacity is restored. But at the same time, all the others will not have time to restore their capacity, which, if this situation is constantly repeated, leads to rapid failure of the batteries.

Replenishing battery energy is possible in three ways:

1. Weak current;
2. Average;
3. Tall.

The first involves choosing a charger for lithium-ion batteries based on the rated capacity of the battery. In this case, the current generated by it should not exceed 10%. This charging method is the slowest and most gentle. With its constant use, the battery life is practically not reduced.

The use of devices with a current of less than half the rated capacity of the battery is considered the golden mean. With it, the battery practically does not heat up and the cycle time is not very long, as in the first case.

The latter method, or charging with a high current almost equal to the rated capacity, is a kind of stress for the battery, leading to a significant reduction in service life. It generates intense heat, requiring active fan cooling. It is used only in extreme cases when you need to charge the battery in a couple of hours.

Watch a video review of chargers for lithium batteries:

There are also so-called smart devices. They are used to charge batteries by professional photographers, used in lighting applications and other similar applications. The cost of such a charger for lithium-ion batteries is quite high, but if the flawless operation of the gadget is important to you, then it is better to invest in the purchase of a device rather than constantly changing batteries.

Smart chargers have a discharge function. It is necessary to completely discharge the battery, thereby eliminating the memory effect. This slightly lengthens the charging cycle, but thereby extends the battery life.

Some models also have a training function. It is used to return partially damaged batteries to working condition.

The best manufacturers

Each product has its own characteristics. Therefore, when choosing a specific brand, you must first focus on the number and type of batteries that will have to be charged. If you plan to work with 4 batteries, then you can choose the Rodition Ecocharger model. This is a small device that can regenerate even disposable alkaline batteries. This function is activated using a toggle switch located on the side panel of the case.

The device has four channels and is capable of monitoring the charge level of each element separately. There is a light indication on the device panel showing which battery has already been restored. You can buy such a device for $20.

Watch a video about Rodition Ecocharger products:

One of the most popular and multifunctional is the La Crosse BC-700 lithium battery charger. It is classified as advanced and is designed for the restoration of nickel-based finger mounts in AA and AAA formats. The features of the device are such that it is capable of simultaneously charging 4 batteries of different capacities.

The devices operate in several modes. There is a current regulator that allows you to select the most optimal value for each case.

Charging stages

Experts recommend starting the process of restoring the battery by completely discharging it. If for some reason you have to charge a battery that is not yet completely discharged, then you should choose an advanced model of the device.

The charging and discharging processes of any battery occur in the form of a chemical reaction. However, charging lithium-ion batteries is an exception to the rule. Scientific research shows the energy of such batteries as the chaotic movement of ions. The statements of pundits deserve attention. If the science is to charge lithium-ion batteries correctly, then these devices should last forever.

Scientists see evidence of loss of useful battery capacity, confirmed by practice, in ions blocked by so-called traps.

Therefore, as is the case with other similar systems, lithium-ion devices are not immune to defects during their use in practice.

Chargers for Li-ion designs have some similarities to devices designed for lead-acid systems.

But the main differences between such chargers are seen in the supply of increased voltages to the cells. In addition, there are tighter current tolerances, plus the elimination of intermittent or floating charging when the battery is fully charged.

A relatively powerful power device that can be used as an energy storage device for designs of alternative energy sources
Cobalt-blended lithium-ion batteries are equipped with internal protective circuits, but this rarely prevents the battery from exploding when overcharged.

There are also developments of lithium-ion batteries, where the percentage of lithium has been increased. For them, the charge voltage can reach 4.30V/I and higher.

Well, increasing the voltage increases the capacity, but if the voltage goes beyond the specification, it can lead to destruction of the battery structure.

Therefore, for the most part, lithium-ion batteries are equipped with protective circuits, the purpose of which is to maintain the established standard.

Full or partial charge

However, practice shows that most powerful lithium-ion batteries can accept a higher voltage level, provided that it is supplied for a short time.

With this option, the charging efficiency is about 99%, and the cell remains cool during the entire charging time. True, some lithium-ion batteries still heat up by 4-5C when they reach a full charge.

This may be due to protection or due to high internal resistance. For such batteries, the charge should be stopped when the temperature rises above 10ºC at a moderate charge rate.

Lithium-ion batteries in the charger are being charged. The indicator shows the batteries are fully charged. Further process threatens to damage the batteries

Full charging of cobalt-blended systems occurs at a threshold voltage. In this case, the current drops by up to 3-5% of the nominal value.

The battery will show a full charge even when it reaches a certain capacity level that remains unchanged for a long time. The reason for this may be increased self-discharge of the battery.

Increasing charge current and charge saturation

It should be noted that increasing the charge current does not speed up the achievement of a full charge state. Lithium will reach peak voltage faster, but charging until the capacity is completely saturated takes longer. However, charging the battery with high current quickly increases the battery capacity to approximately 70%.

Lithium-ion batteries do not require a full charge, as is the case with lead-acid devices. Moreover, this charging option is undesirable for Li-ion. In fact, it is better to not fully charge the battery, because high voltage “stresses” the battery.

Selecting a lower voltage threshold or completely removing the saturation charge helps extend the life of the lithium-ion battery. True, this approach is accompanied by a decrease in the battery energy release time.

It should be noted here: household chargers, as a rule, operate at maximum power and do not support adjustment of the charging current (voltage).

Manufacturers of consumer lithium-ion battery chargers consider long battery life to be less important than the cost of circuit complexity.

Li-ion battery chargers

Some cheap household chargers often work using a simplified method. Charge a lithium-ion battery in one hour or less, without going to saturation charge.

The ready indicator on such devices lights up when the battery reaches the voltage threshold in the first stage. The state of charge is about 85%, which often satisfies many users.

This domestically produced charger is offered to work with different batteries, including lithium-ion batteries. The device has a voltage and current regulation system, which is already good

Professional chargers (expensive) are distinguished by the fact that they set the charging voltage threshold lower, thereby extending the life of the lithium-ion battery.

The table shows the calculated power when charging with such devices at different voltage thresholds, with and without saturation charge:

Charge voltage, V/per cell	Capacity at high voltage cut-off, %	Charging time, min	Capacity at full saturation, %
3.80	60	120	65
3.90	70	135	75
4.00	75	150	80
4.10	80	165	90
4.20	85	180	100

As soon as the lithium-ion battery begins to charge, there is a rapid increase in voltage. This behavior is comparable to lifting a load with a rubber band when there is a lag effect.

Capacity will eventually be gained when the battery is fully charged. This charge characteristic is typical for all batteries.

The higher the charging current, the brighter the rubber band effect. Low temperature or the presence of a cell with high internal resistance only enhances the effect.

The structure of a lithium-ion battery in its simplest form: 1- negative busbar made of copper; 2 — positive tire made of aluminum; 3 - cobalt oxide anode; 4- graphite cathode; 5 - electrolyte

Assessing the state of charge by reading the voltage of a charged battery is impractical. Measuring the open circuit (idle) voltage after the battery has been sitting for several hours is the best evaluation indicator.

As with other batteries, temperature affects idle speed in the same way it affects the active material of a lithium-ion battery. , laptops and other devices is estimated by counting coulombs.

Lithium-ion battery: saturation threshold

A lithium-ion battery cannot absorb excess charge. Therefore, when the battery is completely saturated, the charging current must be removed immediately.

A constant current charge can lead to metallization of lithium elements, which violates the principle of ensuring the safe operation of such batteries.

To minimize the formation of defects, you should disconnect the lithium-ion battery as quickly as possible when it reaches peak charge.

This battery will no longer take exactly as much charge as it should. Due to improper charging, it lost its main properties as an energy storage device.

As soon as the charge stops, the voltage of the lithium-ion battery begins to drop. The effect of reducing physical stress appears.

For some time, the open circuit voltage will be distributed between unevenly charged cells with a voltage of 3.70 V and 3.90 V.

Here, the process also attracts attention when a lithium-ion battery, which has received a fully saturated charge, begins to charge the neighboring one (if one is included in the circuit), which has not received a saturation charge.

When lithium-ion batteries need to be constantly kept on the charger in order to ensure their readiness, you should rely on chargers that have a short-term compensation charge function.

The flash charger turns on when the open circuit voltage drops to 4.05 V/I and turns off when the voltage reaches 4.20 V/I.

Chargers designed for hot-ready or standby operation often allow the battery voltage to drop to 4.00V/I and will only charge Li-Ion batteries to 4.05V/I rather than reaching the full 4.20V/I level.

This technique reduces physical voltage, which is inherently associated with technical voltage, and helps extend battery life.

Charging cobalt-free batteries

Traditional batteries have a nominal cell voltage of 3.60 volts. However, for devices that do not contain cobalt, the rating is different.

Thus, lithium phosphate batteries have a nominal value of 3.20 volts (charging voltage 3.65V). And new lithium titanate batteries (made in Russia) have a nominal cell voltage of 2.40V (charger voltage 2.85).

Lithium phosphate batteries are energy storage devices that do not contain cobalt in their structure. This fact somewhat changes the charging conditions for such batteries.

Traditional chargers are not suitable for such batteries, as they overload the battery with the risk of explosion. Conversely, a charging system for cobalt-free batteries will not provide sufficient charge to a traditional 3.60V lithium-ion battery.

Exceeded charge of lithium-ion battery

The lithium-ion battery operates safely within specified operating voltages. However, battery performance becomes unstable if it is charged beyond operating limits.

Long-term charging of a lithium-ion battery with a voltage above 4.30V, designed for an operating rating of 4.20V, is fraught with lithium metalization of the anode.

The cathode material, in turn, acquires the properties of an oxidizing agent, loses its stability, and releases carbon dioxide.

The pressure of the battery cell increases and if charging continues, the internal protection device will operate at a pressure between 1000 kPa and 3180 kPa.

If the pressure rise continues after this, the protective membrane opens at a pressure level of 3.450 kPa. In this state, the lithium-ion battery cell is on the verge of exploding and eventually does just that.

Structure: 1 - top cover; 2 - upper insulator; 3 - steel can; 4 - lower insulator; 5 — anode tab; 6 - cathode; 7 - separator; 8 - anode; 9 — cathode tab; 10 - vent; 11 - PTC; 12 — gasket

Triggering of the protection inside a lithium-ion battery is associated with an increase in the temperature of the internal contents. A fully charged battery has a higher internal temperature than a partially charged battery.

Therefore, lithium-ion batteries appear to be safer when charged at a low level. That is why the authorities of some countries require the use of Li-ion batteries in aircraft that are saturated with energy no more than 30% of their full capacity.

The internal battery temperature threshold at full load is:

• 130-150°C (for lithium-cobalt);
• 170-180°C (for nickel-manganese-cobalt);
• 230-250°C (for lithium manganese).

It should be noted: lithium phosphate batteries have better temperature stability than lithium manganese batteries. Lithium-ion batteries are not the only ones that pose a danger in energy overload conditions.

For example, lead-nickel batteries are also prone to melting with subsequent fire if energy saturation is carried out in violation of the passport regime.

Therefore, using chargers that are perfectly matched to the battery is of paramount importance for all lithium-ion batteries.

Some conclusions from the analysis

Charging lithium-ion batteries has a simplified procedure compared to nickel systems. The charging circuit is straightforward, with voltage and current limits.

This circuit is much simpler than a circuit that analyzes complex voltage signatures that change as the battery is used.

The energy saturation process of lithium-ion batteries allows for interruptions; these batteries do not need to be fully saturated, as is the case with lead-acid batteries.

Controller circuit for low-power lithium-ion batteries. A simple solution and a minimum of details. But the circuit does not provide cycle conditions that maintain a long service life

The properties of lithium-ion batteries promise advantages in the operation of renewable energy sources (solar panels and wind turbines). As a rule, a wind generator rarely provides a full battery charge.

For lithium-ion, the lack of steady-state charging requirements simplifies the charge controller design. A lithium-ion battery does not require a controller to equalize voltage and current, as is required by lead-acid batteries.

All household and most industrial lithium-ion chargers fully charge the battery. However, existing lithium-ion battery charging devices generally do not provide voltage regulation at the end of the cycle.