Many people probably have a problem with charging a Li-Ion battery without a controller; I had this situation. I received a dead laptop, and there were 4 SANYO UR18650A cans in the battery that were alive.
I decided to replace the LED flashlight with three AAA batteries. The question arose about charging them.
After digging around on the Internet I found a bunch of diagrams, but details are a little tight in our city.
I tried charging from a cell phone charger, the problem is in charge control, you need to constantly monitor the heating, it just starts to heat up, you need to disconnect from charging, otherwise the battery will be damaged in the best case, otherwise you can start a fire.
I decided to do it myself. I bought a bed for the battery in the store. I bought a charger at a flea market. To make it easier to track the end of the charge, it is advisable to find one with a two-color LED that signals the end of the charge. It switches from red to green when charging is complete.
But you can also use a regular one. The charger can be replaced with a USB cord and charged from a computer or charger with a USB output.
My charger is only for batteries without a controller. I took the controller from an old cell phone battery. It ensures that the battery is not overcharged above a voltage of 4.2 V, or discharged below 2...3 V. Also, the protection circuit saves from short circuits by disconnecting the bank itself from the consumer at the moment of a short circuit.
It contains the DW01 chip and an assembly of two SM8502A MOSFET transistors (M1, M2). There are also other markings, but the circuits are similar to this one and work similarly.
Cell phone battery charge controller.
Controller circuit.
Another controller circuit.
The main thing is not to confuse the polarity of soldering the controller to the bed and the controller to the charger. The controller board has “+” and “-” contacts.
It is advisable to make a clearly visible indicator in the bed near the positive contact, using red paint or self-adhesive film, to avoid polarity reversal.
I put everything together and this is what happened.
Charges great. When the voltage reaches 4.2 volts, the controller disconnects the battery from charging and the LED switches from red to green. Charging is complete. You can charge other Li-Ion batteries, just use a different bed. Good luck to all.
Initially, lithium-ion batteries were intended for mobile devices, be it phones, cameras, video cameras, laptops, but in the last decade, the production of lithium batteries has also been launched by most automakers.
Then why assemble it yourself if you can buy a ready-made battery? There are enough reasons:
- factory-assembled lithium batteries are unreasonably expensive;
- it is very difficult to find a battery of suitable dimensions for a motorcycle or car;
- If the assembled battery fits into the installation space with a margin, then it will have a lower capacity.
With your own hands, you can assemble a battery from individual elements, which will be limited only by energy density and price per watt-hour, depending on the type of elements selected:
- NiMH- nickel metal hydride;
- Li-ion- lithium ion;
- Li-pol- lithium polymer;
- LiFePO4- lithium iron phosphate;
- Lead Acid- lead-acid.
Danger of overcharging lithium cells
Lithium cells must be handled with care because they concentrate a lot of energy into a small area when fully charged. Therefore, protected Li-ion and Li-pol batteries have been on sale for a long time.
Back in 1991, Sony drew attention to the explosion hazard of Li-ion cells. Nowadays, all batteries without exception are wound with a two-layer separator between the plates to eliminate the risk of internal short circuit. All branded batteries are equipped with a field-effect transistor protection board, which turns them off in the following cases:
- The battery is excessively discharged - below 2.5 V.
- Overcharged - over 4.2 V.
- The charging current is too high - more than 1C (C is the battery capacity in Ah).
- Short circuit.
- The load current is exceeded - more than 5C.
- Incorrect polarity when charging.
For additional security, there is a thermal fuse that opens the circuit when the lithium element overheats above 90 °C.
How to find a battery with protection?
Lithium batteries are produced in household and technological versions. Batteries for household use have a durable plastic case and built-in electronic protection. Technological elements intended for industrial use are most often produced in an unframed form and do not have built-in protection.
- Protected batteries have the word " protected" in the title, unprotected - " unprotected».
- Batteries with protection are 2–3 mm longer than regular ones due to the board, which is installed at the end near the negative pole.
- The price of batteries with protection for the same capacity is always higher, because the board with electronic components also costs money.
The positive pole of the battery must be connected to the protective board with a thin plate, otherwise the protection will not work.
When individual elements are connected in series, their voltages are summed, but the capacitance remains the same. Even from the same series, batteries have different characteristics, so they charge at different speeds. For example, when charging to a total voltage of 12.6 V, the element in the middle can overcharge to 4.4 V, which is dangerous due to overheating.
To prevent excessive overcharging of unprotected elements, balancing cables are used that are connected to special chargers, for example: iMAX B6 and Turnigy Accucel-6.
Each Li-ion and Li-pol rechargeable battery for household use has the most advanced surge protection in the form of a voltage control circuit, a field-effect transistor switch and a thermal fuse.
Balancing of the protected elements is not required, since if the voltage on any of them increases to 4.2 V, charging is guaranteed to be interrupted.
When assembling a battery from cells without protection, there is a way out - install one voltage control board for all batteries, for example, connecting them according to the 4S2P circuit - 4 in series, 2 in parallel.
There is also no need to balance parallel connected elements.
When batteries are connected in parallel, their voltage remains the same, and their capacities are summed up.
About the capacity of lithium batteries
Capacity is the ability of a battery to deliver current, measured in milliampere hour (mAh) or ampere hour (Ah). For example, a battery with a capacity of 2 Ah can deliver a current of 2 A for one hour, or 1 A for two hours. But this dependence of the current on the load connection time is not linear - at a certain point in the graph, when the current doubles, the battery operating time decreases fourfold. Therefore, manufacturers always indicate the capacity calculated when the battery is discharged with an excessively low current of 100 mA.
The amount of energy depends on the battery voltage, so nickel metal hydride cells with the same capacity have 3 times less energy intensity than lithium ion ones:
- NiMH- 1.2 V * 2.2 Ah = 2.64 watt-hours;
- Li-ion- 3.7 V * 2.2 Ah = 8.14 watt-hours.
When searching for and purchasing rechargeable batteries, give preference to well-known companies such as Samsung, Sony, Sanyo, Panasonic. The batteries from these manufacturers have a capacity that most closely matches that indicated on their case. The inscription 2600 mA on Sanyo elements is not much different from their real capacity of 2500–2550 mA. Counterfeits from Chinese manufacturers with a vaunted capacity of 4200 mA do not even reach 1000 mA, but their price is half as much as the Japanese originals.
To assemble a battery from lithium batteries, you can use:
- soldering;
- junction boxes;
- Neodymium magnets;
Soldering during factory assembly is used extremely rarely, since the lithium element is destroyed by heat, losing part of its capacity. On the other hand, at home, soldering will be the optimal way to connect batteries, since even minimal resistance at the contacts will significantly reduce the total voltage at the common terminals. You need to use a powerful 100 W soldering iron and touch the lithium batteries for no more than two seconds.
Powerful rare earth magnets are coated with a layer of nickel or zinc, so their surface does not oxidize. These magnets provide excellent contact between the batteries. If you want to solder wires to a magnet, do not forget about the Curie temperature, above which any magnet becomes a pebble. The approximate permissible temperature for magnets is 300°C.
If you use a box to connect batteries, then a big advantage becomes obvious, since it will be easier to select batteries by voltage or change a damaged element.
Spot welding is the best method for joining lithium cells when assembling laptop batteries.
It is not profitable to buy a ready-made lithium battery for a car or motorcycle when you can assemble it yourself for a lower price. You can save up to $70 if you don't buy a new laptop battery and replace the cells yourself.
It is difficult to judge savings when assembling powerful lithium batteries to power electric vehicles or autonomous power supply systems at home, since in these cases there are additional costs for control and monitoring equipment.
You may also be interested
- And now to the point:
Regarding the capacity. I understand that if the motor does not pull, for example, up a hill, then it produces a short circuit current. The motor will not burn out because thick wires are wound in it.
But how do you find out what maximum current it produces? And how long will its winding inside withstand this current?
Judging by your letter, you are a highly educated person, at least in the physical sciences, but I am an excellent student at school and institute and now I don’t remember the basics. Treat this fact with understanding - sclerosis is senile. Although I consider myself smart!!!
The questions posed above are aimed at answering the main question - how will it be correct (without the risk of burning the AK) to operate the motor and battery when driving on any terrain (I mean big and small climbs)
I understand this: if I turn off the AK with a toggle switch in a timely manner, and drive the bike up the hill manually. then nothing will happen! How to recognize this moment?
Perhaps there is a special device that signals a high current, or a thermal relay that clearly, I emphasize clearly, turns off the AC?
- And now to the point:
I wrote an email, no response. Perhaps because I typed in the address manually, since copying is not supported on the site.
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Good day
As you asked, I emailed a question from the site, I decided to add a screw to the question, which really needs to be redone, since the charger burned out and it’s sitting idle, help me change Ni-Cd to Li-Ion, also remake chargers or create new ones .
For brevity, I’ll write it like this:
'1o'. Screwdriver “practyl”, battery consists of Ni-Cd 1.2V, 600 mAh – 3 pcs.'2o'. Ermak screwdriver, battery consists of Ni-Cd 1.2V, 600 mAh – 4 pcs.
‘3sh’. Screw “defort”, battery consists of Ni-Cd 1.2V, SC 1200 mAh – 15 pcs.
Accordingly, all akumas are attached in series.
I want to make 3 lithiums in parallel in '1o', it clearly works out: 1.2v * 3 = 3.6v Ni-Cd is just 3.7v Li-Ion, but not 600 mAh, but as much as Li-Ion * 3 mAh . I think this should be cool.
In '2o' it is more difficult: there 1.2v * 4 = 4.8v, Li-Ion 3.7v. It may turn weaker, but the capacity of 4 lithium batteries should cover this drawback (probably). At least I couldn’t think of another modification option, I’ll be glad for ideas and advice.
Now the most interesting thing: I’ve seen a lot of ‘3sh’ alterations, they all almost contradict each other (they offer a board for assembly, others show photos of these burnt boards, a bunch of other things, a sea of disputes on the same issues). Here it turns out that we change 1.2V*15=18V Ni-Cd to (3.7V*5=18.5V Li-Ion)*2 - we get an increased volume, there is enough space in the battery. You need to make a new charger yourself, I think on the basis of the old one (throwing out everything from it and replacing it with new blocks, boards, transceivers and whatever else is needed), because the old one burned out.
Now the most important thing is why I described all this, you understand and can really help, this can be seen from the answers to any questions posed to you, I hope for you:
‘1o’ what kind of board should I buy to have all the protections on it (overcharge/discharge/heating short-circuit and what else should be there)? Does the charger need to be rebuilt? If so, what is needed for this?
‘2o’ all the questions are the same as in ‘1o’, perhaps the idea and advice can be remade differently. I plan to use the charger from ‘1o’ if modification is needed and if it fits.
‘3sh’ what parameters of the board should be for 10 Li-Ion barrels connected according to circuit 5 in series, and each of them is paralleled with the same one? What kind of board is placed in the box of the charger itself, ideally with a pair or three LEDs that would show: on, charging, charged?If it is possible in response to attach links to Ali Express or eBay to all the necessary boards, I would be very grateful (I ask because there are a lot of them out there, they are very similar, but upon closer examination, they are very different. Besides, I’m not really into boards I understand nothing. Solder correctly, package beautifully - I can do that)
PHOTOS
Nowadays lithium batteries are gaining more and more popularity. Especially finger ones, like 18650 , at 3.7 V 3000 mA. I have no doubt that in another 3-5 years they will completely replace nickel-cadmium. True, the question about their charging remains open. If everything is clear with old batteries - collect them in a battery and through a resistor to any suitable power supply, then this trick does not work here. But how then can you charge several pieces at once without using expensive branded balancing chargers?
Theory
To connect batteries in series, usually the positive terminal of the first battery in series is connected to the positive terminal of the electrical circuit. The positive terminal of the second battery is connected to its negative terminal, etc. The negative terminal of the last battery is connected to the negative terminal of the unit. The resulting battery in series connection has the same capacity as a single battery, and the voltage of such a battery is equal to the sum of the voltages of the batteries included in it. This means that if the batteries have the same voltage, then the battery voltage is equal to the voltage of one battery multiplied by the number of batteries in the battery.
The energy accumulated in the battery is equal to the sum of the energies of the individual batteries (the product of the energies of the individual batteries, if the batteries are the same), regardless of whether the batteries are connected in parallel or in series.
Lithium-ion batteries cannot simply be connected to a power supply unit - the charging currents on each element (bank) must be equalized. Balancing is carried out when charging the battery, when there is a lot of energy and it can not be saved much, and therefore, without any significant losses, you can use the passive dissipation of “excess” electricity.
Nickel-cadmium batteries do not require additional systems, since each link, when its maximum charge voltage is reached, stops receiving energy. Signs of a Ni-Cd being fully charged are an increase in voltage to a certain value, and then a drop of several tens of millivolts, and an increase in temperature - so that the excess energy immediately turns into heat.
The opposite is true for lithium batteries. Discharging to low voltages causes chemical degradation and irreversible damage to the element, with an increase in internal resistance. In general, they are not protected from overcharging, and you can waste a lot of extra energy, thereby dramatically reducing their service life.
If we connect several lithium cells in a row and feed them through clamps at both ends of the block, then we cannot control the charge of individual cells. It is enough that one of them will have a slightly higher resistance or a slightly lower capacitance, and this link will reach a charge voltage of 4.2 V much faster, while the rest will still have 4.1 V. And when the voltage of the entire package reaches charge voltage, it may be that these weak links are charged to 4.3 Volts or even more. With each such cycle, the parameters will deteriorate. In addition, Li-Ion is unstable and, if overloaded, can reach a high temperature and, consequently, explode.
Most often, a device called a “balancer” is installed at the output of the charging voltage source. The simplest type of balancer is a voltage limiter. It is a comparator that compares the voltage on the Li-Ion bank with a threshold value of 4.20 V. Upon reaching this value, a powerful transistor switch is opened, connected in parallel to the element, passing most of the charge current through itself and converting the energy into heat. In this case, the can itself receives an extremely small part of the current, which practically stops its charge, allowing its neighbors to recharge. The voltage equalization on the battery cells with such a balancer occurs only at the end of the charge when the elements reach a threshold value.
Simplified diagram of a balancer for a battery
Here is a simplified circuit diagram of a current balancer based on the TL431. Resistors R1 and R2 set the voltage to 4.20 Volts, or you can choose others depending on the type of battery. The reference voltage for the regulator is removed from the transistor, and already at the border of 4.20 V, the system will begin to open the transistor slightly to prevent exceeding the specified voltage. A minimal increase in voltage will cause the transistor current to increase very quickly. During tests, already at 4.22 V (an increase of 20 mV), the current was more than 1 A.
In principle, any PNP transistor operating in the range of voltages and currents that interests us is suitable here. If the batteries are to be charged with a current of 500 mA. The calculation of its power is simple: 4.20 V x 0.5 A = 2.1 V, and this is how much the transistor must lose, which will probably require some cooling. For a charging current of 1 A or more, the power loss increases accordingly, and it will become increasingly difficult to get rid of the heat. During the test, several different transistors were tested, in particular BD244C, 2N6491 and A1535A - they all behave the same.
The voltage divider R1 and R2 should be selected so as to obtain the desired clamping voltage. For convenience, here are a few values, after applying which we will get the following results:
- R1 + R2 = Vo
- 22K + 33K = 4.166 V
- 15K + 22K = 4.204 V
- 47K + 68K = 4.227 V
- 27K + 39K = 4.230 V
- 39K + 56K = 4.241 V
- 33K + 47K = 4.255 V
This is an analogue of a powerful zener diode loaded with a low-resistance load, the role of which here is played by diodes D2...D5. Microcircuit D1 measures the voltage at the plus and minus of the battery and if it rises above the threshold, it opens a powerful transistor, passing all the current from the charger through itself. How all this is connected together and to the power supply - see below.
The blocks turn out to be really small, and you can safely install them directly on the element. You just need to keep in mind that the potential of the negative pole of the battery arises on the transistor body, and you must be careful when installing common radiator systems - you must use insulation of the transistor bodies from each other.
Tests
Immediately 6 pieces of balancing blocks were needed to simultaneously charge 6 18650 batteries. The elements are visible in the photo below.
All elements were charged exactly to 4.20 volts (the voltage was set by potentiometers), and the transistors became hot, although there was no additional cooling - charging with a current of 500 mA. Thus, we can safely recommend this method for simultaneous charging of several lithium batteries from a common voltage source.
Discuss the article SIMULTANEOUS CHARGING OF SEVERAL BATTERIES
In this article, a DIYer will guide us through all stages of battery assembly, from material selection to final assembly. RC toys, laptop batteries, medical devices, electric bicycles and even electric cars use 18650 batteries.
18650 battery (18*65mm) is the size of lithium ion battery. For comparison, regular AA batteries have a size of 14*50 mm. The author made this particular assembly to replace the lead-acid battery in a homemade product he had previously made.
Video:
Tools and materials:
- ;
- ;
- ;
- ;
-Switch;
-Connector;
- ;
-Screws 3M x 10mm;
- Spot resistance welding machine;
-3D printer;
-Stripper (insulation stripping tool);
- Hairdryer;
-Multimeter;
-Charger for lithium-ion batteries;
-Protective glasses;
-Dielectric gloves;
Some tools can be replaced with more affordable ones.
Step one: choosing batteries
The first step is to choose the right batteries. There are different batteries on the market ranging from $1 to $10. According to the author, the best batteries are from Panasonic, Samsung, Sanyo and LG. They are more expensive than others, but have proven themselves to be of good quality and performance.
The author does not recommend buying batteries with the names Ultrafire, Surefire and Trustfire. These are batteries that did not pass quality control at the factory and were purchased at a bargain price and repackaged under a new name. As a rule, such batteries do not have the declared capacity and there is a risk of fire during charging and discharging.
For his homemade product, the master used Panasonic batteries with a capacity of 3400 mAh.
Step Two: Selecting Nickel Strip
Nickel strips are needed to connect the battery. There are two products on the market: nickel plated metal and nickel strips. The author recommends using nickel strips. They are more expensive, but have low resistance and therefore heat up less, which affects the life of the batteries.
Step Three: Spot Welding or Soldering
There are two methods for connecting batteries: soldering and spot welding. The best choice is spot welding. When spot welding, the battery does not overheat. But a welding machine (like the author’s) costs approx. 12 t.r. in a foreign online store and approx. 20 t.r. in a Russian online store. The author himself uses welding, but has prepared several recommendations for soldering.
When soldering, keep contact between the soldering iron and the battery to a minimum. It is better to use a powerful soldering iron (from 80 W) and quickly solder than to heat up the solder area.
Step Four: Check the Batteries
Before connecting the batteries, you need to check each of them separately. The voltage on the batteries should be approximately the same. New high-quality batteries have a voltage of 3.5 V - 3.7 V. Such batteries can be connected, but it is better to equalize the voltage using a charger. For used batteries, the voltage difference will be even greater.
Step five: battery calculation
For the project, the master needs a battery with a voltage of 11.1 V and a capacity of 17,000 mAh.
The 18650 battery capacity is 3400 mAh. When connecting five batteries in parallel, we get a capacity of 17,000 mAh. Such a compound is designated P, in this case 5P
One battery has a voltage of 3.7 V. To get 11.1 V, you need to connect three batteries in series. Designation S, in this case 3S.
So, to obtain the necessary parameters, you need three sections, each consisting of five parallel-connected batteries, connected in series. Package 3S5P.
Step Six: Battery Assembly
To assemble the battery, the master uses special plastic cells. Plastic cells have a number of advantages over connecting them, for example, using a glue gun.
1.Easy assembly of any quantity.
2. There is space between the batteries for ventilation.
3. Vibration and impact resistance.
Collects two 3*5 cells. Installs, in the cell, the first package of 5S batteries with the plus side up, the next five with the minus side up, and the last five batteries again with the plus side up (see photo).
Places the second cell on top.
Step seven: welding
Cuts four nickel strips for parallel connection, with a margin of 10 mm. Cuts ten strips for serial connection.
Places a long strip on the + contacts of the first (when turned over, it will remain the first) parallel 5P cell. Welds the strip. Welds the strips with one end to the + of the third cell and the other to the - second. Welds a long strip to the + third cell (on top of the plates). Flips the block. He welds the plates on the reverse side, taking into account that we are now connecting the third section in parallel, and the first and second sections in parallel and in series (considering that it has been turned upside down).
Step Eight: BMS (Battery Management System)
First, let's understand a little what BMS is.
BMS (Battery Management System) is an electronic board that is installed on the battery to control the process of its charge/discharge, monitor the condition of the battery and its elements, control temperature, the number of charge/discharge cycles, and protect the components of the battery. The control and balancing system provides individual control of the voltage and resistance of each battery element, distributes currents between the components of the battery during the charging process, controls the discharge current, determines the loss of capacity from imbalance, and guarantees safe connection/disconnection of the load.
Based on the received data, the BMS performs cell charge balancing, protects the battery from short circuit, overcurrent, overcharge, overdischarge (high and excessively low voltage of each cell), overheating and hypothermia. The BMS functionality allows not only to improve the operation of batteries, but also to maximize their service life.
Important parameters of the board are the number of cells in a row, in this case 3S, and the maximum discharge current, in this case 25 A. For this project, the master used board with the following parameters:
Model: HX-3S-FL25A-A
Overvoltage range: 4.25~4.35V±0.05V
Discharge voltage range: 2.3~3.0V±0.05V
Maximum operating current: 0~25A
Operating temperature: -40℃~+50℃
Solders the board to the ends of the battery according to the diagram.
Assessing the characteristics of a particular charger is difficult without understanding how an exemplary charge of a li-ion battery should actually proceed. Therefore, before moving directly to the diagrams, let's remember a little theory.
What are lithium batteries?
Depending on what material the positive electrode of a lithium battery is made of, there are several varieties:
- with lithium cobaltate cathode;
- with a cathode based on lithiated iron phosphate;
- based on nickel-cobalt-aluminium;
- based on nickel-cobalt-manganese.
All of these batteries have their own characteristics, but since these nuances are not of fundamental importance for the general consumer, they will not be considered in this article.
Also, all li-ion batteries are produced in various sizes and form factors. They can be either cased (for example, the popular 18650 today) or laminated or prismatic (gel-polymer batteries). The latter are hermetically sealed bags made of a special film, which contain electrodes and electrode mass.
The most common sizes of li-ion batteries are shown in the table below (all of them have a nominal voltage of 3.7 volts):
| Designation | Standard size | Similar size |
|---|---|---|
| XXYY0, Where XX- indication of diameter in mm, YY- length value in mm, 0 - reflects the design in the form of a cylinder |
10180 | 2/5 AAA |
| 10220 | 1/2 AAA (Ø corresponds to AAA, but half the length) | |
| 10280 | ||
| 10430 | AAA | |
| 10440 | AAA | |
| 14250 | 1/2 AA | |
| 14270 | Ø AA, length CR2 | |
| 14430 | Ø 14 mm (same as AA), but shorter length | |
| 14500 | AA | |
| 14670 | ||
| 15266, 15270 | CR2 | |
| 16340 | CR123 | |
| 17500 | 150S/300S | |
| 17670 | 2xCR123 (or 168S/600S) | |
| 18350 | ||
| 18490 | ||
| 18500 | 2xCR123 (or 150A/300P) | |
| 18650 | 2xCR123 (or 168A/600P) | |
| 18700 | ||
| 22650 | ||
| 25500 | ||
| 26500 | WITH | |
| 26650 | ||
| 32650 | ||
| 33600 | D | |
| 42120 |
Internal electrochemical processes proceed in the same way and do not depend on the form factor and design of the battery, so everything said below applies equally to all lithium batteries.
How to properly charge lithium-ion batteries
The most correct way to charge lithium batteries is to charge in two stages. This is the method Sony uses in all of its chargers. Despite a more complex charge controller, this ensures a more complete charge of li-ion batteries without reducing their service life.
Here we are talking about a two-stage charge profile for lithium batteries, abbreviated as CC/CV (constant current, constant voltage). There are also options with pulse and step currents, but they are not discussed in this article. You can read more about charging with pulsed current.
So, let's look at both stages of charging in more detail.
1. At the first stage A constant charging current must be ensured. The current value is 0.2-0.5C. For accelerated charging, it is allowed to increase the current to 0.5-1.0C (where C is the battery capacity).
For example, for a battery with a capacity of 3000 mAh, the nominal charge current at the first stage is 600-1500 mA, and the accelerated charge current can be in the range of 1.5-3A.
To ensure a constant charging current of a given value, the charger circuit must be able to increase the voltage at the battery terminals. In fact, at the first stage the charger works as a classic current stabilizer.
Important: If you plan to charge batteries with a built-in protection board (PCB), then when designing the charger circuit you need to make sure that the open circuit voltage of the circuit can never exceed 6-7 volts. Otherwise, the protection board may be damaged.
At the moment when the voltage on the battery rises to 4.2 volts, the battery will gain approximately 70-80% of its capacity (the specific capacity value will depend on the charging current: with accelerated charging it will be a little less, with a nominal charge - a little more). This moment marks the end of the first stage of charging and serves as a signal for the transition to the second (and final) stage.
2. Second charge stage- this is charging the battery with a constant voltage, but a gradually decreasing (falling) current.
At this stage, the charger maintains a voltage of 4.15-4.25 volts on the battery and controls the current value.
As the capacity increases, the charging current will decrease. As soon as its value decreases to 0.05-0.01C, the charging process is considered complete.
An important nuance of the correct charger operation is its complete disconnection from the battery after charging is complete. This is due to the fact that for lithium batteries it is extremely undesirable for them to remain under high voltage for a long time, which is usually provided by the charger (i.e. 4.18-4.24 volts). This leads to accelerated degradation of the chemical composition of the battery and, as a consequence, a decrease in its capacity. Long-term stay means tens of hours or more.
During the second stage of charging, the battery manages to gain approximately 0.1-0.15 more of its capacity. The total battery charge thus reaches 90-95%, which is an excellent indicator.
We looked at two main stages of charging. However, coverage of the issue of charging lithium batteries would be incomplete if another charging stage were not mentioned - the so-called. precharge.
Preliminary charge stage (precharge)- this stage is used only for deeply discharged batteries (below 2.5 V) to bring them to normal operating mode.
At this stage, the charge is provided with a reduced constant current until the battery voltage reaches 2.8 V.
The preliminary stage is necessary to prevent swelling and depressurization (or even explosion with fire) of damaged batteries that have, for example, an internal short circuit between the electrodes. If a large charge current is immediately passed through such a battery, this will inevitably lead to its heating, and then it depends.
Another benefit of precharging is pre-heating the battery, which is important when charging at low ambient temperatures (in an unheated room during the cold season).
Intelligent charging should be able to monitor the voltage on the battery during the preliminary charging stage and, if the voltage does not rise for a long time, draw a conclusion that the battery is faulty.
All stages of charging a lithium-ion battery (including the pre-charge stage) are schematically depicted in this graph: 
Exceeding the rated charging voltage by 0.15V can reduce the battery life by half. Lowering the charge voltage by 0.1 volt reduces the capacity of a charged battery by about 10%, but significantly extends its service life. The voltage of a fully charged battery after removing it from the charger is 4.1-4.15 volts.
Let me summarize the above and outline the main points:
1. What current should I use to charge a li-ion battery (for example, 18650 or any other)?
The current will depend on how quickly you would like to charge it and can range from 0.2C to 1C.
For example, for a battery size 18650 with a capacity of 3400 mAh, the minimum charge current is 680 mA, and the maximum is 3400 mA.
2. How long does it take to charge, for example, the same 18650 batteries?
The charging time directly depends on the charging current and is calculated using the formula:
T = C / I charge.
For example, the charging time of our 3400 mAh battery with a current of 1A will be about 3.5 hours.
3. How to properly charge a lithium polymer battery?
All lithium batteries charge the same way. It doesn't matter whether it is lithium polymer or lithium ion. For us, consumers, there is no difference.
What is a protection board?
The protection board (or PCB - power control board) is designed to protect against short circuit, overcharge and overdischarge of the lithium battery. As a rule, overheating protection is also built into the protection modules.
For safety reasons, it is prohibited to use lithium batteries in household appliances unless they have a built-in protection board. That's why all cell phone batteries always have a PCB board. The battery output terminals are located directly on the board: 
These boards use a six-legged charge controller on a specialized device (JW01, JW11, K091, G2J, G3J, S8210, S8261, NE57600 and other analogues). The task of this controller is to disconnect the battery from the load when the battery is completely discharged and disconnect the battery from charging when it reaches 4.25V.
Here, for example, is a diagram of the BP-6M battery protection board that was supplied with old Nokia phones: 
If we talk about 18650, they can be produced either with or without a protection board. The protection module is located near the negative terminal of the battery. 
The board increases the length of the battery by 2-3 mm. 
Batteries without a PCB module are usually included in batteries that come with their own protection circuits.
Any battery with protection can easily turn into a battery without protection; you just need to gut it. 
Today, the maximum capacity of the 18650 battery is 3400 mAh. Batteries with protection must have a corresponding designation on the case ("Protected"). 
Do not confuse the PCB board with the PCM module (PCM - power charge module). If the former serve only the purpose of protecting the battery, then the latter are designed to control the charging process - they limit the charge current at a given level, control the temperature and, in general, ensure the entire process. The PCM board is what we call a charge controller.
I hope now there are no questions left, how to charge an 18650 battery or any other lithium battery? Then we move on to a small selection of ready-made circuit solutions for chargers (the same charge controllers).
Charging schemes for li-ion batteries
All circuits are suitable for charging any lithium battery; all that remains is to decide on the charging current and the element base.
LM317
Diagram of a simple charger based on the LM317 chip with a charge indicator: 
The circuit is the simplest, the whole setup comes down to setting the output voltage to 4.2 volts using trimming resistor R8 (without a connected battery!) and setting the charging current by selecting resistors R4, R6. The power of resistor R1 is at least 1 Watt.
As soon as the LED goes out, the charging process can be considered completed (the charging current will never decrease to zero). It is not recommended to keep the battery on this charge for a long time after it is fully charged.
The lm317 microcircuit is widely used in various voltage and current stabilizers (depending on the connection circuit). It is sold on every corner and costs pennies (you can take 10 pieces for only 55 rubles).
LM317 comes in different housings: 
Pin assignment (pinout): 
Analogues of the LM317 chip are: GL317, SG31, SG317, UC317T, ECG1900, LM31MDT, SP900, KR142EN12, KR1157EN1 (the last two are domestically produced).
The charging current can be increased to 3A if you take LM350 instead of LM317. It will, however, be more expensive - 11 rubles/piece.
The printed circuit board and circuit assembly are shown below: 
The old Soviet transistor KT361 can be replaced with a similar pnp transistor (for example, KT3107, KT3108 or bourgeois 2N5086, 2SA733, BC308A). It can be removed altogether if the charge indicator is not needed.
Disadvantage of the circuit: the supply voltage must be in the range of 8-12V. This is due to the fact that for normal operation of the LM317 chip, the difference between the battery voltage and the supply voltage must be at least 4.25 Volts. Thus, it will not be possible to power it from the USB port.
MAX1555 or MAX1551
MAX1551/MAX1555 are specialized chargers for Li+ batteries, capable of operating from USB or from a separate power adapter (for example, a phone charger).
The only difference between these microcircuits is that MAX1555 produces a signal to indicate the charging process, and MAX1551 produces a signal that the power is on. Those. 1555 is still preferable in most cases, so 1551 is now difficult to find on sale.
A detailed description of these microcircuits from the manufacturer is.
The maximum input voltage from the DC adapter is 7 V, when powered by USB - 6 V. When the supply voltage drops to 3.52 V, the microcircuit turns off and charging stops.
The microcircuit itself detects at which input the supply voltage is present and connects to it. If the power is supplied via the USB bus, then the maximum charging current is limited to 100 mA - this allows you to plug the charger into the USB port of any computer without fear of burning the south bridge.
When powered by a separate power supply, the typical charging current is 280 mA.
The chips have built-in overheating protection. But even in this case, the circuit continues to operate, reducing the charge current by 17 mA for each degree above 110 ° C.
There is a pre-charge function (see above): as long as the battery voltage is below 3V, the microcircuit limits the charge current to 40 mA.
The microcircuit has 5 pins. Here is a typical connection diagram: 
If there is a guarantee that the voltage at the output of your adapter cannot under any circumstances exceed 7 volts, then you can do without the 7805 stabilizer.
The USB charging option can be assembled, for example, on this one. 
The microcircuit does not require either external diodes or external transistors. In general, of course, gorgeous little things! Only they are too small and inconvenient to solder. And they are also expensive ().
LP2951
The LP2951 stabilizer is manufactured by National Semiconductors (). It provides the implementation of a built-in current limiting function and allows you to generate a stable charge voltage level for a lithium-ion battery at the output of the circuit.
The charge voltage is 4.08 - 4.26 volts and is set by resistor R3 when the battery is disconnected. The voltage is kept very precisely.
The charge current is 150 - 300mA, this value is limited by the internal circuits of the LP2951 chip (depending on the manufacturer).
Use the diode with a small reverse current. For example, it can be any of the 1N400X series that you can purchase. The diode is used as a blocking diode to prevent reverse current from the battery into the LP2951 chip when the input voltage is turned off. 
This charger produces a fairly low charging current, so any 18650 battery can charge overnight.
The microcircuit can be purchased both in a DIP package and in a SOIC package (costs about 10 rubles per piece).
MCP73831
The chip allows you to create the right chargers, and it’s also cheaper than the much-hyped MAX1555. 
A typical connection diagram is taken from: 
An important advantage of the circuit is the absence of low-resistance powerful resistors that limit the charge current. Here the current is set by a resistor connected to the 5th pin of the microcircuit. Its resistance should be in the range of 2-10 kOhm.
The assembled charger looks like this: 
The microcircuit heats up quite well during operation, but this does not seem to bother it. It fulfills its function.
Here is another version of a printed circuit board with an SMD LED and a micro-USB connector: 
LTC4054 (STC4054)
Very simple scheme, great option! Allows charging with current up to 800 mA (see). True, it tends to get very hot, but in this case the built-in overheating protection reduces the current. 
The circuit can be significantly simplified by throwing out one or even both LEDs with a transistor. Then it will look like this (you must admit, it couldn’t be simpler: a couple of resistors and one condenser): 
One of the printed circuit board options is available at . The board is designed for elements of standard size 0805.
I=1000/R. You shouldn’t set a high current right away; first see how hot the microcircuit gets. For my purposes, I took a 2.7 kOhm resistor, and the charge current turned out to be about 360 mA.
It is unlikely that it will be possible to adapt a radiator to this microcircuit, and it is not a fact that it will be effective due to the high thermal resistance of the crystal-case junction. The manufacturer recommends making the heat sink “through the leads” - making the traces as thick as possible and leaving the foil under the chip body. In general, the more “earth” foil left, the better.
By the way, most of the heat is dissipated through the 3rd leg, so you can make this trace very wide and thick (fill it with excess solder). 
The LTC4054 chip package may be labeled LTH7 or LTADY.
LTH7 differs from LTADY in that the first can lift a very low battery (on which the voltage is less than 2.9 volts), while the second cannot (you need to swing it separately).
The chip turned out to be very successful, so it has a bunch of analogues: STC4054, MCP73831, TB4054, QX4054, TP4054, SGM4054, ACE4054, LP4054, U4054, BL4054, WPM4054, IT4504, Y1880, PT6102, PT6181, VS6102 , HX6001, LC6000, LN5060, CX9058, EC49016, CYT5026, Q7051. Before using any of the analogues, check the datasheets.
TP4056
The microcircuit is made in a SOP-8 housing (see), it has a metal heat sink on its belly that is not connected to the contacts, which allows for more efficient heat removal. Allows you to charge the battery with a current of up to 1A (the current depends on the current-setting resistor). 
The connection diagram requires the bare minimum of hanging elements: 
The circuit implements the classical charging process - first charging with a constant current, then with a constant voltage and a falling current. Everything is scientific. If you look at charging step by step, you can distinguish several stages:
- Monitoring the voltage of the connected battery (this happens all the time).
- Precharge phase (if the battery is discharged below 2.9 V). Charge with a current of 1/10 from the one programmed by the resistor R prog (100 mA at R prog = 1.2 kOhm) to a level of 2.9 V.
- Charging with a maximum constant current (1000 mA at R prog = 1.2 kOhm);
- When the battery reaches 4.2 V, the voltage on the battery is fixed at this level. A gradual decrease in the charging current begins.
- When the current reaches 1/10 of the one programmed by the resistor R prog (100 mA at R prog = 1.2 kOhm), the charger turns off.
- After charging is complete, the controller continues monitoring the battery voltage (see point 1). The current consumed by the monitoring circuit is 2-3 µA. After the voltage drops to 4.0V, charging starts again. And so on in a circle.
The charge current (in amperes) is calculated by the formula I=1200/R prog. The permissible maximum is 1000 mA.
A real charging test with a 3400 mAh 18650 battery is shown in the graph: 
The advantage of the microcircuit is that the charge current is set by just one resistor. Powerful low-resistance resistors are not required. Plus there is an indicator of the charging process, as well as an indication of the end of charging. When the battery is not connected, the indicator blinks every few seconds.
The supply voltage of the circuit should be within 4.5...8 volts. The closer to 4.5V, the better (so the chip heats up less).
The first leg is used to connect a temperature sensor built into the lithium-ion battery (usually the middle terminal of a cell phone battery). If the output voltage is below 45% or above 80% of the supply voltage, charging is suspended. If you don't need temperature control, just plant that foot on the ground.
Attention! This circuit has one significant drawback: the absence of a battery reverse polarity protection circuit. In this case, the controller is guaranteed to burn out due to exceeding the maximum current. In this case, the supply voltage of the circuit directly goes to the battery, which is very dangerous.
The signet is simple and can be done in an hour on your knee. If time is of the essence, you can order ready-made modules. Some manufacturers of ready-made modules add protection against overcurrent and overdischarge (for example, you can choose which board you need - with or without protection, and with which connector). 
You can also find ready-made boards with a contact for a temperature sensor. Or even a charging module with several parallel TP4056 microcircuits to increase the charging current and with reverse polarity protection (example).
LTC1734
Also a very simple scheme. The charging current is set by resistor R prog (for example, if you install a 3 kOhm resistor, the current will be 500 mA).
Microcircuits are usually marked on the case: LTRG (they can often be found in old Samsung phones). 
Any pnp transistor is suitable, the main thing is that it is designed for a given charging current.
There is no charge indicator on the indicated diagram, but on the LTC1734 it is said that pin “4” (Prog) has two functions - setting the current and monitoring the end of the battery charge. For example, a circuit with control of the end of charge using the LT1716 comparator is shown. 
The LT1716 comparator in this case can be replaced with a cheap LM358.
TL431 + transistor
It is probably difficult to come up with a circuit using more affordable components. The most difficult thing here is to find the TL431 reference voltage source. But they are so common that they are found almost everywhere (rarely does a power source do without this microcircuit). 
Well, the TIP41 transistor can be replaced with any other one with a suitable collector current. Even the old Soviet KT819, KT805 (or less powerful KT815, KT817) will do.
Setting up the circuit comes down to setting the output voltage (without a battery!!!) using a trim resistor at 4.2 volts. Resistor R1 sets the maximum value of the charging current.
This circuit fully implements the two-stage process of charging lithium batteries - first charging with direct current, then moving to the voltage stabilization phase and smoothly reducing the current to almost zero. The only drawback is the poor repeatability of the circuit (it is capricious in setup and demanding on the components used).
MCP73812
There is another undeservedly neglected microcircuit from Microchip - MCP73812 (see). Based on it, a very budget charging option is obtained (and inexpensive!). The whole body kit is just one resistor!
By the way, the microcircuit is made in a solder-friendly package - SOT23-5. 
The only negative is that it gets very hot and there is no charge indication. It also somehow doesn’t work very reliably if you have a low-power power source (which causes a voltage drop). 
In general, if the charge indication is not important for you, and a current of 500 mA suits you, then the MCP73812 is a very good option.
NCP1835
A fully integrated solution is offered - NCP1835B, providing high stability of the charging voltage (4.2 ±0.05 V).
Perhaps the only drawback of this microcircuit is its too miniature size (DFN-10 case, size 3x3 mm). Not everyone can provide high-quality soldering of such miniature elements. 
Among the undeniable advantages I would like to note the following:
- Minimum number of body parts.
- Possibility of charging a completely discharged battery (precharge current 30 mA);
- Determining the end of charging.
- Programmable charging current - up to 1000 mA.
- Charge and error indication (capable of detecting non-chargeable batteries and signaling this).
- Protection against long-term charging (by changing the capacitance of the capacitor C t, you can set the maximum charging time from 6.6 to 784 minutes).
The cost of the microcircuit is not exactly cheap, but also not so high (~$1) that you can refuse to use it. If you are comfortable with a soldering iron, I would recommend choosing this option.
A more detailed description is in.
Can I charge a lithium-ion battery without a controller?
Yes, you can. However, this will require close control of the charging current and voltage.
In general, it will not be possible to charge a battery, for example, our 18650, without a charger. You still need to somehow limit the maximum charge current, so at least the most primitive memory will still be required.
The simplest charger for any lithium battery is a resistor connected in series with the battery: 
The resistance and power dissipation of the resistor depend on the voltage of the power source that will be used for charging.
As an example, let's calculate a resistor for a 5 Volt power supply. We will charge an 18650 battery with a capacity of 2400 mAh.
So, at the very beginning of charging, the voltage drop across the resistor will be:
U r = 5 - 2.8 = 2.2 Volts
Let's say our 5V power supply is rated for a maximum current of 1A. The circuit will consume the highest current at the very beginning of the charge, when the voltage on the battery is minimal and amounts to 2.7-2.8 Volts.
Attention: these calculations do not take into account the possibility that the battery may be very deeply discharged and the voltage on it may be much lower, even to zero.
Thus, the resistor resistance required to limit the current at the very beginning of the charge at 1 Ampere should be:
R = U / I = 2.2 / 1 = 2.2 Ohm
Resistor power dissipation:
P r = I 2 R = 1*1*2.2 = 2.2 W
At the very end of the battery charge, when the voltage on it approaches 4.2 V, the charge current will be:
I charge = (U ip - 4.2) / R = (5 - 4.2) / 2.2 = 0.3 A
That is, as we see, all values do not go beyond the permissible limits for a given battery: the initial current does not exceed the maximum permissible charging current for a given battery (2.4 A), and the final current exceeds the current at which the battery no longer gains capacity ( 0.24 A).
The main disadvantage of such charging is the need to constantly monitor the voltage on the battery. And manually turn off the charge as soon as the voltage reaches 4.2 Volts. The fact is that lithium batteries tolerate even short-term overvoltage very poorly - the electrode masses begin to quickly degrade, which inevitably leads to loss of capacity. At the same time, all the prerequisites for overheating and depressurization are created.
If your battery has a built-in protection board, which was discussed just above, then everything becomes simpler. When a certain voltage is reached on the battery, the board itself will disconnect it from the charger. However, this charging method has significant disadvantages, which we discussed in.
The protection built into the battery will not allow it to be overcharged under any circumstances. All you have to do is control the charge current so that it does not exceed the permissible values for a given battery (protection boards cannot limit the charge current, unfortunately).
Charging using a laboratory power supply
If you have a power supply with current protection (limitation), then you are saved! Such a power source is already a full-fledged charger that implements the correct charge profile, which we wrote about above (CC/CV).
All you need to do to charge li-ion is set the power supply to 4.2 volts and set the desired current limit. And you can connect the battery.
Initially, when the battery is still discharged, the laboratory power supply will operate in current protection mode (i.e., it will stabilize the output current at a given level). Then, when the voltage on the bank rises to the set 4.2V, the power supply will switch to voltage stabilization mode, and the current will begin to drop.
When the current drops to 0.05-0.1C, the battery can be considered fully charged.
As you can see, the laboratory power supply is an almost ideal charger! The only thing it can’t do automatically is make a decision to fully charge the battery and turn off. But this is a small thing that you shouldn’t even pay attention to.
How to charge lithium batteries?
And if we are talking about a disposable battery that is not intended for recharging, then the correct (and only correct) answer to this question is NO.
The fact is that any lithium battery (for example, the common CR2032 in the form of a flat tablet) is characterized by the presence of an internal passivating layer that covers the lithium anode. This layer prevents a chemical reaction between the anode and the electrolyte. And the supply of external current destroys the above protective layer, leading to damage to the battery.
By the way, if we talk about the non-rechargeable CR2032 battery, then the LIR2032, which is very similar to it, is already a full-fledged battery. It can and should be charged. Only its voltage is not 3, but 3.6V.
How to charge lithium batteries (be it a phone battery, 18650 or any other li-ion battery) was discussed at the beginning of the article.
