Battery charge equalization ensures long operating time and extends service life. Lithium: balancing or separate charge? Balancing connection diagram for li ion batteries

15.10.2023

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 accurately.

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.

85 kopecks/pcs. Buy MCP73812 65 RUR/pcs. Buy NCP1835 83 RUR/pcs. Buy *All chips with free shipping

Peculiarities:

-Balance

-Current control

Description of pins:

4S mode:	3S mode:
"B-" - general minus battery "B1" - +3.7V "B2" - +7.4V "B3" - +11.1V "B+" - general plus of the battery	"B-" - general minus battery "B1" - short-circuit to "B-" "B2" - +3.7V "B3" - +7.4V "B+" - general plus of the battery "P-" - minus load (charger) "P+" - plus load (charger)

Peculiarities:

-Balance: HCX-D119 control board for 3S/4S Li-Ion batteries has a built-in balancer function. At the same time, during the charging process of the battery, the voltage on each of the cells is equalized to a value of 4.2V.
In order to use the voltage equalization function, you need to keep the battery at a voltage of 12.6/16.8 V for at least 60 - 120 minutes after the end of the active phase of charging the battery. For the balancer to operate, it is important that the voltage is no higher than 12.6 / 16.8V: if these voltages are exceeded, the controller will enter a protection state and the batteries will not be balanced

-Voltage control on each cell: When the voltage on any of the cells exceeds the threshold values, the entire battery is automatically turned off.

-Current control: When the load current exceeds the threshold values, the entire battery is automatically switched off.

- Can work with 3S batteries(3 series batteries) The HCX-D119 controller is 100% compatible with 3S (11.1V) Li-Ion batteries. To switch the controller to 3S mode, you need to jumper the contacts R8, and move the resistor R7 to R11 (R7, however, remains open) and connect the “B1” pad to the “B-” pad

Description of pins:

4S mode:	3S mode:
"B-" - general minus battery "B1" - +3.7V "B2" - +7.4V "B3" - +11.1V "B+" - general plus of the battery "P-" - minus load (charger) "P+" - plus load (charger)	"B-" - general minus battery "B1" - short-circuit to "B-" "B2" - +3.7V "B3" - +7.4V "B+" - general plus of the battery "P-" - minus load (charger) "P+" - plus load (charger)

Typically, in any system consisting of several batteries connected in series, the problem of unbalancing the charge of the individual batteries arises. Charge equalization is a design technique that improves battery safety, runtime, and service life. The latest battery protection ICs and charge indicators from Texas Instruments - the BQ2084, BQ20ZXX family, BQ77PL900 and BQ78PL114, included in the company's product line - are essential for implementation of this method.

WHAT IS BATTERY UNBALANCE?

Overheating or overcharging will accelerate battery wear and may cause fire or even explosion. Software and hardware protections reduce the danger. In a bank of many batteries connected in series (usually such blocks are used in laptops and medical equipment), there is a possibility of the batteries becoming unbalanced, which leads to their slow but steady degradation.
No two batteries are the same, and there are always slight differences in battery state of charge (SOC), self-discharge, capacity, resistance and temperature characteristics, even if we are talking about batteries of the same type, from the same manufacturer and even from the same production batch. When forming a block of several batteries, the manufacturer usually selects batteries that are similar in SSB by comparing the voltages on them. However, differences in the parameters of individual batteries still remain, and may increase over time. Most chargers determine the full charge by the total voltage of the entire chain of batteries connected in series. Therefore, the charging voltage of individual batteries can vary widely, but not exceed the voltage threshold at which overcharge protection is activated. However, the weak link - a battery with low capacity or high internal resistance - may experience higher voltages than other fully charged batteries. The defectiveness of such a battery will appear later during a long discharge cycle. The high voltage of such a battery after charging is complete indicates its accelerated degradation. When discharged for the same reasons (high internal resistance and low capacity), this battery will have the lowest voltage. This means that when charging a weak battery, the overvoltage protection may work, while the remaining batteries in the unit will not yet be fully charged. This will result in underutilization of battery resources.

BALANCING METHODS

Battery imbalance has a significant adverse effect on battery life and service life. It is best to equalize the voltage and SSB of batteries when they are fully charged. There are two methods of balancing batteries - active and passive. The latter is sometimes called "resistor balancing". The passive method is quite simple: batteries that need balancing are discharged through bypass circuits that dissipate power. These bypass circuits can be integrated into the battery pack or placed in an external chip. This method is preferable for low-cost applications. Almost all excess energy from batteries with a large charge is dissipated in the form of heat - this is the main disadvantage of the passive method, because it reduces the battery life between charges. The active balancing method uses inductors or capacitors, which have negligible energy losses, to transfer energy from highly charged batteries to less charged batteries. Therefore, the active method is significantly more effective than the passive one. Of course, increasing efficiency comes at a cost - the use of additional, relatively expensive components.

PASSIVE BALANCING METHOD

The simplest solution is to equalize the battery voltage. For example, the BQ77PL900, which provides protection for battery packs with 5 to 10 batteries in series, is used in leadless tools, scooters, uninterruptible power supplies, and medical equipment. The microcircuit is a functionally complete unit and can be used to work with a battery compartment, as shown in Figure 1. Comparing the battery voltage with programmed thresholds, the microcircuit, if necessary, turns on the balancing mode. Figure 2 shows the operating principle. If the voltage of any battery exceeds a specified threshold, the charge stops and bypass circuits are connected. Charging is not resumed until the battery voltage drops below the threshold and the balancing procedure stops.

Rice. 1.BQ77PL900 chip used in stand-alone
operating mode to protect the battery pack

When applying a balancing algorithm that uses only voltage deviation as a criterion, incomplete balancing is possible due to the difference in the internal impedance of the batteries (see Fig. 3). The fact is that internal impedance contributes to the voltage spread during charging. The battery protection chip cannot determine whether the voltage imbalance is caused by different battery capacities or differences in their internal resistance. Therefore, with this type of passive balancing there is no guarantee that all batteries will be 100% charged. The BQ2084 charge indicator IC uses an improved version of voltage balancing. To minimize the effect of internal resistance variation, the BQ2084 performs balancing closer to the end of the charging process, when the charging current is low. Another advantage of the BQ2084 is the measurement and analysis of the voltage of all batteries included in the unit. However, in any case, this method is only applicable in charging mode.

Rice. 2.Passive method based on voltage balancing

Rice. 3.Passive voltage balancing method
uses battery capacity inefficiently

Microcircuits of the BQ20ZXX family use the proprietary Impedance Track technology to determine the charge level, based on determining the SSB and battery capacity. In this technology, for each battery, the charge Q NEED required to achieve a fully charged state is calculated, after which the difference ΔQ between the Q NEED of all batteries is found. Then the microcircuit turns on the power switches, through which the battery is balanced to a state of ΔQ = 0. Due to the fact that the difference in the internal resistance of the batteries does not affect this method, it can be used at any time: both when charging and discharging the batteries. Using Impedance Track technology, more accurate battery balancing is achieved (see Figure 4).

Rice. 4.

ACTIVE BALANCING

In terms of energy efficiency, this method is superior to passive balancing, because To transfer energy from a more charged battery to a less charged one, instead of resistors, inductances and capacitances are used, in which there are practically no energy losses. This method is preferred in cases where maximum battery life is required.
Featuring proprietary PowerPump technology, the BQ78PL114 is TI's latest active battery balancing component and uses an inductive converter to transfer power. PowerPump uses an n-channel p-channel MOSFET and an inductor that is located between a pair of batteries. The circuit is shown in Figure 5. The MOSFET and inductor make up the intermediate buck/boost converter. If the BQ78PL114 determines that the top battery needs to transfer energy to the bottom battery, a signal of about 200 kHz with a duty cycle of about 30% is generated at the PS3 pin. When the Q1 key is open, energy from the upper battery is stored in the throttle. When switch Q1 closes, the energy stored in the inductor flows through the flyback diode of switch Q2 into the lower battery.

Rice. 5.

Energy losses are small and mainly occur in the diode and inductor. The BQ78PL114 chip implements three balancing algorithms:

by voltage at the battery terminals. This method is similar to the passive balancing method described above;
by open circuit voltage. This method compensates for differences in the internal resistance of batteries;
according to SZB (based on predicting the battery condition). The method is similar to that used in the BQ20ZXX family of microcircuits for passive balancing by SSB and battery capacity. In this case, the charge that needs to be transferred from one battery to another is precisely determined. Balancing occurs at the end of the charge. When using this method, the best result is achieved (see Fig. 6)

Rice. 6.

Due to the large balancing currents, PowerPump technology is much more efficient than conventional passive balancing with internal bypass switches. When balancing a laptop battery pack, the balancing currents are 25...50 mA. By selecting the value of the components, you can achieve balancing efficiency 12-20 times better than with the passive method with internal keys. A typical unbalance value (less than 5%) can be achieved in one or two cycles.
In addition, PowerPump technology has other obvious advantages: balancing can occur in any operating mode - charge, discharge, and even when the battery delivering energy has a lower voltage than the battery receiving energy. Compared to the passive method, much less energy is lost.

DISCUSSION OF THE EFFECTIVENESS OF ACTIVE AND PASSIVE BALANCING METHOD

PowerPump technology performs balancing faster. When unbalancing 2% of 2200 mAh batteries, it can be done in one or two cycles. With passive balancing, the power switches built into the battery pack limit the maximum current value, so many more balancing cycles may be required. The balancing process can even be interrupted if there is a large difference in battery parameters.
The speed of passive balancing can be increased by using external components. Figure 7 shows a typical example of such a solution that can be used in conjunction with the BQ77PL900, BQ2084 or BQ20ZXX family of chips. First, the internal battery switch is turned on, which creates a small bias current flowing through resistors R Ext1 and R Ext2 connected between the battery terminals and the microcircuit. The gate-source voltage across resistor RExt2 turns on the external switch, and the balancing current begins to flow through the open external switch and resistor R Bal.

Rice. 7.Schematic diagram of passive balancing
using external components

The disadvantage of this method is that an adjacent battery cannot be balanced at the same time (see Fig. 8a). This is because when the internal switch of the adjacent battery is open, no current can flow through resistor R Ext2. Therefore, key Q1 remains closed even when the internal key is open. In practice, this problem is not of great importance, because With this balancing method, the battery connected to Q2 is quickly balanced, and then the battery connected to the Q2 key is balanced.
Another problem is the high drain-source voltage V DS that can occur when every other battery is being balanced. Figure 8b shows the case when the upper and lower batteries are balanced. In this case, the voltage V DS of the middle key may exceed the maximum permissible. The solution to this problem is to limit the maximum value of the resistor R Ext or eliminate the possibility of simultaneously balancing every second battery.

The fast balancing method is a new way to improve battery safety. With passive balancing, the goal is to balance the battery capacity, but due to the low balancing currents, this is only possible at the end of the charge cycle. In other words, overcharging a bad battery can be prevented, but this will not increase the operating time without recharging, because too much energy will be lost in the bypass resistive circuits.
When using PowerPump active balancing technology, two goals are simultaneously achieved - capacity balancing at the end of the charge cycle and minimal voltage difference at the end of the discharge cycle. The energy is stored and transferred to the weak battery rather than dissipated as heat in the bypass circuits.

CONCLUSION

Correctly balancing battery voltage is one of the ways to increase the safety of battery operation and increase their service life. New balancing technologies monitor the condition of each battery, which increases their service life and improves operational safety. PowerPump's fast active balancing technology increases battery life and allows batteries to be balanced as efficiently and effectively as possible at the end of the discharge cycle.

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 assembling, the batteries must again be charged equally, otherwise, when connected, large currents will flow, 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 Amps). 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 SERIAL 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 your 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 critical 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.

I have an old screwdriver, it had been sitting idle for quite a long time, so the batteries had a long life. And recently I needed it to assemble the kitchen. If you are interested in how I revived it by converting it to lithium for less than 100 rubles, then welcome to cat.

I have a drill like this - 18 volts, 9N*m

Off the top of my head I could think of three options.
1. buy a new inexpensive screwdriver for 1500-2500 rubles - simple, quick, but this is not our method, as the old drill will lie like a dead weight, and you won’t be able to throw it away,
2. order NiCd batteries - about 900-1200 rubles - what's the point if you can get a new one for 1500 rubles?
3. convert to lithium, but here the budget may be different. After reading the question on the mask, I found out that to convert to lithium, ideally you need:
- board 3S, 4S or 5S, depending on the size of the battery (I need 5 batteries for an 18 volt drill, respectively, 5S - about 800 rubles)
- a balancing board is desirable (if the protection board does not have a balancer), especially desirable if the batteries are not new or from different batches
- the Li-ion batteries themselves, preferably current ones, those designed for high operating currents - from 350 rubles per piece, for 5 pieces - from 1700 rubles.
As a result, it turns out to be a little expensive for my cheap old drill (see point 1), so I decided to make my own ultra-budget version with balancing blackjack.
I had an old laptop battery (they gave it away for nothing), and when I took it apart I found these Samsung cans in it. With the exception of 2 cans, the rest were quite working, I charged each one in a power bank

I checked them after charging for short circuit current (no more than 1 second - this can be dangerous, as the banks are without protection).

As you can see, the banks are quite alive - the short-term short-circuit return current is from 10 to 20A.
I sketched out this modification scheme, and I will do it according to it.

Since the batteries are not current, to facilitate their operation, it was decided to place 2 batteries in parallel (with an operating current of, for example, 10A, the current supplied by each battery will be 10/2 = 5A). To do this, it is advisable to select pairs with similar current output characteristics. I'm fixing the diagram:

In principle, my drill, judging by the characteristics, is not particularly powerful, so in principle it would be possible to install one can at a time, although they will most likely last less, but since I had 10 batteries, I decided to install all 10.
I didn’t take pictures of the assembly process; in principle, there’s nothing interesting there; you can solder the batteries to already welded petals without fear of overheating.
Since all 10 batteries did not fit into the old unit, it turned out a little collective farm

well, never mind, take the blue (whatever it was) electrical tape and hide everything unnecessary -

already better)
As you can see on the side, I removed the charging and balancing connector, which I unsoldered from a broken video card (or motherboard, I don’t remember). Since I need 10 contacts, I had to use this db15, if I had used fewer batteries I would have used db9 - they are easier to find

All that remains is to solder the charger. As voltage sources of 5 volts, I took 5 unnecessary chargers from mobile phones, I just found 5 of them, although they are all different, for different currents from 600 to 900 mA. Ideally, use the same ones, so charging would occur approximately simultaneously and it would be possible to evaluate which banks take longer to charge.
Important! You need to do it exactly according to the scheme, using each charge controller with its own separate 5-8V power supply, that is, the power supplies must be galvanically isolated from each other. One powerful power supply cannot be used for all controllers - there will be a short circuit of the batteries (the TP4056 has a common input and output case - minus).
To reduce the size of the structure, I removed the chargers from the cases. I glued the TP4056 charge controller to the rear side with double-sided tape and put the structure into a separate case

This is what it looks like when turned on at 220V

The charge controller lights up blue - an indication that the load is not connected (or the battery is charged), red and green - LEDs for mobile phone chargers.
Now let's connect the battery -

It can be seen that only 3 banks are charging (the red diode is on), and the remaining 2 are not (the blue diode is on). This is because I recently charged it, and only 3 out of 5 batteries were discharged. Thus, it is clear that with each charge the entire battery is balanced - this is the main advantage of this scheme, this is especially important when using such batteries from a laptop battery.

For clarity, I made a video, perhaps I missed something in the story, then look at the video -

Let's summarize.
pros
1. Cheap - I only needed to buy TP4056 charge controllers, which cost me 60 rubles for 5 pieces, the rest was available or I got it for free. Now delivery from this seller is only paid, + about $1 more, you can probably find it cheaper.
2. Balancing batteries with each charge.

Minuses
1. There is no current protection, so I do not set the chuck lock to lock (drill icon), so the current protection is purely mechanical - the chuck clicks and is not blocked when clamped, no short-circuit current occurs. In principle, I think this protection is sufficient.
2. If you don’t have old cell phone chargers, it will be a little more expensive. But you can also ask your friends about them - probably many have them lying around idle.
3. No overdischarge protection. Well, here you need to look: if the power drops, go straight to charging! In general, this is lithium, you don’t have to wait for the battery to run out like with nickel, but it’s better to charge it when possible - this way the batteries will last longer.

In general, I consider this scheme to have the right to life, especially for the resuscitation of such inexpensive and not super-powerful screwdrivers.
ps they gave in the comments