Active battery balancing scheme. DIY balancer for li-ion batteries. Diagram and description. How to properly charge lithium-ion batteries
I welcome everyone who stopped by. The review will focus, as you probably already guessed, on two simple headsets designed to monitor Li-Ion battery assemblies, called BMS. The review will include testing, as well as several options for converting a screwdriver for lithium based on these boards or similar ones. For anyone interested, you are welcome under cat.
Update 1, Added a test of the operating current of the boards and a short video on the red board
Update 2, Since the topic has aroused little interest, I will try to supplement the review with several more ways to remake Shurik to make a kind of simple FAQ
General form:
Brief performance characteristics of the boards:
Note:
I want to warn you right away - only the blue board has a balancer, the red one does not have a balancer, i.e. This is purely an overcharge/overdischarge/short circuit/high load current protection board. And also, contrary to some beliefs, none of them have a charge controller (CC/CV), so for their operation a special board with a fixed voltage and current limitation is required.
Board dimensions:
The dimensions of the boards are very small, only 56mm*21mm for the blue one and 50mm*22mm for the red one: 
Here is a comparison with AA and 18650 batteries: 
Appearance:
Let's start with: 
Upon closer inspection, you can see the protection controller – S8254AA and balancing components for the 3S assembly: 
Unfortunately, according to the seller, the operating current is only 8A, but judging by the datasheets, one AO4407A mosfet is designed for 12A (peak 60A), and we have two of them: 
I will also note that the balancing current is very small (about 40ma) and balancing is activated as soon as all cells/banks switch to CV mode (second charge phase).
Connection: 
simpler, because it does not have a balancer: 
It is also based on the protection controller – S8254AA, but is designed for a higher operating current of 15A (again, according to the manufacturer): 
Looking at the datasheets for the power mosfets used, the operating current is stated to be 70A, and the peak current is 200A, even one mosfette is enough, but we have two of them: 
The connection is similar: 
So, as we can see, both boards have a protection controller with the necessary isolation, power mosfets and shunts to control the passing current, but the blue one also has a built-in balancer. I haven't looked into the circuit too much, but it looks like the power mosfets are paralleled, so the operating currents can be multiplied by two. Important note - maximum operating currents are limited by the current shunts! These scarves do not know about the charging algorithm (CC/CV). To confirm that these are precisely protection boards, one can judge by the datasheet for the S8254AA controller, in which there is not a word about the charging module: 
The controller itself is designed for a 4S connection, so with some modification (judging by the datasheet) - soldering the connector and resistor, perhaps the red scarf will work: 
It’s not so easy to upgrade the blue scarf to 4S; you’ll have to solder on the balancer elements.
Board testing:
So, let's move on to the most important thing, namely how suitable they are for real use. The following devices will help us for testing:
- a prefabricated module (three three/four-register voltmeters and a holder for three 18650 batteries), which appeared in my review of the charger, although without a balancing tail: 
- two-register ampere-voltmeter for current monitoring (lower readings of the device): 
- step-down DC/DC converter with current limiting and lithium charging capability: 
- charging and balancing device iCharger 208B for discharging the entire assembly
The stand is simple - the converter board supplies a fixed constant pressure 12.6V and limits the charging current. Using voltmeters, we look at what voltage the boards operate at and how the banks are balanced.
First, let's look at the main feature of the blue board, namely balancing. There are 3 cans in the photo, charged at 4.15V/4.18V/4.08V. As we can see, there is an imbalance. We apply voltage, the charging current gradually drops (lower gauge): 
Since the scarf does not have any indicators, the completion of balancing can only be assessed by eye. The ammeter was already showing zeros more than an hour before the end. For those interested, here is a short video about how the balancer works in this board:
As a result, the banks are balanced at 4.210V/4.212V/4.206V, which is quite good:
When applying a voltage slightly higher than 12.6V, as I understand it, the balancer is inactive and as soon as the voltage on one of the cans reaches 4.25V, the S8254AA protection controller turns off the charge:
The situation is the same with the red board; the S8254AA protection controller also turns off the charge at 4.25V:
Now let's go through the load cutoff. I will discharge, as I mentioned above, with an iCharger 208B charger and balancing device in 3S mode with a current of 0.5A (for more accurate measurements). Since I don’t really want to wait for the entire battery to drain, I took one dead battery (green Samson INR18650-25R in the photo).
The blue board turns off the load as soon as the voltage on one of the cans reaches 2.7V. In the photo (no load->before shutdown->end):
As you can see, the board turns off the load at exactly 2.7V (the seller stated 2.8V). It seems to me that this is a little high, especially considering the fact that in the same screwdrivers the loads are huge, therefore, the voltage drop is large. Still, it is advisable to have a cutoff of 2.4-2.5V in such devices.
The red board, on the contrary, turns off the load as soon as the voltage on one of the cans reaches 2.5V. In the photo (no load->before shutdown->end):
Here everything is generally fine, but there is no balancer.
Update 1: Load test:
The following stand will help us with the output current:
- the same holder/holder for three 18650 batteries
- 4-register voltmeter (control of total voltage)
- car incandescent lamps as a load (unfortunately, I only have 4 incandescent lamps of 65W each, I don’t have any more)
- HoldPeak HP-890CN multimeter for measuring currents (max 20A)
- high-quality copper stranded acoustic wires of large cross-section
A few words about the stand: the batteries are connected by a “jack”, i.e. as if one after another, to reduce the length of the connecting wires, and therefore the voltage drop across them under load will be minimal: 
Connecting cans on a holder (“jack”): 
The probes for the multimeter were high-quality wires with crocodile clips from the iCharger 208B charger and balancing device, because HoldPeak’s do not inspire confidence, and unnecessary connections will introduce additional distortions.
First, let's test the red protection board, as it is the most interesting in terms of current load. Solder the power and can wires: 
It turns out something like this (the load connections turned out to be of minimal length): 
I already mentioned in the section on remaking Shurik that such holders are not really designed for such currents, but they will do for tests.
So, a stand based on a red scarf (according to measurements, no more than 15A): 
Let me briefly explain: the board holds 15A, but I don’t have a suitable load to fit into this current, since the fourth lamp adds about 4.5-5A more, and this is already beyond the limits of the board. At 12.6A, the power mosfets are warm, but not hot, just right for long-term operation. At currents of more than 15A, the board goes into protection. I measured with resistors, they added a couple of amperes, but the stand was already disassembled.
A huge plus of the red board is that there is no protection blocking. Those. When the protection is triggered, it does not need to be activated by applying voltage to the output contacts. Here's a short video:
Let me explain a little. Since incandescent lamps have low resistance when cold, and are also connected in parallel, the scarf thinks what happened short circuit and the protection is triggered. But due to the fact that the board does not have a lock, you can warm up the coils a little, making a “softer” start.
The blue scarf holds more current, but at currents of more than 10A, the power mosfets get very hot. At 15A the scarf will last no more than a minute, because after 10-15 seconds the finger no longer holds the temperature. Fortunately, they cool down quickly, so they are quite suitable for short-term loads. Everything would be fine, but when the protection is triggered, the board is blocked and to unlock it, you need to apply voltage to the output contacts. This option is clearly not for a screwdriver. In total, the current is 16A, but the mosfets get very hot: 
Conclusion: My personal opinion is that a regular protection board without a balancer (red) is perfect for a power tool. It has high operating currents, an optimal cut-off voltage of 2.5V, and is easily upgraded to a 4S configuration (14.4V/16.8V). I think this is the most optimal choice for converting a budget Shurik for lithium.
Now for the blue scarf. One of the advantages is the presence of balancing, but the operating currents are still small, 12A (24A) is somewhat not enough for a Shurik with a torque of 15-25Nm, especially when the cartridge almost stops when tightening the screw. And the cutoff voltage is only 2.7V, which means that under heavy load, part of the battery capacity will remain unclaimed, since at high currents the voltage drop on the banks is significant, and they are designed for 2.5V. And the biggest disadvantage is that the board is blocked when the protection is triggered, so use in a screwdriver is undesirable. It is better to use a blue scarf in some homemade projects, but again, this is my personal opinion.
Possible application schemes or how to convert Shurik’s power supply to lithium:
So, how can you change the power supply of your favorite Shurik from NiCd to Li-Ion/Li-Pol? This topic is already quite hackneyed and solutions, in principle, have been found, but I will briefly repeat myself.
To begin with, I’ll just say one thing - in budget shuriks there is only a protection board against overcharge/overdischarge/short circuit/high load current (analogous to the red board under review). There is no balancing there. Moreover, even some branded power tools do not have balancing. The same applies to all tools that proudly say “Charge in 30 minutes.” Yes, they charge in half an hour, but the shutdown occurs as soon as the voltage on one of the banks reaches the nominal value or the protection board is triggered. It is not difficult to guess that the banks will not be fully charged, but the difference is only 5-10%, so it is not so important. The main thing to remember is that a balanced charge lasts for at least several hours. So the question arises, do you need it?
So, the most common option looks like this:
Network charger with stabilized output 12.6V and current limitation (1-2A) -> protection board ->
The bottom line: cheap, fast, acceptable, reliable. Balancing depends on the state of the cans (capacity and internal resistance). This is a completely working option, but after a while the imbalance will make itself felt in the operating time.
More correct option:
Network charger with stabilized output 12.6V, current limitation (1-2A) -> protection board with balancing -> 3 batteries connected in series
In summary: expensive, fast/slow, high quality, reliable. Balancing is normal, battery capacity is maximum
So, we’ll try to do something similar to the second option, here’s how you can do it:
1) Li-Ion/Li-Pol batteries, protection boards and a specialized charging and balancing device (iCharger, iMax). Additionally, you will have to remove the balancing connector. There are only two disadvantages - model chargers are not cheap, and they are not very convenient to service. Pros – high charging current, high can balancing current
2) Li-Ion/Li-Pol batteries, protection board with balancing, DC converter with current limiting, power supply
3) Li-Ion/Li-Pol batteries, protection board without balancing (red), DC converter with current limiting, power supply. The only downside is that over time the cans will become unbalanced. To minimize imbalance, before altering the shurik, it is necessary to adjust the voltage to the same level and it is advisable to take cans from the same batch
The first option will only work for those who have a model memory, but it seems to me that if they needed it, then they remade their Shurik a long time ago. The second and third options are practically the same and have the right to life. You just need to choose what is more important – speed or capacity. I believe that the last option is the best option, but only once every few months you need to balance the banks.
So, enough chatter, let's get to the remodeling. Since I don’t have experience with NiCd batteries, I’m talking about the conversion only in words. We will need:
1) Power supply:
First option. Power supply (PSU) at least 14V or more. The output current is desirable to be at least 1A (ideally about 2-3A). We will use a power supply from laptops/netbooks, from chargers (output more than 14V), power supplies LED strips, video recording equipment (DIY power supply), for example or: 
- Step-down DC/DC converter with current limiting and the ability to charge lithium, for example or: 
- Second option. Ready blocks power supply for Shuriks with current limiting and 12.6V output. They are not cheap, as an example from my review of the MNT screwdriver -: 
- Third option. : 
2) Protection board with or without balancer. It is advisable to take the current with a reserve: 
If the option without a balancer is used, then it is necessary to solder the balancing connector. This is necessary to control the voltage on the banks, i.e. to assess imbalance. And as you understand, you will need to periodically recharge the battery one by one with a simple TP4056 charging module if imbalance begins. Those. Once every few months, we take the TP4056 scarf and charge one by one all the banks that, at the end of the charge, have a voltage below 4.18V. This module correctly cuts off the charge on fixed voltage 4.2V. This procedure It will take an hour and a half, but the banks will be more or less balanced.
It’s written a little chaotically, but for those in the tank:
After a couple of months, we charge the screwdriver battery. At the end of the charge, we take out the balancing tail and measure the voltage on the banks. If you get something like this - 4.20V/4.18V/4.19V, then balancing is basically not needed. But if the picture is as follows - 4.20V/4.06V/4.14V, then we take the TP4056 module and charge two banks in turn to 4.2V. I don’t see any other option other than specialized chargers-balancers.
3) High current batteries: 
I have previously written a couple of short reviews about some of them - and. Here are the main models of high-current 18650 Li-Ion batteries:
- Sanyo UR18650W2 1500mah (20A max.)
- Sanyo UR18650RX 2000mah (20A max.)
- Sanyo UR18650NSX 2500mah (20A max.)
- Samsung INR18650-15L 1500mah (18A max.)
- Samsung INR18650-20R 2000mah (22A max.)
- Samsung INR18650-25R 2500mah (20A max.)
- Samsung INR18650-30Q 3000mah (15A max.)
- LG INR18650HB6 1500mah (30A max.)
- LG INR18650HD2 2000mah (25A max.)
- LG INR18650HD2C 2100mah (20A max.)
- LG INR18650HE2 2500mah (20A max.)
- LG INR18650HE4 2500mah (20A max.)
- LG INR18650HG2 3000mah (20A max.)
- SONY US18650VTC3 1600mah (30A max.)
- SONY US18650VTC4 2100mah (30A max.)
- SONY US18650VTC5 2600mah (30A max.)
I recommend the time-tested cheap Samsung INR18650-25R 2500mah (20A max), Samsung INR18650-30Q 3000mah (15A max) or LG INR18650HG2 3000mah (20A max). I haven’t had much experience with other jars, but my personal choice is Samsung INR18650-30Q 3000mah. The Skis had a small technological defect and fakes with low current output began to appear. I can post an article on how to distinguish a fake from an original, but a little later, you need to look for it.
How to put all this together:
Well, a few words about the connection. We use high-quality copper stranded wires with a decent cross-section. These are high-quality acoustic or ordinary SHVVP/PVS with a cross-section of 0.5 or 0.75 mm2 from a hardware store (we rip the insulation and get high-quality wires of different colors). The length of the connecting conductors should be kept to a minimum. Batteries preferably from the same batch. Before connecting them, it is advisable to charge them to the same voltage so that there is no imbalance for as long as possible. Soldering batteries is not difficult. The main thing is to have a powerful soldering iron (60-80W) and an active flux (soldering acid, for example). Solders with a bang. The main thing is to then wipe the soldering area with alcohol or acetone. The batteries themselves are placed in the battery compartment from old NiCd cans. It is better to arrange it in a triangle, minus to plus, or as popularly called “jack”, by analogy with this (one battery will be located in reverse), or there is a good explanation a little higher (in the testing section): 
Thus, the wires connecting the batteries will be short, therefore, the drop in precious voltage in them under load will be minimal. I do not recommend using holders for 3-4 batteries; they are not intended for such currents. Side-by-side and balancing conductors are not so important and can be of smaller cross-section. Ideally, it is better to stuff the batteries and the protection board into the battery compartment, and the step-down DC converter separately into the docking station. The charge/charged LED indicators can be replaced with your own and displayed on the docking station body. If you wish, you can add a minivoltmeter to the battery module, but this is extra money, because the total voltage on the battery will only indirectly indicate the residual capacity. But if you want, why not. Here : 
Now let's estimate the prices:
1) BP – from 5 to 7 dollars
2) DC/DC converter – from 2 to 4 dollars
3) Protection boards - from 5 to 6 dollars
4) Batteries – from 9 to 12 dollars ($3-4 per item)
Total, on average, $15-20 for a remodel (with discounts/coupons), or $25 without them.
Update 2, a few more ways to remake Shurik:
The next option (suggested from the comments, thanks I_R_O And cartmann):
Use inexpensive 2S-3S type chargers (this is the manufacturer of the same iMax B6) or all kinds of copies of B3/B3 AC/imax RC B3 () or ()
The original SkyRC e3 has a charging current per cell of 1.2A versus 0.8A for copies, should be accurate and reliable, but twice as expensive as copies. You can buy it very inexpensively at the same place. As I understand from the description, it has 3 independent charging modules, something akin to 3 TP4056 modules. Those. SkyRC e3 and its copies do not have balancing as such, but simply charge the banks to one voltage value (4.2V) at the same time, since they do not have power connectors. SkyRC's assortment actually includes charging and balancing devices, for example, but the balancing current is only 200mA and costs around $15-20, but it can charge life-changing devices (LiFeP04) and charge currents up to 3A. Anyone interested can check out model range.
Total for this option You need any of the above 2S-3S chargers, a red or similar (without balancing) protection board and high-current batteries: 
As for me, it’s a very good and economical option, I’d probably stick with it.
Another option suggested by comrade Volosaty:
Use the so-called “Czech balancer”: 
It’s better to ask him where it’s sold, it’s the first time I’ve heard about it :-). I can’t tell you anything about currents, but judging by the description, it needs a power source, so the option is not so budget-friendly, but seems interesting in terms of charging current. Here is the link to. In total, for this option you need: a power supply, a red or similar (without balancing) protection board, a “Czech balancer” and high-current batteries.
Advantages:
I have already mentioned the advantages of lithium power supplies (Li-Ion/Li-Pol) over nickel ones (NiCd). In our case, a head-to-head comparison – a typical Shurik battery made of NiCd batteries versus lithium:
+ high energy density. A typical 12S 14.4V 1300mah nickel battery has a stored energy of 14.4*1.3=18.72Wh, and lithium battery 4S 18650 14.4V 3000mah - 14.4*3=43.2Wh
+ no memory effect, i.e. you can charge them at any time without waiting for complete discharge
+ smaller dimensions and weight with the same parameters as NiCd
+ fast charging time (not afraid of high charge currents) and clear indication
+ low self-discharge
The only disadvantages of Li-Ion are:
- low frost resistance of batteries (they are afraid of negative temperatures)
- balancing of the cans during charging and the presence of overdischarge protection is required
As you can see, the advantages of lithium are obvious, so it often makes sense to rework the power supply...
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Why do we need balancers for 12-volt batteries? When you have a 12-volt system, then all the batteries, no matter how many there are, are connected in parallel, and they always have the same voltage. But when we switch to 24 or 48 volts, a problem appears with different voltages on series-connected batteries. Because of this, when charging, some batteries go into overcharge and begin to “boil”, while others are undercharged, and as a result, the entire battery chain quickly loses capacity and generally becomes unusable.
And even completely identical batteries over time still vary in voltage, so even batteries purchased from the same batch will not save you from the problem. To solve this problem, various balancing devices have long been used, these are either separate balancers for each battery, or units for 24 and 48 volts. Balancers can significantly extend the service life of the battery.
In the near future I myself will be switching to 24 volts, since the currents in the system have already become large and I will also need balancers. In my search, I found several options that differ in capabilities, price and principle of operation, and below I will review these balancing devices.
VICTRON BATTERY BALANCER
The first ones I came across were these balancers (photo below). Judging by the description, these are active balancers with a balancing current of 0.7A. Active means that energy from a more charged battery flows into a less charged one, and is not simply burned at the resistance. But I’m not completely sure about this since the descriptions on different sites vary. This balancer is for two batteries, that is, 24 volts; with the addition of a battery, the number of balancers must be increased. At 48 volts you already need three such balancers.This balancer cannot be adjusted for different types of lead batteries. There is an operation indication and an alarm relay; it closes if the voltage difference across the battery exceeds 0.2 volts. The price for this balancer was simply killer; at the time of writing, the price on the website was 6220 rubles. For 48 volts you need three of them and in total you need to pay 18,660 rubles plus delivery.
Connection diagram of these balancers to the battery. LED indicators and alarm relays:
Green: On when battery voltage is over 27.3V
Orange: On when deviation is greater than 0.1V
Red: alarm (deviation more than 0.2V)
Alarm relay: normal open contact closes when the red LED turns on. The contact remains closed until the deviation decreases to 0.14 V, or until the battery voltage decreases to 26.6 V. The alarm relay is reset using a button connected to two terminals.
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The downside is that the price is too high, the balancing current is only 0.7A, and there is no way to customize it to suit your battery type. There are more best analogues at a reasonable price.
Charge equalization device ELNI 2/12 for 2 batteries 12V
I also found this balancer. This is already clearly an active balancer, clearly superior to the first one in terms of balancing current; this one has a current of 5A compared to 0.7A for the first one. The price is really not small either - 3600-3900 rub. on different sites.This balancer constantly monitors the voltage of batteries connected in series, and equalizes the voltage by transferring energy between the batteries. And it does this not only during charging, when the battery is almost fully charged, but constantly if there is an imbalance. And the balancing current here can reach 5A, which means that the balancer can cope even with large imbalances in capacity.
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On this site, I did not find anything original that was not available on Aliexpress. There are, of course, a lot of balancers, but they were all bought in China and sold here at exorbitant prices. So why overpay if you can buy on Aliexpress yourself what our resellers offer.
Active balancer for 12V battery
I found this balancer on Aliexpress. This is an active balancer with a maximum balancing current of 10A. It monitors the voltage on series-connected batteries and equalizes the voltage by transferring energy between batteries with an accuracy of 10mV. Each balancer is placed on its own battery, and the balancers are connected to each other. You can view the description and buy here Balancer 12V. The price at the time of writing is 1,700 rubles, and this is not expensive for such a powerful active balancer.
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The manufacturer of these balancers produces several various types balancers There are 2 volt balancers available for sale for individual lead-acid “cans”. Also balancers for lithium-ion batteries for 3.6 and 4.2 volts. And balancers for 6 and 12 volt batteries. All Balvnsirs can be viewed here - Catalog of balancers 2/3.6/3.8/4.2/6/12 volts
24 volt battery balancer (12*2)
I also found another popular and cheap balancer for batteries. This is a balancer for two 12-volt batteries; you can install several if the system is 48 volts or higher. Balancing current is up to 5A, which is pretty good. The only thing I still don’t understand is whether it is active or passive, but judging by the size and the absence of a radiator, it is an active balancer. The price of this balancer is 1760 rubles, you can see it here - Double Balancer for 12V battery
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The price is very attractive, and the balancing current is a very decent 5A, so it can cope even with a large difference in capacity and voltage between the batteries in the system.
Balancer for (12×4) 48 volt battery
Here is another excellent active balancer for batteries, it is made in the form of a 48-volt unit, that is, for four batteries connected in series. The balancing current is up to 10 amperes, and this is just great, it will eliminate even a large imbalance. View the full description and buy it mono using this link on aliexpress - Balancer for 48V battery (12×4), price 3960 rubles.
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So far this is all I have been able to find, although of course not everything, but this is the main thing. There are controllers for solar panels with built-in balancers, but they are still very expensive. There are chargers with balancing, but they are inappropriate here. There are all kinds electronic circuits, which can be made to work as balancers, there are options for making balancers yourself.
Sent by:
No, we're not talking about fishing bait, or even about circus acrobats balancing under a big top. We will talk about how to achieve a balance of parameters of batteries connected in series.
As you know, a battery cell is a fairly low-voltage device, so they are usually connected in packs in series. Ideally, if the parameters of all batteries are the same, we have a source with a voltage n times greater than a single cell, and we can charge and discharge it as a single higher-voltage battery.
Alas, this will only be the case ideally. Each battery in this pack, like everything in this world, is unique, and it is impossible to find two completely identical ones, and their characteristics - capacity, leakage, state of charge - will change with time and temperature.
Of course, battery manufacturers try to select the parameters that are as close as possible, but there are always differences. And over time, such imbalances in characteristics may also increase.
These differences in the characteristics of the cells lead to the fact that the batteries operate differently and, as a result, the total capacity of the composite battery will be lower than that of its constituent cells, this time, and secondly, the resource of such a battery will also be lower, because it is determined by the “weakest” battery, which will wear out faster than others.
What to do?
There are two main criteria for assessing the degree of cell balancing:
1. Voltage equalization on the cells,
2. Equalization of charge in cells.
You can also achieve your goals in achieving these balancing methods in two ways:
1. Passive and
2. Active.
Let's explain what was said.
With the balancing criteria, everything is clear, either we simply achieve equality of voltages on the cells, or somehow calculate the charge of the battery and ensure that these charges are equal (in this case, the voltages may differ).
There is nothing complicated with the implementation methods either. In the passive method, we simply convert the energy in the most charged battery cells into heat until the voltages or charges in them are equal.
In the active method, we transfer charge from one cell to another in any way possible, with minimal losses if possible. Modern circuitry easily implements such abilities.
It is clear that it is easier to dissipate than to pump, and it is easier to compare voltages than to compare charges.
Also, these methods can be used both during charging and discharging. Most often, of course, 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 much loss, you can use the passive dissipation of “excess” electricity.
When discharging, only active charge transfer is always used, but such systems are very rare due to the greater complexity of the circuit.
Let's look at the practical implementation of the above.
When charging, in the simplest case, a device called a “balancer” is placed at the output of the charger.
Next, in order not to write it myself, I’ll simply insert a piece of text from an article from the site http://www.os-propo.info/content/view/76/60/. We are talking about charging lithium batteries.
"The simplest type of balancer is a voltage limiter. It is a comparator that compares the voltage on the LiPo bank with a threshold value of 4.20 V. Upon reaching this value, a powerful transistor switch is opened, connected in parallel to the LiPo bank, passing through most of the charge current (1A or more) 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. In fact, the voltage equalization on the battery cells with such a balancer occurs only at the end of the charge when the cells reach a threshold value.
In such a scheme, the task of charging and leveling a pair of different packs is actually feasible. But in practice such balancers are only homemade. All branded microprocessor balancers use a different operating principle.
Instead of dissipating the full charge currents at the end, the microprocessor balancer continuously monitors the bank voltages and gradually equalizes them throughout the charging process. To the jar that is charged more than others, the balancer connects in parallel some resistance (about 50-80 Ohms in most balancers), which passes part of the charging current through itself and only slightly slows down the charge of this jar, without stopping it completely. Unlike a transistor on a radiator, which is capable of taking on the main charge current, this resistance provides only a small balancing current - about 100 mA, and therefore such a balancer does not require massive radiators. It is this balancing current that is indicated in technical specifications balancers and is usually no more than 100-300mA.
Such a balancer does not heat up significantly, since the process continues throughout the entire charge, and the heat at low currents has time to dissipate without radiators. Obviously, if the charging current is significantly higher than the balancing current, then if there is a large spread of voltages across the banks, the balancer will not have time to equalize them before the most charged bank reaches the threshold voltage."
End of quote.
Example working diagram The following can serve as the simplest balancer (taken from the site http://www.zajic.cz/).
Fig.1. Simple scheme balancer
In fact, this is a powerful zener diode, by the way, very accurate, loaded with a low-resistance load, the role of which is played here by diodes D2...D5. Chip D1 measures the voltage at the plus and minus of the battery and if it rises above the threshold, it opens powerful transistor T1, passing through itself all the current from the charger.
Fig.2. A simple balancer circuit.
The second circuit works similarly (Fig. 2), but in it all the heat is released in transistor T1, which heats up like a “kettle” - the radiator can be seen in the picture below.
In Fig. 3 it can be seen that the balancer consists of 3 channels, each of which is made according to the scheme in Fig. 2.
Of course, the industry has long mastered such circuits, which are produced in the form of a complete microcircuit. Many companies produce them. As an example, I will use the materials of the article on balancing methods published on the RadioLotsman website http://www.rlocman.ru/shem/schematics.html?di=59991, which I will partially change or remove so as not to bloat the article.
Quote:
" Passive balancing method.
The simplest solution is to equalize the battery voltage. For example, the BQ77PL900 chip provides protection for battery packs with 5-10 batteries connected in series. The microcircuit is a functionally complete unit and can be used to work with a battery compartment, as shown in Figure 4. Comparing the voltage of the bank with the threshold, the microcircuit, if necessary, turns on the balancing mode for each of the banks.
Fig.4. Chip BQ77PL900, and the second analogue, where it is better visible internal organization(taken from here http://qrx.narod.ru/bp/bat_v.htm ).
In Fig. Figure 5 shows the principle of its operation. If the voltage of any battery exceeds a predetermined threshold, the field-effect transistors are turned on and a load resistor is connected in parallel to the battery cell, through which the current bypasses the cell and no longer charges it. The remaining cells continue to charge.
When the voltage drops, the field switch closes and charging can continue. Thus, at the end of charging, the same voltage will be present on all cells.
When applying a balancing algorithm that uses only voltage deviation as a criterion, incomplete balancing is possible due to the difference in the internal resistance of the batteries (see Fig. 6.). The fact is that part of the voltage drops across this resistance when current flows through the battery, which introduces an additional error into the voltage spread during charging.
The battery protection chip cannot determine whether the imbalance is caused by different battery capacities or differences in their internal resistances. Therefore, with this type of passive balancing there is no guarantee that all batteries will be 100% charged.
The BQ2084 chip uses an improved version of balancing, also based on voltage changes, but in order 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.
Rice. 5. Passive method based on voltage balancing.
Rice. 6. Passive voltage balancing method.
Microcircuits of the BQ20Zхх family use proprietary Impedance Track technology to determine the charge level, based on determining the state of charge of the batteries (SBC) and battery capacity.
In this technology, for each battery, the charge Qneed required to fully charge it is calculated, after which the difference?Q between the Qneed of all batteries is found. The chip then turns on power switches that discharge all cells to the level of the least charged until the charges are equalized
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 battery. However, as mentioned above, it is stupid to use this method when discharging, because there is always not enough energy.
The main advantage of this technology is more accurate battery balancing (see Figure 7) compared to other passive methods.
Rice. 7. Passive balancing based on SZB and capacitance.
Active balancing
In terms of energy efficiency, this method is superior to passive balancing, because To transfer energy from a more charged cell to a less charged one, instead of resistors, inductances and capacitances are used, in which there is practically no energy loss. 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 n-channel p-channel field effect transistors and a choke, which is located between a pair of batteries. The circuit is shown in Fig. 8. The field switches and inductor make up a buck/boost converter.
For example, if the BQ78PL114 determines that the upper cell is more charged than the lower one, then a signal is generated at the PS3 pin that opens transistor Q1 with a frequency of about 200 kHz and a duty cycle of about 30%.
With Q2 closed, a standard buck switching regulator circuit is obtained, with the internal diode of Q2 shorting the inductor current while Q1 is closed.
When pumping from the lower cell to the upper one, when only key Q2 opens, we also get a typical circuit, but this time of a step-up pulse stabilizer.
Keys Q1 and Q2, of course, should never be opened at the same time.
Rice. 8. Balancing using PowerPump technology.
In this case, energy losses are small and almost all the energy flows from a highly charged to a weakly charged jar. The BQ78PL114 chip implements three balancing algorithms:
- by voltage at the battery terminals. This method is similar to the passive balancing method described above, but there is almost no loss;
- by open circuit voltage. This method compensates for differences in the internal resistance of batteries;
- according to the battery charge state (based on predicting the battery state). 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. Using this method it is achieved best result(See Fig. 9.)
Rice. 9. Active balancing according to the algorithm for equalizing the battery charge state.
Due to the large balancing currents, PowerPump technology is much more efficient than conventional passive balancing with energy dissipation. 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 just one or two cycles.
In addition, PowerPump technology has other 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." (End of partial quotation.)
Let's continue the description of active methods of transferring charge from one cell to another with the following circuit, which I found on the Internet on the website "HamRadio" http://qrx.narod.ru/bp/bat_v.htm.
A capacitive storage device, rather than an inductive one, is used as a charge pumping circuit. For example, so-called voltage converters based on switched capacitors are widely known. One of the popular ones is the ICL7660 microcircuit (MAX1044 or the domestic analogue KR1168EP1).
Basically, the microcircuit is used to obtain a negative voltage equal to its supply voltage. However, if for some reason the negative voltage at its output turns out to be greater in magnitude than the positive supply voltage, then the microcircuit will begin to pump charge “in the opposite direction,” taking it from the negative and giving it to the positive, i.e. she is constantly trying to equalize these two tensions.
This property is used to balance two battery cells. The diagram of such a balancer is shown in Fig. 10.
Fig. 10. Balancer circuit with capacitive charge pumping.
Microcircuit with high frequency connects capacitor C1 to either the upper battery G1 or the lower battery G2. Accordingly, C1 will be charged from a more charged one and discharged into a more discharged one, each time transferring some portion of the charge.
Over time, the voltages on the batteries will become the same.
The energy in the circuit is practically not dissipated; the efficiency of the circuit can reach up to 95...98% depending on the voltage on the batteries and the output current, which depends on the switching frequency and capacity C1.
At the same time, the actual consumption of the microcircuit is only a few tens of microamps, i.e. is below the self-discharge level of many batteries, and therefore the microcircuit does not even need to be disconnected from the battery and it will constantly slowly do the job of equalizing the voltage on the cells.
In reality, the pumping current can reach 30...40mA, but the efficiency decreases. Typically tens of mA. Also, the supply voltage can be from 1.5 to 10V, which means that the microcircuit can balance both ordinary Ni-Mh fingers and lithium batteries.
Practical note: in Fig.10. shows a circuit that balances batteries with a voltage of less than 3V, so its sixth leg (LV) is connected to output 3. To balance lithium batteries with more high voltage, pin 6 should be left free, not connected anywhere.
Also, with this method it is possible to balance not only two, but also large quantity batteries. In Fig.11. shows how to do this.
Fig. 11. Cascading of charge transfer microcircuits.
Well, and finally, another circuit solution that implements capacitive charge transfer from one battery to another.
If the ICL7660 was a multiplexer that could connect capacitor C1 to only two sources, then taking a multiplexer with a large number of switching channels (3, 4, 8) you can equalize voltages on three, four or eight banks with one chip. Moreover, the banks can be connected in any way, either in series or in parallel. The main thing is that the supply voltage of the microcircuit is higher than the maximum voltage on the banks.
The circuit of the so-called “reversible voltage converter”, described in the magazine “Radio” 1989, No. 8, is shown in Fig. 12.
Fig. 12. Reversible voltage converter as a balancer on the 561KP1.. multiplexer
Up to four elements can be connected to the leveling device. Capacitor C2 is alternately connected to various elements, ensuring the pumping of energy from these elements and equalizing the voltage on them
The number of cells in the battery may be reduced. In this case, instead of the excluded elements, it is enough to connect a capacitor with a capacity of 10..20 μF.
The balancing current of such a source is very small, up to 2 mA. But since it works constantly, without being disconnected from the batteries, it fulfills its task - equalizing the charges of the cells.
In conclusion, I would like to note that the modern element base makes it possible to balance the cells of a composite battery with virtually no losses and is already simple enough to cease to be something “cool” and inaccessible.
And therefore, a radio amateur who designs battery-powered devices should think about switching to active methods of transferring energy between banks in a battery, at least the “old-fashioned way”, focusing on the equality of voltages between battery cells, and not the charges in them.
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Of course separate charge. But this is only for my specific case.
Often you have to work in the field without a network; a screwdriver is always at hand. The batteries were already old and needed improvement. I shook out the dead NiCds from the screwdriver cartridges and stuffed them into both LiPo cases, each holding 5 cans. It’s a blunder, but you also need to charge it in the field or in the car, and it’s advisable to charge it with balancing, because all 5 cans in each account behave differently, which is affected by the ketai. Balancing during charging can be done in different ways, there are countless ways. The simplest is to brake the recharged cans with a load and transfer them to heat. This is what the desktop IMAX B6 does, but I don’t like that it takes a long time to charge the entire battery when balancing is turned on.
I figured it out and thought that the easiest way in terms of circuit design would be to charge each cell in the battery separately. Somehow, while Googling balancing methods, I came across a similar idea:
"Bloody cheaters... When I was thinking about this, I was going to build a bunch of DCDC"s where voltage of each contact is individually controlled => each cell might be charged with individual charge plan. Apparently, this is just too complex. "
But it seemed less complicated to me: we make a DC-DC with 5 outputs and attach a charger microcircuit to each one, of which there are a legion for Li-Ion! And, I thought, there should be less heat: there’s no need to slow down the banks! (Yeah, right now, the charging mikruhs are heating up like bastards!)
Here is a diagram drawn:
The circuit is simple, the only problem was with the choice of transistor. With a broad gesture, I first plugged in the IRLS3034, whose shutter capacity was too much for the LM3478 driver, so I had to install something less flashy. For each channel - an STC4054G, a cheap option that satisfies the task. Here is the assembled board, spread out in one layer: 
The manufacturer of the STC4054G charging chip recommends making the tracks on the board as thick as possible and, if possible, using polygons on both sides of the board for heat dissipation. I didn’t listen to the idiot, but in vain: the mikruhi heat up as they should, even with the charge current set at 400 mA per can.
And from another angle: 
Charges and heats up, infection: 
Well, if it gets hot, it needs to be cooled. I selected a convenient aluminum case, drilled the cover for connectors, fasteners and LEDs. Round holes - with a round cutter, rectangular - with a rectangular one) 
Assembled and ready to sail: 
There was an idea to paint it black, but I was too lazy. And this is pampering - this hedgehog is destined to live in the car under his feet, closer to the cigarette lighter.
Next time I'll think about balancing. I really like the idea of a Robinhood transformer that takes from rich banks and gives it to the poor banks in a battery. It seems like the efficiency is higher and there is less heat. But again, the rich batteries are milked back and forth until the poor ones fill up; This isn't very good, is it?
UPD: According to transformer parameters and ratings. The transformer wound on a not very good core, what was at hand, 2 x MP140-1, KP19x11x4.8. The primary is 21 turns of 0.35 wire, the secondary is simultaneously 11 turns of 0.51 wire. Frequency setting R1C1 - at ~100 kHz, 4.7 kOhm/0.1 µF. Divisor in feedback R2R3 - 21kOhm/8.2kOhm. R4 - 75 kOhm, shunt R5R6 - 0.1 Ohm each (total 0.05 Ohm). VD1 - SMBJ15, VD2 - SM4005. VD4 is some kind of Schottky from 1 A, C5 - 330 µF x 25V, VD8 - 5V1 zener diode, C10 - 0.1 µF. R7 - 470 Ohm, R12 - 2 kOhm, which gives approximately 400 mA.
There are a lot of chargers on the market now. Automatic machines or not, with or without capacitance measurement. Most chargers are universal and can charge elements of any chemistry. Lithium ion and lithium polymer are increasingly used in various devices.
Not long ago I converted the screwdriver battery to lithium-ion 18650 cells. I charge it with a Turnigy smart charger. But not everyone has this charger.
Needed for assembly
I decided to put together a simple Charger with balancer for lithium ion. The charger has 3 identical independent channels. They can charge from one element to three. If necessary, you can add any number of channels. I have three of them, that is, 3S or 11.1 volts.The case for the balancing charger is the case from a burned-out D-link router. If possible, take a larger case; it becomes very cramped to work in it.
One of the main components is the power supply for each channel. Their role is played by tablet charger boards, with an output of 5 Volts and a current of 1 Ampere (or can be bought on Ali Express -.
The charge controllers are boards from China -. Each channel has its own controller. I have boards without protection, but in this case it is not needed. You can use controller boards together with connectors; I don’t have them on two of them; they were removed for other projects. The price for these modules is cheap. If you are modifying devices based on lithium-ion and lithium-polymer, then these controllers are indispensable.
Making a balancing charger
The charge controller boards need to be soldered to the outputs of the charging boards. It can be done separately. I soldered it on thick wires from the power cable, so the structure is more rigid.
The charge controller boards have LEDs that indicate charge and end of charge. They need to be desoldered. Instead, there will be regular LEDs of different colors. They will be attached to the windows where the router's LEDs previously blinked.
I soldered wires from an old cable to the LEDs. hard drive computer. If there are LEDs with a common anode (plus), then it is better to use them. I didn’t have any of these, so I used what I had.
In place of the old LEDs, we solder cables with LEDs. In the photo I have a 3mm green LED. I had to replace them, they turned out to be scorched, I didn’t check them before unsoldering.
For the back panel you need to cut out the trim. We make cuts in it for the power switch and the 4-pin output connector. The connector was removed from an old hard drive. You can use any one for the required number of pins, with a current of 1-2 Amperes.
The switch was removed from the old computer power supply. We fasten the cover with two screws for rigidity.
We glue the output connector with epoxy glue or soda with super glue. For speed, I glued both one and the other.
Charging board with controllers, glued with thermal glue. But before fixing, I soldered the network wires.
We solder one of the network wires to the switch. The second, directly to the second wire of the power cord.
Now we glue the LEDs. I glued it with hot glue, or you can use baking soda and super glue.
Solder the output jumpers.
Plus the first controller on the first leg of the output connector. Minus it on the second leg and connect it to the plus of the second controller. And so on.
We twist the body and put it aside.
Let's make a wire for this charger.
I used two pieces of wire from computer unit nutrition. I soldered it in order from the first contact of one connector to the contact of the second.
Connect the charger to the screwdriver battery (). The red LED indicates the charging process is in progress. When charging is complete, the green LED lights up. Accordingly, the icons on the case light up: Wi-Fi, second and fourth computers.
This is the charger we got. The costs are minimal, but the benefits are great.
This device can charge lithium polymer assemblies, those that modelers use in their vehicles. The main thing is to make the correct charging wire.
