Lipo battery charger. Charger for LiPo batteries. Field charging is safer
Airsoft guns
Recently there have been a lot of questions about LiPo batteries. I decided to write an article about charging, using and selecting LiPo batteries.
For example, consider the ZIPPY Flightmax 1000mAh 2S1P 20C battery
Everything that comes before the number 1000 is the name of the manufacturer or trademark.
1000mAh is the battery capacity.
2S1P– 2S is the number of batteries in the assembly. Each battery has a voltage of about 3.7 volts, so the voltage of this battery is 7.4 volts. 1P is the number of assemblies. That is, if we take 2 identical batteries, connect them with electrical tape and solder the power wires in parallel (plus with plus, and minus with minus), then we will get a doubling of the capacity, such a battery is designated 1000 2S2P and is actually equal in operation to 2000 2S1P. Usually only single assemblies are used, so 1Ps are not spoken or written.
20C– maximum discharge current, measured in battery capacities.
To calculate how many amperes a LiPo can deliver when the engine is loaded, you need to multiply the Capacity by the amount of C and divide by 1000 (since the capacity is indicated in milliamps/hours). The maximum current of this battery will be 20 Amps. For 2200 20C - 44 amperes, 1200 30C = 36 Amps and so on.
Charging LiPo batteries
LiPo batteries are charged with a current of 1C (unless otherwise indicated on the battery itself; recently they have appeared with the ability to charge with a current of 2 and 5C). The standard charging current of the battery in question is 1 Ampere. For a 2200 battery it will be 2.2 amperes, etc.
The computerized charger balances the battery (equalizing the voltage across each battery bank) during charging. Although you can charge 2S batteries without connecting the balancing cable (white connector in the photo), I highly recommend always connect the balancing connector! 3S and large assemblies should only be charged with the balancing cable connected! If you don’t connect and one of the cans reaches more than 4.4 volts, then you will be in for an unforgettable fireworks display!
You can protect yourself and charge in special packages - they are not flammable and are specially designed to reduce harm in the event of a LiPo battery fire.
We continue the story about charging LiPo batteries.
Usually, about 90% of the battery’s capacity is quickly filled into the battery, and then recharging begins with balancing of the cans. The more charged ones and those that have approached the limit are shunted and the charge goes to the remaining banks. That's why it can charge a pair of 3S batteries as one 6S.
The battery charges to 4.2 volts per cell (usually a few millivolts less).
Storage mode
On a “smart” charger, you can put the LiPo into storage mode, and the battery will be recharged/discharged to 3.85V per cell. Fully charged batteries will die if stored for more than 2 months (maybe less). Tested by personal experience. They say that they are also completely discharged, but for a longer period.
I store batteries in a plastic case. It's comfortable. An acquaintance keeps it and carries it in the fields in the above-mentioned packages. LiPo is an ordinary battery and if you do not short-circuit the contacts and do not pierce it through, it will not cause any problems during storage and transportation.
LiPo Operation
It is not recommended to discharge a LiPo battery below 3 volts per cell - it may die. You can use sound indicators, but there is a chance that it will squeal at the most inopportune moment and you will be bombarded with balls from head to toe, like the last horse! The sound tweeter is connected to the balance connector and when it beeps, it’s time to change it or get a secondary one.
When the motor consumes more current than the battery can supply, the LiPo tends to swell and die. So you need to strictly monitor this! Use wattmeters for monitoring.
There is one more nuance during operation - our battery is 1000mAh 20C. In theory it supplies 20A. Motors usually allow you to exceed the recommended currents by 20%, but I exceeded them by 80% :)
In reality, batteries do not hold their maximum current output very well. For example, my 2200 20C delivers a current of 44A for only 2-3 minutes, then there is a voltage drop, although according to calculations it should deliver at least 5 minutes.
So when choosing a LiPo battery, we look at the maximum current declared for the selected motor and add a reserve. So for a motor that consumes 8-12A, our 1000mAh 20C is quite suitable, but for 16-18A I would choose either one with a higher current output, for example 25-30C, or take a larger capacity, for example 1600 20C.
Lipo models are high quality products from the field of radio controlled electronics. Batteries for them must also correspond to the quality and durability of radio-controlled products.
The Lipo charger is considered one of the most common devices in its field. They are distinguished by power, charging speed, housing and size. They are sold in a wide variety. There are batteries of 1.6, 2.2, 2.65, 3.8, 4, 5, and even 6000 milliamps. They are made mainly in a hard protective case, which makes the device more durable, protecting it from various mechanical damage.
Principle of operation
A LIPO battery is charged with 1C current (unless it is indicated to charge differently on the battery itself. The fact is, today, scientific and technological progress does not stand still, and chargers with the ability to recharge at 2C and 5C levels have already begun to appear ). The basic charging current of this battery starts from 1 Ampere. For example, a 2200 milliamp battery requires 2.2 amps of charging power. This charging procedure will also apply to other types of chargers of this type.
The computerized charger performs battery balancing (equalizing the volt load on each battery cell) during recharging. Although you can charge using 2S batteries, without using the balancing cable, shown in the white connector in the photo, it is strongly recommended to connect the balancing connector. 3S and newer charging capabilities must only be used with the balancing wire connected. If you do not follow these instructions, the device may overvoltage and subsequently cause a fire in the house.
Where is it profitable to purchase this type of charger?
Our online store deals with direct sales of high-quality radio equipment. We purchase radio-controlled models and spare parts for them exclusively from trusted suppliers. Here you can choose chargers for Lipo models of the highest quality at very affordable prices.
For charging high-capacity LiPo batteries, inexpensive charging balancers are not entirely suitable due to the limited charging current, as a result of which the charge of high-capacity batteries (2...5A) is extended over a very long time. The proposed charger is designed for charging 2S...3S LiPo batteries of high capacity with their balancing and individual shutdown of the banks, on which the voltage has reached 4.2 volts.
This circuit is designed for charging 2S and 3S batteries, but if you need to charge 4S or 5S batteries, it is enough to increase the number of cells. All cells are the same.
Let's look at the principle of operation of the memory using the example of one cell. The basis is a precision zener diode TL431 with an adjustable switching threshold. The switching threshold is set by a resistive voltage divider at the output of the zener diode control electrode. Until the zener diode turns on, all the charging current flows through the battery. The zener diode is connected in parallel to the battery through a 1 kohm resistor, and the voltage on the positive bus, as well as on the resistive divider (and on the control electrode of the zener diode) gradually increases as the battery is charged. When the battery voltage reaches 4.2 Volts, the zener diode opens and the voltage drop across the 1 Kom resistor opens the KT816 power transistor. The charging current now passes through it. The signaling LED lights up. A chain of 4 series-connected powerful diodes and the junction of the FE transistor is a powerful zener diode with a stabilization voltage of about 4.2 Volts, which prevents the battery from discharging through the open junction of the transistor. Select the *1.5 Kom resistor in such a way that when the voltage on the corresponding battery bank reaches +4.2 Volts, the zener diode opens and the signal LED lights up.
Modified scheme.
Transformer TN36 or similar.
Transistors KT816 (collector current 3 A).
Diodes – powerful KD226 diodes with a current of at least 2 A.
Powerful wirewound variable resistor 10…..20 Ohm to regulate the charge current.
Ammeter 1….3 A, to control the charge current.
Each transistor has a small radiator 20 x 40 mm made of 1 mm aluminum.
The output voltage supplied from the rectifier to the balancer must exceed the voltage of the battery being charged. The rectifier uses a diode bridge with a current of 3 A and a capacitor of 2200 uF x 36 Volt.
For one can, the voltage from the rectifier should be about 6 Volts.
For two cans, the voltage from the rectifier should be about 11 Volts.
For three cans, the voltage from the rectifier should be about 15 Volts.
For four cans, the voltage from the rectifier should be about 20 Volts.
If necessary, you can switch the transformer windings.
The cutoff voltage of a charged can is 4.2 volts.
The charging current for batteries is set by a powerful wirewound variable resistor 10...20 Ohms within 1...2 A, and for small capacity batteries within 0.5 A.
I've been using this charger for two years. I charge 1.8……….3.0 A batteries.
Installation
Negative of the printed circuit board for three charging cells (3S LiPo). View from the paths.
Option for the design of the charger. Front view. The diodes are lit - the charge is complete.
Back view. The axis of the variable wirewound resistor for setting the current is visible.
General view of the interior.
View of the printed circuit board.
Visible are a variable resistor, a diode bridge, and a filter capacitor.
Especially for skeptics and adherents of microcontrollers, I want to say the following.
I in no way deny the advantages of microcontrollers over 80s technologies!
But the circuit design and technologies of the 80s are accessible even to beginning radio amateurs, which cannot be said about microprocessors. In this article I just want to show that using simple Soviet radio elements, you can, without much effort and material costs, assemble this or that device needed for business in a couple of days!
Alexander Degtyarev, Vladikavkaz
Additional article
With the sequential charging method, one of the main requirements that must be met is the following: the voltage in any section of the charged lithium battery during charging must not exceed a certain value (the value of this threshold depends on the type of lithium element). It is impossible to ensure that this requirement is met during sequential charging without taking special measures... The reason is obvious - the individual sections of the battery are not identical, so the maximum permissible voltage on each section during charging is achieved at different times. A situation arises when we must stop charging, since the voltage on some sections has already reached the maximum permissible threshold. At the same time, some sections remain undercharged. This is bad mainly because as a result the total capacity of the battery decreases, so we will have to stop discharging the battery at the moment when the voltage on the “weakest” (undercharged) section reaches its minimum permissible threshold.
To prevent the voltage from increasing during charging above a certain threshold, a balancer is used. Its task is quite simple - to monitor the voltage on a separate section, and as soon as the voltage on it reaches a certain value during charging, give a command to turn on the power switch, which will connect a ballast resistor in parallel to the section being charged. Moreover, if the residual charging current (and it is already quite small towards the end of charging, due to the small potential difference between the voltage on the battery being charged and the voltage at the output of the charger) will be less (or equal) to the current flowing through the ballast resistor, then the increase in voltage on the charging section will stop. At the same time, charging of the remaining sections, the voltage on which has not yet reached the maximum permissible values, will continue. The charging process will end when the balancers of all sections of the battery are activated. The voltage in all sections will be the same and equal to the threshold to which the balancers are set. The charging current will be zero, since the voltage on the battery and the voltage at the output of the charger will be equal (no potential difference - no charging current). Only current will flow through the ballast resistors. Its value is determined by the size of the series-connected ballast resistors and the voltage at the output of the charger.
The voltage control function itself could easily be performed by any comparator equipped with a reference voltage... But we don’t have a comparator (more precisely, we have one, but it’s not convenient or profitable for us to use it). We have TL431. But, to be honest, there is no comparator from it. She can compare the voltage with the reference voltage very well, but she cannot issue a clear, unambiguous command to the power switch. Instead, when approaching the threshold, it smoothly begins to drive the power switch into the active (half-open) mode, the key begins to get very hot, and, as a result, we have not a balancer, but complete nonsense.
This very problem, which did not allow the TL431 to be fully used, was solved the other day. The casket simply opened (but it took more than two years to open it) - it was necessary to turn the TL431 into a Schmitt trigger. Which is what was done. The result was an ideal balancer - accurate, thermally stable, quite simple, with a clear command to the power switch.
Below are two schematic diagrams of balancers designed to control the thresholds of LiFePO4 and Li-ion batteries.
It was possible to turn the TL431 into a Schmitt trigger by adding transistor T1 and resistor R5 to the pnp circuit. It works like this - the divider R3, R4 determines the threshold of the controlled voltage. At the moment when the voltage on the control electrode reaches 2.5 Volts, TL431 opens, and transistor T1 also opens. In this case, the collector potential increases, and part of this voltage through resistor R5 enters the control electrode circuit TL431. At the same time, TL431 enters saturation like an avalanche. The circuit acquires a pronounced hysteresis - switching on occurs at 3.6 Volts, and switching off occurs at 3.55 Volts. In this case, a control pulse with very steep edges is formed in the gate of the power switch, and the power switch cannot enter the active mode. In a real circuit, with a current through the balancing resistor equal to 0.365 Amperes, the voltage drop at the drain-source junction of the power switch is only 5-6 mV. At the same time, the key itself always remains cold. Which, in fact, was what was required. This circuit can be easily configured to control any voltage (divider R3, R4). The maximum balancing current is determined by resistor R7 and the voltage on the battery section.
Briefly about accuracy. In an actually assembled five-section balancer for a LiFePO4 battery, the balancing voltages fell within the range of 3.6-3.7 Volts (the maximum allowable voltage for LiFePO4 is 3.75 Volts). During assembly, ordinary (not precision) resistors were used. In my opinion, this is a very good result. I believe that there is no special practical sense in achieving greater accuracy when balancing. But for many, this is more a matter of religion than physics. And they have the right and the opportunity to achieve greater accuracy.
The figure below is a separate balancer board, and, for example, a six-section balancer board. Obviously, by cloning a separate balancer board, you can easily make a balancer board for any number of sections and any proportions. This is the charging and balancing device I now use. I use the power supply described in the article about the adaptive current limiting inverter. But you can use any other stabilized power supply by modifying it with a shunt.
The balancer is made in the form of a separate board. It connects to the battery balance connector during charging.
A few words about components. TL431 and pnp bipolar transistor (almost any will do) in SOT23 packages can be found on computer motherboards. There you can also find power switches with “digital” levels. I used CHM61A3PAPT (or FDD8447L) in TO-252A packages - they fit perfectly, although the characteristics are very redundant (for currents up to 1A, you can find something simpler).
In modern devices for monitoring lithium batteries, the functions described above are assigned to the microcontroller. But these are much more complex devices to replicate, and their use is not always justified. I think it’s not bad at all when you have a choice.
This is what the balancer looks like “live”. For the quality of workmanship, I again apologize - to save time, I again drew the board with an ordinary permanent felt-tip pen.
Surely, every radio amateur has encountered a problem when connecting lithium batteries in series, he noticed that one runs out quickly and the other still holds a charge, but because of the other one, the entire battery does not produce the required voltage. This happens because when charging the entire battery pack, they are not charged evenly, and some batteries gain full capacity while others do not. This leads not only to rapid discharge, but also to failure of individual elements due to constant insufficient charging.
Fixing the problem is quite simple; each battery cell needs a so-called balancer, a device that, after the battery is fully charged, blocks its further recharging, and uses a control transistor to pass the charging current past the cell.
The balancer circuit is quite simple, assembled on a precision controlled zener diode TL431A and a direct conduction transistor BD140.
After much experimentation, the circuit changed a little, 3 1N4007 diodes connected in series were installed in place of the resistors, the balancer, in my opinion, became more stable, the diodes get noticeably warm when charging, this should be taken into account when laying out the board.
Principle of operation very simple, as long as the voltage on the element is less than 4.2 volts, charging is in progress, the controlled zener diode and transistor are closed and do not affect the charging process. As soon as the voltage reaches 4.2 volts, the zener diode begins to open the transistor, which shunts the battery through resistors with a total resistance of 4 Ohms, thereby preventing the voltage from rising above the upper threshold of 4.2 volts, and allows the remaining batteries to charge. A transistor with resistors calmly passes a current of about 500 mA, while it heats up to 40-45 degrees. As soon as the LED on the balancer lights up, the battery connected to it is fully charged. That is, if you have 3 batteries connected, then the end of the charge should be considered the lighting of the LEDs on all three balancers.
Settings It’s very simple, we apply a voltage of 5 volts to the board (without a battery) through a resistor of approximately 220 Ohms, and measure the voltage on the board, it should be 4.2 volts, if it differs, then we select a 220 kOhm resistor within small limits.
The charging voltage needs to be supplied approximately 0.1-0.2 volts more than the voltage on each element in the charged state, example: we have 3 series-connected batteries of 4.2 volts each in the charged state, the total voltage is 12.6 volts. 12.6 + 0.1 + 0.1 + 0.1 = 12.9 volts. You should also limit the charge current to 0.5 A.
As an option for a voltage and current stabilizer, you can use the LM317 microcircuit, the connection is standard from the datasheet, the circuit looks like this.
The transformer must be selected based on the voltage of the charged battery + 3 volts according to the variable, for correct operation of the LM317. Example: you have a 12.6 volt + 3 volt battery = a transformer needs 15-16 volt alternating voltage.
Since LM317 is a linear regulator, and the voltage drop across it will turn into heat, we must install it on a radiator.
Now a little about how to calculate the divisor R3-R4 for voltage stabilization, but very simply according to the formula R3+R4=(Vo/1.25-1)*R2, the Vo value is the end-of-charge voltage (maximum output after the stabilizer).
Example: we need to get 12.9 volts output for 3. batteries with balancers. R3+R4=(12.9/1.25-1)*240=2476.8 Ohm. which is approximately equal to 2.4 kOhm + we have a trimming resistor for precise adjustment (470 Ohms), which will allow us to easily set the calculated output voltage.
Now calculate the output current, the resistor Ri is responsible for it, the formula is simple Ri=0.6/Iз, where Iз is the maximum charge current. Example: we need a current of 500 mA, Ri=0.6/0.5A= 1.2 Ohm. It should be taken into account that a charging current flows through this resistor, so its power should be 2 W. That's all, I'm not posting the boards, they will be when I assemble a charger with a balancer for my metal detector.
I needed a charger for a 3-can lithium battery and in order not to buy the classic iMax B6, I looked into Bengood to see what alternative there was. It turned out there were many alternatives, and comparing the charging capabilities and your wallet, the choice fell on the subject. The order was paid for, shipped the next day (thanks to the store!) and the languid wait began. What is the result and conclusion - please, under cat.
A month later the parcel was received. The packaging is standard for beng: a black plastic bag, the product is wrapped in polyethylene foam. The box was slightly damaged but not fatally. The insides survived. 
Included: box, charger, instructions in English, cable. The cable is short with an American plug - it went into the trash. A cable from a portable tape recorder is used as a replacement. 
The charger is a kind of box 88x55x30mm, black plastic, normal quality.
On the front side there are 3 two-color (red/green) LEDs indicating the status of the can. Green - charged, red - charging. The missing can's LED lights up green. 
That is, when charging is turned on without a battery, all the lights turn green. A bit strange algorithm. 
Electrical parameters promised by the manufacturer:
Supply voltage: 110-220V
Power: 20W
Outgoing current (load current): 1600mA, 3x700mA is indicated on the case.
Weight: 100g - actually less.
Instructions
Let's move on to the autopsy. The case opens easily - 4 screws.
As you can see, the screws were not selected or the case was not made correctly - all the posts into which the screws were screwed burst.
The board appears to be of good quality, as is the installation. 
On the reverse side, the flux is washed off but not completely; there are also “snot” of hot-melt adhesive that are fixed to the LED stands.
The power supply is made on the popular DK112 chip, and the charging part is made on the even more popular :) TP4056 chip, which everyone knows from the compact Li-po battery charging board. One TP4056 per channel. The current-setting resistor is 1.5 kOhm, which according to the specification corresponds to a maximum charge current of 780 mA. For the first time I see the Chinese underestimating the parameters of the device)))
By the way, the charge current to the jar can be adjusted by changing the resistance of the resistor. This is in case you don’t need such a high charging current, but this charging is available or is suitable for some other reason.
780 mA is not a small current, and if you triple it, then the heating should be decent. That’s right - when charging, the box gets warm but not hot, most likely because the chips are located far from the case. It would be nice to stick a radiator on the chips, but there is nothing suitable yet. Let's see how long the TP4056's resources will last - in the reviews on Benga there is one about a burning channel. Fortunately, the TP4056 chips themselves cost ten per dollar, so you can easily change them.
Battery charge
A 2S battery (4500x2) with a charge of approximately 70% was connected to the charger. 
The charger carefully charged it, one LED went out, then the second. 
Result: one bank is 4.17V, the second is 4.2V. Good result. 
For comparison, I measured the battery with a buzzer and a multimeter. 
Later, a 2S battery (300x2) was charged and one bank was also undercharged: 4.16/4.20V. The reason is in the TP4056 chips, either Chinese tolerances or rejection...
If desired, you can replace the TP4056, which is undercharging, in order to get ideal charging.
It is not yet known what maximum current the charger produces when charging a 3S battery and whether the built-in power supply draws out, since there is no such battery at hand, and how to measure the current on three channels, you can, of course, measure the total current after the power supply comes out, but next time.
In general, let's summarize.
Pros: has a built-in power supply, can balance the charge between banks, good price.
Minuses: the cooling system for the charging part is poorly implemented (it is advisable to install radiators on the TP4056, drill additional holes in the case for better ventilation), a short cable with a flat plug, the final charging result is not ideal (although this may be my nit-picking).
Conclusions: I liked the charger and has a right to exist. If you do not need multi-charging and, for example, have only one device with a multi-cell battery, then this charger will be a good choice for using it near an outlet.
If you have the desire and direct hands, the charging can be upgraded to obtain a more accurate charge voltage.
