Hi all! I would like to talk a little about Li-ion 18650 batteries. Various wireless devices occupy an increasingly important place in everyday life: portable and easy-to-use cordless drills, laptops that allow you to work for a long time without using an electrical network. All this makes our daily life more convenient and easier. But a special place is occupied by the use of autonomous battery devices not near the house, where you can always charge the device, but far from power sources.
On a camping trip, hunting or fishing, the most necessary, and sometimes irreplaceable, electrical device is a flashlight. Modern flashlights equipped with LEDs have a huge number of advantages. But the main characteristic of any electric flashlight, of course, is the duration of its operation. For tourists who go on multi-day trips, it is the duration of the flashlight that is of great importance when choosing. And this characteristic directly depends on the type of battery that comes with the flashlight.
The compactness and lightness of equipment plays an important role for any tourist. Therefore, important characteristics for batteries are size and weight - the smaller the better. At the same time, the batteries must have a large capacity, which will ensure long and uninterrupted operation of the flashlight, often the main source of light in the dark. Modern technologies make it possible to combine small size and weight with high battery capacity.
One of the most common batteries for LED flashlights are 18650 batteries. These compact batteries with a relatively large capacity are best suited for modern light sources, often used by tourists, fishermen and hunters.
A little theory about 18650 lithium batteries
The name itself indicates the dimensions of the battery - 18 millimeters in diameter, 65 millimeters in length. Despite the fact that they look similar in appearance to the AA-size batteries that many are familiar with (the so-called “pen-type” batteries), 18650 batteries are larger in size. In addition, a distinctive feature of 18650 batteries is the voltage, which at the output is 3.7 V, versus 1.5 V for smaller batteries. The capacity of 18650 batteries varies: from 1600 to 3600 mAh. It is necessary to pay attention to the fact that the capacity of a high-quality battery cannot exceed 3600 mAh. Batteries can be used in flashlights either individually or in a Power Bank system - a device that combines several identical batteries.
One of the main qualities and advantages of batteries is the absence of memory effect and extremely low level of self-discharge. 18650 batteries can withstand up to 1000 charge/discharge cycles, which is a very good indicator for portable batteries. Gradually, the battery charge life decreases, but with the help of special technical devices, the capacity can be restored; the only condition for restoration is the absence of mechanical damage to the battery.
It must be taken into account that in order to use the battery resource more rationally, you should not completely discharge it. It is optimal to recharge the battery when the capacity is reduced to 40% of the nominal value. If used properly, the battery will serve reliably for a long time. Despite their many advantages, 18650 batteries have one drawback associated with their design. Batteries often fail quickly if they are overcharged or overheated. Overcharging causes the battery to heat up, causing the battery to catch fire or explode. Manufacturers have provided an option to protect batteries from overheating. When using 18650 batteries in a Power Bank, when connected in series, an electronic board is installed in the circuit, which limits the charge of the entire device to a given capacity.
For 18650 batteries, used, for example, in flashlights, an individual system of protection against overcharging and subsequent overheating is used. The protection is a small electronic protective board that is installed on the negative terminal of an unprotected lithium-ion battery and welded to the case with steel tape. This prevents not only overheating, but also a short circuit, which can damage not only the battery, but also the charger. The entire structure is packed in thermal film. To charge 18650 batteries, you will need a special charger that is suitable for all types of batteries of this size. For example, the ARE-X1 Fenix Charger, the i1 NiteCore Charger, or the Robiton SmartCharger Pro Charger.
Almost all modern lithium-ion batteries have excellent energy capacity, as well as high compact dimensions. It is with their help that you can power high-power devices with the greatest efficiency. And for this it is absolutely not necessary to buy a ready-made charger in a store, because there is a more budget-friendly option that radio amateurs will especially like - to assemble a charger for lithium-ion batteries with your own hands.
Precautions: overcharging is prohibited
It is extremely important to remember one simple thing before starting to assemble a battery for batteries - lithium batteries are strictly prohibited from recharging. They have very strict requirements for the charging mode and operation, so they cannot be charged to a voltage greater than 4.2 V. It is even better to be guided by information about the safe threshold for each individual can. By the way, even a lower threshold may be indicated there, which is considered acceptable for this instance.
It’s even better if you’re going to do your own lithium battery charging, check the materials and equipment used several times. If you have doubts about the accuracy of your voltmeter readings or the origin of the cans, as well as the maximum permissible power of their charge, it is better to set the threshold even lower. The optimal range will be within 4.1–4.15 V. In this case, charging batteries that do not have a built-in protection board will be safe for you.
Otherwise, there is a high probability of strong heating and swelling of the cans, copious release of gas with a strong unpleasant odor, and even their subsequent explosion. Check everything several times before proceeding with assembly and charging.
How to assemble a lithium charger DIY batteries
One of the simplest, if not the simplest, option for creating a charger. It involves the use of the LM317 chip. It is cheap and widely available, plus it is equipped with a charge indicator.
The setup comes down to setting the output voltage to 4.2 Volts using trimming resistor R8. Just be sure to not have the battery connected. The charging current is also set by selecting resistors R4 and R6. The recommended power of resistor R1 should be at least 1 Watt.
When the LED on the circuit goes out, this signals the completion of the battery charging process. In this case, the charging current will never decrease to zero.
Microcircuits of the LM317 type, like its analogues, are very widely used in all kinds of current and voltage stabilizers. At the same time, you can buy them at any radio market, and they will cost mere pennies.
The disadvantage of the circuit can be considered the supply voltage, which must be from 8 to 12 V. This is due to the fact that for the normal functioning of the microcircuit, a difference between the voltage on the automatic transmission and the supply voltage is required to be at least 4.25 V, that is, power the device using the USB port will not work.
The sequence for collecting lithium battery charging with your own hands is as follows:
- select a suitable case;
- attach the power supply (5 V) and the elements of the specified circuit to it (necessarily in the correct order);
- take brass and cut out two strips from it, attach them to the sockets;
- using a nut, set the distance between the contacts and the battery that you are going to connect;
- attach the switch if you want to later be able to change the polarity on the sockets (if not, leave everything as is).
But if the task is to assemble a charger designed to work with 18650 batteries, then you should immediately move on to more complex circuits, or buy a ready-made device. Without the appropriate technical skills, it will not be possible to assemble the unit. Sometimes it’s really easier to spend a little more money, but take a factory charger with the necessary parameters and protection.
How to assemble a charger for lithium-ion batteries with your own hands?
Since Li-Ion batteries are sensitive to sudden voltage during charging, special chips are built into branded batteries. They provide voltage control and do not allow the permissible limits to be exceeded. Therefore, in order to assemble a charger for 18650 lithium batteries with your own hands, you need a more complex circuit than the one discussed above.
This version of the battery will be much more difficult to create than the previous one, and at home it is only possible if you have certain skills and relevant experience. In theory, you can get a charger whose characteristics are in no way inferior to branded batteries. But in practice this is not always the case.
Have you assembled a charger at home from scrap materials? Tell us about your results in the comments.
Of the huge variety of li-ion batteries, the 18650 battery is especially in demand. Long service life and stable battery parameters are ensured by compliance with a number of rules, but the main condition affecting the performance of 18650 lithium-ion batteries is their correct charging.
18650 battery
The main positive characteristics of 18650 lithium batteries are the ability to accumulate a large amount of charge, store this charge for quite a long time, the lack of memory properties and a meager specific gravity.
The memory effect is primarily characteristic of nickel-cadmium batteries. This effect means some loss of battery capacity if it is charged until it is completely discharged.
For 18650 battery and othersli-ion batteries has its own marking:
- The first two digits indicate the diameter in millimeters;
- The next two numbers indicate the length in millimeters;
- The last digit indicates the type of battery (0 indicates the cylinder).
At the initial stage of production and use, such batteries were explosive due to uncontrolled chemical reactions inside and cases of short circuits inside the batteries. To prevent such breakdowns, all rechargeable batteries in general and 18650 batteries in particular are equipped with special boards with controllers that prevent damage to the battery due to critical overheating and depressurization.
Optimal storage conditions for lithium-ion batteries are achieved at a temperature of 5°C with a 40% battery discharge.
How to charge a 18650 battery
Well-known charger manufacturers use a two-stage battery charging method.
The two-stage charging method includes:
- The task of the charger at the first stage is reduced to charging with a stabilized current. The charging current is determined by the nominal capacity of the battery with a coefficient of the order of 0.2 to 0.5. During charging, the voltage automatically increases to maintain a stable current. At a voltage of 4.2V, the charging process stops at this stage. By this point, the battery manages to replenish its capacity by 70-80%. In order to reduce charging time, a rapid charging process is used for lithium batteries. In this case, the charging current is taken with a coefficient of 0.5-1.0;
- Charging 18650 in the second stage takes place with a constant voltage. The 18650 charging board supports Ucharge ~ 4.15-4.25V and controls the current value. The current value during charging gradually decreases to a value of 0.05-0.01 of the battery capacity. Accordingly, the charging process is considered complete.
In addition to the above-mentioned charging stages, a preparatory battery charge is applicable for 18650 li-ion batteries. Charging is carried out with a reduced current until the voltage on the battery reaches 2.8V.
Despite its indispensability, the two-stage charging system has some disadvantages. Since the voltage on the battery is measured while a large charging current passes through it, depending on the internal resistance of the battery, such measurements may vary. In this regard, the voltage can reach 4.3-4.4V, which has an extremely negative effect on the battery. In practice, it is better to use chargers with current pulses if there are gaps between them. During these intervals, the voltage on the battery is measured. The closer the voltage is to the value of a fully charged battery, the shorter the pulse the charger produces. Accordingly, when the measured voltage reaches 4.15V, the supply of pulses will stop.
Charger circuits
Radio amateurs quite often wonder how to charge lithium-ion batteries and how to charge with maximum savings of resources, effort and time. The presence of the necessary element base and basic knowledge will not leave the radio amateur without a charger.
The assembled DIY 18650 charger, shown in the picture below, is adjusted by setting the output voltage to 4.2V with trimming resistor R8 and the charging current with resistors R4, R6. The charging process is considered complete after the HL1 LED goes out.
Important! For normal operation of the LM317 chip, charging for 18650 batteries must have an input voltage in the range of 8-12V.
Homemade charging for 18650, which contains MAX integrated circuits (1551 or 1555), is qualitatively different from its competitors in a number of properties and features:
- Ability to charge the battery from USB or from a separate power supply;
- No external transistors and diodes;
- Protection against excessive overheating by artificially reducing the charging current.
It will not be difficult to obtain a pulse charger for 18650, assembled with your own hands, due to the absence of a microcircuit in the device. The presented charger for 18650 fulfills all the requirements and functions of pulse charging. An additional advantage of the charger is the ability to replace the element base with domestic analogues. A smart charger for 18650 batteries, assembled and tested with your own hands, will last no worse than the purchased charger.
The presented topic revealed the following questions: how to charge the battery, how to charge a li-ion battery. When using a charger for 18650 batteries, purchased or homemade, the main thing is to carefully check the output values. Next, you can pay attention to additional options in the form of LCD displays, the number of channels, the presence of backlight, and a car adapter.
Video
Many people probably have a problem with charging a Li-Ion battery without a controller; I had this situation. I received a dead laptop, and there were 4 SANYO UR18650A cans in the battery that were alive.
I decided to replace the LED flashlight with three AAA batteries. The question arose about charging them.
After digging around on the Internet I found a bunch of diagrams, but details are a little tight in our city.
I tried charging from a cell phone charger, the problem is in charge control, you need to constantly monitor the heating, it just starts to heat up, you need to disconnect from charging, otherwise the battery will be damaged in the best case, otherwise you can start a fire.
I decided to do it myself. I bought a bed for the battery in the store. I bought a charger at a flea market. To make it easier to track the end of the charge, it is advisable to find one with a two-color LED that signals the end of the charge. It switches from red to green when charging is complete.
But you can also use a regular one. The charger can be replaced with a USB cord and charged from a computer or charger with a USB output.
My charger is only for batteries without a controller. I took the controller from an old cell phone battery. It ensures that the battery is not overcharged above a voltage of 4.2 V, or discharged below 2...3 V. Also, the protection circuit saves from short circuits by disconnecting the bank itself from the consumer at the moment of a short circuit.
It contains the DW01 chip and an assembly of two SM8502A MOSFET transistors (M1, M2). There are also other markings, but the circuits are similar to this one and work similarly.
Cell phone battery charge controller.
Controller circuit.
Another controller circuit.
The main thing is not to confuse the polarity of soldering the controller to the bed and the controller to the charger. The controller board has “+” and “-” contacts.
It is advisable to make a clearly visible indicator in the bed near the positive contact, using red paint or self-adhesive film, to avoid polarity reversal.
I put everything together and this is what happened.
Charges great. When the voltage reaches 4.2 volts, the controller disconnects the battery from charging and the LED switches from red to green. Charging is complete. You can charge other Li-Ion batteries, just use a different bed. Good luck to all.
Homemade charger for 18650 batteries.
Once I needed to charge an 18650 battery for a flashlight in the garage, but there was no charger at hand. I have no desire to carry the iMax B6 with me, so I decided to charge it myself at minimal cost.
To charge, you need a 18650 battery holder. Since the holder was going to be used in other places in addition to charging, I decided to buy a lot of several holders. This works out cheaper than buying one at a time.
I ordered a plastic battery holder for the bike. Lot of 4 pcs. cost $1.91 (with coupon)
The parcel arrived in a regular gray Bikov package. Inside are kilometers of baby bumps and, in fact, goods. 
The plastic is normal, the wires are pressed in. A standard size 18650 battery (65mm) fits without problems. Batteries with protection (69 mm) also fit. 
In the photo, a standard size battery is inserted into the holder. When removing the battery, the first question arose: the plastic goes on the sides of the battery to prevent it from spontaneously falling out, but removing the battery becomes problematic. You can, of course, pry off the 18650 with a screwdriver, but the chance of scratching the battery is very high. It was decided to modernize the holder by gluing a strip of fabric (ribbon) in the middle. 
After such an upgrade, the battery can be removed very easily.
The charger requires a charge controller. On eBay, I immediately went to a familiar seller from whom I buy electronics. After a short search I found one for lithium batteries. I bought a controller for $1.11 with an input for a temperature sensor, although you can also find a simpler controller from him for less than a dollar ().
The controller looks like this: 
The scarf has a standard MicroUSB input, which allows you to charge batteries from a computer USB port or from a network charger that has a USB output (for example, here)
The TP4056 chip is soldered on the board (for those interested, there is one)
From the seller's website, the characteristics of the board are:
input voltage: 4V-8V maximum output charging current: 1000mA
the charging D1 indicator lights, charging is completed D2 indicator
PCB board size: 37.3 (mm) x15 (mm)
A short description of the board in pictures:
According to the datasheet, if you increase the resistance of R4 to 2.4 kOhm, you can reduce (limit) the charge current to 500 mA.
I glued the board to the battery holder with a heat gun.
I laid and soldered the wires there too
If you apply voltage to the USB port, the D2 indicator lights up green, and the D1 indicator starts blinking red (the battery is not inserted into the holder). 
When the battery is inserted and external power is connected, the D1 indicator lights up 
On a partially charged battery, readings taken from the USB port:
U=5.02V I=0.49A. Battery voltage 4.21 V
measurements at the beginning of the charge
After charging is completed, the D2 indicator lights up green 
On a fully charged battery, readings taken from the USB port:
I=0.00A. Battery voltage 4.21 V
measurements at the end of the charge
Next, I decided to check whether I had fully charged the battery with a homemade charger. To do this, I waited a couple of hours and tried to charge the iMax B6 battery with a current of 0.5 A. 
As you can see on the indicator, the battery took almost 10 minutes to charge and took only 14 mAh. Moreover, the current almost immediately dropped to 0.1A and remained there for the entire 10 minutes.
By the way, the last photo shows another use of the holder for 18650 batteries.
Up close, the holder with terminals for iMax B6 looks like this: 
I glued the tape with regular superglue. I cut off the sides of the holder (3 pieces) with a utility knife, leaving only one side for safety.
Next, I tried to discharge the battery to understand whether the 18650 would give up its capacity, and at the same time, after discharging, check how much current was consumed at the initial moment of charging from the USB port. 
The photo shows that the 18650 worked 100% (the capacity is written on the battery itself)
Initial charging moment: 
This 1365mAh battery was charged from a completely discharged state in just over 3 hours.
Briefly the pros and cons:
Minuses
It is difficult to remove the battery from the holder. After a little modification, this minus is removed.
Notes (not pros or cons)
I noticed a small bug in the charger. If you apply power to the USB port and then insert the battery, charging will not start. That is, you need to first insert the battery, and then apply voltage to the charger.
pros
1) Price. Fully charge 18650 batteries for $1.5.
2) Possibility of adjusting the charging current by replacing resistor R4 (the datasheet has a table that shows which resistor needs to be installed to set the charging current)
3) Compact
conclusions
For $1.5 and half an hour of time, I got a compact charger, which completely suits me.