In this article we will try to understand the main specifications and datasheet of the Li-Ion cell 18650 2600 mAh, which is one of the most popular Li-ion batteries, and preferred by all electronic professionals due to its high efficiency, in terms power delivery and compact dimensions.
Li-Ion batteries are one of the most advanced forms of batteries which are designed to charge and discharge at high efficiency rates, compared to any other form of batteries.
Li-Ion batteries are able to charge significantly quickly by storing the voltage and current at almost 90% efficiency, and are able to deliver the same with almost the same amount of efficiency. That's the reason today all advanced and state-of-the-art gadgets depend on Li-Ion batteries for their functioning and performance.
In this article we are discussing the 18650 2600mAh Li-Ion Cells which look quite similar to the well known traditional AAA 1.5V cells, but are a lot more powerful and efficient with their ratings.
Difference Between AAA 1.5 Cell and 18650 2600 mAh Li-Ion Cell
The main differences between these two counterparts can studied as given below:
- AAA cells are rated at 1.5V whereas the 18650 2600 mAh cells are rated at 3.7V
- AAA cells are rated at maximum 1000 mAh, 18650 cells have the capacity as high as 2600 mAh
- Only Ni-Cd variants of AAA cells are chargeable with lower efficiency, while all 18650 2600 mAh are chargeable with great efficiency.
- AAA are mostly use-and-throw types having short life span, 18650 2600mAh have long life span and can be charged and discharged many 100 times with sustained efficiency.
Main Electrical Datasheet and Specifications
The main electrical datasheet and specifications of the 18650 2600 mAh cell can be understood from the following explanation:
- Nominal Voltage: 3.7V
- Maximum Ah rating: 2600 mAh
- Internal Impedance: around 70 milliohms
- Minimum Low Voltage Cut-off Limit: 3 V
- Recommended Full Charge or maximum Charge Cut-OFF Limit: 4.2V
- Recommended Charging and Discharging Rate: @0.52 Amps
- Possible Fast Charging and Fast Discharging Rate: @1.3 Amps at controlled case temperature
- Maximum allowable Charging and Discharging: @2.6 Amps in pulsed form and under controlled case temperature.
- Allowable Case Temperature range during Charging: 0 to 45 degrees Celsius
- Allowable Case Temperature range during is Discharging: -20 to 60 degrees Celsius.
How to Charge a 18650 2600 mAh Battery
Just as any other 3.7V Li-Ion battery , the 18650 2600mAh Battery must be charged with constant current constant voltage (CC/CV) rate, wherein the charger voltage must be rated at a constant 4.2V, and with a constant 0.52 ampere current.
The battery should be charged until its terminal voltage reaches 4.2V when the charging supply should be cut-off.
While discharging, an identical pattern as above must be followed wherein the connected load must be preferably rated to consume current at not more than 0.52 amps, and must be disconnected before the battery reaches around 3.1V.
Simple (CC/CV) Auto cut-off Charger Circuit for Charging 18650 2600mAh Battery
The above figure shows a simple 18650 2600mAh Battery charger circuit using a single LM317 IC regulator and an IC 741 based opamp stages.
Rx may be calculated as given below:
Rx = 1.2 / 0.6 = 2 ohm/ 1/2 watt
If you want to use fixed resistor instead of the 4k7 preset, you can calculated the same with the following formula;
VO = VREF (1 + R2 / R1) + (IADJ × R2)
where is = VREF = 1.25, R1 = 240 ohms, R2 = for 4k7 preset
Current ADJ is just 50 µA and therefore too small to be considered in the formula, you can remove it.
Alternatively you could also try this software
Setting up the circuit is easy
Keep the 10K preset slider to ground position. Apply minimum 6V at the input, and adjust the 4K7 pot to produce a precise 4.2V across the points where the battery is supposed to be connected.
Now, slowly adjust the 10k preset until the LED just lights up, seal the preset with epoxy glue.
Do this without connecting a battery.
That's all, the auto cut off system is all set now.
You can confirm the set up by attaching a discharged 18650 cell across the indicated points, then switch ON the supply, and wait until the red LED lights up. When this happens you can assume that the battery is fully charged, and can be removed for usage.
Simpler 18650 Charger Designs
As explained in other related post, charging Li-ion battery is not critical and can be done with a simple circuit, provided a couple of criteria are maintained.
The first condition is that the battery or the cell must be charged at a calculated constant current rate which does not heat up the battery above 37 degrees Celsius.
The second condition is to ensure the battery does not get overcharged and is cut off at exactly 4.2 V.
If an auto cut off charger seems difficult to build, this can be avoided simply by lowering the full charge threshold at 4.1 V. This level might slightly reduce the back up time, but nevertheless the battery will enjoy a good health, longer life, and moreover the charger could be built using ordinary parts or a single LM317 IC as shown below:
Adjust the pot to get an exact 4.1 V at the output for the 18650 cell.
- R1 = 240 ohms
- D1---D4 = 1N4007
- POT = 4k7 pot
- C1 = 1000uF/25 V
- Transformer = 0-6V/1 amp
Where can 18650 2600mAh Battery be Used
It can be used in all sorts of battery based applications which have to go through relentless power usage for a specific purpose, such as LED flashlights, emergency lights, drones and quadcopters, DC drill machines, hair trimmers etc.
These cells can be also effectively used in power bank circuits, an example power bank circuit can be seen below:
As we can see in the figure, two 18650 2600 mAh cells are connected in series inside a compact enclosure, and the output terminal are configured for charging the desired cellphone during emergency usage.
To render the power bank in ready or stand by position, it should be first charged using a charger that is explained in the previous section of this article. The input voltage must be set at 8.4V.
Once fully charged the power bank should be removed from the charger, during this time the battery voltage may drop to its standard level of 3.8V each constituting a total voltage of 7.6V.
The attached diodes make sure that the final output from the power bank is dropped to around 5.2V, while the 2 ohm resistor adds a current control feature to the output. This resistor value may need to be adjusted depending on the type of cellphone connected with the output, so that the charging is optimally and efficiently implemented
Once the above standby by state achieved, this 18650 2600mAh based power bank could be carried outdoors by the user for the intended emergency charging purpose.
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