The world is shifting away from fossil fuels and will one day become fully electric. In the present world, Lithium-ion is the most promising chemistry of all batteries. Most of the battery packs used in Laptops, RC Toys, Drones, Medical devices, Power tools, e-bikes, and electric cars (EV) are based on 18650 batteries. It is one of the most mature Li-ion formats available, is produced in high volume, and enjoys a low cost per Wh.
The 18650 (18mm diameter and 65mm length) battery is a size classification of lithium-ion batteries. It is the same shape, but a bit larger than an AA battery. AA batteries, by comparison, are sometimes called 14500 batteries because they have a 14mm diameter and 50mm height.
Earlier I have made a Solar Power Generator which is working really nice till now. But the main problem is its weight, it is really heavy. The main weight of the Solar Generator is due to the heavy lead-acid battery inside it. So I decided to make a light and compact 18650 Li-Ion Battery Pack.
In this Instructable, I will show you, how to make a 18650 battery pack for applications like Power Bank, Solar Generator, e-Bike, Power wall etc. The fundamental is very simple: Just to combined the number of 18650 cells in series and parallel to make a bigger pack and finally to ensure safety adding a BMS to it.
At the end of this project, I made a custom 3D printed enclosure for the battery pack.
Full Video Tutorial:
You will find many types of 18650 cells on the market in the price range of $1 to $10, but which are the best? I will highly recommend buying 18650 cells from branded companies like Panasonic, Samsung, Sanyo, and LG. These cells have well-documented performance characteristics and excellent quality control. Reputed brand 18650 cells are generally costly, but if you consider for long time use then they are worth having it.
Don't buy any cells with the word FIRE in the name like Ultrafire, Surefire, and Trustfire. In reality, these cells are just factory rejects, purchased by companies like Ultrafire and repackaged in their own branded cover. Many used batteries are repaired as new and white-labeled. They sell the battery by marking capacity up to 5000mAh, but in actual their capacity is between 1000 to 2000 mAh. Another major problem with these cheap 18650 cells is the high risk of explosion when overheated during the charging or discharging.
In this project, I have used green Panasonic 18650B cells of capacity 3400 mAh from GearBest.
To make the battery pack, you have to connect the 18650 cells together by means of Nickel strips or thick wire. Generally, Nickel strips are widely used for this. In general two types of nickel strips are available in the market: nickel-plated steel strips and pure nickel strips. I will suggest buying a pure nickel. It is a little bit costlier than nickel-plated steel, but it has much lower resistance. Low resistance means, less heat generation during the charging and discharging, which leads to longer useful battery life.
Nickel strips come with different dimensions and lengths. Choose the strips according to the current rating.
You have two options to connect the 18650 cells together: 1. Soldering 2. Spot Welding
The best choice is always Spot welding, but Spot Welder is much costlier than a good quality Soldering Iron.
Soldering:
You should know why Spot welding is preferred over soldering, the problem with soldering is that you apply a lot of heat to the cell and it doesn’t dissipate very quickly. This enhances the chemical reaction in the cell which damages the cell's performance. Ultimately you will lose some capacity and life of the cells.
But if you are not interested to buy a costly Spot Welder, you can solder the nickel tabs to the cell by following some precaution and tricks:
1. To minimize the contact time of your soldering iron on the cell, make sure the surface is scuffed up sufficiently and you use plenty of flux to allow for fast solder flow.
2. It is better to have a good quality high wattage (min 80W) iron with good thermal capacity so it can deliver the heat to the joint quickly so you don't have to hold the iron to the battery for ages and let the heat see into it, causing damage to the battery.
Spot Welding:
The reason we spot weld is because it securely joins the cells together without adding much heat to them. There are two grades of spot welders currently available in the market: hobbygrade and professional grade. A decent hobby-grade Spot welder costs around $200 to $300, whereas a good professional grade may cost around ten times more. So I will suggest buying a hobby-grade spot welder from any online store like Banggood, Aliexpress, or eBay. I am using the SUNKKO 709A 1.9kw Spot Welder from Banggood.
Before connecting the cells in parallel, first, check the individual cell voltages. For paralleling the cells, the voltage of each cell should be close to each other, otherwise, a high amount of current will flow from the cell with a higher voltage to the cell with a lower voltage. This can damage the cells and even result in fire on rare occasions.
If you are using brand new cells, the cell voltage is near 3.5 V to 3.7 V, you can join them together without worrying much. But if you are going to use an old laptop battery, be sure the cell's voltage is nearly the same, otherwise, charge the cells to the same voltage level by using a good Li-Ion Battery Charger. I used my Nitecore SC4 Charger to charge all the 18650 cells before joining them together.
To make the battery pack, you have to first finalize the nominal voltage and capacity of the pack. Either it will be in terms of Volt, mAh/ Ah, or Wh. You have to connect the cells in parallel to reach the desired capacity (mAh) and connect such parallel group in series to achieve the nominal voltage (Volt).
For this project let the requirement is: 11.1 V and 17 Ah Battery Pack
Specification of 18650 Cells Used: 3.7V and 3400 mAh
Capacity(mAh):
The desired capacity of the battery pack = 17 AH or 17000 mAh.
The capacity of each cell = 3400 mAh
No of cells required for parallel connection = 17000 / 3400 = 5 nos
Commonly cells in parallel are abbreviated in terms of 'P', so this pack will be known as a “5P pack”.When 5 cells are connected in parallel, ultimately you made a single cell with higher capacity ( i.e. 4.2V, 17000 mAh )
Voltage:
The desired nominal voltage of the battery pack is 11.1V.
The nominal voltage of each cell = 3.7 V
No of cells required for series connection = 11.1 /3.7 = 3 nos
Commonly cells in series are abbreviated in terms of ‘S’, so this pack will be known as a “3S pack”.
So we have to connect the 3 parallel groups (5 cells in each group) in series to make the battery pack.
The final pack configuration is designated as a “3S5P pack” with a final specification of 11.1V,17AH.
The world is shifting away from fossil fuels and will one day become fully electric. In the present world, Lithium-ion is the most promising chemistry of all batteries. Most of the battery packs used in Laptops, RC Toys, Drones, Medical devices, Power tools, e-bikes, and electric cars (EV) are based on 18650 batteries. It is one of the most mature Li-ion formats available, is produced in high volume, and enjoys a low cost per Wh.
The 18650 (18mm diameter and 65mm length) battery is a size classification of lithium-ion batteries. It is the same shape, but a bit larger than an AA battery. AA batteries, by comparison, are sometimes called 14500 batteries because they have a 14mm diameter and 50mm height.
Earlier I have made a Solar Power Generator which is working really nice till now. But the main problem is its weight, it is really heavy. The main weight of the Solar Generator is due to the heavy lead-acid battery inside it. So I decided to make a light and compact 18650 Li-Ion Battery Pack.
In this Instructable, I will show you, how to make a 18650 battery pack for applications like Power Bank, Solar Generator, e-Bike, Power wall etc. The fundamental is very simple: Just to combined the number of 18650 cells in series and parallel to make a bigger pack and finally to ensure safety adding a BMS to it.
At the end of this project, I made a custom 3D printed enclosure for the battery pack.
Full Video Tutorial:
You will find many types of 18650 cells on the market in the price range of $1 to $10, but which are the best? I will highly recommend buying 18650 cells from branded companies like Panasonic, Samsung, Sanyo, and LG. These cells have well-documented performance characteristics and excellent quality control. Reputed brand 18650 cells are generally costly, but if you consider for long time use then they are worth having it.
Don't buy any cells with the word FIRE in the name like Ultrafire, Surefire, and Trustfire. In reality, these cells are just factory rejects, purchased by companies like Ultrafire and repackaged in their own branded cover. Many used batteries are repaired as new and white-labeled. They sell the battery by marking capacity up to 5000mAh, but in actual their capacity is between 1000 to 2000 mAh. Another major problem with these cheap 18650 cells is the high risk of explosion when overheated during the charging or discharging.
In this project, I have used green Panasonic 18650B cells of capacity 3400 mAh from GearBest.
To make the battery pack, you have to connect the 18650 cells together by means of Nickel strips or thick wire. Generally, Nickel strips are widely used for this. In general two types of nickel strips are available in the market: nickel-plated steel strips and pure nickel strips. I will suggest buying a pure nickel. It is a little bit costlier than nickel-plated steel, but it has much lower resistance. Low resistance means, less heat generation during the charging and discharging, which leads to longer useful battery life.
Nickel strips come with different dimensions and lengths. Choose the strips according to the current rating.
You have two options to connect the 18650 cells together: 1. Soldering 2. Spot Welding
The best choice is always Spot welding, but Spot Welder is much costlier than a good quality Soldering Iron.
Soldering:
You should know why Spot welding is preferred over soldering, the problem with soldering is that you apply a lot of heat to the cell and it doesn’t dissipate very quickly. This enhances the chemical reaction in the cell which damages the cell's performance. Ultimately you will lose some capacity and life of the cells.
But if you are not interested to buy a costly Spot Welder, you can solder the nickel tabs to the cell by following some precaution and tricks:
1. To minimize the contact time of your soldering iron on the cell, make sure the surface is scuffed up sufficiently and you use plenty of flux to allow for fast solder flow.
2. It is better to have a good quality high wattage (min 80W) iron with good thermal capacity so it can deliver the heat to the joint quickly so you don't have to hold the iron to the battery for ages and let the heat see into it, causing damage to the battery.
Spot Welding:
The reason we spot weld is because it securely joins the cells together without adding much heat to them. There are two grades of spot welders currently available in the market: hobbygrade and professional grade. A decent hobby-grade Spot welder costs around $200 to $300, whereas a good professional grade may cost around ten times more. So I will suggest buying a hobby-grade spot welder from any online store like Banggood, Aliexpress, or eBay. I am using the SUNKKO 709A 1.9kw Spot Welder from Banggood.
Before connecting the cells in parallel, first, check the individual cell voltages. For paralleling the cells, the voltage of each cell should be close to each other, otherwise, a high amount of current will flow from the cell with a higher voltage to the cell with a lower voltage. This can damage the cells and even result in fire on rare occasions.
If you are using brand new cells, the cell voltage is near 3.5 V to 3.7 V, you can join them together without worrying much. But if you are going to use an old laptop battery, be sure the cell's voltage is nearly the same, otherwise, charge the cells to the same voltage level by using a good Li-Ion Battery Charger. I used my Nitecore SC4 Charger to charge all the 18650 cells before joining them together.
To make the battery pack, you have to first finalize the nominal voltage and capacity of the pack. Either it will be in terms of Volt, mAh/ Ah, or Wh. You have to connect the cells in parallel to reach the desired capacity (mAh) and connect such parallel group in series to achieve the nominal voltage (Volt).
For this project let the requirement is: 11.1 V and 17 Ah Battery Pack
Specification of 18650 Cells Used: 3.7V and 3400 mAh
Capacity(mAh):
The desired capacity of the battery pack = 17 AH or 17000 mAh.
The capacity of each cell = 3400 mAh
No of cells required for parallel connection = 17000 / 3400 = 5 nos
Commonly cells in parallel are abbreviated in terms of 'P', so this pack will be known as a “5P pack”.When 5 cells are connected in parallel, ultimately you made a single cell with higher capacity ( i.e. 4.2V, 17000 mAh )
Voltage:
The desired nominal voltage of the battery pack is 11.1V.
The nominal voltage of each cell = 3.7 V
No of cells required for series connection = 11.1 /3.7 = 3 nos
Commonly cells in series are abbreviated in terms of ‘S’, so this pack will be known as a “3S pack”.
So we have to connect the 3 parallel groups (5 cells in each group) in series to make the battery pack.
The final pack configuration is designated as a “3S5P pack” with a final specification of 11.1V,17AH.
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