Nov 14, 2019 Pageview：163
The world is moving away from fossil fuels and one day it will become fully electric. Lithium ion is one of the most promising technology of all batteries in the present world. Many Laptops, RC Robots, Drones, Medical Devices, Power Tools, E-Bikes and Electric Cars (EV) battery packs are based on 18650. It is one of the most mature available Li-ion formats, manufactured in high volume and enjoying low cost per Wh.
18650 Lithium ion cells are a great way for projects to be powered. That offers a 3.7V nominal voltage that is not enough for most applications because let's assume you want to control a BLDC motor with an ESC which needs 9V to begin so we need to achieve more voltage by linking them in series. In this article it has been discussed that how you can build a 18650 li-ion battery Pack with a BMS circuit and all the stuff you need to learn before you build one!
How do you make a 18650 battery pack?
Following are the steps that are needed to make a 18650 battery pack.
1-Check the battery and charge it
First, we need to test all the cells ' efficiency to ensure that all the cells are at the same voltage. It is essential for all the cells to be at the same voltage, because cells may end up charging each other and that result in unexpected results.
18650 cell is capable of supplying 3.7 V nominal voltage, 3 V minimum voltage and 4.2 V peak voltage. So if we consider nominal voltage, connecting 6 cells in series gives us 22.2 V which is a configuration of 6S1P. Where 6S stands for 6 series cells and 1P stands for 1 parallel cell. By adding another 6 cells in parallel, not only can we double the capacity, but we can also deliver the amount of current Pack.
3-Pack building and spot welding
For building pack it is recommended to buy tiny black plastic spacers that snap like Lego to create the battery pack and can be very useful because instead we don't need to use adhesive. Now make 2 pairs of 6 plastic spacers, insert alternating patterns into the cells.
After this, measure the distance between two cells and it is about 25 mm. So you have to use Nickel Ribbon to tag 25 mm on it and to snap it using sharp scissors. Now put the nickel pieces on top of the cells and use a spot welder to attach the nickel ribbon and top of the battery to create a series connection.
Now you can install and plug XT60 and label it for the day, but you can also add a BMS ( battery management system ) that brings overload, over discharge, and some of the battery pack even have Balance charging. We just have to solder it to the battery pack. Many BMS also doesn't provide Balance loading so you need to add Balance charging connector and you're done with it!
Figure 1 18650 battery pack done
What do you need when you make a 18650 battery?
It is necessary to know what things do you need to make a 18650 battery so that you can arrange it before start making the battery and it will eventually save your time, the things that are needed is given below;
1-18650- lithium ion cells
In power everything from laptop batteries and in electric vehicles, 18650 batteries are used. It is a rectangular, cylindrical type of lithium-ion battery, measuring 18 mm in diameter by 65 mm in length (give or take a few 1/10s of a millimetre). You can buy them online from places like banggod.com in a pack of 4 or 6 or you can take them out of old laptop batteries.
2-Battery management system
A battery management system (BMS) is an electronic system that manages a rechargeable battery (cell or battery pack), such as preventing the battery from operating outside its safe operating area, tracking its condition, measuring secondary data, reporting data, managing, authenticating and regulating its environment. This effectively adds over-charge, over-discharge safety and some of them also provide a shift in the balance.
Replacing the typical general adhesive with a qualified battery holder, the combination is very convenient, the contact is better and the maintenance of the battery is also convenient.
One of the aims of spot welding is to fuse two or more components together in a mainly permanent manner. You can buy one or you can rent one.
Nickel ribbon is widely used in battery construction due to its ease of use in spot welding and soldering as well as its high resistance to corrosion over time that is why you need it too.
Comparing making to buying a 18650 battery
To compare whether it’s better to make a 18650 battery or buy it lets take an example then the result can easily be evaluated
A man decided that he would need thirteen 18650 cells in series after some calculations, but chose to double the capacity by adding another 13 in parallel. Which gave him a battery pack of 5 Ah capacity with a nominal voltage of 48.1 V and one that could provide a steady current of 40 A. He bought a kWeld battery spot welder instead of attaching them by soldering the nickel strips, adding to the build cost. He powered his new battery pack with his bench power supply, and he installed a Battery Management System (BMS) to worry about inconsistent loading of the cells over the lifespan of the battery pack. This resulting battery pack is just right to use in eBike engine.
He found it was only a tiny bit cheaper after adding all the costs than the rates of equivalent eBay battery packs, which were € 24.4 per Ah (US$ 29.5 per Ah). The only way to make it cheaper is to make multiple packs, spreading the battery spot welder's one-time cost. So that it means that there is not much difference in price of buying a new one or to make it at home so it's up to your choice.
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