DIY Lithium-Ion Battery Pack

DIY Lithium-Ion Battery Pack

If you’re working on electronics or any robotics projects you will be always in need of battery pack. You can easily get a ready-made online or in your local hobby electronics stored. But making yourself is something special and it will be less expensive. You can even use cells from your old laptop battery 🔋

Things you need

  • 18650 Battery (The quantity depends upon the capacity and voltage requirements.)
  • BMS Board (I have used 3S 20A BMS)
  • 18650 Solder-less connectors (Since I had access to 3D printing I have made my own)
  • XT60 Connector

Before we begin a big shoutout to sponsor of this content Digitspace

DigitSpace is an open-source hardware provider catering to future creators. They supply innovative, user-friendly open-source hardware products ranging from boards to corresponding components and kits for worldwide community of engineers, designers, inventors, and makers who love creating electronics.

Determine Capacity and voltage requirement

Here comes the main part where you need to decide what your requirements. How much output voltage and what capacity(aH) you need for your battery pack. Here are some basics of cell arrangements.

  • Connecting cells in series will increase the voltage but the current will be the same
    Connecting two 3.7v 2000mAh cell in series will give you 7.4v 2000mAh
    3.7v+3.7v = 7.4v [Here current will be same]
  • Connecting cells in parallel will increase the current but voltage will be the same
    Connecting two 3.7v 2000mAh cell in parallel will give you 3.7v 4000v
  • You can also mix both series and parallel to get the desired current at the desired voltage
    Say you need 7.4v and 4000mAh then take 4 cells, Connect 2 cells in series and other 2 also in series. Now connect both pair to each other in parallel

    If you need to learn more about series cell arrangement please refer to this article by battery-university

For this project I will be using LG LGABC21865 cell, The cell specification goes like this
Capacity : 2800mAh Rated
Voltage : 3.72 V

I will be making an 11.1V cell 2800mAh battery pack, by connecting 3 cells in series.

Check the cell voltage

If you’re using brand new cells then nothing to worry much the cell voltage should be near to 3.7 V. But if you’re using old recycled batteries from old laptops then be sure that all cells are good and check voltage are nearly the same. If the voltage is different for large value then charge each cell to the same voltage before connecting to each other.

Making the battery pack

If you have access to 3D printing you can print the 18650 connectors. Here is the.STL files here
Or else you can get 18650 connectors from online or your local hobby electronics shop. If you don’t have access to spot welding it’s highly recommended to buy solder-less 18650 connectors, it will make your work easier.
Arrange the cells in such a way that the alternative cell is upside down. refer to the image for better clarification

Connect the Battery Management System board [BMS]

A battery management system is electronic circuitry that protects the battery pack from operating outside its safe operating region.
BMS prevents the battery pack from overcharging and over-discharging
The BMS I have used in this project is 3S 20A BMS board

Connection Diagram

Its highly recommended that you insulate all exposed region a polyimide tape or insulation tape. For ease of use, I have soldered a female XT60 connector to the end.
If you any doubts regarding this project please feel free to ask your doubt in the comment session.

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