Whether you are building the entire ebike yourself, or are planning to replace the battery of your existing ebike, DIY might be a great option. Not only are DIY batteries cheaper, but they also offer a layer of customization and quality control that you can’t find on store bought ones. In this article, I will be discussing how to build a DIY ebike battery from 18650 cells.
An ebike battery can be made from 18650 cells by arranging them in rows and columns and joining opposites in a combination of series and parallel connections. The cells can then be attached to a battery management system to add a layer of security and stability.
While that is the gist of it, there is a lot more to it. Fear not, as I will be explaining the full process step by step in detail. So, let’s not wait any further and get started with this project.
18650 cells are Lithium-ion rechargeable batteries similar in design to AA batteries. But they are much larger and structurally different. They can easily be recharged and used in anything from home appliances to power tools. To know more about these cells, check out this paper by Panasonic.
Ebikes are basically bicycles powered by electric motors. They are very similar to the average paddle-powered bicycle in design but are much better suited for long journeys and daily commutes around the city.
What we are going to be doing is making a very basic battery that we can recharge and use to power an ebike motor. The theory here is that we are going to create a bunch of smaller units by joining cells in parallel. Afterward, we will create a functioning battery by joining multiple of those units in serial.
Most ebike batteries fall within the 24-volt to 48-volt threshold. Some can even go as high as 100 volts. You can make any sized battery with the same basic principles we will be discussing here. To keep everything simple we will be making a small 24-volt battery with 14 18650 cells.
That is the basic concept here. There are of course a lot of practical things you need to take care of. You need to take certain measurements into account and we will be discussing all of those later in this article. So, with that out of the way, let’s get into actually building your battery.
Things You Will Need
Here is a list of things you will be needing in this project;
- 18650 Cells
- Pure Nickel Strips
- Spot Welder
- Soldering Iron and Solder
- Hot Glue Gun or Plastic Brackets
- Battery Management System
- Heat Resistant Non-Conductive Tape
- Packaging Materials Such as Shrink Wrap or Tape (Optional)
Arranging The Cells
Plan the connections on paper and draw diagrams, this will help you keep everything in check. I advise that you draw a diagram for both sides of the battery. And before connecting the cells make sure that they all have almost the same voltage. A few hundredth decimal points more or less are not a problem but make sure that they are not too different.
We will be joining 2 cells together in parallel, their positives will be connected together and so will their negatives. Our 14 cells will make 7 of these units. All 7 of these units are virtually a cell on their own with double the power.
Our battery will have 2 rows and 7 columns of 18650 cells. You can attach them all using either hot glue or plastic brackets. There are a lot of options for plastic brackets out there. Gluing can feel a bit messy but you can make it much more compact.
After that, we will be connecting the 7 units in serial connection in a sort of zig-zag pattern. On one side, the first positive connection will be untouched, the second and third units will have their positives and negatives connected. This will create a box-like shape. Then we will connect the fourth and fifth’s positives and negatives together.
The same will go for the last two units. After that, you are to turn over the battery and do the reverse on the other side. Now the other negative end will go untouched and the other ones will have positive to negative connections. The two untouched positive and negative ends will serve as the two main connecting points of your battery.
How will these connections happen you may ask? You will do it by spot welding pure nickel strips. Make sure to use pure nickel strips, and also make sure to weld in multiple points of contact on each end of the cells. Use multiple layers of nickel strips if you feel the need to reinforce the connections.
Connecting The BMS Board
Now that we have the basic structure of our battery completed, it is time to attach the BMS or Battery Management System. Your battery will work without a BMS but it is not safe at all. A BMS board adds overcharge and over-discharge protection. And it also keeps the voltage stable between all the cells so none of them fail or deteriorate.
A BMS board will have sensor connectors and the main connection points. Connect the positive and negative ends of the battery to the positive and negative points on the BMS. Also, connect the positive charge and discharge wires to the positive connection point of the Battery.
The negative charge and discharge wires, however, will need to be connected to the C-Pad and B-Pad on the BMS. Next comes the sensor wires. The sensor connector will come with the BMS, connect that, and look for the marking on the board to determine which wire is for which connection.
The first B1+ will connect to the first positive section, the B2- will connect to the first negative section, the B3+ will connect to the second positive section, and so on. Try to solder all the wires to the middle portion of the nickel strips and not on the cells to avoid heating them. Use wires thicker than the sensor ones on the charge and discharge connections.
Additional Steps to Make the Battery Safe
There are a few things here and there that you should be mindful of to keep the battery safe and make it last longer. Use heat-resistant non-conductive tape to seal away the connections on the cells to avoid short-circuiting.
Add a layer of foam insulation between the battery and the BMS to avoid heat. Avoid contacting your spot welder to the cells directly. You can further add protection by insulating the whole battery with foam and sealing it within a shrink wrap. Use RCA or Anderson connectors on the charging connections to make the connection safe.
Building a DIY ebike battery can be a fun way to both enhance your ebike and save some money. If you are careful with the layout and follow all the safety measures, you can easily have a safe and high-quality battery ready for your ebike. Making one yourself gives you extra assurance of its quality and adds a ton of customizability.
I hope you found this guide on “How to build a DIY ebike battery from 18650 cells” helpful in one way or another. I hope I was able to answer all your questions properly. Thanks for reading till the end, stay safe, and until next time, goodbye.