How to Make a 18650 Li-ion Battery Pack!

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About: Hi, I'm Nemeen, Electronics Enthusiast! I have seen a huge decline in electronics hobbyist in past few years. I started this channel in order to inspire you to create. Hopefully, you will find something tha...

18650 Li-ion cells are a great way to power Projects. Which provides a nominal voltage of 3.7V which is not sufficient for most of the application for let's say you want to power a BLDC motor with an ESC which requires 9V to start. So we need more voltage which can be achieved by connecting them in series. So in this tutorial, I will show you how you can make a 18650 Li-ion Battery Pack with a BMS circuit and all the things you need to know before you built one!

Step 1: Watch the Video!

If you don't want to read all the stuff watch video tutorial I made for you!

Step 2: Everything We Need

  1. 18650 Li-ion cells - 18650 batteries are used for powering everything from laptop batteries to electric vehicles. It is a standardized type of lithium-ion battery, cylindrical in shape and measuring 18mm in diameter by 65mm in length (give or take a few 1/10s of a millimeter). You can buy them in a pack of 4 from sites like banggod.com or you can extract them from old laptop battery which I have already shown in my previous tutorial
  2. BMS - A battery management system (BMS) is an electronic system that manages a rechargeable battery (cell or battery pack), such as by protecting the battery from operating outside its safe operating area, monitoring its state, calculating secondary data, reporting that data, controlling its environment, authenticating it and / or balancing it. Basically, it adds over charge, over discharge Protection and some of them also offers balance changing.
  3. Plastic Spacer- Replacing the traditional general adhesive with a professional battery holder, the combination is very convenient, the connection is more firm, and the battery maintenance is also convenient. It is the best choice for battery packs. It makes building battery pack much less painful.

  4. Spot welder - One of the purposes of spot welding is to join 2 or more components together in a mainly permanent fashion. you can buy one or built one which I have already shown in my previous tutorial

  5. Nickel Ribbon - Nickel ribbon is commonly used in battery building due to its ease of use in spot welding and soldering as well its high corrosion resistance over time.

Step 3: Check the Battery and Charge Them Up!

First, we need to check the capacity of all the cells & make sure all the cells are at the same voltage. It is mandatory that all the cells are at the same voltage else cells will end up charing each other and it can lead to unexpected results.

Step 4: Calculations!

18650 cell can provide a Nominal voltage of 3.7V, Minimum voltage of 3V and Maximum voltage of 4.2V. So if we consider nominal voltage, connecting 6 cells in series will give us 22.2V which is a 6S1P Configuration. Where 6S means 6 Cells in series and 1P means 1 cell in Parallel. By adding another 6 Cells in parallel we can not only double the capacity but also the amount of current Pack can deliver.

Keeping these things in my mind I decided to built 6S1P Configuration.

Step 5: Building the Pack and Spot Welding

For building the battery pack I brought those tiny black Plastic spacers which snap like Lego and can be very useful as we don't need to use adhesive instead. Now make 2 pairs of 6 plastic spacers, Insert the cells in alternation pattern.

Now I measured the spacing between 2 cells and it was about 25mm. So I used Nickel Ribbon marked 25mm on it and used sharp scissors to snap it. Now Place the Nickel pieces on top of cells and make a series connection use a spot welder to fuse nickel ribbon and battery top.

Step 6: Adding BMS

Now we can add and XT60 plug and call it for the day but we can also add a BMS which adds over charge, over discharge and some of the also add Balance charging to the battery pack. we just have to solder it to the battery pack as shown on the board. Also, some BMS like mine does not offer Balance charging so you need to add and Balance charging connector and You are done!

Step 7: Done!

If you like my work

Feel free to check out my YouTube channel for more awesome stuff:

https://www.youtube.com/c/Nematics_lab

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    19 Discussions

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    Waterwolf

    Question 19 days ago on Step 4

    Ok! So I take a bunch of 18650 cells and follow your directions to build a battery pack. Now that I've built the pack, just how do I calculate the mah of the battery pack and then convert it to ah. Could you please email me with the answer at waterwolf28@hotmail.com. I found this page very helpful, but a wireing diagram for the BMS would make things better. Good job either way, very helpful.Thanks for the help.

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    rich.altmaier

    3 months ago

    Hi Nematic, could you add your wiring diagram to the instructable? That is a significant omission!
    Thanks

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    auto13142828

    3 months ago

    I have an old 24v ebike that uses two 12v SLA batteries. What would I need for it?

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    drutkows

    3 months ago

    Did you check to see how well the BMS module balanced the batteries during charging and discharging? Does thte BMS you show stop charging when the cells are fully charged? I bought a couple of different ones on eBay, but haven't gotten around to see how they work. My plan is to replace by NiCad batteries with LiIon in my power tools.

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    RaymondR6drutkows

    Reply 3 months ago

    Raw or plain Li-ion cells always need protection against voltage overcharging and current overload, so these BMS boards offer some protection. The packaged cells as found in cellphones have the protection built in. Some even carry a fuse and will blow if overloaded or shorted, and some will open even if overheated. Only use these types for experimenting if you can control the charging and loading because the fuse is irreplaceable.

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    dejandejanovicdrutkows

    Reply 3 months ago

    This BMS module is "only" protection. Does not have balance function.
    But, as protection board, works fine.

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    drutkowsdejandejanovic

    Reply 3 months ago

    Please explain. What does it 'protect' against? Does it stop charging when 1 or more cells are at 4.2 volts?

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    dejandejanovicdrutkows

    Reply 3 months ago

    Something like that.
    Entire circuit is cutoff when first cell reach below values.
    Over charge detection voltage: 4.28V
    The over discharge release voltage: 2.9V

    Most important is voltage level, but has also other protection, like shorts, and overcurrent.

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    RaymondR6

    Tip 3 months ago

    For anyone planning to replace older lead-acid, nickle-cadmium, or nickel-metal-hydride cells with lithium-ion cells, remember that Li-ion cells don't like overcharging. They will warm up, and some will even expand (gassing), which can lead to a catastrophic explosion and damage to the equipment. Always use the nominal 3.7 VDC as the divisor for replacing packs according to the original battery charging voltage. For example, if you wish to replace a lead-acid 12 VDC battery with Li-ion, be careful that most 12 VDC charging circuits go up to 15 volts, so use 15 /3.7 = 4 cells in series. The minimum will still be 3 * 4 or 12 volts, so this is acceptable.

    Ni-Cad or Ni-MH hold just 1.25 VDC each, so one Li-ion cell can replace three of the older cells (3.75 volts). But some are set up in batteries with just two cells in series or 2.5 V, so even one Li-ion cells is too much. You may need to drop the voltage with a resistor, two silicon diodes in series (1.4 V), or a voltage regulator. This needs more than just cells in series.

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    Jfieldcap

    Tip 3 months ago

    A few things to keep in mind when you are working with salvaged 18650 cells:

    If you use any more than a 1P configuration, you should capacity test each cell and match cells with similar capacities. This helps ensure both cells remain relatively evenly charged without one cell charging the other. It's also nice to know the actual mAh rating of your pack.

    Additionally, if you plan to use your battery pack in a high-power application, you should probably also measure the internal resistance of each cell and try to use cells with low, similar resistances. This makes sure your cells don't run too hot, and also helps to make sure they all discharge at about the same rate.

    1 reply
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    hoozdman

    3 months ago on Step 7

    Nice build.
    Q: do you need to provide an equivalent charge for the output? ie would a 12v DC charger charge it all or would you need something beefier?

    1 reply
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    dejandejanovichoozdman

    Reply 3 months ago

    12V is near, but still enough for 3S battery connection.
    This project is 6S, and required charger 25.2V output.

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    dejandejanovic

    3 months ago

    Thanks for project.
    Would like to mention two things:
    - for additional security, required is 18650 insulation on positive side of battery
    - kapton or other tape below BMS.
    - wrapping the pack with shrink pvc or any other tape is also required. The user should not afford to create shortcut on BMS
    - and the nickel strip is not pure, but small cover of nickel on steel strip. Sunkko Spot Welder
    with 6P, and 5A parameters would made holes through pure 99% nickel.
    Banggod and many other like Aliexpress, Amazon sellers, Ebay, are offering wrong description!

    2 replies
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    billbillt

    3 months ago

    GREAT JOB.. JUST WHAT I NEED.. THANKS FOR SHARING....

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    audreyobscura

    3 months ago

    Thanks for building on your previous Instructables to post this project! Well done!

    1 reply
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    Nematic!audreyobscura

    Reply 3 months ago

    Always trying to make projects connecyed to each other :)