How to Make a 18650 Li-ion Battery Pack!

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!

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Comments

[grantpeers]

Hi, I just read you Instructable: How to Make a 18650 Li-ion Battery Pack! I have been trying to build a successful circuit to replace the 18V NiCd battery pack on my electric drill. THe question I have is whetehr you know of a circuit that can be used for high discharge required by the drill.

I bought a circuit off EBAY (https://www.banggood.com/3_7V-100A-5S-BMS-Li-ion-LMO-Ternary-Lithium-Battery-Protection-Board-With-Balance-p-1245836.html?cur_warehouse=CN)

- it works except if you pull the trigger too fast. Any advice please? TIA

[Yakudala]

For how much can you sell me the laser cutting machine?. I need more of your help to build this 18650 battery pack and what can it be used for?, Can it power the house or electric car?

[JohnC430]

Car maybe but not a house. That is too big

[ItsGraGra]

Unbelievable

[JohnC430]

the pack is already connected to the balancer. what is the purpose of the 7 pin plug? Am I misunderstanding something?

[Jfieldcap]

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.

[Korishan]

This is kind of correct. If you use more than 1"S" configuration, they need to be matched in capacity. Cells in parallel are not critical in the capacity matching. Cells/packs in series is highly critical in capacity matching as that is was determines when the cells/packs reach full charge or not.

I agree with the high-power application. Additionally, I would suggest using LiFePO4 cells for super high-powered applications, or where space is limited but still need high amps.

[Jfieldcap]

That's right, although a BMS (which should always be used with salvaged cells in any pack over 1S, even with capacities matched) will help take care of that some.

You'll still want capacities to be close though, otherwise different sections of the battery pack will discharge faster, making the overall capacity effectively lower, and making charging times increase (because the BMS has to balance the cells every time.)

[dejandejanovic]

Correct.

[auto13142828]

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

[Korishan]

If you use cells of the Lithium Ion variant, then you should go with 8s, not 7s. It's better to run the DC motor slightly higher voltage than to make it run at a higher amperage. The lower the voltage, the more amps are drawn until the batteries can't supply it.
So, with standard Li-Ion cells, we have the following numbers:
8s @ 29.6V Nominal
Upper voltage: 33.6V (4.2V fully charged, but best to only charge to 4.0V for increased life cycles)
Lower voltage: 22.4V (2.8V fully discharged. but best to only discharge to 3.2V for increased life cycles)
If you only used 7s, then it'd be 25.9V Nominal
Upper voltage: 29.4V @ 4.2V/cell
Lower voltage: 19.6V @ 2.8V/cell

As you can see, 19.6V is actually lower than what lead acid would be. LA's would be considered discharged at 21V (10.5V/battery) which is actually almost dead flat and not good. A better bottom voltage is 22.2 (11.1V/battery), which again, is higher than the 7s Li-Ion.

Now, if you go with LiFePO4 cells, which is highly recommended for EV's of any sort, then you'd need to go 10s as their voltage range is smaller than Li-Ion. Their voltage range is ~2.4 - 3.4V with a nominal of around 3.2-3.3V.
However, they fit LA replacement far better as they match closer to the voltage range of the LA.
Upper voltage: 34.0V
Lower voltage: 24.0V

These values can be a little different depending on the manufacturer of the cells and what chemistry they used, as the voltage of the cells can be slightly different. There are some LiFePO4 cells that are 2.2 - 3.3V, and others that go up to 3.7V.
Also note, LiFePO4 cells handle over charge faaar better than Li-Ions do. They don't explode and light on fire as quickly, or as volatile as Li-Ions

[Waterwolf]

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 [e-mail]. 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.

[Korishan]

It is important to note that each parallel section of the series needs to have the same capacity. So no matter what the mAh or Ah rating of the cells are, each parallel section "must" equal the same rating as the other packs. Otherwise the BMS will work extremely hard to keep the packs balanced.
This is something that is failed to be mentioned in the video and the instructable.
Once you have the capacity of each cell, you then add up all the cells capacity in that pack. ie, if you have 3 cells, and they are 1800mAh, 2200mAh, 1950mAh. Combined in parallel they would have a sum total of 5950mAh. To convert to Ah, just divide by 1000, or 5.95Ah. If you want to convert to Wh (Watt-hours), then we take the nominal voltage and multiple by the Ah. So if we have 1s pack (no others connected in series), then nominal voltage is 3.7V, multiply by 5.95Ah = 22.015Wh. Important to note that you should convert mAh to Ah before the conversion, or you need to at least divide the result by 1000 after getting Wh to get the right amount.

[redeno]

To calculate the total amperage of the pack you would take the capacity of each cell and multiply by the number of cells. In the case of this instructable, it would be 2500 mAh * 6 cells, for a total capacity of 15000 mAh. To convert for mAh (milliamp hour) to Ah (amp hour) you take that number and multiply by 0.001 (or simply move the decimal place three numbers to the left, so that 15000.0 mAh becomes 15.0 Ah). Another way of thinking about it is that one Ah is a thousand mAh.

[RaymondR6]

"mah" is milli-Amp-hour and "ah" is "Amp-hour" So just divide the "mah" by 1,000 (or move the decimal point three digits to the right) to convert to "Ah" ("Amp" uses the upper case "A"). Each cell has the "mAh" rating printed on the label, so to match all the cells in series, they must have the same rating, or the pack must be devalued to the lowest capacity cell rating in the series.

[charlessenf-gm]

"Place the Nickel pieces on top of cells"
Curious to learn why you did NOT place the strips 'under' the plastic holders.
I only got to look at your pictures (2D) so please forgive me if the reason would have been obvious had I the parts in hand!
It seemed that, where connecting 2 cells, the holder would help in placing / holding the connecting strip even as it was 'welded' in place.

[Korishan]

Because the plastic holders go "around" the cells to hold them. You can get a better view if you watch the video.

[MauriceC24]

J'aurais bien aimé avoir un schéma de branchement du BMS, et surtout le diamètre des câbles nécessaires au branchement.
Merci pour cet instructables.

[rich.altmaier]

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

[drutkows]

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.