DIY Professional 18650 Battery Pack

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The world is shifting away from fossil fuels and will one day become fully electric.In the present world ,Lithium-ion is the most promising chemistry of all batteries. Most of the battery packs used in Laptops,RC Toys, Drones, Medical devices, Power tools, e-bikes and electric cars (EV) are based on the 18650.It is one of the most mature Li-ion formats available, is produced in high volume and enjoys a low cost per Wh.

You can find all of my projects on : https://www.opengreenenergy.com/

The 18650 (18mm diameter and 65mm length ) battery is a size classification of lithium-ion batteries.It is the same shape, but a bit larger than a AA battery. AA batteries by comparison are sometimes called 14500 batteries, because they have a 14mm diameter and 50mm height.

Earlier I have made a Solar Power Generator which is working really nice till now.But the main problem is its weight, it is really heavy.The main weight of the Solar Generator is due to the heavy lead acid battery inside it.So I decided to make a light and compact 18650 Li Ion Battery Pack.

In this Instructable, I will show you, how to make a 18650 battery pack for applications like : Power Bank, Solar Generator, e-Bike, Power wall etc.The fundamental is very simple : Just to combined the number of 18650 cells in series and parallel to make a bigger pack and finally to ensue safety adding a BMS to it.

At the end of this project, I made a custom 3D printed enclosure for the battery pack.

Disclaimer:I cannot be held responsible for any loss of property, damage, or loss of life if it comes to that. This tutorial was written for those who have knowledge on rechargeable lithium ion technology.Please do not attempt this if you are novice. Stay Safe.

Step 1: Parts and Tools Required

Parts Required:

1. 18650 Battery ( GearBest / Amazon )

2. BMS ( Banggood / Amazon)

3. Ni Strips ( Banggood / Amazon )

4. Battery Level Indicator ( Banggood )

5. Rocker Switch ( Aliexpress / Banggood )

6. DC Jack ( Banggood /Aliexpress )

7. 18650 Battery Holder ( Banggood )

8. 3M x 10mm Screws (Banggood / Aliexpress )

Tools Used

1. Spot Welder ( Banggood /Amazon)

2. 3D Printer ( GearBest )

2. Wire Stripper/ Cutter ( Amazon )

3. Hot Air Blower ( GearBest )

3. Multimeter ( Amazon )

5. Li Ion Charger ( GearBest )

Safety Equipment :

1. Safety Googles ( Amazon )

2. Electrical Gloves ( Amazon)

Step 2: Selecting the Right 18650 Cells for the Battery Pack

You will find many types of 18650 cells in the market in the price range $1 to $10, but which are the best? I will highly recommend to buy 18650 cells from branded companies like Panasonic , Samsung, Sanyo and LG. These cells that have well documented performance characteristics and excellent quality control. Reputed brand 18650 cells are generally costly, but if you consider for long time use then they are worth to have it.

Don't buy any cells with the word FIRE in the name like Ultrafire, Surefire and Trustfire. In reality, these cells are just factory rejects, purchased by companies like Ultrafire and repackaged in their own branded cover .Many used batteries are re wrapped as new and white-labeled.They sells the battery by marking capacity up to 5000mAh, but in actual their capacity are in between 1000 to 2000 mAh. Another major problem with these cheap 18650 cells are that high risk of explosion when overheated during the charging or discharging.

In this project, I have used green Panasonic 18650B cells of capacity 3400 mAh from GearBest.

Step 3: Choosing the Right Battery Strips

To make the battery pack, you have to to connect the 18650 cells together by means of Nickel strips or thick wire.Generally Nickel strips are widely used for this. In general two types of nickel strips are available in the market : nickel-plated steel strips and pure nickel strips. I will suggest to buy the pure nickel. It is little bit costlier than the the nickel plated steel, but it has much lower resistance. Low resistance means, less heat generation during the charging and discharging, which leads to longer useful battery life.

Nickel strips comes with different dimension and length.Choose the strips according to the current rating.

Step 4: Spot Welding Vs Soldering

You have two options two connect the 18650 cells together : 1. Soldering 2. Spot Welding

The best choice is always Spot welding, but Spot Welder is much more costlier than a good quality Soldering Iron.

Soldering :

You should know why Spot welding is preferred over soldering, the problem with soldering is that you apply a lot of heat to the cell and it doesn’t dissipate very quickly. This enhance the chemical reaction in the cell which damages the cell's performance. Ultimately you will loose some capacity and life the cells.

But if you are not interested to buy a costly Spot Welder, you can solder the nickel tabs to the cell by following some precaution and tricks :

1. To minimize the contact time of your soldering iron on the cell, make sure the surface is scuffed up sufficiently and you use plenty of flux to allow for fast solder flow.

2. It is better to have a good quality high wattage ( min 80W ) iron with good thermal capacity so it can deliver the heat to the joint quickly so you don't have to hold the iron to the battery for ages and let the heat seep into it, causing damage to the battery.

Spot Welding :

The reason we spot weld, because it is securely join the cells together without adding much heat to them.There are two grades of spot welders currently available in the market: hobby grade and professional grade. A decent hobby grade Spot welder costs around $200 to $300, where as a good professional grade may costs around ten times more.So I will suggest to buy a hobby grade spot welder from any online store like : Banggood, Aliexpress or eBay.I am using the SUNKKO 709A 1.9kw Spot Welder from Banggood.

Step 5: Check the Cell Voltage

Before connecting the cells in parallel, first check the individual cell voltages.For paralleling the cells,the voltage of each cells should be near to each other, otherwise a high amount of current will flow from the cell with higher voltage to the cell with lower voltage.This can damage the cells and even result in fire on rare occasions.

If you are using brand new cells, the cell voltage are near 3.5 V to 3.7 V, you can join them together without worrying much. But if you are going to use old laptop battery, be sure the cells voltage are nearly same, other wise charge the cells to the same voltage level by using a good Li Ion Battery Charger.I used my Nitecore SC4 Charger to charge all the 18650 cells before joining them together.

Step 6: Battery Pack Capacity and Voltage

To make the battery pack, you have to first finalize the nominal voltage and capacity of the pack.Either it will be in term of Volt , mAh/ Ah or Wh. You have to connect the cells in parallel to reach the desired capacity (mAh ) and connect such parallel group in series to achieve the nominal voltage (Volt ).

For this project let the requirement is : 11.1 V and 17 Ah Battery Pack

Specification of 18650 Cells Used : 3.7V and 3400 mAh

Capacity (mAh):

Desired capacity of the battery pack = 17 AH or 17000 mAh.

Capacity of each cell = 3400 mAh

No of cells required for parallel connection = 17000 / 3400 = 5 nos

Commonly cells in parallel is abbreviated in term of ‘P’, so this pack will be known as a “5P pack”.When 5 cells are connected in parallel, altimately you made a single cell with higher capacity ( i.e 4.2V , 17000 mAh )

Voltage(Volt) :

The desired nominal voltage of the battery pack is 11.1V.

Nominal voltage of each cell = 3.7 V

No of cells required for series connection = 11.1 /3.7 = 3 nos

Commonly cells in series is abbreviated in term of ‘S’, so this pack will be known as a “3S pack”.

So we have to connect the 3 parallel groups (5 cells in each group ) in series to make the battery pack.

The final pack configuration is designated as “3S5P pack” with a final specification of 11.1V ,17AH.

Step 7: Assemble the 18650 Cells

From the previous step, it is clear that our battery pack is made up of 3 parallel groups connected in series ( 3 x 3.7V = 11.1V ) and each parallel group have 5 cells ( 3400 mAh x 5 = 17000 mAh).Now we have to arrange the 15 cells properly for making the electrical connection among them and with the BMS board.

Place the first parallel group of cells (5 nos) positive side up, then place the second parallel group negative side up and then finally the last parallel group positive side up.For better under standing you can see the above picture.

You can assemble the cells to make the pack by using hot glue or by using plastic 18650 battery holder.I used plastic 18650 cell holders/spacers to assemble the 15 cells.The main advantages of using this cell holders are

1. You can make the custom pack of any size according to your requirement.Its like a solving a puzzle.

2. It provide space between the cells, which allow fresh air to pass and the battery get cooled easily.

3. It makes your battery pack solid and reliable.

4. It provide safety anti vibration to your battery pack

Step 8: Spot Weld the Nickel Strips

Now it is time to know the procedure for using the Spot Welder ( I am talking about the Spot welder that I have used in this project).The Spot welder have three welding choices: fixed welding head, fixed welding head with foot switch, movable spot welding pen with foot switch.I prefer to use the second option.Before welding you have to prepare the nickel strips and welder.

Cut the nickel strips :

Lay your nickel strip on top of the 5 cells ( parallel ), ensuring that it covers all cells terminals, leave 10mm excess strips for connecting it to the BMS and then cut it.For series connection cut small nickel strips as shown in the figure.You will need four long strips for parallel connection and 10 small strips for series connections.

Connect the first parallel group negative terminal to the positive terminal of the second group and then negative terminal of the second group to the positive terminal of the third group.

Weld the Battery Strips :

This spot welder can be used to weld the pure nickel as well as nickel plated steel strips.You have to adjust the welder pulse and current knob according to the thickness of the nickel strips.

For 0.15 mm nickel strips, press the pulse knob 4P and current knob to 4-5.Similarly for 0.2 mm nickel strip , press the pulse knob 4P,6P and current knob to 7-8.Make sure the welding pen is compressed with the nickel strip and battery terminal, then press the foot switch.You will notice a small spark, and two dot mark on the strip.

Successful Welding :

You can check the weld quality by pulling on the nickel strip. If it doesn’t come off with hand pressure, or requires a lot of strength, then it’s a good weld. If you can easily peel it off, then you have to increase the current.

Safety : Before starting the spot welding, always wear safety goggles.

Step 9: Adding the BMS

A battery management system (BMS) is any electronic system that manages a a lithium battery pack and the main functionalities are

1. Monitors all of the parallel groups in the battery pack and disconnect it from the input power source when fully charged ( near 4.2V )

2. Balance all the cells voltage equally

3. Doesn't allow the the pack from over-discharged.

The two important parameter required to buy a BMS are : i) Number of cells in series - like 2S / 3S / 4S

ii). Maximum discharge Current - like 10A/ 20A /25A /30A

For this project, I have used a 3S and 25A BMS board.These are the specifications of that BMS :

Over voltage range: 4.25~4.35V ± 0.05V

Over discharge voltage range: 2.3~3.0V ± 0.05V

Maximum operating current: 0~25A

Working temperature: -40℃ ~ +50℃

How to Connect ?

Connect the BMS as shown in the wiring diagram.The BMS have four soldering pads : B- ,B1,B2 and B+.You have to connect the first parallel group negative terminal bus to the B- and positive terminal bus to the B1. Similarly the third parallel group negative terminal bus to the B2 and positive terminal bus to the B+.

You can spot weld the nickel strips to the BMS or solder it to the PCB pad.I preferred to solder the nickel strips to the PCB for sturdy connection.First apply soldering flux to the PCB pads and end of the nickel strips.After that tin all the pads by applying little amount of solder and then solder them together.

Credit : The wiring diagram is taken from Banggood product page.

Step 10: 3D Printed Enclosure

The battery pack have all around exposed nickel strips, to avoid any accidental shorting,I designed an enclosure for it.I used Autodesk Fusion 360 to design the enclosure for my battery pack. The enclosure have two parts : Main Body and top lid.You can download the .STL files from Thingiverse.

I used my Creality CR-10S 3D printer and 1.75 mm green PLA filament to print the parts . It took me about 6.5 hours to print the main body and around 1.2 hours to print the top lid.

My settings are:

Print Speed : 70 mm/s Layer

Height : 0.3

Fill Density : 100%

Extruder Temperature : 205 degC

Bed Temp : 65 degC

Step 11: Wiring the Components

Normally a standard battery have only two terminal for connecting the load and to charge the battery.Apart from this, I have added a battery level indicator, to see the battery level when ever required.I have used a 5mm DC jack ( 12V /3A ) for input/output , 3S battery level indicator module to see the battery status and a rocker switch to ON/OFF the battery level indicator.

Now let's move on to the wiring of the components. I've prepared this simple wiring diagram for all the components . It's pretty simple!To insulate the conductive parts, I used heat shrink tubing.

Note : Don't solder the wires ( P+ and P- ) to the BMS before installing the components in to the enclosure.

Step 12: Final Assembling

First install the components in to the respective slots in the 3D printed enclosure.You can see the above picture.

Solder the positive (red wire ) from the DC jack and Rocker switch to the P+ of the BMS , negative wires from the DC jack and Battery level indicator to the P- of BMS.

Then apply hot glue at the base of the battery compartment, then secure the battery pack.So that it will seats firmly and prevent any loosing of wire connections.

Finally, screw the top lids in place! I used 3M x 10 screws for securing the lid.Now the battery pack is ready to use.

Charging the Battery Pack :

You can charge the battery pack by a 12.6V DC adapter like this.You can get it easily from aliexpress or eBay.

Hope you enjoyed reading about my project as much as I have enjoyed building it.If you’re thinking about making your own I would encourage you to do so, you will learn a lot. If you have any suggestions for improvements, please comment it below .

Thanks !

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85 Discussions

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TerryB160

2 days ago on Step 12

Not trying to be an ahole but you can buy these 4 pack and 8 pack 18650 holders that charge the batteries with a phone charger... From Ebay for $2 each and link as many as you can afford. And pull the power from the usb port.

Also I can't understand how a battery could know if it's being charged by another battery or charger.

Nice set-up I believe it looks all good except for that last part where you used a glue gun to create adhesion between battery pack and the battery case (cool way of building your case, nice job by the way!). Correct me if i am wrong but doesn't glue gun glue conduct electricity?

So by the way you had done that last step.... doesnt that cause either a short, or a serious loss drain or leaky in the cell pack?

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BrandonM286

Question 9 months ago on Step 10

Sir could you please make a video on how to design box for the 3d printer with what software you used I would like to use your idea and expand on it and make some modifications need more instructions

2 answers
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samuelezra49BrandonM286

Answer 21 days ago

Hi you can either use AUTOCAD or solidworks these are the two design software I really love to use most especially the solidworks, thanks to my lecturer who introduced them to me

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EnmanuelH2BrandonM286

Answer 7 months ago

You can use Google SketchUp to design 3d objects to print, you can even find already built boxes at SketchUp warehouse page : https://3dwarehouse.sketchup.com/?hl=en

Also in the post he said that was using Autodesk 360 to design it, and you can download his design, from the link he posted.

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samuelezra49

21 days ago

Hello sir I really love your project and I would love to see more. I'm now on of your fans, following you already. Keep it up for sharing, as sharing is caring, please I actually need exact what you made to power my DC fan at home because the temperature over here is unbearable. How can I get the materials. Can I get them from you. I'm actually an electronics student.
Better still can I have your email address. Thanks as I look forward to your response.

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govind21

Question 2 months ago on Step 3

How to select the size of busbar if i know the current rating for my module. Kindly help me in this.

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richard7667

Question 2 months ago on Step 9

I'm interested in a battery pack with 21700 protected cells for my amateur radio. However I'm concerned with tightly packing the cells, as you show. Tesla has a patent where they seperate the cells with a polymer based insulation material that is also fire resistant. Have you considered this?

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gkns

3 months ago

Hi,
If I connect load and charger together to this battery, Will it function as a UPS?

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marciokoko

4 months ago

How do I calculate how many volts and amps the solar panel used to charge a 2s battery pack.

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JensE6

4 months ago

i would like to make my own car battery with 18650 cells, but can you help me, i would like it to be around 14 volt, and i ofc want it to be charged with th cars alternator, i also have a big sound system that have a max peak at about 15kw, would the cells be able to provide that anou t of power? if i would make it lets say 50AH or more, pleade help, been searchi g all over the internet

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gkns

Question 5 months ago

Hi Thanks for sharing this! What is the max discharge current rate? (don't know if I missed it among the details)

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sidgeorge

Question 7 months ago on Introduction

Can I use a 24v 4ah li-ion power tool battery (greentree 24v 4ah) for an electric wheelchair with two 250 watt brushless motors?Thank you

1 answer
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garzosidgeorge

Answer 5 months ago

As long as your pack is rated for more than "6C" discharge rate you should have enough power. 4Ah is a really high capacity for a single cell, therefore it's probable that you will have at least a xS2P pack. If a single cell can provide at least 12Amps you can use them. Unluckily there's no way to know that without knowing which kind of cell you do have.

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ntsarb

6 months ago

Very interesting article! I am confused about the following:

If the power supply is not designed for LiPo batteries, how would it be possible to achieve an efficient charging process (glide paths for Amp and Voltage)? Experts recommend using a LiPo charger, alongside the battery pack's BMS, as the batteries will otherwise not get charged properly and perform optimally (as intended). Is this not true, or am I missing something?

I'd like to use 24x (or 28x) Samsung Q30 (18650/3000mAh/20A) batteries, to build a 24Volts battery pack, to power 2xRazon E100 motors (100W each). I'm not sure if I should build 4x battery packs of 6S (and how to combine them, to increase the total capacity - mAh?), each supported by a 15A BMS (60A total), or a single battery pack of 6S4P (15A BMS), or a single battery pack of 7S4P (40A BMS). What's the best way forward, for an efficient (and safer) battery pack?

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RobPaige

1 year ago

Given that you have a 3D printer, why mess about with soldering/welding the nickel to the batteries to begin with? Why not just print caps with space to run the strips, which would allow for easy replacement of the cells when they've worn out? I know with that solid connection there's less resistance, but is it really that dramatic?

2 replies
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AirsoftSloRobPaige

Reply 7 months ago

It would be very sensitive unless you put a lot of force on it. Any vibration could separate the joint and possibly cause a short.

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ReneA4RobPaige

Reply 1 year ago

oh yes it is. Also work clean, clean the parts so no, like hand, grease will be there

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keyur.rakholiya

1 year ago

which charge controller i should use if i want to charge this battery pack with solar panel's out put?

1 reply