DIY Professional 18650 Battery Pack

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Introduction: DIY Professional 18650 Battery Pack

About: I am a DIY hobbyist by passion and Power Engineer by profession. Most of my works are related to Solar Energy and Arduino. Apart from Electronics I love 3D printing, Woodworking and to make crafts from used …

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 18650 batteries. It is one of the most mature Li-ion formats available, is produced in high volume, and enjoys a low cost per Wh.

◆ Follow me on Instagram @ opengreenenergy

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 of rechargeable lithium-ion technology. Please do not attempt this if you are a novice. Stay Safe.

Full Video Tutorial:

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 (Creality CR10S )

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 of $1 to $10, but which are the best? I will highly recommend buying 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 having 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 rewrapped as new and white-labeled. They sell the battery by marking capacity up to 5000mAh, but in actual their capacity is between 1000 to 2000 mAh. Another major problem with these cheap 18650 cells is the 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 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 buying a pure nickel. It is a little bit costlier than 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 come with different dimensions and lengths. 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 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 enhances the chemical reaction in the cell which damages the cell's performance. Ultimately you will lose 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 securely joins 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, whereas a good professional grade may cost around ten times more. So I will suggest buying a hobby-grade spot welder from any online store like Banggood, Aliexpress, or eBay.I am using the SUNKKO 709A 1.9kw Spot Welderfrom 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 cell should be near to each other, otherwise, a high amount of current will flow from the cell with a higher voltage to the cell with a 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 is near 3.5 V to 3.7 V, you can join them together without worrying much. But if you are going to use an old laptop battery, be sure the cell's voltage is nearly the same, otherwise, 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 terms 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):

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

The capacity of each cell = 3400 mAh

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

Commonly cells in parallel are abbreviated in terms of ‘P’, so this pack will be known as a “5P pack”.When 5 cells are connected in parallel, ultimately 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.

The 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 are abbreviated in terms 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 a “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 has 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 understanding, you can see the above picture.

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

1. You can make a custom pack of any size according to your requirement.It's like solving a puzzle.

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

3. It makes your battery pack solid and reliable.

4. It provides 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 has three welding choices: fixed welding head, fixed welding head with foot switch, movable spot welding pen with the footswitch. 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 the 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 footswitch. 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 an electronic system that manages 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 pack from over-discharged.

The two important parameters 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 :

Overvoltage 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 has 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 a sturdy connection. First, apply soldering flux to the PCB pads and end of the nickel strips. After that tin all the pads by applying a little amount of solder and then solder them together.

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

Step 10: 3D Printed Enclosure

The battery pack has 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 has two parts: The 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 deg C

Bed Temp: 65 deg C

Step 11: Wiring the Components

Normally a standard battery has 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 whenever 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 into the enclosure.

Step 12: Final Assembling

First, install the components into 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 loss 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 below.

Thanks!

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Participated in the
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Metal Contest 2017

Participated in the
Metal Contest 2017

3 People Made This Project!

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135 Comments

0
SurendraV5
SurendraV5

Question 3 days ago

I wank to make 48v 20ah li ion battery pack with BMS chrage for my Ebike. Please suggest me with suitable diagram and components.

0
RobinH61
RobinH61

16 days ago

Great article and some prudent facts. I have a scaling question. I wish to scale this to provide power at 36V (10S) @ 3A max draw. Any suggestions? Do I really need a 20A BMS board? It seem that that's about all that's available.

0
cobourgdave
cobourgdave

4 weeks ago

A little late in noticing your instructable (2 yrs). This an excellent tutorial executed in a very professional way. For myself many thanks. You are certain to get many positive comments.

0
alcidesvas2689
alcidesvas2689

Question 1 year ago

your idea is great!!! Good job! i have a question, I need 24 Volts, what is better, built one of 24 V or can I create 2 of this and connected in serial? can I connected this in serial, the BMS is gonna support it?

0
Junkwood
Junkwood

Answer 4 months ago

make one

0
AswinS11
AswinS11

1 year ago

HOW TO CHARGE THIS BATTERY PACK

0
Junkwood
Junkwood

Reply 4 months ago

with a battery charger

0
ronlimel
ronlimel

Question 11 months ago on Introduction

Hi, I would like to make a 12V Li-Ion battery pack with eighty-eight (88) 18650 cells, using a BMS advertised as "4S, 12V, 100A". I would like to know if I should connect twenty-two (22) 18650 cells in parallel, making it a 4S, 22P arrangement, as shown in the diagram attached. I checked with the vendor, but could not get a straight answer - the best they could do was "We have not tried that"! I'm guessing that they are just re-sellers. Thanks for your advice.

0
Junkwood
Junkwood

Answer 4 months ago

search for lithium ion battery calculator, there's lots of programs available to help you decide on what layout suits you. 18650 cells can have slightly different outputs so it depends what cells you go for also.

0
DavidShortPSL
DavidShortPSL

Question 5 months ago

I'd like to create a 12v, 100Ah battery pack so, based on one of your Instructables, I've calculated I'd need a 30 x 3 matrix. This seems like it might be a little unwieldy. Is there a better way to configure a battery of this size? Thank you.

0
Junkwood
Junkwood

Answer 4 months ago

Probably be better with a Lithium iron phosphate battery, you can do them diy style also with great results. Using the 18650 lithium ion cells like that would work but they are faster charging I think thats the issue. For collecting solar energy the LifePo4 battery is better, i think, because it is better for slower charging and discharge so you can properly utilise the collected energy. If you want to use 18650 cells you can buy kits now very cheaply to fit the cells together that require no welding or solder, not sure they would have been so readily available at the time of this project.

0
Kenkenny3
Kenkenny3

4 months ago

Hello
please I want to start my lithium ion battery pack,
I want to get recommendation on the best spot-welding machine to buy thanks.
You can contact me on konnectkenny@gmail.com.

0
Junkwood
Junkwood

Reply 4 months ago

This was made in 2017, now you can buy cell connectors from amazon, ebay etc for extremely cheap and they cut out the need to spot weld, it really isn't something you should do especially if you are using recycled cells as if you have an issue with a cell you can easily change it out when using the bolt together kit as opposed to pointlessly spot welding the cells. It also means if you make any mistakes with your layout you can change it, or if you want to re-configure for different volt/amp output you don't risk damaging the cells. Have a search for Lithium ion diy kits. It will save you a lot of money, problems, damaged cells and it will leave your options open if you want to reuse the cells for a different application.

0
Lee Wilkerson
Lee Wilkerson

Tip 5 months ago

I suggest using a 12V incandescent or Halogen automotive lamp across the batteries when originally voltage matching them. This will provide a minimum load which your digital meter won't offer @1 Megohm or more per volt unless your meter has a specific battery test function.

0
Lee Wilkerson
Lee Wilkerson

5 months ago

In case anyone is interested, allow 163.8 Cubic Centimeters for 25 batteries for different battery counts - 11.7 * 11.7 * 7 cm (4.5 * 4.5 * 2 3/4 in).

0
NathanC152
NathanC152

Question 10 months ago

Hi, I have a 3P 3S connected to a basic BMS to power a 12v desktop pc, but I'm stuck figuring out how to allow power passthrough, eg charge the pack while the remaining power goes directly to the pc. Right now it just turns off when I plug/unplug power, even with charged battery pack :(

0
Lee Wilkerson
Lee Wilkerson

Answer 5 months ago

Use a 'Y' connector or a 'T' so the charger current goes directly to the battery pack and the computer simultaneously. This is normally done inside the computer case. When running from the battery pack, I suggest unplugging the charger just in case of incompatibility inside your charge source.

0
JensE6
JensE6

2 years 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

0
Lee Wilkerson
Lee Wilkerson

Reply 5 months ago

50AH does not address the question. For a car battery, you need at least several HUNDRED Amps. That's why you buy a battery with, say, 550 CCA. If one series of 18650 batteries can deliver 10A, you need 55 parallel groups.

0
MrPeterMoran
MrPeterMoran

Reply 1 year ago

Please see my informative answer to the first question!