15600mA Power Bank @ Just Rs.370 ($6)

Recently I have ordered a Power Bank Kit from Hong Kong (China) costing just Rs. 370 ($6). The Kit arrived only with the cabinet and PCB. The required 18650 cells were not included. In market 18650 cell costs around Rs.150 ($2) each. Six of such cell would have made a hole in my pocket costing Rs.900 ($13).

To save the cell cost, I have arranged an old laptop battery and disassembled it. All laptop batteries are made of at least 4 to 6 18650 cells. I tested them and they were giving 3.67 to 3.72 volt, even after the battery was not used since 2 years. Generally, 18650 cells are rated for 2600mA it means 15600mA for 6 cells. Following steps describes how to assemble the Power Bank.

Step 1: The Package

The package I have received from Hong Kong containing PCB and plastic cabinet.

Step 2: Old Laptop Battery

CAREFULLY disassemble the laptop battery with a flat screw driver. Try not to puncture the cells inside the battery case, it may start fire due to short circuit. You may have heard about battery fire and explosion cases in Mobile phones. Remove the charging/discharging circuit inside the battery and remove the 18650 cells. The cell are connected in series and parallel (both). Cut the connecting wires and strips and separate each cell. Check the voltage of each cell. Remove the cells where are giving less than 3.5 volt.

Step 3: 18650 Cells Removed From Laptop Battery

These are the cells recovered from old laptop battery. All the 18650 cells has a ring on one side which indicate +ve side. Unlike generally available AA and AAA cells which has a clear +ve terminal protruding over the cell body, 18650 cells has flat surface on both terminals.

Remove all the connecting wires and strips from cell's top and bottom terminals and make them clear.

Step 4: Prepare Connecting Wire

We need to connect all the 6 cells in parallel. Prepare two copper strips or flatten two twisted braided wire pieces.

Step 5: Prepare the Cells for Soldering

Pre-solder the cells by applying solder on both the terminals. Be careful, do not melt the plastic insulation, specially from the +ve terminal.

Step 6: Connect the Cells in Parallel

Connect all the cells in parallel. To solder, hold all top +ve sides on a clamp (I clamped them using two thick books) and start soldering the copper strip on each cell's terminal. Repeat the same process for -ve terminal.

Step 7: Battery Pack

This is the final battery pack you will get. All the +ve and -ve terminals are now connected through a copper wire each. Paste a proper insulating tape on both the sides.

Step 8: Install the Power Bank Kit PCB

Install the PCB in the plastic case carefully. You may need some trimming/filing of PCB and case.

Step 9: Install Battery Pack

Carefully install the battery pack inside the cabinet. Do not apply excessive pressure as the connection between the cell and copper wire may break. Cut the excess copper wire. The PCB has a mark B+ and B- which indicate +ve and -ve terminal connections to the battery. Solder the battery pack's +ve to B+ and -ve to B-.

Step 10: Install Button and LED Indicator Riser

Install provided button and acrylic LED indicator riser at given place, inside the power bank case. I have also glued them so that they will remain at their place when closing the case.

Step 11: Test the Power Bank

Finally test the power bank by connecting a mobile or any other device. The LED will lit up showing how much charge is left. There are 4 level indicators (25% each). Connect a mobile charger to power bank and check whether the LEDs blinking or not. Hold the button for 5 seconds and the White Torch LED will lit up. Hold the button for another 5 seconds and it will be off. (your kit may not come with torch function)

If every thing is working fine, close the cabinet/case. Now you can charge 4 devices at a time. Enjoy.

Step 12: !!! SAFETY !!!

As old/used 18650 cells are used in this project, the cells should be balanced with the others, or you run a higher risk of failure. It will be better if you use brand new 18650, although it will increase the project cost and spoil the charm. I have not included any information regarding cell balancing. Alternative to 18650 are normal AA NiMH batteries.

Comments

[arierep60]

Nice Instructable buddy, but unfortunately your pack does not have 15600mAh because those old 18650 cells are not new and doesn't have full capacity.

You should test each cell to check the real capacity, and for that you can charge them to full voltage (4.2v) let them rest for 24h and then discharge each one till it reaches 3v, and that's the real capacity of each cell.

1A discharge is the best to get real capacity but if you want you can discharge only 0.5A because in your powerbank you will not request much current from the pack.

Hope this is useful for you ;)

[mahesh_jo]

Thanks for the information.

[altomic]

aliexpress sells DIY powerbanks with that hold 6x18650 batteries for US$2.50 delivered. though I prefer the 5x18650 with the LCD screen that shows capacity for US$4.20. both come with terminals in place so need to solder, just insert batteries and you are good to go.

[mahesh_jo]

Thanks for the Info.

[OculumForamen]

I have a few 18650's around my mess of a shop, but I have to say that I use NiMH rechargeable AA battteries in my Power Bank. I have been using them for some ttime, and I haven't experienced any problems or significant loss of recharge time over the last two or so years. This is a much safer alternative to lithium cells like the 18650. Especially if the lithium cells are used, there can be some serious problems with used 18650s, and keeping a power bank in your pocket or in a back pack can result in serious injury to you or others near you. Because of this, I stayed with the rechargeable AA batteries and making a power bank out of them is super easy, since once the power bank is condstructed, you can use regular AAs in it if you run out of rechargeable power. If you make the above project with used 18650s, make sure that they are balanced with the others, or you run a higher risk of failiure. Just sayin', other than that, this is a cool project, it would be worth it to use new cells in it, that way it will have a good long life. Adafruit industries has excellent cicuitry for power banks.

[mahesh_jo]

Thank you very much for the useful information. I am including an extra step regarding safety.

[OculumForamen]

No problem. There is another instructable that goes over balancing 18650s, but I can't remember who it was. It might have been on you tube also, but you need a special electronic device that I don't have. I have seen Litium cells fail, and there is no way that I was going to carry 4 of them in my pocket! Even being close to one when it fails is a bad idea! So yeah, be careful witth those used cells! But the kit you bought is totally cool, I may order one too, if you can convert them to use NiMH or NiCad AA batteries. I just need to mention that even new cells should be balanced to make your project function at peak performance, so, that is what stops me from using them.

[mahesh_jo]

Thanks. Just one query. Why dont we bother to carry them in our laptop for years? Why dont we heard news about laptop catching fire or exploding even if these cells are being charged discharged for years? Does the laptop charging/discharging circuit contains any protection for individual cells? While opening a few laptop batteries I have not seen any such provision except a temp. sensor on one of the cells. I think they fail when they get very hot or punctured.

[Matlek]

This is cool! I have a lot of these 18650 cells that I have kept from old computers, I need to make more powerbanks with them!

But I am wondering, do the 18650 cells have protection circuits? I think it is quite risky (though I am not a pro with li-ion batteries) to connect them in serie or in parallel without individual protection circuits. Here is a forum talking about it.

Also be careful when you're using a soldering iron with the li-ion cells, it can damage the batteries and you don't want one to explode. I have done this I have to admit, but then I have used magnets to connect them, and I think it it much more safe ;) Here is an example!

[mahesh_jo]

Thanks for the given links. I assume that circuit provided with the kit has inbuilt overcharging protection (I have not gone through it in detail). But that would be for entire bank not individual cell. Cell level protection will increase the size.

You are right, while soldering the cells we should take care or heating but if cabinet has enough space we can use springs also..

[hubi]

I use another Power Bank pack. This one http://www.ebay.de/itm/External-Dual-USB-Power-Ban...
no need to solder the LiIons and a display that shows actual current and voltage.

[mahesh_jo]

Yes, I have also gone through it but it was a
bit costly and requires 4 cells. As I have 6 good cells laying, I
decided for this one.

[XaviOrin]

I actually have a ton of laptop batteries just laying around and my own battery bank is about to the end of it's life. Definitely inspired by your tutorial and ordered my own bank kit from wish. thanks!!

[Swansong]

That's a good way to reuse those old laptop cells :)