Wednesday 7 January 2015

Do it Yourself Power-Bank Part-3

So the previous part(part-2) was completely about working and construction of Control Circuit

Since we have built the Control circuit and also adjusted and connected the Booster circuit to Usb socket, now its time to connect the dots and complete the Puzzle.
See below to understand how to connect all the parts that we have gathered or built so far.

Now after you gathered all parts and connected them together as shown above, all you need is a decent housing (plastic case ) for your Powerbank. 

What i generally do is get a plastic box from the General store and make necessary holes or modifications in it and use it, but it is upto you for what type of housing you would like to use.

Here are some images of mine below:

So if you have built it successfully then congrats you have made yourself a Powerbank that you can use when your mobile battery is out of power or to power other electronic portable devices that are generally powered by computer USB port(5v).

But if you are stuck somewhere in the build process then you can just leave a comment and i will try to help you out.

And finally a demo video of it in action:

Some extra stuff:

The batteries that i have used here are from one of my old laptop battery pack. I had said that in 1st part of this series that i will explain how to use old laptop batteries. 

I took 3 cells and connected them in parallel ( i.e. positive to positive and negative to negative). So since each cell was of 4.2v and 2600mAh then my total rating is 4.2v 7800mAh.

Most laptop battery-packs internal contain these 18650 size Li-ion batteries in parallel sets of 3 or 4 Cells in series.

If your laptop battery is of 10.8v or 11.1v then it will contain generally 3 cells in series and 1 or more sets in parallel. If it is 14.4v then it will contain 4 cells in series and the rest is same.

The capacity generally written on battery as 4400mAh or 5600mAh or 2600mAh is defined by the battery material concentration itself and the number of battery sets in parallel.

The above image has 3 cells in series and 2 such sets in parallel. Each cell was of 2600mAh so the total capacity rating would be 10.8v 5200mAh.

When the laptop informs us the laptop battery is damaged or the capacity has depleted to very low. Most of the time it happens so that the actual cells still have 80% of juice in them.

But the battery gauge (a chip which calculates battery capacity and wear) gives wrong information. Unfortunately it is not possible most of the times to reset or override this and bring back the battery to life. Because the battery gauge chip communicates all information on a one way like traffic from battery to motherboard(from the computer we cannot send data to the battery) and even if you get your hands dirty and open up the battery to directly reprogram the chip it sometimes it stores most of its calculation info deep down locked in its protected memory.

Most battery gauge chips nowadays come with advanced security features such that if we try to tamper with their data then it will lock itself and show the battery as dead when inserted in computer.

As you can see in the above picture the battery-packs are not manufactured to be refurbished or dis-assembled and re-assembled again. Because the top and base covers which are made up of plastic are fused together. So once you try to open them it will definitely break some part of the cover.

If you are lucky enough then you may be able to open it up without breaking the cover. However we don't need the cover. What we need to do is the remove the battery connection from the circuit safely by proper desoldering.

Then disconnect the batteries in series and divide them into individual pieces and then check each cell's voltage using a multimeter.

Now those cells which have a voltage of 2.8v (strictly) or more can be used rest are to be disposed of safely or sent for recycling. If you try to charge a battery which has less than 2.8v it could pose dangerous threats like explosion. So you are at your OWN RISK.

And before finally using it you should like charge it at 4v to 4.2v maximum constant voltage and monitor if the battery temperature starts increasing then get rid of it. I would recommend you to charge at 4v only because it is safe(float charging) as at 4v you can leave the battery connected to the charger for like ever and it won't harm the battery. But this method of charging is slower and charges a Li-ion to 80% of its full capacity only.

Its normal for most used cells to decrease voltage quickly when loaded but you can do a quick calculation and find out its real capacity by giving a constant load that shouldn't exceed current draw by 70% of the maximum rating of the battery.

So this was a quick intro regarding  re-usage of laptop battery cells in Robotics or electronic projects. If you have any doubts you can post a comment.


neutronstriker An Electronics and Tech Enthusiast

I am a Tech enthusiast who loves to build stuff like new gadgets and tinker around with electronic devices doing some DIY stuff, writing some code and in the process providing something back to the community.


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