I guess you probably also belong to the majority of the worlds population that owns a smartphone and you probably had more than one during the past few years of smartphone evolution.
With them, come used lithium ion batteries that you can not just keep on using inside your new phone.
So you are stuck with useless batteries. I have 3 of them and I did not change my phone because the batteries were dead.
They did not get hot or start to swell so they are still able to power devices. The average lithium battery has 80% of it's original capacity left after 2 years of usage, which is the period in which I usually buy a new smartphone (not because of the better specs but because of major hardware issues).
And think about the energy that went into extracting the raw materials, producing the battery and shipping it.
Considering all that it would be a real shame to just let them slowly die or throw them away.
In this instructable and in my video, I want to show you how to build a device that enables you to repurpose your old phone batteries as a powerbank for newer devices.
Step 1: Materials
Let's start with what you will need for to build your own recycled powerbank.
The materials are:
- a used lithium ion battery
- a lithium ion charging and protection board with 5V 1A max. input ( less is more in therms of battery life)
- a 5V dc step up converter with 600ma max. output (")
- some wire
- a few arduino pins and slots
- a paper clamp
- some leftover acrylic and screws
- a switch
The required working equipment consists of
- a knife
- a pair of pliers and a wire cutter
- a soldering ion
- a hot glue gun
- a drill or dremel tool
Step 2: How Do the Boards Work?
Let's take a look at the lithium ion charging and protection board. It has three important functions.
The first is charging. Lithium ion cells have a certain charging pattern. When they are nearly full, their current consumption drops. The board will recognize that and stop charging as soon as the cell voltage reaches 4.2V.
On it's output the board features a protective circuit consisting of an over current and an under voltage protection. Such a protective circuit is already integrated in modern phone batteries and therefore not necessary but it will allow you to use unprotected cells like you would find them in old laptop batteries as well. The charging current of the board can be adjusted through a resistor. It should be somewhere between 30 to 50% of your battery's capacity.
The DC converter takes the dc voltage from the battery and turns it into a square wave that is send through a little coil. Through inductive processes a higher voltage is achieved. It is converted back to DC and can be used to power 5V devices.
Now you know what you are dealing with, time to start making .
Step 3: Planning
Before you begin to make the enclosure, take your measurements and make a plan.
My device is supposed to be held in place by the paper clamp, so it will be bolted to the enclosure. The two pcbs will sit on top of each other with the in- and output at the top and the battery pins at the bottom.
Some phone batteries tend to have a different polarity than others, so the device needs pins with interchangable polarity. To add this type of functionality I used the arduino pins and slots.
A piece of three slots with the middle metal connector ripped out and the 2 outer ones bend to the side can be used as a battery connector.
The counterpart will be a row of 4 pins with positive wires connected to the outer two and a negative wire connected to the two in the middle.
This way the polarity can be changed by plugging the battery connector in on either the right or the left side.
Step 4: Make the Enclosure Parts
Time to make the enclosure. For this you use your measuring tool to find the right with and use the knife to scratch the surface about ten times. Then you can keep in without the measuring tool and more force. When you are about half way through, place your pliers next to the cut and bend the materieal until it breaks.
When all the parts are cut out sand and test fit them. Fix them on a stable surface and start making the holes for screws, switches, inputs, outputs and pins using a dremel tool.
Step 5: Solder the Boards Together
Before you can assemble the parts you need to wire the boards. The shematic shows how they have to be connected. The small switch turns the dc converter on and off.
Step 6: Put the Pieces Together
Use hot glue to stick the pcb's together and to stick the onto one if the plastic pieces. Glue all the pieces in place and screw the clamp on.
Plug tha battery pins in and test it.
If it does not work, try plugging the charging cord in.
Step 7: Use It!
Now you have a new purpose for your old batteries.
My enclosure is definitely not the best looking solution but it's nice to show the concept. I bet that you can come up with some much more creative ideas.
In my next instructable and my next video, I will show you another way to recycle those old batteries so follow me to be up to date.