Power bank have become a very useful in today's world.

There are many variety of them available in market .
i have been using a Xiaomi power bank which costed me 1000 INR i.e 14$.
It is really good but as a Maker i wanted to make one.
Recently i completed this project.
1 $ Power bank

Special thanks to my friend Vrajesh , without the enclosure was not possible

[He donated this for operation ]

NOTE This has been eligible in hack your day and hand tools contest :D

Specification

2200 mah
Rechargeable
1 A output
1 $ Cost

List of item required

Step 1: Salvaging Laptop Battery for Free Battery

Ok the 1 $ is only possible because i got so many free batteries from my old laptop battery.

Please pardon me the photos are not so good as i clicked in a rush ,i actually cut my finger while trying to open it.

OK to salvage batteries you need to have some

Preacaution

(1) Misusing the battery may cause the battery to get hot, rupture, or ignite and cause serious injury. Be sure
to follow the safety rules listed below:

Do not place the battery in fire or heat the battery.
Do not expose the battery to water or salt water, or allow the battery to get wet.
Do not solder directly onto the battery.
subject it to strong impacts or shocks.
Do not pierce the battery with nails, strike the battery with a hammer, step on the battery, or othewise
Do not carry or store the batteries together with necklaces, hairpins, or other metal objects.
metal object (such as wire).
Do not connect the positive terminal and the negative terminal of the battery to each other with any
Do not install the battery backwards so that the polarity is reversed.
Do not install the battery backwards so that the polarity is reversed.

(2) Do not disassemble or modify the battery. The battery contains safety and protection devices which, if

damaged, may cause the battery to generate heat, rupture or ignite.

(3) Do not place the battery on or near fires, stoves, or other high-temperature locations. Do not place the

battery in direct sunshine, or use or store the battery inside cars in hot weather. Doing so may cause the

battery to generate heat, rupture, or ignite. Using the battery in this manner may also result in a loss of

performance and a shortened life expectancy.

Step 2: Soldering Wire to Battery

Soldering Li-Ion is a big problem even for the more experienced techs out there.Many try to solder Li-Ion cells or phone batteries. It is not advised by the battery manufacturers to heat them up regardless the reason.By using heat on Li-Ion cells, you can damage the plastic separator, pressure protections or even the main internal lithium layers.

Speaking of physics…heat requires time to transfer. Yes, thermal damage amount depends on the materials quite a lot, but the key to not overheating components or, in this case, Li-Ion batteries is the limited heat exposure time.

if your soldering iron takes quite a lot to heat up (30 sec +), remove it’s tip in favor of a thinner one. A 1mm wire tip will heat up significantly faster than a 2mm wire tip. Do not exaggerate though. If it’s too thin, it will melt.

I had to apply and remove quickly to avoid damage. Using pointed Tip is also better

Step 3: Preparing the Boast Converter

The lithium ion batteries hav a voltage of 4.2 in the full charge state and 3.0v on discharged condition .

So we need to regulate the output with a 5V regulated as Phone need 5 V to charge.
To provide the regulated 5V DC output we need a boost converter.

What is a Boost converter ?

A boost converter is a DC-to-DC power converter with an output voltage greater than its input voltage. It is a class of switched-mode power supply (SMPS) containing at least two semiconductors (a diode and a transistor) and at least one energy storage element, a capacitor, inductor, or the two in combination. Filters made of capacitors (sometimes in combination with inductors) are normally added to the output of the converter to reduce output voltage ripple.

Boost converters are easily available and they are cheap i bought a 1A 5V Boast converter.

NOTE :

Power input is equal to power output

Input Voltage x Input Current = Output Voltage x Output Current

The Boost converter has two input just input + and input -

Be careful with polarity

Step 4: Making the Case for USB Out

The Enclosure should be of a mouth freshener but i actually forgot the brand which it belongs.My friend was having it when i saw it and rushed to him.He said that he finished all .To his surprise i came for the enclosure not the mouth freshener :P.He Donated This for a noble cause.

The Cap was best for the USB female Out .
I started by drilling a hole of 3.2mm i max i had with my Dremel.
Then i using grinding bit i started to remove the left and right portion of the holes to fit the USB.
Later i realize silicon carbide is better for the job .
So i changed the bit and it worked.
I didn't had the files with me so there was a little imperfection but the USB fits perfectly in that.

Step 5: Adding Recharging Pin

Ok i Admit i can use the 4056 module directly.
But i didn't do that as i have a single charging module for now and many Li -ion battery so i made two pins to be used to charge the battery .
the connection are given in the previous step.
i had to mark the polarity on header confusion can burn the whole face.

I actually used a long male header pushed it to make equal on each side.
the top is outside and the bottom is inside the enclosure.
The inner connector connects to female connector which can be removed easily.
thus can be troubleshooted easily

Step 6: Adding Turn on Switch

Lastly the most important thing, we need a switch to turn on and off the power bank.

This was done the same way the USB part was done.
Only challenge was to make a the switch tightly fixed
i tried a lot of configurations and then settle for the inside outside configuration.
rather than pulling the switch from inside i pulled the wires solder it and then pushed the switch and it firmly fits in the enclosure.

Lastly lets calculate.

Battery 0$

Enclosure 0$

Boost Converter 0.9 $

switch 0.05$

Total 1$

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Further Improvement