DIY guide for electronic engineers: How to make your own portable power bank

A self-made portable power bank. Through the following introduction, I hope it can give you some inspiration, let's DIY together!

Are you still worried about not being able to answer important calls or delay your work because of the battery life of your mobile phone? Then learn to make a power bank yourself. Even if you carry two or more mobile phones of different brands, models and interfaces, it will be stress-free. A power bank can solve the battery life problem that has been bothering you and bring great convenience to your life. So what are you hesitating about? Come and DIY with us...

Picture of the homemade portable power bank

Figure 1. Homemade portable power switch and interface diagram

Nowadays, mobile phones have bigger and bigger screens, better and better performance, and more and more entertainment-oriented. However, in order to be as thin as paper, the battery is becoming less and less durable. In order to use the mobile phone for a long time, many people have started to buy a second battery, but it is often not enough. Some mobile phone users who cannot replace the battery are even worse off. Therefore, portable power banks have become popular.

Generally speaking, this portable power supply consists of four parts: charging, boosting, protection and battery. First of all, the battery is generally a rechargeable lithium battery, with sheet-shaped lithium polymer batteries and standard lithium batteries in 18650 packages being the most commonly used. Depending on the situation, the capacity can be increased and the use time can be extended by connecting in parallel. Then, there is a charging circuit to charge the battery. Generally, for the convenience and efficiency of charging, a standard 5V power supply is used, and the interface is MINI USB. The charging action of the lithium battery is controlled and managed by a dedicated lithium battery charging chip. The boosting part is to increase the output voltage of the lithium battery from the average 3.7V voltage to 5V to output to the external power supply, because it is basically controlled by a switch circuit, the efficiency is very high, and the loss of the line itself can be ignored. The protection part can be connected separately or integrated in the charging and discharging part, mainly to prevent short circuits and overcharge and overdischarge, which will affect the safety and life of the lithium battery.

Material

Lithium battery box: This is a standard dual 18650 lithium battery box purchased online. It can accommodate two standard 18650 batteries and a control circuit of appropriate size.

Figure 1. Appearance of lithium battery box

This is the inside of the battery box. It is a parallel structure, which is very convenient.

Figure 1. Lithium battery box interior

Look at the way the battery is put in. Friends who are familiar with batteries can guess what kind of battery this is. Hehe...

Figure 1. Finished integrated circuit board

Finished integrated circuit board: In order to simplify my workload, this is a finished integrated circuit board purchased online, with charging, boosting, and battery protection fully integrated, with a maximum charging current of 0.5A and a maximum output of 0.5A, which is enough to charge a mobile phone at ordinary times. The socket above is a MINI USB port.

3M double-sided tape: for fixing

Figure 3M double-sided tape for fixing

Use 3M double-sided tape to fix the standard USB port, then cut a piece of plastic block of appropriate size, fix it with Henkel instant glue, and cut a suitable notch on the upper plastic cover to place the MINI USB port.

Figure Fixed standard USB interface

Look at the appearance, stacked together, it fits just right.

wiring

Put it on, weld it, and connect the wires. It's very simple.

Fix it and it's basically done. In this picture, a simple connection method is used to short-circuit the D+D- port of the output port, which can meet the charging identification requirements of most smartphones.

Compatibility

In order to improve adaptability, for example, the fruit machine can also be charged, an external identification resistor board is connected, which is backward compatible with the D+D- port direct short-circuit mode of the output port, which is perfect and compatible with 99% of the models.

Figure 1. External resistor version to increase compatibility

Finished Product

Figure 1. Finished wiring diagram Figure


2. Portable power bank flashing blue light

Looking at this faint blue light, it still feels very good, haha.

Four-battery version

Figure 4 Solar Panels

Diagram interface diagram

This is the 4-battery version, made at the same time, and I'll show it here... Later I added two small LEDs for lighting, so I won't take a new photo. Making a portable power bank yourself is much more economical than buying a ready-made one, haha...