Build-Your-own-Power-Bank-for-your-Travel-and-IoT-Projects

This Project explains how to build a cost-effective power bank for mobile phones during travel and for powering up the IoT Projects as DIY (Do It Yourself).

On highways, there is every likelyhood that mobile towers are built in such a way that continuous signals are available for the mobile data and hence battery will last for more time. But during normal road and train journies, our travel passes through ups, downs, curvatures and amidst big hills. During these times, no mobile signals will be available or the signals will be very feeble. Thus, we travel constantly in and out of a tower’s range and into the next one . The device (mobile or any electronic device that uses data) ping each tower when entering and leaving it’s range. Signal searching becomes more aggressive when signals from other cell towers (not registered with the SIM card inside the mobile) are within the range of the mobile. The radio inside the device (transmitter and receiver section on the mobile), uses more power during such signal fluctuations to maintain the network level, that results in more power usage which leads to battery drain. Worst case being, the mobile switches off before reaching the destination point. Carrying a power bank(s) in such scenarios will avoid frustration, especially, when there are limited charging points.

Readymade power banks are available on the market. But, they are not only costly but also the troubleshooting is a difficult task. In the light of this fact, I present DIY power bank which is cost-effective and also easy to replace when there is a problem with the battery or charging electronics. It works well during travel and also can be used for testing embedded and IoT projects.

MATERIALS AND METHOD

Power bank mainly consists of three parts:

• Lithium-ion or Lithium-polymer battery
• Battery charging electronic circuit
• Case to hold both the above

BATTERY

In this explanation I concentrate on Lithium-ion batteries, due to its popularity. In fact, the Nobel Prize in Chemistry for the year 2019 is being shared by three scientists for their invention: "Development of Lithium-ion Batteries"

Certain advantages of Li-ion batteries include:

• lighter and more compact compared Lead-acid batteries still found in cars
• rechargeable, unlike disposable zinc and alkaline batteries used in medical-electronic devices and toys
• unlike Nickel-Cadmium rechargeable batteries that contains toxic Cd, Li-ion batteries doesn't contain toxic metal
• Li-ion battery doesn't have "memory effect", which is prevalant in Ni-Cd cells
• Li-ion cells are availble in portable sizes and shapes: cylindrical and rectangular

Following are the images of Li-ion batteries used in power banks, laptops, mobile phones etc.

In the above, Li-ion batteries shown in (a) and (b) are used in mobile phones, tablets while that are used in power banks and laptops is shown in (c). Li-ion batteries used in power banks and laptop's power supplies, and general power supplies are numbered as 18650 with 3.7V and current ratings is shown below:

The cross-sectional views of both type of batteries are shown below. Working of the battery is out of the scope this presentation.

ELECTRONIC CHARGING CIRCUIT

Charging a LI-ion 18650 battery can be accomplished by different methods. Due to the developments in VLSI technology, many charging circuits are coming in the form of ICs. These ICs in conjunction with PCB mountable miniature L,C,R components will be used as battery chargers. Certain popular charger ICs are:

• HT4928S
• SW2808S
• 134N3P
• MC34063A
• TP4056
• HX3589
• ST6845

The Hotchip HT4928S and SW2808S are very popular among these chips. Further, these ICs are widely used in power bank circuits. The HT4928S is a highly integrated mobile power supply management system (MPSMS). It has a built-in charge management module, LED(s) indicator module, and a boost discharge management module. It is available in 8-pin SOP package. This chip is described as: "5V-Step-Up-Power-Module-Lithium-Battery-Charging-Protection-Board-Boost-Converter-LED-Display-USB". The inernal architecture and the pin configuration of HT4928S are shown below:

The circuit diagram and the end product wherein the SW2808S and supporting components soldered in the form of PCB are shown below:

Now, it is time to understand the assembling of the individual components. In the above figure I have shown the assembled PCB that goes in to the design of power bank. The assembly consisting of the aluminium casing, battery holder is shown in the following figure.

A small thin square steel plate that is soldered to the PCB (marked (+) on PCB) acts as positive terminal, and one end of a long wire is soldered to the PCB (marked (-) on PCB) and the other end of the wire is wound in a tapered spiral shape which fits in to the plastic battery holder acts as negative terminal, as shown in the figure above. The spacing between the positive plate and negative spiral end is such that, the 18650 battery just fits exactly as shown in the figure below. The approximate size of the battery is 6.5cm. in length and 1.7cm. in diameter. Power bank constructed in this a way gives an output of 5V at 1A rating.

The power bank cases are available commercially at the following:

[(https://www.amazon.in/HeSale-Aluminium-Power-18650-Battery/dp/B084X8KV7K)]

The power bank shown above can be charged with mobile chargers with micro USB2.0B termination. I used Motorola and Redmi mobile chargers (shown below) to successfully charge the power banks. Check your charger specifications before use. Use only eligible chargers to charge your power bank, otherwise it may lead to explosion of battery/catching up fire/spoiling of the charger circuit/spoiling of charger itself.

Such Li-ion batteries with high charge density and long life are used in Tesla cars. The following video (YouTube) shows the working of Li-ion battery and its use in Tesla cars.

[(https://www.youtube.com/watch?v=VxMM4g2Sk8U)]

Please go through the following website which is very useful to know about Li-ion batteries.

[(https://www.ionenergy.co/resources/blogs/battery-safety/)]

My Experience in using the Power Bank

As shown in the above figures, I bought the Aluminium cases and Batteries separately. I charged the battery (with the mobile chargers shown in the above images) for about three to four hours. During charging, the Red LED blinks at approximately 1 sec., continuosly. Once the battery charges to full, blinking stops and the Red LED glows continuosly. I used the power bank to power up my IoT circuits (Please check my repository images). When connected to load, Red LED will be off, the Blue LED glows continuosly, until it supplies 5V to the load. Once the voltage drops (due to unsupported load current), the Blue LED goes off. Now, the battery needs to be charged.

DISCLAIMER

Before you work with this project in any way, please make sure you understand what you are doing. Electronic circuits and batteries can be harmful and dangerous when not used with proper care and administration.

If you are trying to duplicate or use this project in any which way possible (partially or completely), you agree that you understand all the risks associated with it, doing it at your own risk and no body can be held responsible or accountable for any damage or harm that might be caused due to your use of this project.

" USE THE PROJECT AT YOUR OWN RISK "