Custom power bank for electronics projects

A common problem when making battery-powered electronic projects is how to have a stable 5V output from a battery that is constantly reduced in voltage.

Additionally, when using lithium batteries, you must make sure that the battery is never discharged beyond a set voltage in order to prevent permanent damage to the battery chemistry.

To solve this, there are a variety of modules like the TP4056 and others that solve part of the puzzle but it's always up to the project maker to decide how to mount the battery and where to place the control electronics.

When working on the RGB play button, I used a power bank module to protect the battery and also to have a way how to charge it and while at it, I came to the idea that I can actually make a custom PCB that can then be used to solve this problem.

I had the PCB manufactured by my friends at PCBWay and you can read all about it as well as how to assemble it for yourself.

Tools and materials used in the project:

• Power bank PCB - https://www.pcbway.com/project/shareproject/Electronics_Project_Powerbank_55fa070c.html
• CB-18650-PC2 battery holder - https://s.click.aliexpress.com/e/_DdRH3cr
• Power bank module: https://s.click.aliexpress.com/e/_DBhJtvv
• 18650 battery cell - https://s.click.aliexpress.com/e/_DkKXHkP
• Soldering station - https://s.click.aliexpress.com/e/_DegRGVH
• Multimeter - https://s.click.aliexpress.com/e/_DBxGXqT
• USB Power Meter - https://s.click.aliexpress.com/e/_DDrl1Ll
• Wire snips - https://s.click.aliexpress.com/e/_DnB0wMb
• Resistors kit - https://s.click.aliexpress.com/e/_DELZuOJ
• RGB Flash LEDs - https://s.click.aliexpress.com/e/_DEtrn1h
• Soldering helping hand - https://s.click.aliexpress.com/e/_DFVA1Yn

The Power Bank PCB

The PCB is a neat way how we can assemble everything down to a neat package and manage the wire mess that might appear otherwise.

On it, we have a position for the battery holder (CB-18650-PC2) and the power bank module right next to it. Additional to that, there is a position for a resistor with multiple holes so different size resistors can be used.

At the far end, there are several output positions so we can use them to solder wires to it for our projects.

The tracks on the PCB are actually doubled up on both the top and bottom layers so there is no problem in whatever current your project needs.

The PCB can be ordered directly from PCBWay at: https://www.pcbway.com/project/shareproject/Electronics_Project_Powerbank_55fa070c.html for only $5!

The Control Module

To control the charging of the 18650 cells as well as to provide a steady 5V output for the project, I'm using a so-called power bank module. These modules are used in small power banks and are readily available online.

The board has two USB ports, one for charging (micro USB) and a standard female USB port for the output.

The board has two downsides. The first one is that there are no direct pads for the output 5V so in order to use that power and transfer it to the PCB as output, we need to solder wires directly to the USB pad. Since the USB is easily accessible, this is not a big problem if you have at least some experience with soldering.

The second issue with the board is that it is designed in such a way that it will turn off if the current draw is less than 60mA. For situations where we have a higher load, this is not a problem but if our project requires less than that, we can add a dummy load resistor to the output so that the module stays on.

Optional On/Off Switch

The J1 position on the PCB disconnects the battery from the circuit. I've added this in the PCB so it can be used to add a switch in the circuit if we ever want to completely turn off the device that we are working on.

In cases where we want to have just a regular power bank, the pads for the switch can be soldered together so the entire module is always on.

Soldering the Battery Holder

To start making the power bank module, we first need to solder the battery holder.

Since the battery holder can be soldered in any direction, the PCB has markings of B1 and B2 respectively for the battery terminals.

Depending on how you orient the holder and its markings, you will need to make sure that you then orient the power bank module in the same way, so for example, if you connect the positive side of the battery holder to B1, the module B+ terminal will also need to be soldered to B1.

Soldering Jump Wires to the 5V Output

Out of all assembly, this is probably the most tricky part as it requires a steady hand and a soldering iron with a small tip.

I first carefully added some fresh solder to the outside pads on the USB port which are the 5V output on the right and GND on the left.

Then I used a bare copper wire and I carefully soldered it in place on both pads. I made sure to leave some extra as that can be clipped later on once we solder the module to the main PCB.

Soldering the Module

Now with the module prepared we need to apply solder to both the pads on the main PCB as well as to the battery terminals on the power bank module.

Once we have solder on both, we can tread in the output wires that we've soldered previously and align the polarity as explained previously.

With the two solder blobs next to each other, we can place the soldering iron on top of both and that will connect the two PCBs together. We can then repeat the procedure on the other terminal and once that is done, we can solder the output wires from the bottom.

Testing the Output

To test out the output, we can now plug in any USB-powered device and if we did everything right, it should now work.

To make sure that the voltage is right, I used a USB tester and it properly showed the 5.1V on the output.

Additionally, I also used my multimeter to verify that the output voltage is also present on the OUT pins on the main PCB.

Charging

To charge the board, we can simply plug a charger cable into the micro USB port and the red LED will start blinking indicating that the battery is being charged. When full the LED will stop blinking and depending on the module, you might even have a second LED that will power on.

Since the switch port is between the battery and the module, we must have it in the ON position when charging the battery so please keep that in mind.

Keeping the Output ON

As mentioned before, these modules will turn off if the current is less than 60mA. Since the current draw will still be present, it will then turn on again, but that will reset any microcontroller that we have attached so that might be an issue depending on the application.

To prevent this from happening, the added R1? position can be used to add an additional resistor to the circuit so more current can be pulled through the module and it will stay on. You can use Ohm's law for this where a 470 Ohm resistor will add an additional 10mA of current to the load of the project.

Depending on the application, you might not need this as in the case where I placed two RGB flashing LEDs on the output and that was enough to keep the module constantly on.

I hope that you liked this project and that you found it interesting. I have many others that you can check out and you can also consider subscribing to my YouTube channel or check out my website.