## Introduction: 40000mAh LiPo Power Bank

In this instructable, I will share the 40000mAh Lithium Polymer Power Bank Project with you.

I am not good at writing instructables and my English sucks. Hope you guys will understand what I mean.

## Step 1: Designs and Find Suitable Parts

As I am a student, I can’t afford too much in building this power bank. However, I still need to satisfy what I am targeting. At least 4 USB Port rated 1.2A and at least 1 port that can go up to 2A. And here are all those design sketches, just for my reference. Of course, you may not need to follow these circuit diagrams, but these circuit diagrams help me to build the power bank with modules. (And yes, I didn’t make my own pcb except the indicator part.)

Just ignore the copyright on the right hand corner :)

## Step 2: Choice of Battery

I use LiPo Battery in all of my projects. They are relatively expensive compare to Li-ion but with a much lower risk of explosion and lighter. In this project, I am using 4 3.7V 10AH Battery. I use this battery because it was on sale. It only cost 4.2 USD per battery.

## Step 3: Step-up Circuits

Organically, I was planning to use FP6276,
which was an IC that uses to step up the voltage with only 4 extra components. However, my first try with my custom made PCB failed even I follow its datasheet’s sample circuit. As a result, I changed my mind and use the “Mobile booster” step-up circuits that you can easily find on ebay .

For the port that needs to output 2A, I use another pre-built module here. The red module can output up to 3A. Hence, I connect 2 use ports to the module’s output and you can draw 1.5A out of each port or 3A when using only one of the two ports.

## Step 4: IMUS Black Magic - the SAB Charge Technology

Our Laboratory introduced the SAB Charge Architecture
in the winter of 2016, which stands for “Stand-alone Battery Charging”. For each battery built in, there is a stand alone TP4056 that control its charging and DW01 with 8205A for protection. If you don’t know what I am talking about, you can just skip this step and proceed. SAB Charge Architecture is an open sources project from our Laboratory, you will see more of this in the future posts. Its working principle is as simple as described in the circuit diagram above.

With SABC, you can charge your battery with a current of n * 0.9, where n = the number of SAB Charge Controller.

## Step 5: Battery Indicator

As the SAB Charge is used, there is a diode at
the Bat+ output, hence, an voltage drop occurs. Normal ICs that design for LiPo battery indication will not work anymore. To solve this problem, an ATtiny 24 that power by the step-up converter and read the Bat+ output voltage to detect the battery left. For normal LiPo, the voltage range should lies between 4.2 to 3.6V. However, with SAB Charge, the voltage range will drops to 3.8 to 2.7V. Hence, you have to write an indicator that make use of the new voltage range instead of the original one.

The DIY LED strip pcb that use for battery indication and the code for ATtiny has been attached with this step.

## Step 6: Universal Port 2.0

Another Black Magic for IMUS’s Power Bank
was the Universal Port (UP for short) . As this power bank was designed for camping uses, this power bank has to handle extreme charging inputs like 9V or even 12V. To solve this problem, the UP1 was introduced back into 2015, and the UP2 minimized the voltage regulation circuits and support up to 18V for solar panel charging.

The UP1’s circuit board as shown above was used in the UP2. The different is that the UP2’s input will pass through an buck converter to step down the voltage to 9V first before handling the input to linear converter to reduce power loss.

## Step 7: Casing Design

You know, I am not a designer. So I just use the simplest design that can possibly be used on a power bank when designing this thing. It looks sort of ok, but due to the high cost of metal, I change the casing back to plastic in the final moment.

As there are too many trial and error in the development process, if you are really creating your own giant power bank, PLEASE READ THIS DEVELOPMENT LOG BEFORE YOU DO SO. All details are included inside this pdf like circuit diagram, pictures of development and reason why some version has failed.

## Step 9: Finished~

And here are the finished 40000mAh power bank.

The one on the right was another power bank project back into 2015 that has a capacity of 21000mAh.

## Step 10: IMUS Laboratory

I hope you like this project. We mainly focus on open source home-brew technology (or black magic) development. If you encountered and problem or questions during the process of making a similar power bank, feel free to left us a comment below.