Introduction: PCB - the World's Smallest LiPo Charging Board

About: We build a lot of projects... Hopefully, we'll bring more to Instructables soon.

Over the course of my project building life, I have faced the same problem over and over – battery management electronics are oversized. Which leads to any battery powered project increasing in size, sometimes by a magnitude or two.

Even those tiny LiPo battery charger boards you can get from many different sellers today will still feel like they will burst your project’s miniature enclosure. But there is a way to beat this, with the WSLC, the World’s Smallest LiPo Charger board.

We made this for some future projects coming out, where real-estate is at an all-time high price. The board works so well that we thought we should share with the rest of the maker community out there.

If you do use this for a project, message me!

Step 1: Gather Your Tools

- Soldering Iron

- A soldering iron with a finer tip would be best for SMD parts

- Solder

- Tweezers – to help with the soldering of small SMD components

- Flux (optional)

- Autodesk EAGLE PCB design software

Step 2: Background

So many projects need batteries, and if you actually equip your creation with a battery pack, you want it to have the power to last a while.

Lithium-polymer batteries are the way to go. They are light, and they have a high energy density compared to alkalines. Plus, they are rechargeable.

They one issue with LiPo batterie is the fact that additional electronics are needed to charge them. There are plenty of off-the-shelf solutions that can be had for under $20, but they are all kind of big. They aren’t huge, but they all seem to be just big enough to be a pain when trying to find a place to fit it into a project.

It was the intention of this project to create a truly tiny charger for lithium-polymer batteries, and it is indeed small, measuring 0.40”x0.450”. As small as it is, by selecting smaller footprint SMD components, the board could have been made smaller. While going tinier was an option, it was decided to keep the board at its present size so that it could be assembled without a magnifying glass or fear of losing components.

Step 3: Parts List / BOM

Step 4: The MCP73831T

Like so many of its larger cousins, the mini charging board is built around Microchips Technology’s MCP73831T special purpose IC. We used the 5 pin SOT-23 package but is also available in a lead-less 2x3mm DFM package.

The MCP73831T are self-contained little devices designed to handle the task of charging lithium-polymer batteries. You don’t have to do anything other than give it a battery power and mount it to a PCB.

Maximum input voltage 6 volts. Typically receiving power from a USB port or charger.

Step 5: Schematic and Board

Maximum input voltage 6 volts. Typically receiving power from a USB port or charger.

The board has a red and a green LED. When a battery and a power source are connected, the MCP chip will evaluate the battery. If it isn’t at full charge (about 4.2 volts), then the chip will charge the battery. When the battery reaches full charge, the red LED will turn off and the green LED will light up.

Step 6: Generate Gerber Files and Ordering PCBs

You don't need to do this yourself, I attached the files you need to have these made.

However, if you want to know the process on how to do this, please take a look at our other PCB projects:

Remote controlled ice block

Skateboard floodlight, PCB version

Shakelight nightlight, PCB version

Keypad PCB

As always, order from OSH PARK. Once you upload the gerber zip file, you should see the above PCB view.

Follow the instructions on their site and order away!

Step 7: Installing Components

Once again, see our other projects for how to place SMT (surface mount) components.

Remote controlled ice block

Skateboard floodlight, PCB version

Shakelight nightlight, PCB version

Keypad PCB

For this project, I recommend buying a circuit board holder, as seen in the pics above. It is such a small board, it will move around from you breathing.

I like this circuit board holder, but it isn't the only one out there.

Step 8: Testing the Board

The mini charger board can be functionally tested with a battery and a 5-volt source like the aforementioned USB port. However, checking a board this way might take a while. If the battery under test is in a state under low charge, it may take several hours before the green LED lights.

There is a faster way. The schematic below shows how to construct a simple “faux” battery that will fool the charger board. You can get away with a 2-watt resistor as is shown but a higher wattage rating is better. At 2 watts, the resistor will get got after a while. If possible, parallel several high watt resistors to get the desired value.

By starting with the power supply at about 4 volts and slowly bringing raising the applied voltage, you will be able to see the board transition from the charging state (red LED lit, green LED off) into the charging finished state (green LED lit, red LED off). Remember, the board must also be connected to a separate 5-volt supply while performing this test.

Step 9: Can It Get Smaller?

Yes, indeed.

We may make a new version, removing the indication LEDs. They take up almost half the board size right there.

We could use even smaller SMT components.

More on this later....