High efficiency lipo charger with integrated fuel gauge sensor

This is the second generation of the high-efficiency lipo charger with an incredible efficiency of up to 94%! It allows charging a single lipo from as little as 200mA up to a whooping 2A for massive lipos. With an integrates lipo fuel gauge IC (MAX17048), you can accurately tracks the voltage as volts or as percentage or even set up alerts.

Why did you make it?

Based on some good feedback from users who were interested in the previous revision of the high-efficiency lipo charger, some users suggested a new revision with an integrated fuel gauge IC, since often, the battery voltage needs to be tracked from a micro-controller and normally requires yet another pcb. This version aims to solve both of these issues in a single pcb, while also being more user-friendly and packed with more features.

What makes it special?

To improve user-friendliness, it offers the following improvements compared to the last revision:

• two LEDs instead of one. The first one shows if the board has power, the second one is the status led of the lipo-charger IC
• integrated JST connector and optional pads for lipo (+ and -). This means you can connect a lipo directly by soldering or via the JST connector
• short-circuit and over-voltage protection on the JST connector. This can save your lipo and this pcb!
• Adjustable charging current without soldering by setting the integrated DIP switch
• integrated fuel gauge IC (MAX17048) with a stand-by current of only 3uA! This chip has several libraries available (e.g. Adafruit) and can be interfaced via I2C, hence only two pins are required
• hackable via bottom pads. For the tech-savvy with good soldering skills, it's even possible to break out the integrated LED, set a custom charging current via a resistor or disable the power LED
• small form factor of only 30x30mm and slim pcb (1mm) allow for a total height of only 6mm
• low deep-sleep current. Although it packs two ICs, when idle, only consumes max. 10uA.

Documentation

⚠️ Before anything, make sure you have a lipo connected to the board via the JST-connector. Although it has reverse-polarity protection, please check the polarity of the battery's JST connector with the board.

⚠️ The USB-C connector is a "simple" USB i.e. it does not have the fancy communication to communicate with USB-C-PD chargers. If you do not see a green light when connecting to the board, try a non-PD charger or use a USB-A to USB-C cable

Setting output current

The output current can be easily set via the on-board slide switches on the board. First, set all sliders to the off position, i.e. away from the ON mark on the slider. Then, push a single slider in the ON-direction.

• For 2A output current, set the slider with #1 to the ON side, ensuring all others are in the other position
• For 1A output current, set the slider with #2 to the ON side, ensuring all others are in the other position
• For 500mA output current, set the slider with #3 to the ON side, ensuring all others are in the other position
• For 200mA output current, set the slider with #4 to the ON side, ensuring all others are in the other position

Pinouts

• Bat+ (Connected to the lipo's positive side). Use this to draw power from the lipo
• GND pins (3 pins). Connected to ground
• VCC. The power input for the fuel-gauge IC chip. This is handy if you want to provide the chip with external current. By default, you can simply connect this to BAT+, which provides power from the lipo
• QSTART. Quick-start input. It allows reset of the MAX17048 through hardware
• SDA. SDA pin used by I2C communication
• SCL. SCL pin used by I2C communication

Communicating with the fuel-gauge IC

Since there are already existing libraries for the IC used in this board, please refer to the tutorial by Adafruit:

In summary it boils down to the following:

• Connecting SDA, SCL and GND from the board to your Micro-Controller. GND goes to GND, SDA and SCL lines can be chosen by your choice to any digital pin

• Downloading and adding the MAX1704X library to your IDE e.g. ArduinoIDE: MAX1704X library

• Choosing the correct board and serial port from the boards menu

• Choosing the basic example from the examples tab of this library
• Flashing the code available from here: Demo Code