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Lithium Ion Charger

From Francois Louw

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Contents


Basic Single Cell Lithium Ion Battery Charger (MCP73831)

I have a bunch of 18650 lithium cells laying around, empty, but no means of charging them. So lets build a small battery charger to charge them.

The purpose is to make a small charger that I can use with any Lithium Ion cell to charge. The 18650 cells that I have are 2700mAh cells, and charging at just under 500mA takes about 6.5 hours to charge a single cell form empty to full. This is not a good solution to charge big cells, but it gets the job done. Maybe in the future I will make a faster charger for those cells.

Specifications

  • Single cell charger
  • Small
  • Low component count
  • Cheap
  • Indicator LEDs

Hardware and Schematic

BOM

  • Microchip MCP73831
  • 1K Resistor x2
  • 2.2K Resistor
  • LED 3mm Red
  • LED 3mm Green
  • 4.7uF Capacitor x2
  • PCB

And here is the schematic. This schematic is basically taken straight from the datasheet, with the exception of the Status LEDs. The Status pin is tristate when not charging, Low when charging, and High when fully charged. This circuit shows both leds on when no battery is present, Red (LED1) when charging and Green (LED2) when fully charged. The 2.2KOhm resistor sets how fast the charger charges. A value of 2.2KOhm will give just under 500mA charge. Higher value means slower charge. The minimum value according to the datasheet is 2.0KOhm which will give 500mA charging current.

LionSchematic.jpg


I didnt make a proper PCB for this project, I used a small SOIC header board as a base and soldered the components onto it. Not pretty but it works.

Results

That is it. Nothing more needs to be done. Tested and it works. Charged a 280mAh cell in 45min. The 2700mAh cells take forever to charge (6-7 hours) but it works.

WARNING! The MCP73831 is VERY sensitive. Any reverse voltage, or short circuit will fry the chip immediately! Be Carefull!

Here are photos of the charger front and back.

LIONSmallFront.jpg
LIONSmallBack.jpg