Lion or Lipo battery charging circuit design:

Other Hardware Motors, Mechanics, Power and CNC
1

I have some questions regarding Lion or Lipo battery charging circuit design:

  1. I have read that if I want to charge a single cell, I need a two stage design. Constant Current until the cell reaches threshold charging voltage which is something like 4.2 +1% Volts or something (depending on the datasheet), and then Constant Voltage until the current reaches around 10% nominal current. I have learned this listening to the guy on EEEblog.

My Question is:
Can I treat a 3 cell series 12 Volt Lion battery like a single large battery and charge both anode and cathode of the big battery in Constant Current and Constant Voltage until the big battery reaches threshold charging voltage which is the single cell's threshold voltage times 3?
or is this bad practice, and I should be charging every cell individually?

  1. Must I use constant current and then constant voltage or, can I simply apply constant voltage and thats it.
  2. if I am applying constant voltage can I draw from the battery at the same time?
  3. do I need to smooth out battery voltage while drawing from the battery?
  4. how much maximum voltage can I charge with a USB connection, maximum current?
  5. do designers use IC's or do they just design all of their own stuff like constant current or step down circuites?
2
  1. Bad practise. Individual cells need to be balanced.
  2. CC/CV is correct. Anything else is not.
  3. Yes
  4. Don't understand the question
  5. USB standard is 5V and 1.5A.
  6. There are many dedicated charger ICs.

Steve

3

The problem with LiPos is the risk of fire or explosion if you mistreat them.

You can get microchips at very reasonable prices that manage the charging process safely. I had built my own circuit from a website I found but I felt I had to watch it closely and keep adjusting things. Recently I bought some Microchip MCP73831/2 ICs and all the worries went away. I'm not sure whether I got the xxx1 or xxx2 version. And they are only suitable for a single LiPo.

...R