Hello,

I am attempting to charge a 3.1V, 5.5mAh lithium ion coin cell battery. My project is a unique situation in which we will only be able to plug our device into power source infrequently and for short intervals 10 to 15 seconds (in which charging of the battery will take place). However the device only needs to use the battery for 10 - 15 seconds after the power is pulled from it (battery discharge), so I'm not draining the battery too much either. My load takes about 20 mA.

Do I have to use a lithium ion recharger IC? Or can I get away with a simple circuit because I'm just charging the battery for 15 second intervals?

Furthermore, I was researching how you are supposed to recharge lithium ion batteries with the four different stages. Why do you have to charge every battery to 4.2 volts? Especially because my battery is 3.1 Volts, why would you do that?

I have three different power supply voltage options to charge the battery (12V, 5V, or 3.3V). Before reading the article about charging I would have thought I could just have a current limiting circuit from the 3.3 V power supply to charge my 3.1V battery? Why will this not work?

Thanks,

Surfline

 

LiIion Rechargeable cells require accurate heat and current control during charging, there is a high risk of fire even with "somewhat ok" systems - See: Flaming Dell Laptops

Trying to recharge a non-rechargeable LiIon will result in a leak or explosion, they aren't like Alkaline or the old Carbon batteries in that regard at all. Only try with the recharge rated.

As far as your circuit, think about the absolute worse case scenario, would it be charged more than 10 seconds by a sequence of events? Probably so. If the goal is low price, look for a NiMH solution, though self-discharge is greater, it has improved to the point they are used in notebooks for memory backup.

What is the current draw from the cell in your circuit for the 10-15 seconds of draw? If you tape an LED around a CR2032 cell, they stay lit around a dozen hours at 10-15mA drain. If that was spread out into 10-15 second bursts, a standard CR 2032 with no charging system, such as PC motherboard clock batteries, would be the longest lived solution for the cost.

 

I was planning on using a 3.1V 5mAh rechargeable lithium ion battery (The Seiko MS621FE-FL11E battery). The load draws about 20mA of current from the battery.