Cheap LIR2032 Coin Cell Charger

The LIR2032 is a rechargeable lithium coin cell battery. I use them in small robots.

Step 1:

For charging I hacked a lithium battery charger circuit board with a TP4056 chip.
They are available on the Internet for a very low price.

Step 2:

These circuit boards are designed to charge cells at 1A, this is way too much for the LIR2032.

Luckily they are easy to modify and obtain a different charging current.

In the TP4056 datasheet you can find that R4 is the resistor which determines the charging current. On a new purchased board, you can identify the resistor by it's marking 122 (R4 = 1.2K)

Step 3:

A save charging current for the LIR2032 is 35mA.
Also in the datasheet you can find a formula to calculate the replacement resistor for R4:

Ibat=(Vprog/Rprog)*1200 (Vprog = 1V)

So if you use a 33K resistor for R4 you get about 36mA, that should be good. (resistor marking: 333 or 3302)

I changed the resistor, mine was 0603, that's tiny! But this board is also available in different designs with 0805 components, making it a little easier.

Step 4:

As a last step i soldered a battery holder on a piece of prototype board. You can make this how you want, but keep the polarity in mind.

Now you can plug in the mini usb.

When charging, a red LED lights up.
And when the battery is fully charged, a green or blue LED will light up.

Comments

[johnw4431a]

I considered changing R4 to 33k but was put off by someone who reported that the charger module did not work properly when he used large R4 resistor values. The data sheet for the TP4056 only specifies current programming resistors as high as 10k. Are you sure that you actually get 36mA charge current? There is a LTC4054 device made by Analog Devices that will definitely work at 36mA.

[BurgersBytes]

In the upgraded version of board R3 may be the charging current resistor:
https://usa.banggood.com/Upgrade-Version-3_2V-or-3...

[Uren]

Can I use the Coin battery cell (LIR2032) while charging?

I don't have access to SMD resistors and if I have it might be expensive and could only bought in bundle. Is there any alternative to reduce the current?

[Uren]

Can I use the battery while charging?

[needfulthing]

I was just wondering, the LIR2032 only has 40mAh, your robots must be really small :)

[needfulthing]

Dumb me just found your mini lightseeker project :)

[guillaumetorreilles]

[edit] I made some pliers with one polarity on each side, this way any type of coin cell fits right in

[BGprojectz]

The pliers are a good idea! Thx!

But be carefull, use only with rechargeable batteries.

[guillaumetorreilles]

[edit] I made some pliers with one polarity on each side, this way any type of coin cell fits right in

[guillaumetorreilles]

Works just fine, thanks!! Any type of lithium coin cell I have works with it ^^