Cheap LIR2032 Coin Cell Charger

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About: Interested in everything that has to do with technology or science, but especially electronics and robots. Visit my site: http://bgprojectz.weebly.com/ or youtube: https://www.youtube.com/channel/UCPxUQL1lB...

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.

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8 Discussions

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Uren

Question 6 months ago

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?

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Uren

Question 6 months ago on Step 4

Can I use the battery while charging?

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needfulthing

1 year ago

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

1 reply
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guillaumetorreilles

3 years ago

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

1 reply
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None

The pliers are a good idea! Thx!

But be carefull, use only with rechargeable batteries.

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guillaumetorreilles

3 years ago

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

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guillaumetorreilles

3 years ago

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