16.1.14

$1 Lithium Coin Cell Charger

Got a buck? Make a charger for LiR2032 coin cells. It could hardly be cheaper or easier.



This Lithium battery charger circuit board, based around a TP4056 chip, will set you back all of $0.90. That may be an overestimate. I won an auction this week for 5 of them and paid $1.36, shipping included.



The board is designed to charge high-capacity cells at 1 A, which is exactly what I have been using it for. But it can easily be hacked to charge tiddly coin cells at much lower rates. The charge rate is set by a resistor, identifiable as R4 on the schematic:



Sure enough, R4 on the PCB can be identified as 1.2 KΩ by its marking (122). According to the TP4056 datasheet that value fixes the default charging rate at 1 A. That's way higher than the 45 mA maximum recommended for a rechargeable LiR2032 coin cell so I unsoldered R4 and replaced it with a 33 KΩ surface mount resistor. Other charging rates can be set with reference to the table below.



All that remained was to wire up the output terminals to a coin cell holder ($0.10) with the aid of a scrap of stripboard and a male pin header. About the only thing you can do wrong is wire the terminals the back to front, which I duly did. Here's what it looked like from the back after I had corrected my mistake.



Now just plug in a mini USB cable and wait an hour or so. The green LED marked D2 will light up when the battery is fully charged.

One last thing. Do not attempt to recharge CR2016 and CR2032 cells. It is a generally good idea only to recharge rechargeable cells. Unless you are Afroman. Or you are trying to commit insurance fraud by setting your house on fire. Then it's OK.


Materials




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3 comments:

Unknown said...

Afroman's charging of primary cells is not quite as unlikely as it may seem. Alkaline cells can be "recharged" a number of times. Results vary with specific brand and size and phase of moon and ... . But it generally does work. One battery company (at least) took advantage of this capability sold a range of Alkaline rechargeables at one stage. | It's held by some, who may or may not be worth listening to, that "dirty DC" works best - 1/2 wave AC with a resistor across the diode so you get eg about 10% discharge on one 1/2 cycle compared to the charge current on the charge half cycle. - Russell McMahon (New Zealand)

Anonymous said...

http://www.100y.com.tw/pdf_file/02-EEMB-Lir2032.pdf

Anonymous said...

Here is a review of the new charger module with a protection circuit: https://www.youtube.com/watch?v=Qw4psECqpwI&list=UUmHvGf00GDuPYG9DZqQKd9A

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