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Have fun with lithium batteries

How not to burn your house

pepinorabanitopepinorabanito
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This is not a new project but a warning for those who use DS3231 clock PCB with EEPROM 24C32, because a few days ago I was awakened by an explosion in the middle of the night, but I only noticed the smell of magic smoke and I did not find the origin; everything was working in the house and I went back to bed. In the morning I saw it and I could hardly believe it: the CR2025 battery that had been installed in that clock for several years exploded, after having heated up a lot, and suddenly I understood what the diode and the resistor on the PCB were for, to which I did not pay the attention they required. I really don't understand what they are doing there when usually a primary lithium battery is used, which should have exploded much earlier. The resistor is no longer on the PCB and the battery will take a while to come back.

I have searched the net and found no references to this problem. I'd be surprised to be the first to have fun with this.

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pepinorabanito wrote 10/29/2024 at 20:43 • point

Last night DS3231 died suddenly and quietly. Maybe it missed the battery.

It is the first to fall of those I have from Aliexpress, probably rescued from the scrap box of the production line, like the HTU21D, which usually mismeasure humidity and occasionally die. The only reason it might be a good idea to buy such dirty cheap circuits is because of the PCB, which allows you to put ICs bought from reliable suppliers on it.

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Per Jensen wrote 10/14/2024 at 12:01 • point

I've been telling people about this for years. Almost all these RTC-boards are made by someone that just followed an application note blindly, and they forgot to note on the board that it will trickle-charge the cell. Remove the zener diode and it will not do that anymore.

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OWlchanMagican wrote 10/14/2024 at 02:01 • point
It could be a grain of sand or something stuck between the power pins, or your screw accidentally made the circuits touch, or you should call an exorcist. Because this is also the first time I've heard of an rtc module spontaneously exploding (usually they don't work and I have to replace them with another one).

  Are you sure? yes | no

Per Jensen wrote 10/14/2024 at 11:59 • point

No this is actually fairly common. The diode on the board is actually a Zener diode. It's a circuit to trickle charge a rechargeable cell. No one ever uses the rechargeable cells so the circuit is wrong. If you have any of these RTC boards, remove the zener so it doesn't try to charge the cell.

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