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OA47

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Joined: 11/04/2012
Location: Australia
Posts: 926

Posted: 05:43am 08 Dec 2023

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I have a handful of these DS3231 RTC modules in the shed and have found that the 3V battery does not last long when the devices are not powered. I have searched for replacement leaded batteries but unfortunately the cost of the replacement battery is higher than the purchase price of the module including the battery. As I don't like the thought of the wastage I have been able to replace the leaded battery with a standard button battery that cost around 50 cents. With the help of a slither of heat shrink and some tinned wire I was able to connect the new battery and restrain it at the same time. Maybe this hack may help other shedders with these modules.

Merry Christmas
0A47

TassyJim

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Joined: 07/08/2011
Location: Australia
Posts: 6098

Posted: 06:59am 08 Dec 2023

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I use CR2032 battery holders on flying leads. Cost $1 plus battery and lasts a long time

Those soldered on batteries are a nuisance.

Jim

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Volhout
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Joined: 05/03/2018
Location: Netherlands
Posts: 4238

Posted: 08:07am 08 Dec 2023

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OA47,

Please be carefull. Some of these RTC's require rechargable batteries (in other words, they charge the battery when powered). Silver cell's will not be charged, in fact they may get damaged. B.t.w. nice that you could still get silver cells. I recall these where prohibbitted in Europe for their mercury content. My old calculator (HP12C) used 3 of these silver cells and would run 20 years on them...

Volhout
Edited 2023-12-08 18:10 by Volhout

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Mixtel90

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Joined: 05/10/2019
Location: United Kingdom
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Posted: 08:41am 08 Dec 2023

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Those tiny modules are ok, I think. All they have on them is the DS3231, two 4k3 pullup resistors on SDA & SCL and a decoupling cap. I can't find any other components apart from the battery. Supply negative and battery negative are common, the battery + terminal is the closest to the connector. If there's PCB space and a GND connection you only need to run one wire to power it from an external battery (take the old one off first!). The DS3231 won't charge the battery.
Edited 2023-12-08 18:49 by Mixtel90

Mick

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TassyJim

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Posted: 10:37am 08 Dec 2023

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Some of the modules DO have a resistor for charging and that needs to be removed.

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ville56
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Joined: 08/06/2022
Location: Austria
Posts: 95

Posted: 10:57am 08 Dec 2023

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Had one running for almost a year with a CR2032 as delivered from china. It turned out that there was a charging circuit included, consisting of a diode and a resistor. Had the project box opened to update the firmware (Webmite) and found the battery dangerously swelled, presumably short before cracking. Did abandon the charging circuit as the rechargable batteries are far too expensive.

73 de Gerald

73 de OE1HGA, Gerald

Plasmamac

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Joined: 31/01/2019
Location: Germany
Posts: 554

Posted: 12:09pm 08 Dec 2023

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Search for a“ LIR 232“

Plasma

Mixtel90

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Posted: 12:44pm 08 Dec 2023

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Yes, Jim, some of the modules do charge the battery. The tiny modules I have definitely don't (I've checked) - there's nowhere to put a resistor. :)
Edited 2023-12-08 22:45 by Mixtel90

Mick

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JanVolk
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Joined: 28/01/2023
Location: Netherlands
Posts: 144

Posted: 02:30pm 08 Dec 2023

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Mick, OA47 and others.

It is true that the module as shown in the first image has two 4K7 resistors and a small decoupling capacitor.
The resistors are for the SDA and SCL as a pullup resistor and for the charging section with the 4K7 SCL resistor and a coupling plus button cell and battery pin DS3231.
So a current can flow to the battery, but also back via the same resistor if the module is included in a circuit because there is no diode on this module.
A cold cap can also be used as a backup battery.
If you want to use a normal 3V button cell battery, disconnect the battery pin of DS3231 from the PCB and connect it with a loose wire to the plus 3V button cell battery.
There are also DS3231 modules with RTC and an eeprom with I2C where a resistor and diode are present in series as a charging circuit. These must be interrupted if you want to use a normal 3V button cell.

Jan.

Mixtel90

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Posted: 03:34pm 08 Dec 2023

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From the data sheet:

Quote The device is UL recognized to ensure against reverse charging when used with a primary lithium battery.

(When the battery is connected to the Vbat pin, which it is on these). There is NO charging path so a cap won't work in this design.

There is no appreciable current flow from the battery when VCC is present (100nA max leakage). It draws about 3uA max. 0.84uA typ. while timekeeping with VCC off.
Edited 2023-12-09 01:36 by Mixtel90

Mick

Zilog Inside! nascom.info for Nascom & Gemini
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