Cheap DS3231 module warning - Page 1
Forum section: electronics / projects

author: james_s
author_rank: Super Contributor
timestamp: August 11, 2018, 10:31:45 pm
content: Maybe this is widely known but I was not aware of it until I stumbled across mention somewhere online. Those cheap DS3221 modules available from China surprisingly seem to work very well but there is a catch. Someone noticed theirs had a resistor between Vcc and the battery which causes the battery to be trickle charged when the module is powered. I checked on a couple of mine and sure enough, the CR2032 primary cell had been charged up to over 4.2V when it's supposed to be a 3.6V battery. One of them had been running for a while and was leaking all over, I had to replace the socket.If you're using one of these modules, take a close look at the board, and remove the resistor located just above the battery holder with the pins facing down.

author: tsman
author_rank: Frequent Contributor
timestamp: August 11, 2018, 11:18:52 pm
content: Yeah. The ones I got came with a LR2032 cell included hence the charging resistor. Just the usual issues with people selling something they don't have a clue about and zero documentation.

author: james_s
author_rank: Super Contributor
timestamp: August 11, 2018, 11:25:44 pm
content: I have about half a dozen of them and none came with a cell, it seems they could have at least printed a note on the PCB or provided a jumper. Given it's the backup for a low power RTC chip I don't see a lot of value in a rechargeable cell, a CR2032 ought to last years in most cases.I can't really complain though, for only a buck or two it offers exceptional accuracy. I don't know if it's a genuine Maxim chip but it performs like one. Desoldering a resistor is a small price to pay for the low price of the module but I do wish I'd known a year ago that I needed to.Another odd thing about these boards is they all seem to come with a separately wired EEPROM on the same board, a feature I've never used.

author: oPossum
author_rank: Super Contributor
timestamp: August 11, 2018, 11:34:27 pm
content: Some DS1307 modules have the same problem. The fix for them is to remove D1 & R4, and replace R6 with a jumper.

author: iMo
author_rank: Super Contributor
timestamp: August 12, 2018, 02:22:22 pm
content: I've looked at my ebay's DS3231 modules (with the eeprom on it) and the resistor there is 200ohm (in series with a diode). The Vcc with that modules here is 3.3V so hard to say what the actual "charging current" would be. A simulation with an 1n4148 shows 13nA charging current. Afaik a few uA charging could be ok with those cr2032.With 5V Vcc (5.5V is the maximal Vcc voltage of the DS3231 according to the datasheet, typical Vcc is 3.3V) the current would be about 6.7mA - that is not good with CR2032, sure.

author: james_s
author_rank: Super Contributor
timestamp: August 12, 2018, 04:33:45 pm
content: Even at 3.3V, why would you want *any* charging current with a battery that isn't rechargeable? That's just asking for trouble.

author: james_s
author_rank: Super Contributor
timestamp: August 12, 2018, 04:46:18 pm
content: Oh I've charged various primary cells and I know it works to some degree, however I've never had good enough results to bother doing it. Alkaline batteries have enough problems leaking without pushing things by trying to recharge them. Given a CR2032 costs a few pennies and typically lasts a year or more I see no point in trying to recharge it.

author: james_s
author_rank: Super Contributor
timestamp: August 12, 2018, 04:59:35 pm
content: Well despite this little snag, now that I know this I wouldn't hesitate to buy more of these modules, I mean they're dirt cheap and they work very well once that resistor is removed. If I were designing them though I'd leave the resistor out by default since CR2032 primary cells are far more common than rechargeable types. Someone could easily install a resistor there if they need it. At any rate once the issue is known these are a great deal.

author: james_s
author_rank: Super Contributor
timestamp: August 12, 2018, 05:08:58 pm
content: I wonder if that explains why these RTC boards all seem to have an EEPROM on them? Or maybe they were designed for some specific project and then everyone started building them for general sale?

author: tsman
author_rank: Frequent Contributor
timestamp: August 12, 2018, 05:19:05 pm
content: Quote from: james_s on August 12, 2018, 05:08:58 pmIt doesn't look like it was designed for something specific and then repurposed. These modules look like the generic modules sold for Arduino and Raspberry Pi experimentation.My guess is that somebody designed in the EEPROM as a value-add since more features = better and then everybody else added it to their designs to keep up. oPossum's module is different + smaller but still has that additional EEPROM.

author: iMo
author_rank: Super Contributor
timestamp: August 12, 2018, 05:40:00 pm
content: People buying modules do not like pcbs with empty pads and not populated parts on it - therefore the clever vendors populate them rather all..Back to the CR2032 - the power consumption of the DS3231 is about 1.8uA in average (with the default temperature measurement profile). Then there is the self discharge, maybe 1uA as well. I saw some discussion in past where people advised to have a couple of uA "charging current" (via an large resistor) to compensate a little bit that drain.

author: james_s
author_rank: Super Contributor
timestamp: August 12, 2018, 05:47:42 pm
content: Quote from: tsman on August 12, 2018, 05:19:05 pmThe smaller board is the DS1307 and the larger board is the DS3231. I'm actually not sure why people still use the DS1307 since the accuracy and drift is much worse. From Maxim the DS3231 is much more expensive but these modules from China are almost the same price.The source of these Chinese Dallas/Maxim parts is a bit of a mystery to me as they are far cheaper than buying from a reputable source however they seem to function every bit as well as the genuine part. The MAX7219 is a similar situation, I can buy a whole module with an 8 digit LED display or a 8x8 LED matrix on a PCB for much less than the cost of a bare IC from Maxim. Unlike a lot of cheap clone parts out there, I've not been able to find any functional difference. The Dallas NVRAM chips from China on the other hand, those are another story.

author: kololimilimo
author_rank: Newbie
timestamp: February 01, 2025, 05:52:30 pm
content: I solved this problem by breaking positive link from CR2032 to DS3231, then added 1N4148 between the two terminals such that when you remove the main power, CR2032 will keep the clock running. CR2032 should not be charged in any way. I lost Three cells from three Clocks I had made, one of the bulging cells is shown plus the added 1N448 to prevent charging, similar to those used in computers. Timekeeping is ok after the changes.

author: Georgy.Moshkin
author_rank: Frequent Contributor
timestamp: February 02, 2025, 01:46:31 am
content: As topic was revived, I want to share my experience with DS3231SN chips. During a global chip shortage, I couldn't find DS3231 chips at sane price. The ones I've bought turned out to be improperly desoldered (overheat?), cleaned and re-packaged in reels. Plastic package looked pretty good, but there were uneven solder remains on some leads. Almost all chips failed after reflow soldering. Surprisingly, the ones I've manually desoldered from the cheap modules using hot plate always worked. I still wonder how refurbished chips made look so well - no single scratch on the surface. Maybe some kind of plastic etching, or some coating.