Hi.
I've read quite a bit about the DS3231 rtc clock module being designed incorrectly for charging the button battery that's used on it as a power source backup. With the CR2032 button it used to be shipped with, these would blow up after time as these are not rechargeable and it has an included charging circuit.

others suggested replacing the battery with a rechargeable LIR2032. However it was said the circuit was also incorrect for trickle charging this too.

Can a 5.5V super capacitor be used instead? If so, what would be an acceptible farad capacity.

Also, if the cr3202's last up to a 8 years (at power down it consumes 3uA from the 210mah battery), then how long could the fully charged super capacitor run it? Does it lose voltage even when not used? Sorry for so many questions.

 

Going of what I've read the DS3231 ships with a "cheap" CR2032 battery and replacement with a decent quality one is recommended on receipt. This should give 5-7 years service I would imagine.

The CR2032 is not a rechargeable battery so why design the DS3231 to recharge it and following on from that a super capacitor wouldn't get charged anyway so cannot be used.

 

As far as I can remember, Super Caps do have fairly high self discharge, certainly with respect to batteries. I would imagine the charge hold time is measured in days at the most. If you were going to power the circuitry regularly, a super cap may be an option, with a series diode and charge current limiting resistor from the supply, but remember they are only 2.7V if you use just one. So a dual 5.5V one as you say will be needed. But a battery will last a few years most probably so what is the life of the project?

 

Thanks Paulkteg. I have bought some decent spare batteries and replaced it in the unit already. The circuit however does supply some sort of charge as its operated via a 5v supply. Is it enough to charge the capacitor - not sure.

Dendad, if the held charge in a super capacitor is only days, then it's pointless. This is for a scoreboard I've designed and built which I'm installing for our club tomorrow. I was writing up "maintenance" notes for it. In doing so I realised that if the battery goes flat, it's not just a matter of replacing it. The current date and time will be lost and someone (if it's not me), would have to connect a laptop loaded with Arduino software and re-upload the program. In my notes I said to keep the 5v on, remove the battery and replace it. This will ensure it doesn't lose the time/date during replacement. I suggested to do this every 5 years to be safe. But if someone forgets, it will be a problem.

 

How about modifying the code to allow setting the time from push buttons on the case? I'm sure there is some sample code out there for doing just that.
Then it does not really matter.

 

Even with such high accuracy, the clock will be off after several years.

 

How about modifying the code to allow setting the time from push buttons on the case? I'm sure there is some sample code out there for doing just that.
Then it does not really matter.

That's an excellent idea. I could allow for date and time entry by a button combination, then on completion, the same combination.