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We have the 2032 mount on Frankenso which as far as I understand is set for a non-rechargeable CR2032 battery.



At the moment this is mostly about using real time for data log filename. Couple of questions:

What would we need to change in the schematics to use LIR2032 - the re-chargable version? Pros and cons?

And a tactical question: how to I charge this drained LIR2032 I have here? Can I simply power it with 3.3v for some time? For how long? With or without some resistor?

PS: http://hackaday.com/2014/01/17/1-coin-cell-charger/

PS: "charging circuit is included in the module" so I will charge using the RTC board I have: http://www.hobbyist.co.nz/sites/default/files/docs/RTC/Tiny_RTC_schematic.pdf

russian wrote:We have the 2032 mount on Frankenso which as far as I understand is set for a non-rechargeable CR2032 battery.



At the moment this is mostly about using real time for data log filename. Couple of questions:

What would we need to change in the schematics to use LIR2032 - the re-chargable version? Pros and cons?

And a tactical question: how to I charge this drained LIR2032 I have here? Can I simply power it with 3.3v for some time? For how long? With or without some resistor?

PS: http://hackaday.com/2014/01/17/1-coin-cell-charger/

I would not bother with rechargeable coin cells, they are massively expensive.
I did a quick search in the datasheet and it seems the worst case average current on the STM32F407 VBAT pin when using the backup SRAM and the RTC is 2µA.
If I am not mistaken this means a >10 years battery life for a CR2032 coin cell.
CR2032 coin cells are cheap as chips, I can get 10 of them for 2 euros at the budget store. The LIR2032 seems to cost around 4 euros a piece.
Also complicates the circuit and cost of the ECU.

For most installs the ECU can be powered by the car battery anyway, so the battery life for the coin cell goes further up.
If you want more reliability and rechargeability you can also have a look at gold caps / super capacitors, that would also be an option.

In a perfect world, the ECU <i>will</i> be powered from the vehicle battery, with wake up signals from the key switch, which would make having a battery on board only useful if one is changing the vehicle's battery, or has disconnected the ECU for some purpose.

abecedarian wrote:In a perfect world...

that's SO off-topic perfect world... right...

russian wrote:

abecedarian wrote:In a perfect world...

that's SO off-topic perfect world... right...

Yeah, OT, but reasonable?

I seem to recall replacing the auto battery from time to time. There are folks that will disconnect a battery for off season storage and such. I think it's reasonably to expect the battery will be disconnected for prolonged periods of time.

My gut intuition is to say CR2032 is what everyone else does, so we should do the same. However I'm also reasonably ignorant about the details of how to use a LIR2032. I know of some PLC applications that come with a capacitor that does about the same thing, but you have to charge those at least once every couple weeks.