I'm curious about this as well: what voltage range will the Overo's RTC accept safely?

We have an application that's going to use 4 Overo COMs on a custom board that will be powered off for possibly a few months before it is deployed on the International Space Station.  I'd like to set the clocks on the ground before handing them over to be integrated into the payload and vibration tested, etc.

So I'm wondering if a 500mah LiPo cell (~3.7volt) would do the job.  It should have enough power to run 4 Over RTCs for a long time, but I'm not sure if handing them 3.7 volts will work or not.

Ideas?

Jeremy


On Mon, Aug 5, 2013 at 10:03 PM, Jonathan Kunkee <jonathan.kunkee@gmail.com> wrote:
I haven't dealt with the RTCs on Gumstixen, so I'm curious:

What voltage does the RTC expect?
What's the forward drop of your charger-blocking diode? (It sounds like a low-enough current application that a GaAs or germanium diode would work fine, with their lower forward voltages.)
Have you measured the peak current consumption of the not-otherwise-powered RTC? What is the I-V curve of the battery like? (L-Ions are usually able to keep a steady voltage over a wide range of peak loads, but I'm used to bigger ones.)

If the questions are good food for thought, I'm glad; if the information gets shared here, all the better.

Good luck,
Jon Kunkee


On Mon, Aug 5, 2013 at 10:33 PM, Michael Wynne <michael.wynne1@gmail.com> wrote:

I have seen this with the AirSTORM. I tried using some rechargeable 123A lithium cells thinking they would last for long periods of being powered off, but they didn't. Then I tried a regular lithium 2032 button cell and those were dead in a matter of several days. I thought they might heat up and explode because there does seem to be voltage at the RTC Vbackup, though the current must be extremely small because they didn't even get warm. That might explain why the relatively large lithium cells didn't really charge.

Since then I've moved to the recommended Lithium Vanadium Pentoxide rechargeable battery (http://wiki.gumstix.org/index.php?title=Coin_cell). It's very small, but seems to last as long as the others I've tried. Though I haven't conducted extensive testing yet. I have 10 units with this battery and I think I've only seen one go dead and loose the time after being powered off for about 3-4 days. The bottom line is these batteries should be lasting longer. I can leave a desktop PC unplugged for a month and a small battery will keep the RTC going, so what's the deal with these COM's?

At this point I have other projects to worry about, but I intend to investigate further when I can. If anyone can offer any other suggestions I would also be grateful.

-michael

On Aug 5, 2013 5:31 PM, "Nye, Philip" <Philip.Nye@acuitybrands.com> wrote:
I am getting reports of the system clock on the Gumstix (overo earth storm) losing big jumps of time - hours or days. This is most likely happening during power cycles though I have not been able to catch it happening. The overo is on our own board which has a non-rechargeable 3V lithium coin cell backing up the RTC.

Does anyone else have experience of anything like this? or pointers to what might be happening?

Is there anything in the backup battery circuitry which could cause the backup battery to drain at an abnormal rate? I know the circuit will trickle-charge a rechargeable cell and ours has a series diode to prevent unwanted back current.

Philip


------------------------------------------------------------------------------
Get your SQL database under version control now!
Version control is standard for application code, but databases havent
caught up. So what steps can you take to put your SQL databases under
version control? Why should you start doing it? Read more to find out.
http://pubads.g.doubleclick.net/gampad/clk?id=48897031&iu=/4140/ostg.clktrk
_______________________________________________
gumstix-users mailing list
gumstix-users@lists.sourceforge.net
https://lists.sourceforge.net/lists/listinfo/gumstix-users

------------------------------------------------------------------------------
Get your SQL database under version control now!
Version control is standard for application code, but databases havent
caught up. So what steps can you take to put your SQL databases under
version control? Why should you start doing it? Read more to find out.
http://pubads.g.doubleclick.net/gampad/clk?id=48897031&iu=/4140/ostg.clktrk
_______________________________________________
gumstix-users mailing list
gumstix-users@lists.sourceforge.net
https://lists.sourceforge.net/lists/listinfo/gumstix-users



------------------------------------------------------------------------------
Get your SQL database under version control now!
Version control is standard for application code, but databases havent
caught up. So what steps can you take to put your SQL databases under
version control? Why should you start doing it? Read more to find out.
http://pubads.g.doubleclick.net/gampad/clk?id=48897031&iu=/4140/ostg.clktrk
_______________________________________________
gumstix-users mailing list
gumstix-users@lists.sourceforge.net
https://lists.sourceforge.net/lists/listinfo/gumstix-users