Backup "batteries" installed

Gennady Kupava gb at
Mon Nov 8 17:51:42 CET 2010

Hi, Benjamin and list

Yesterday i followed suggestion about capacitors and installed them.
Huge thanks for suggestion - one big annoyance fixed for me too! Now my
time is kept while i am replacing battery without any troubles, for far
i tested only few minutes of life without battery.

I did some measurements, that according to our pcf setup (qtmoko v28,
uboot), charge current is 200uA. According to my measurements with
multimeter capacitor were fully charged after 6 minutes. Also it may be
useful to note that self-discharge of capacitor is much higher than
li-ion battery and actually it is chaged only than our PMU is in Active
state (FR turned on or suspended). So it may discharge if it were laying
for a while _with_ main battery installed and then main battery removed
without turning on device.

I think also my story of finding capacitors may be helpful. Given that
digikey delivery for my country costs $120, i tryed some nearby shops
and internet in attempt to find this part without any luck. But it
turned out (from forums) that such capacitors are common in other phones
(like N70 and btw common reason to problems). So, i finally just walk to
nearby mobile repair service on nearby cheapest marketplace and bought 2
used capacitors from broken phones for $3. I left with feeling i payed
too much :)

Soldering were not really easy especially that after reading docs i
understood that part should be heated with extreme care, but i followed
suggestions, put it upside-down and cut some outputs.

Thanks and regards,

В Чтв, 04/11/2010 в 21:23 -0400, Benjamin Deering пишет:
> I have had the capacitors installed for a few days now and they are 
> still working well.  I left the FR with a dead battery overnight and 
> when I plugged it in in the following day, it had the correct time.
> The digikey part number is: 728-1037-1-ND and the manufacturer's number 
> (seiko) is: XH414H-II06E.  I would recommend looking around on the site 
> to see if you can find one with the correct bracket.
> Ben
> On 10/30/2010 03:03 AM, Dr. H. Nikolaus Schaller wrote:
> > Am 29.10.2010 um 19:05 schrieb Benjamin Deering:
> >
> >    
> >> Hello,
> >>
> >> I finished installing capacitors as replacements for the dead backup
> >> batteries in my Freerunners today at lunch.  They seem to be working,
> >> though I've only tried removing the main battery for under a minute so
> >> far.  Someone on the GTA-02-core list said a 220uf capacitor would power
> >> the RTC for 2 minutes.  If that is correct, the .07f caps I used should
> >> work for about 10 hours.
> >>      
> > Please report some test results.
> >
> >    
> >> The parts I got from digikey weren't an exact fit, but I was able to
> >> make them work.
> >>      
> > Looks interesting. Do you have the exact order number at DigiKey?
> >
> >    
> >> Be sure to wear safety glasses if you try this, I had one of the old
> >> batteries explode when I was removing it.
> >>      
> > Oops! So it was not really dead an had enough energy inside. Maybe,
> > just the voltage was too low to run the RTC?
> >
> >    
> >> Pictures:
> >>      
> > Good work!
> >
> > Nikolaus
> >
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> >
> >
> >    
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