[Coco] Survey of Coco realtime clock users

[Gene Heskett]

On Friday 30 November 2007, Arthur Flexser wrote:
>On Fri, 30 Nov 2007, Gene Heskett wrote:
>> On Friday 30 November 2007, Robert Gault wrote:
>> >Arthur Flexser wrote:
>> >> Out of curiosity, how'd you go about replacing the battery?  It looked
>> >> like the battery was potted in epoxy or something and not at all easy
>> >> to replace.  On the other hand, it was rated to last 10 years.  How
>> >> long did yours hold out for?  I never heard of a case of one finally
>> >> giving out.
>> >>
>> >> Art
>> >
>> >Not sure exactly when I bought it but a expect at least 10 years ago.
>> >
>> >Right the battery is potted and I doubt it would be safe to try to
>> >remove the epoxy. I measured the voltage on the exposed DS1216 leads and
>> >found several with about 1vDC. The battery is a lithium and should be
>> >about 3vDC.
>> >
>> >Marty Goodman posted some suggestions on replacing the battery but I'm
>> >not sure he actually did it. While one should remove the battery from
>> >the circuit, I decided placing a new one in parallel would be sufficient.
>> >
>> >Radio Shack has all lithium batteries at the same price so I bought the
>> >largest one, about 5 to 6 times larger than the one in the Smartwatch.
>> >Should last 50-60 years :)  Solder connected it to DS1216 pin4 +v and
>> >pin8 ground. Pre-tested this with two dry cells in series.
>> >
>> >Works great!
>>
>> But that is probably a recharger for the internal lithium cell, and a
>> larger version of one of those just exploded in Korea, fatally breaking
>> the ribs and spine of the man who had it in his shirt pocket.  Those
>> button cells are NOT designed to be recharged, ever.

I should have said potentially, rather than probably.

>So that epoxy DOES have a function, after all!  It's a safety feature to
> contain the explosion!  (Or perhaps an anti-safety feature to create more
> shrapnel when it goes off?)  ;-)
>
>Art
>
I suspect the latter in terms of practical effect, Art.  Granted these aren't 
nearly so big as a cellphone battery either, but those are designed to be 
recharged _if_ bought from a reputable maker.

FYI, IBM considers its reputation in batteries pretty seriously, given all the 
publicity about laptop fires and such, that they bought a dozen supposedly 
IBM branded batteries from a dealer in NY recently, found they were all bogus 
and quite dangerous, and has sued them for 1 million per battery in trademark 
damages, and triple damages for each battery so sold.  That would be 48 
million just for the ones they bought but they are asking for that, and all 
profits from every sale of record that discovery can find.  The story is on 
slashdot, about 2 days ago I think.

The problem isn't so much during the recharging as it is if the battery 
develops an internal short, encouraged by overcharging even a very small 
amount.  They are very low resistance devices and even that button cell can 
deliver several amps under short circuit conditions.  Nicads are pikers when 
it coomes to heating up fast under that sort of load, whether its external, 
or internal to the cell.  There are patents galore in the semiconductor 
business over the last few years just for controller chips that can charge 
one rapidly without overcharging under any conditions.  I would hope that 
there is a diode to prevent that in the smartwatch.
 
-- 
Cheers, Gene
"There are four boxes to be used in defense of liberty:
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-Ed Howdershelt (Author)
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