Hi all,

(I'm copying this only to the thumb-gps list and to TZ, the most recent commenter, as I don't know all the parties in the header of TZ's message.  You guys can forward it to whomever else may need to see it.)

Speaking strictly as a potential user of the thumb-gps device and amateur interested party, I would rather see a supercap, if feasible.  I hate the idea of devices having batteries that I have to worry about failing in 5-10 years.  I've had the cmos batteries fail in a few computers, sometimes preventing them from booting.  It can get really ugly trying to revive them  A good high efficiency dc-dc converter chip should allow you to drain all but the last bit of energy from the cap while maintaining whatever working voltage you need.  I cannot speak to size issues, as I have never designed a circuit board with one.  The GlobalSat BU-353 that I have has a supercap, I believe.  Exact backup time is not stated, but I believe it's a few days.

Sincerely,

Ron

On 5/9/2012 1:12 PM, tz wrote:
For a given size (and circuit board footprint) a supercap will have much less capacity and it has an exponential voltage decay curve, so it might have plenty of charge but not at a voltage that will hold the data.  This usually means hours, not days of backup.

A good rechargeable lithium will last several years, maybe longer as there will be no charge/discharge, maintains voltage until it is nearly exhausted, and can hold the data for days or weeks.

On Wed, May 9, 2012 at 12:55 PM, Dave Taht <dave.taht@gmail.com> wrote:
On Wed, May 9, 2012 at 9:47 AM, Eric S. Raymond <esr@thyrsus.com> wrote:
> Dave Taht <dave.taht@gmail.com>:
>> What would be the change in cost and delay in manufacturing to switch to
>> using a supercap, rather than battery?
>
> Why would a supercap be better?

Effective lifetime of... forever. no need for replacement. insanely
fast recharge. smaller (probably). What's not to like?

I am not in a huge hurry to get into manufacturing, and I merely
wanted to cost out what what it would do to the bom, any changes to
the PCB, and get an estimate for the time it would take to do. I think
it will bump the unit cost up slightly,
but what price, forever?

> --
>                <a href="http://www.catb.org/~esr/">Eric S. Raymond</a>



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