It doesn't work that way. Microampere DC-DC converters? That isn't a swap, it is a redesign, if microamp converters are possible - the base losses are high so you won't hit a high efficiency. You get high efficiencies when dealing with lots of amps. For it to last overnight you would need a very large (physically) cap.<br>
<br>There would be no booting problem. It would merely lose the real-time clock and/or location backup so would take a bit longer starting.<br><br>The battery (or cap) only kicks in when the power goes away and is only needed to make the startup faster, e.g. cycling power on the computer or router. USB should be constantly providing 5V 99.9% of the time.<br>
<br>I could argue that if surviving only a short power disconnect is ok, then a supercap might be better, but then it is probably a large engineering change since the caps and batteries usually have vastly different footprints.<br>
<br>Good batteries can last decades - even Supercaps have a finite lifetime. It is a matter of cost, both in redesign, size, and reliability. But do you want to add $5-$10 to the cost of the unit to make a cheap ($30-$50) GPS last over a decade? Buy a second, seal it hermetically, and put it in your freezer.<br>
<br>If you want to add a few thousand in NRE costs, there are a lot of other things I would redesign. Use a USB 2.0 chip to get 125uS jitter. Allow for a detachable or external antenna (which can be run to the window). Find a more optimal chipset. Maybe a coin-cell port so the battery can be replaceable. But the point was to be as cheap as possible so in this case it is adding one wire.<br>
<br>You can always break yours open and if you can find a supercap with the specs (Sparkfun has a 3.3v available, but don't put more than 3.3v on it), you can swap the part.<br><br><div class="gmail_quote">On Wed, May 9, 2012 at 1:50 PM, Ron Frazier (NTP) <span dir="ltr"><<a href="mailto:timekeepingntplist@techstarship.com" target="_blank">timekeepingntplist@techstarship.com</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><u></u>
<div text="#000000" bgcolor="#ffffff">
Hi all,<br>
<br>
(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.)<br>
<br>
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.<br>
<br>
Sincerely,<br>
<br>
Ron<div><div class="h5"><br>
<br>
On 5/9/2012 1:12 PM, tz wrote:
<blockquote type="cite">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.<br>
<br>
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.<br>
<br>
<div class="gmail_quote">On Wed, May 9, 2012 at 12:55 PM, Dave Taht <span dir="ltr"><<a href="mailto:dave.taht@gmail.com" target="_blank">dave.taht@gmail.com</a>></span>
wrote:<br>
<blockquote class="gmail_quote" style="border-left:1px solid rgb(204,204,204);margin:0pt 0pt 0pt 0.8ex;padding-left:1ex">
<div>On Wed, May 9, 2012 at 9:47 AM, Eric S. Raymond <<a href="mailto:esr@thyrsus.com" target="_blank">esr@thyrsus.com</a>>
wrote:<br>
> Dave Taht <<a href="mailto:dave.taht@gmail.com" target="_blank">dave.taht@gmail.com</a>>:<br>
>> What would be the change in cost and delay in manufacturing to
switch to<br>
>> using a supercap, rather than battery?<br>
><br>
> Why would a supercap be better?<br>
<br>
</div>
Effective lifetime of... forever. no need for replacement. insanely<br>
fast recharge. smaller (probably). What's not to like?<br>
<br>
I am not in a huge hurry to get into manufacturing, and I merely<br>
wanted to cost out what what it would do to the bom, any changes to<br>
the PCB, and get an estimate for the time it would take to do. I think<br>
it will bump the unit cost up slightly,<br>
but what price, forever?<br>
<div><br>
> --<br>
> <a href="<a href="http://www.catb.org/%7Eesr/" target="_blank">http://www.catb.org/~esr/</a>">Eric
S. Raymond</a><br>
<br>
<br>
<br>
</div>
<div>--<br>
Dave Täht<br>
SKYPE: davetaht<br>
US Tel: <a href="tel:1-239-829-5608" value="+12398295608" target="_blank">1-239-829-5608</a><br>
<a href="http://www.bufferbloat.net" target="_blank">http://www.bufferbloat.net</a><br>
</div>
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<br>
</div></div><pre cols="72">--
(To whom it may concern. My email address has changed. Replying to former
messages prior to 03/31/12 with my personal address will go to the wrong
address. Please send all personal correspondence to the new address.)
(PS - If you email me and don't get a quick response, don't be concerned.
I get about 300 emails per day from alternate energy mailing lists and
such. I don't always see new messages very quickly. If you need a
reply and have not heard from me in 1 - 2 weeks, send your message again.)
Ron Frazier
timekeepingdude AT <a href="http://techstarship.com" target="_blank">techstarship.com</a>
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