Re: [Gumstix-users] A few projects and ideas on top of the Gumsti x platform

[Michael M. B. <mmb...@gm...>]

Holly, I wonder if even with LiIon one might get slightly better performanc=
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with a supercap IF one is doing really "peaky" stuff. Maybe not WiFi, or=20
ypur ebooks, but cellphone digital or the like. I'm probably going to see i=
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there's any supercap payoff with my WiFi app, even though it's likely to be=
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a wash -- it's a prototype and I'm just messing around. I'm going to be=20
using LiFeS primary cells during part of my testing.

It's always a pleasure to read your posts.

On 9/7/05, Holly Gates <hg...@ei...> wrote:
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> > Holly Gates writes:
> > > The supercap extended the AAA lifetime from
> > > something like 20 minutes to a few hours.
> >
> > This is a very interesting observation. Have you checked whether
> > the pulsed current kills the batteries faster due to some weird
> > electrochemical effect, or whether the current peaks simply cause
> > the voltage to reach below the critical level earlier ?
> >
> Both. If you draw above a certain current from an alkaline battery, it
> will actually reduce the amount of power you can get out of the battery.
> I.e. if at 100mA you could last for 4 hours, at 400ma you will last for
> less than 1 hour. The other effect, as you guessed, was that on a
> current spike the battery voltage would sag significantly which would
> eventually be enough to hang the gumstix. The two things combined to
> give an extremely short battery life; what one would expect to be
> something like 5 or 6 hours based on steady state draw and battery rated
> capacity ended up being about 20 minutes.
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> Adding the supercap helped by smoothing the voltage dips which caused
> the gumstix to hang earlier than it otherwise might. It also helped the
> ultimate battery capacity by knocking down the current spikes.
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> > > http://www.positron.org/projects/h2/cases.shtml
> >
> > Wow, how many gumstixes are there on your desk ? Eight ? :-)
> >
> Probably something like that. When I took these pictures I was building
> 10 of these ebooks for a customer, which practically killed me since
> every one is meticulously handbuilt over ~20 hours!
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> So far I think we must have used 50-70 gumstix. Hopefully climbing in to
> the 100s before long...
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> -Holly
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> > -- Pascal
> >
> >
> >
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> September 19-22, 2005 * San Francisco, CA * Development Lifecycle=20
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A
> Security * Process Improvement & Measurement * http://www.sqe.com/bsce5sf
> _______________________________________________
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Michael M. Butler : m m b u t l e r ( a t ) g m a i l . c o m
Churchill once said, "When you're going through hell, KEEP GOING".