Alt-BEAM Archive
Message #02072
To: beam@corp.sgi.com
From: Bob Shannon bshannon@tiac.net
Date: Wed, 07 Apr 1999 00:30:32 -0700
Subject: [alt-beam] Re: Microcore memory for 100Farad caps.
Paul B. Webster VK2BZC wrote:
>
> Steven Bolt wrote:
>
> > Make the calculation. 1 ampere * second = 1 farad * volt
>
> > Let's say 3V: 100 * 3 = 300 ampere * second
> > Translate that to wattsecond by again multiplying by volt: 900ws
> > Convert that to milliwatt-hour: 900 * 1000 / 3600 = 250 mAh
> > Which equates to two AAA nicads.
>
> Eh? Let me try that. 100 Farad is it? It=CV
>
> Let's say that we can afford a drop from 3V to 1V, so C*V = 100 x 2
> which is 200 Ampere-seconds. Divide by 3600 to get Ampere-hours and
> scale up by 1000 to get milliampere-hours, gives 83 mAh.
Sounds right to me.
> Probably comparable to the AAAA (or whatever) Ni-Cds out of a 9V
> "213"-style battery. Two of these would supply 2.5V fully charged and
> you would run them down to 2.2V or 2.0V.
Probably very similar to a pair of VL2320 lithium pentoxide cells, but
at
many times the size and weight of a small battery.
A VL2320 3 volt rechargable lithium coin cell is a 3 volt, 30 mah
battery thats 23 mm in diameter and maybe 4 mm thick in the leaded
package. They are very light, and far surpass a gold series capacitor
in energy density.
> The big question is indeed internal resistance. While Ni-Cds are only
> about 50% efficient at energy storage, these capacitors might be little
> better or a lot worse at currents above a couple of milliamps.
> --
> Cheers,
> Paul B.
If you want to drive a SE, expecially a cmos logic SE, the small VL2320
or similar cells (with a series resistor) are a good choice. If you
want current for a walker, its hard to go wrong with small packs of
Varta Ni-MHD cells and a solar constant current charger. You can build
a small charger and battery pack is less space than a 1.5 farad gold
series capacitor.
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