[En-Nut-Discussion] Re: Mass storage, RTC daughter board for the Ethernut-2.

[Arius - Rick Collins]

At 10:59 AM 10/21/2004, you wrote:
>On Thu, 21 Oct 2004 08:00 pm, en-nut-discussion-request at egnite.de wrote:
>Hi Douglas / Evening Mailing List.
>
> > (3) How much current would a 1 Farad capacitor supply at 5v, and for how
> > long?
>
>It can hold the DS1302 RTC in working order, using only 1uW/sec according to
>the spec.
>
>Given Watt sec = (E^2 * C)/2 and E = 5VDC, C = 1F then  W.Sec = 12.5x10^6 sec.
>which divided by (60 sec x 60 mins x 24 hours ) approximates to 144 days.
>So about 100 to 130 days would be a good expectation given sods law;
>i.e. circuit - temperature changes, device leakage, humidity variations etc.

You calculated this very differently from the calculation you did for the 
Ethernut board.  This calculates the total power and you have to figure 
instead how long it takes for the voltage to drop to an unusable 
level.  That is a log calculation while this equation is a linear one.



Rick Collins

rick.collins at arius.com

Arius - A Signal Processing Solutions Company
Specializing in DSP and FPGA design       http://www.arius.com
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