>-----Original Message-----
>From: Jesse Lackey [mailto:jesse@CELESTIALAUDIO.COM]
>Sent: 17 February 2004 01:52
>To: PICLIST@MITVMA.MIT.EDU
>Subject: Re: ] Using two 9V in parallel for greater capacity... ok?
>
>
>Ah, but power-capacity wise, one gets:
>550mAh * 7.25V ("nominal" mid-discharge) = ~4W
>2500mAh * 1.25V ("nominal" mid-discharge) = ~3.2W
>
Not quite true as I did suggest using 3 AA cells, which gives:
2500mAh * 3.75 = ~9.4W/hours.


>I need 4.7-5V to run things.  (A part that is not a PIC requires 5V)
>
>The the DC/DC cost & efficiency may be different for 6->9.25V -> 5V vs.
>1->3V -> 5V.  And with diodes (see posts in other thread) I can use one
>9V or two 9V, user's choice.
>
>But I still may go with 2x (or 3x AAA), a decision based on
>cost, size, and my client's whim.  :)
>
>J

For a 5 volt output you can get extremely efficient fixed voltage switchers
from e.g. Maxim that require very few external components.

The 9 volt soltuion obviously appeals from the simplicity point of view, but
if this project is for long term operation, there will be considerable cost
savings if you can use AA cells.  Even better, (if it would fit) a single
alkaline C cell is rated for around 8Ah (and D cells are around 18Ah!).




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