jamesp@intertex.net wrote:
> The only problem I have with the scenario at the bottom of the page is
> that I don't believe that 3AH for a double A battery (cell) is
> accurate.  I would think maybe half of that would be a good estimate.
> But even given this reduction in cell capacity, the longevity is still
> good.

Usually when I've been carefully considering battery capacity it has been
rechargeables or other than AA primary cells so I guessed just to fill in
some roughly plausible numbers.  I knew that NiMH were available in the
2.0-2.5Ah range, so I figured primary cells would be a bit more.

I looked around a bit now, and you're right in that normal alkaline AA
primary cells seem to be in the 2.5-3.0 Ah range, but derate to about half
that under 500mA load.  However lithium primary AA batteries are just about
3.0Ah and stay that way under 500mA load.  I think it would be a bit extreme
to recommend lithium batteries in a portable PIC programmer but they would
give you about twice the life in the extreme case of 500mA load on the
batteries during programming.

I think my estimate was very conservative for the typical case.  One minute
and 500mA per programming operation is way above average.  A real worst case
or even typical is hard to specify because there are so many different PICs
and target circuits out there.  The fact that most of them can be programmed
in under 20 seconds with under 250mA battery drain is of no consequence to
the field service guy who only ever updates a fully loaded 30F6010 in a
circuit that draws a additional 50mA beyond the PIC.

All in all, I think a reasonable worst case with two AA alkaline batteries
is 180 programming operations, with 500 typical over a broad mix of target
systems.  Even though it's less than my quick back of the envelope
calculation, I think it is well within acceptable range for the end user.


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