On Mon, 28 Jul 2003 06:35:22 +0900, James Annan <
[email protected]> may have said:
>I've seen a figure for typical internal resistance of an AA alkaline as .4 Ohms, so you can do your
>own sums (but although this figure seems to have been competently estimated, it doesn't seem to
>match the results above for the bike light).
I see this all the time in the battery area. The specs say one thing, the results say something
entirely different. It has never made any sense to me, and I've learned that the only way to find
out if a given battery/device combination is viable is to try it and see. There have been some
*expensive* disappointments in that area over the years. Most recently, it turned out that a lithium
ion battery pack rated for 20F was actually much too temperature sensitive to power my digital
camera in sub-freezing outdoor work; I had to build an extension cord and use a cobbled-together
alkaline pack in an inner pocket of my jacket. That worked, but it was still aggravating.
>I am surprised by your results for the flashgun as it is contradicted by almost everything I have
>heard about using different cell types in digital cameras (another high current application), plus
>my own experience of the same. Of course alkalines do have a greater total capacity and basic
>voltage supplied, so there is no question that they will perform better in some applications.
Digitals are another entirely different bunch; I've noticed that many of them tend to be quite
finicky about their power. I've been waiting for the SLR bodies to drop within my range before
getting another one; I've been underwhelmed by the rangefinder models I've used so far since not a
dratted one of them provides a manual focus method.
I think the flashgun works as it does in part because the demand decay matches the supply decay to a
certain extent; the alkalines deliver a surge before the voltage starts to fall, and the demand from
the flash is highest for the 1 to 1.5 seconds after the unit fires; it tapers to a very low load
after 3 to 4 seconds with fresh alkalines or with the 8-cell NiMH pack. The NiMH batteries I've been
using have a remarkably *constant* supply capability, with almost immediate voltage fall-off under
surge load. Interestingly, the manufacturer used to supply a 6-cell NiMH holder for this unit which
had a different power contact arrangement so that it was better matched to the circuitry, but my
experience with it was less than stunning to say the least. That's why I built the 8-cell external
pack. (I can't *quite* justify a Quantum for this beast, but I may eventually end up buying one.)
Anyway, back on topic (sort of), I got a look at the "beam" pattern from the Cateye 5-LED unit
today, and I think I'll keep shopping. It's better than I had feared, not as good as I had hoped,
and not *quite* enough for what I need. The mass-produced tech in that area is getting close to
making a really useful product, though. In a few more years, I think we'll see a different picture.
--
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