[geeks] Batteries

[Doug McLaren]

On Thu, Dec 14, 2006 at 02:52:36PM -0500, Sridhar Ayengar wrote:

| I'm looking for AAA-sized rechargeable batteries.  Good capacity would 
| be nice, but the main thing I'm looking for is that it should be able to 
| supply a fairly high peaky current draw.

Well, NiCds tend to have slightly lower resistances than NiMH cells
(which leads to increased current capacity), but a lot less total
capacity.  And AA and especially AAA cells are not known for their
ability to handle high discharge rates.

Also note that when you have cells of a fixed size (AAA) and a fixed
chemistry (NiMH) that in order to get more total capacity you have to
give up something else, as there's only so much electrolyte that you
can squeeze in there.  What this tends to mean in practice is that the
really high capacity cells tend to have high internal resistances

How high of a current draw are you talking about?  Anything more than
4 amps or so and you probably should be looking at something other
than AAA cells if at all possible.

As for where to get the get AAA cells for high discharge rates, look
into the R/C battery sellers.  Most people have gone LiPo, but it
wasn't that long ago that AAA packs were quite popular for park
fliers.

Do you need a pack of AAA cells or individual cells?

Places to check out include :

http://www.batteriesamerica.com/newpage8.htm
http://www.batteriesamerica.com/newpage3.htm
http://radicalrc.secure-mall.com/shop/?shop=1&cat=69&cart=501222
   (Radical RC's individual NiMH cells)

The RadicalRC site gives internal resistances and suggested power
levels for their packs, which you won't find at most sites not
catering to R/C use.  These Sanyo NiMH AAA cells handle high discharge
rates a lot better than the (far cheaper) cells you'll find at
Wal-Mart.

-- 
Doug McLaren, dougmc at frenzied.us
Q: What do Winnie the Pooh and John the Baptist have in common?
A: The same middle name.