On Wed, 1 Jun 2011 09:06:40 -0700, "William Sommerwerck"
wrote:
Several years ago I ran tests using name-brand AA alkalines and 2500mAh NiMH
cells to power a STAX headphone amplifier. (This was not completely valid,
because I had no idea what the alkaline cells' rated capacity was. Does
anybody know?)
It varies radically with load. With a very light load, it's as high
as 2000 ma-hr. With a heavy 1 amp load, as little as 550 ma-hr.
However, even that's not consistent. I was comparing Costco Kirkland
alkaline AA batteries, with the equivalent Duracell, Ray-o-Vac, etc
cells. The cheapo Kirkland cells were far better with a 1A load, but
sucked with a light load. Duracell was the exact opposite. The
differnces were not huge, but they were reproducable.
More than you ever wanted to know about alkaline batteries:
http://www.powerstream.com/AA-tests.htm
Note the variations by brand and type and the NiMH cell in the bottom
graph.
Much to my surprise, I discovered that the rechargeable cells powered the
unit as long as the throwaways. This means I'd break even after only 10
recharges. Even if I was off by 50%, I'd still need only 20 recharges.
Headphone amps sound like a light load. Got a number for the average
current drain?
The shortened life of fast recharging has to be weighed against the cost of
using throwaways. In practice -- particularly with heavy-drain devices --
you don't need many charge/recharge cycles to break even.
I killed a small Canon camera by using alkalines. It was apparently
designed for the normal terminal voltages found with NiCd and NiMH.
When I stuffed in an alkaline cell, the camera overheated after about
30 shots, and died. Canon covered it under the warranty.
Also, NiMH can handle short duration high current loads much better
than alkaline. That's they type of load found in many digital
cameras. Alkaline might be an option for a low current load such as
your headphones, but they wouldn't last long in a high current camera.
This is why I carry multiple sets of NiMH cells for my flashes and other
heavy-drain devices. With multiple sets, I don't have to worry about rapid
recharging, and can stick with 0.2C or 0.3C.
I've had problems with self discharge in previous NiMH batteries. So,
I have a 117VAC/12DC fast (4C / 15 min) charger in the camera bag.
When I need to shoot lots of photos, I give it a quick charge. Maybe
the LSD (low self discharge) NiMH will eliminate this problem.
--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060
http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558