"Dave Plowman (News)" wrote in
:
Trouble with rechargeables is they don't maintain the same performance
throughout their life - which makes knowing when they must be changed
rather hit or miss. Plus the fact that most give little warning of running
out - unlike an alkaline - due to the different voltage discharge curves.
So what might be a benefit on a high power demand device like a drill etc
is a liability on a low current one.
All of which makes perfect sense - in the context of a NiMH or NiCd. As most
of this talk has gone to discussing microphones, consider a moderate steady
load. You want that to be supplied with equal constancy, if possible. If
nothing else you know what you'll get during the discharge if it IS constant
in voltage and has adequate current. Lithium ion cells do this fine. They
fall off at the end but not so fast as Ni-based cells. Actually the fade time
at end of discharge when powering a microphone should be fairly long, you'd
get early warning if you knew what to look for. You might still get a couple
of hours of use from start to end of fall anyway, if current demand is less
than 50 mA (examples below), given two CR123A cells. Total use is more than a
half a day easily, even with the lower 800 mAH capacity. With light loads the
safety is very good. Newer batteries even have the clout to power a drill, if
they have lithium titanate anodes. Their shelf life is actually BEST at
around 40% charge so they don't mind being left waiting around, and they can
be charged at any time. They store very well when cold so they won't mind
travel in an unheated truck. They work fine at sub-freezing temperatures too,
so long as you don't go too low, and not many things demand that of them in
use.
Time to running flat is long enough to give you the nice early warning you
can expect from alkalines, but is flatter for longer, before that happens.
And when you've charged them many times, the loss of capacity even after
hundreds of charges and a couple of years of use, will still give you better
performance after a charge, than an alkaline fresh out of the box. If you
charge them each night they'll probably never run flat, and as they'll spend
most of their lives at around 40% charge, give or take 40%, they should last
a long time.
If reliability is critical, run their first couple of charges in a non-
critical situation. Label them with coloured electricians' insulating tape to
code them, or whatever it takes to identify and organise. If I had to put
batteries in 100 microphones I'd rather use lithium ions than alkalines given
what I've seen of them so far on similar steady loads in critical situations
(hours in cold and darkness with a flashlight making the difference between
safety and injury).
http://web.telia.com/~u85920178/tx/bug.htm
http://www.zingsmusic.com/product_in...oducts_id=4483
(Two different systems, same 30 mA supply current, so I'm assuming it's a
good guide).
That said, this one takes 50 mA..
http://www.shure.com/ProAudio/Produc...us_pro_104c_ug