Jim Weir wrote:
Without going into a long song and dance, 5 watts peak is what most of us call a
watt-and-a-half (CW, RMS, or any other way of saying it). Figuring that a
transmitter (overall, from synthesizer to finals) is 50% efficient, that means
you are sucking 3 watts during transmit. If the ICOM uses 4 cells, this means
that the batteries have to put out 500 mA (half an amp) during transmit. This
is pushing the limits on AA cells (see later).
According to Duracell's data sheets, Their AA Ultra battery will still be putting
out 1.2V after 1 hour at a 500 mA load and 1.1 V after 2 hours. One hour of
transmitting adds up to a lot of hours of flying.
Disregarding the scare tactics of somebody who doesn't know what they are
talking about, current state of the art NiMH batteries are by far the optimum
solution for handheld transceivers.
If you are using that transceiver every day or two or even once a week, I would
agree. For something that is used only occasionally or just for emergencies,
rechargeable batteries are a bad choice.
Yes, the self-discharge is about 30% a
**MONTH**, so if you don't go flying for a month, the batteries are down to 70%
the next time you go to the airplane. Big flippin' deal.
So I got the details wrong, "big flippin' deal". The fact still remains that NiMH
batteries have the worst (highest) self discharge rate of any of the commonly used
battery chemistries. You didn't get all the details right either, I looked them up
again. NiMH batteries loose 15 to 20% of their capacity in the first 24 hours
after charging and then 15 to 20% more per month. You may find this acceptable for
emergency equipment, but I don't. Put in Alkaline or non rechargeable Lithiums and
you can forget about it for 2 to 5 YEARS, that's a lot better than having to
remember to charge it every month or two.
You can now get AA NiMH cells (http://www.thomas-distributing.com/batteries.htm)
with 2200 mAh ratings, which should be good for six months, even WITH
self-discharge. You can also go the thomas FAQ page for the truth about
self-discharge instead of listening to a ranting from somebody who didn't do
their homework.
The nice part about both NiMH and nicad are that you can draw AMPS from them
without getting into internal resistance effects. They will put out five to ten
times the short-circuit current than will a regular alkaline cell.
NiMH don't have "memory" (nicads, more or less, still have some memory), which
means that if you don't completely discharge them before charging them, they
"remember" the level at which they were discharged and won't go any lower. NiMH
do not exhibit this effect. NiMH also have many more charge-discharge cycles
than do nicads.
Who's not doing their home work now? According your source, NiMH batteries are good
for 250 to 500
cycles and NiCd are good for 500 to 1,000 cycles. While NiMH have a significantly
lower tendency to develop memory that the old NiCds were so bad about, they still do
(according to most of the material I have read) have a slight tendency to developing
a memory. Even your source recommends periodic conditioning of NiMH, why would you
need to if they didn't have any memory tendency?
Did you even read the source I posted? Here is another one.
http://www.cadex.com/b_02_2_0_nickel.asp
--
Chris Woodhouse
Oklahoma City
"They that can give up essential liberty
to obtain a little temporary safety
deserve neither liberty nor safety."
-- Benjamin Franklin, 1759 Historical Review of Pennsylvania