On Mon, 12 Dec 2011 04:26:03 -0800, "William Sommerwerck"
wrote:
Four of the cells were 2700mAh Sanyo AAs. They all measured about 1.23V,
rather lower than the 1.4V NiMH cells commonly charge up to, but close to
the "nominal" 1.25V of NiMH and nicad cells. Contrary to Urban Legend, they
were not completely discharged.
NiMH cells do NOT totally discharge themselves. They discharge to
about 50% of capacity (by self-discharge) and then just sit there.
For example, here are some curves I ran for an Energizer 2300ma-hr
cell:
http://802.11junk.com/jeffl/NiMH/Energizer-NiMH-2300.jpg
and for an Duracell 2050ma-hr cell:
http://802.11junk.com/jeffl/NiMH/Duracelll-NiMH-2050.jpg
There were brand new cells used to test the assertion that NiMH cells
need to be charge cycled a few times before they reach full capacity.
Basically, that's true.
Note the voltages (under 1C load). For the Energizer, it starts off
at 1.35v and starts to die at about 1.10v. If you put a load on your
Sanyo cells, I'm fairly sure your 1.23v no load voltage will drop to
something around 1.18v. In other words, your Sanyo batteries
self-discharged until they were almost dead, and stopped.
I recently had a similar experience to what you found. I have two old
Norelco rotary shavers. I received both with dead batteries and
replaced them with NiMH cells of dubious origin. I only charge them
when needed, except this time, when a dry squall dropped a few trees
through the power lines.
http://802.11junk.com/jeffl/pics/2011-12-03-Storm/
When I dug out the shavers, the LCD indicator showed a nearly full
charge (about 80%). However, when I tried to use it, both lasted less
than 60 seconds. My guess(tm) is that I hadn't charged it since last
winter (9 months).
That's fairly close to what you observed. There was sufficient
voltage for the LCD indicator to proclaim a nearly full charge, but
not enough stored energy to do much useful work.
--
# Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060
# 831-336-2558
#
http://802.11junk.com
# http://www.LearnByDestroying.com AE6KS