My experience with newer NIMH high capacity cells indicates that their
capacity improves considerably, after at least several charge/discharge
cycles.
If I hadn't been aware of the NIMH chemistry's low initial capacity before I
purchased them, I would've been seriously disappointed at their initial test
results.
I've also seen, but not tried, cells that are claimed to be
pre-conditioned.. so they're supposedly ready for use after the first
charge.
My testing was controlled, and didn't perform any deep discharging, like
that which could happen with a cordless power tool, for example.
The cells I'm presently using are Powerizer 4500 mAh sub-C cells (in packs
of 5) and Tenergy 10,000 mAh D cells (also in packs of 5).
For the first couple of cycles, the capacity is about 50% and gradually
improves to full capacity after 5 or more cycles (at reasonable rates).
I'm using 1A charge rate for the 4500, and 2A for the 10k packs now..
although I wouldn't consider higher rates of 2A and 4A to be detrimental, as
long as the cells don't heat up.
The MRC Super Brain 977 will provide a reading for the discharge mAh, and
prevents damaging deep discharges.
Readouts will include rate, time and mAh.. so test results can be noted and
compared.
Charging and discharge rates are completely adjustable, which makes this
model fairly versatile.. and it can be input with vehicle 12V for charging
packs of less than 12V.
I also bought a MRC 992, which has a port for a USB cable (which I don't
have), and since the 992 doesn't have the discharge capability, I don't care
much about plotting charging cycles.
Sophisticated chargers can detect problems in charging rates and then shut
down, but less advanced chargers will continue to supply charging current.
I have experienced fault Errors with both of the MRC units, which I consider
a valuable feature.. there were 2 questionable older AA cells in the 4-cell
holder, and I'd marked those 2 cells previously becaue they had elevated
temperatures when charged with a different charger in the past.
I also have some negative-pulse chargers which continuously monitor the
state of charge. For these chargers, I just write the begin time on a
sticker, to see how long the packs have charged when they're finished.
Another handy item is a continuous rate discharging unit, made for cycling
commercial ENG camera batteries, as part of a conditioning cycle. Anton
Bauer ADM is a 2A rate for 12-14V packs.
As mentioned numerous times in the past, there are many different grades of
cells, and certain cell types have specific features that the others don't.
Traditionally, the best quality rechargeable cells are from Japan, and those
cell makers provide lots of specifications for their products.
I'm convinced that overheating cells is damaging, and precautions should be
taken to prevent overheating.
Unattended charging is generally high risk, as many battery pack temperature
cutouts are rated so high (65 C), that by the time the air in the plastic
housing reaches the cutout temp, the core temps of the cells are already
beyond a safe/reasonable range.
--
Cheers,
WB
..............
"Jeff Liebermann" wrote in message
...
Per a previous discussion, I decided to test whether new NiMH
batteries need to be conditioned or charged several times before
reaching their rated capacity. Apparently they do.
The test setup is a West Mtn Radio CBA-IIv1 battery analyzer.
http://802.11junk.com/jeffl/NiMH/cba-II.jpg
I didn't want to wait 20 hrs per test to get the official rated
capacity, so I elected to run the tests at 1C which resulted in about
a 45 minute test, but also resulted in a much lower capacity result.
It also caused some unexpected errors. The design of the CBA-II does
not include a Kelvin probe connection to eliminate any losses in the
cables and connectors. It measures the voltage at the load, instead
of at the battery. This is not a problem at low load currents, but at
2 amps, results in considerable error.
Two new (out of the package) batteries were used. An Energizer NiMH
2300 ma-hr cell, and a Duracell 2050 ma-hr cell. Between tests, the
batteries were quick charged in a Radio Shack 23-1305 NiMH quick
charger (15 min). Each battery was discharged 3 times and the
discharge curves plotted.
Note that the Energizer package says 2450 ma-hr, while the battery is
marked 2300 ma-hrs.
http://802.11junk.com/jeffl/NiMH/energizer.jpg
The Energizer cell showed no change in capacity between discharges.
http://802.11junk.com/jeffl/NiMH/Energizer-NiMH-2300.jpg
Using 1.0VDC as the end point, the measured cell capacity is:
Run 1 1785 ma-hr
Run 2 1890 ma-hr
Run 3 1895 ma-hr
The Duracell cell showed a larger change.
http://802.11junk.com/jeffl/NiMH/Duracelll-NiMH-2050.jpg
Using 1.0VDC as the end point, the measured cell capacity is:
Run 1 1200 ma-hr
Run 2 1270 ma-hr
Run 3 1385 ma-hr
The net improvement over 3 charge-discharge runs is about 10% for the
Energizer and 15% for the Duracell. Not huge, but certainly
measurable. Whether it is worth the effort conditioning the battery
before use, is debatable.
--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558