On 12/24/2012 2:10 PM, Jeff Liebermann wrote:
On Mon, 24 Dec 2012 11:28:48 -0800, "William Sommerwerck"
wrote:

http://802.11junk.com/jeffl/NiMH/Duracelll-NiMH-2050.jpg
shows that the first charge cycle results in a 1180mA-hr capacity,
while the third charge cycle increased it to 1360mA-hr or about 15%
increase. Is that what you mean by "slammed"?

No. It means hitting it hard with a high charge current.

Yuck. Why would I want to do that? If there were dendrites in NiMH
batteries like in NiCd, then perhaps it would make sense. Besides if
such a high current blast was necessary to produce a proper battery,
or to produce bigger numbers on the data sheet, the manufacturers
would already be doing it.

Where did you see this recommendation? I couldn't find anything with
Google under "NiMH slamming" variations, except under National
Institute of Mental Health. I did find this blurb that recommends
against the practice:
http://forums.dpreview.com/forums/post/25581821

I've noticed that my NiMH battery collection (flashlights, cameras,
GPS, radios, etc) spent much of their time in the charger simply
recovering from self discharge.

I've never had that problem -- as far as I can tell. I've had cells that sat
around for the better part of year deliver 20 or 30 flashes, with rapid
recycling.

Perhaps my cameras and GPS require a higher minimum state of charge
than your flash? When I used to leave my conventional NiMH batteries
in the camera for a few months, it would usually be good for one or
two photos before complaining. I always kept a spare set of charged
NiMH with the camera in case I run out. They were also only good for
a few shots.

http://www.stefanv.com/electronics/sanyo_eneloop.html
Scroll down to the two pink graphs near the bottom of the article. The
conventional battery is down to half capacity in 75 days, and 1/4
capacity in 150 days.

Incidentally, this article:
http://www.stefanv.com/electronics/using_nimh.html
covers quite a bit of ground on dealing with NiMH batteries, including
trickle charging, and a home made NiMH computah controlled charger:
http://www.stefanv.com/electronics/battman2.html
and a simplified USB powered charger:
http://www.stefanv.com/electronics/usb_charger.html
I'm tempted...

Most of my cells have been close to rated capacity. In one case, a cell was
about 20% low, and MAHA replaced it.

I didn't know that Maha made batteries:
http://www.mahaenergy.com/batteries/
$4.25/ea for AA in a 4 pack is not cheap. Somewhat more expensive
than Sanyo Eneloop. I dunno.

There are other low self discharge NiMH batteries available.
Duracell Pre Charged
http://www.duracell.com/en-US/product/rechargeable-staycharged-batteries.jspx
Rayovac Hybrid or Platinum:
http://www.rayovac.com/Products/Rechargeable-Batteries-and-Chargers/Everyday-Use-best-battery-charger.aspx
Kodak Pre-Charged
http://store.kodak.com/store/ekconsus/en_US/pd/ThemeID.3925700/Ni-MH_Pre-Charged_Rechargeable_Batteries_AA/productID.158853000

http://www.mahaenergy.com/mh-c9000/
Nice charger/analyzer. I dunno the break-in and battery-forming
features. Stressing the battery doesn't seem like a good way to
increase battery life though it might produce rated capacity earlier.
However, it's a much better charger than the common consumer junk
chargers, and would probably be a good charger for the OP.

Agreed. Thomas sometimes sold the C9000 for ~ $40, but those days seem over. I
have two, so I don't have to wait if a lot of cells need charging.

I'm finding prices from $50 to $140 (including tax and shipping).
http://www.ebay.com/sch/i.html?_nkw=maha%20mh-c9000&_sop=15


+1 on the c9000

I've had good results with the older
Enloop charger...the one with the single led that can
charge an odd number of cells.

There are two categories of dendrites.
Dendrites that have already shorted need to be vaporized with
short-duration
high-current. That clears the short and blasts a bigger hole in the
separator.
Causes higher self-discharge and faster dendrite regrowth.
Back in the day when NiCds were expensive and shorted ones were free,
it made a lot of sense for hobby projects.

The second class is those that have not yet pierced the separator.
For those, I'm a fan of burp charging. Same process you'd use
for plating when you want a smooth surface.
I did some experiments, but I had nowhere enough data to draw a
conclusion. And I concluded that the cost of powering the computer
and the programmable power supply and load probably exceeded the benefit.

The biggest problem with charging batteries is determining when to
stop.

I had a friend who did radio repair for the city.
Back in the day, police radios were terminated by a thermal switch.
That worked surprisingly well, but only because the battery was
predictably depleted during the shift.
If you stuck a charged radio into the charger, you did some damage.
He had a lot of failed batteries from people who left the radio off
all day and stuck it back in the charger.

There's so much variability in temperature, thermal time constant,
voltage gradient, etc. that it's best to measure change than
absolute value.
I'm a fan of 0deltaV termination with timer and temperature fail-safe
for NiMH cells.