From: J�rgen Exner on
SMS wrote:
> Thomas T. Veldhouse wrote:
>> I prefer to carry an inverter for in-car charging [aka cigarette
>> lighter adapter], which delivers a LOT more power, in excess of 60
>> watts in my case.
>
> The car outlet can supply about 120 watts in most cars, are you saying
> the performance is better on the 401FS with an inverter and the AC
> supply, than it is directly from the car with the DC cord?

Well, both, the conversion to household power by the inverter and back to
charging load by the charger involve losses. So it is certainly not more
efficient.
But who cares about those losses which are maybe a few watts total compared
to the losses of the car engine which range in the many kW area. It's really
negligable, something like burning an additional interior lamp or so.

jue


From: SMS on
Thomas T. Veldhouse wrote:

> Did you even read it? The low charge rate [which is recommended by Maha] for
> AA batteries is 300mA. For AAA it is 200mA. These are the RECOMMENDED rates
> [slow switch setting] for use on the MH-C401FS.

You have to look at each charger individually, and not generalize,
because not every charger determines end-of-charge int the same way.

Read the spec on the MH-C401FS and how it determines end-of-charge.
Actually I don't believe the spec, because negative Delta V is never
used for NiMH, only NiCad, you want to use zero Delta V for NiMH. If you
aren't looking at dT/dt, there's no advantage in the faster charge time,
and I'm pretty sure that the MH-C401FS doesn't use dT/dt.

> I recommend the Maha MH-C9000 with Sanyo Eneloop batteries. The Rayovac or
> Hybrio are a bit more economic, but don't appear to have as consistant
> capacity.

Remember the story of the girl who had to write a report about penguins
and was given a huge book detailing everything in the world known about
penguins. In her report she wrote: "this book told me more about
penguins than I wanted to know". I kind of feel that way about the
MH-C9000 and the La Crosse BC-900

Maha boasts about the MH-C9000 "Endless programming possibilities - over
10,000 ways!" and "29 selectable charging and discharging rate <sic>." I
know that you can just go to automatic mode and not worry about choosing
one of the more than 10,000 configurations, but then what's the point of
spending that much? I don't think I'd spend the time to do battery
matching and grouping, cycling, or forming charges. I wouldn't use the
high charge rates because, according to the experts, high temperature
kills batteries. I wouldn't want to do the automatic cycling, since the
number of cycles of NiMH batteries are so limited.

Read the fifth paragraph at "http://www.buchmann.ca/chap8-page1.asp"
From: SMS on
Thomas T. Veldhouse wrote:

> The Costco in Coon Rapids, MN. They carry both the Duracell and the Sony
> charger. They are a few feet apart in the aisle ... oddly, not directly
> adjacent to each other.

I was in Costco yesterday (Sunnyvale, CA), and they had neither charger.
Maybe they are phasing out the Duracell, but haven't gotten the Sony yet.
From: ASAAR on
On Fri, 13 Jul 2007 09:33:57 -0500, Ron Hunter wrote:

> Since a battery is a chemical storage device, and the size is fixed, I
> would expect a theoretical maximum value at some point. Certainly the
> power density to weight of the Lithium cell is greater, but I don't know
> about the power density to volume....

Right, the maximum capacity has been changing more and more
slowly, and recent increases are partly due to changes in
construction and materials that allow more of the chemical "soup" to
fit into the fixed AA volume. Another part has been achieved, I
believe, by cheating. By slightly increasing the AA dimensions to
stuff even more "soup" into the AA bowl. In the past I never had
problems inserting AA batteries into devices, whether alkaline, NiCD
or NiMH. In recent years, though, NiMH batteries have been a tight
fit in some devices. Only once did I find some that were marginally
(and invisibly) longer, and they really could be installed in a
couple of radios only by applying so much force that I feared that
the stress would eventually fracture the radio's cases. More common
are NiMH AA cells that have a very slightly larger diameter. I
haven't found that this has caused problems with any cameras, but in
some flashlights and radios the fit was tight enough to make the
difference noticeable when inserting them, and a slight problem when
removing them, where I'd have to shake the device or swing it with
some force to help get them moving.

I already explained the similar power density (capacity) to
volume. You say "but I don't know about the power density to
volume....". What part of the explanation seems questionable?
This may help. As I said, Energizer rates their lithium AA cells at
3,000 mAh, and they also rate their alkaline AA cells as high as
2,900 mAh, higher than even NiMH cells. What accounts for the
better performance of lithium cells is the high internal resistance
of alkaline batteries. At the very low currents I mentioned
previously that are drawn by clocks, smoke alarms, etc., the
capacity of alkalines remains very high, 2,900mAh at currents of
25ma. Clocks and smoke alarms use much less than this, so at their
current load, alkalines may even be good for slightly more than
3,000mAh. But at the higher discharge rates typical of cameras, the
capacity is significantly lower, about 2,050mAh at the 250mA level,
1,950 for 500mA loads, and 1,500 for 1,000mA loads.

Canon's A640 demonstrates this quite well. Using its LCD to view
photos in playback mode, both alkalines and their NB-3AH NiMH cells
(rated between 2,300mAh and 2,500mAh) are expected to last for 20
hours. This suggests that the current drawn by the camera is fairly
low for this use, probably between 100mA and 125mA. Taking pictures
uses greater currents, so that's why alkaline batteries aren't as
good for as many shots, but with the efficient A630/A640 the
difference between using alkalines vs. the NB-3AH NiMH cells is
slight. 1,200 vs. 1,500 shots when the LCD is off and the flash
isn't used. To *really* use a lot of current, you'd take many
pictures using the flash, and when you do that, the difference
becomes much more pronounced, 500 shots using the NiMH batteries,
and much less using alkalines, 280 shots for the A640 and 350 shots
for the A630. Notice how Canon rates the A630 and the A640 for the
same number of shots (1,200) for the less demanding current load?

It would be interesting to know what part of the A640 consumes
greater currents. Maybe it involves the sensor, but it could also
be differences in how the motors are used. They both use 2.5" LCDs.

From: SMS on
Ron Hunter wrote:

> Since a battery is a chemical storage device, and the size is fixed, I
> would expect a theoretical maximum value at some point. Certainly the
> power density to weight of the Lithium cell is greater, but I don't know
> about the power density to volume....

I did some calculations with some batteries I have on hand, even though
both are now available with higher capacity.

Weight
------
One 7.4V 1800 mAH BP-511 was 177.6 mWH/gram
Four 1.2V Panasonic 2300 mAH AA cells were 98.6 mWH/gram

If I keep the weight the same, and use 2.0AH for the Li-Ion and 2.7AH
for the AA, it's 197mWH/g for the Li-Ion, and 116 mWH/gram for the NiMH.

The Li-Ion has a very large weight advantage (in percentage terms anyway).

Volume
------
The volume equations are a bit more difficult because of the shapes. The
batteries, both the Li-Ion pack and the AAs take up more volume in the
camera than their actual volume. For four AA cells, the rectangular
volume is 42.5cc, and the mWH/cc is 260 for four 2.3AH cells. For the
BP-511, the rectangular volume is 44.2 cc, and the mWH/cc is 301, for
the 1.8AH pack. This assumes no space at all between the AA cells, which
is not the case in reality.

If the AA cells were 3000 mAH, and the Li-Ion was 2000mAH, then they
would be about equal.

The volume advantage of Li-Ion is small, and declining, at least for
camera batteries. For larger batteries, using prismatic cells, Lithium
based batteries still have a big advantage.