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Aren't rechargeables for high current applications?

 
 
Phil Allison
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      12-07-2008

"SMS"
> Phil Allison wrote:
>
>> ** Clearly the battery type switch alters the threshold voltage for
>> triggering the "low batt" warning.

>
> If you use CHDK on Canon cameras, you can get a somewhat better idea of
> the remaining capacity. But the problem with NiMH batteries is that the
> voltage doesn't decline linearly with capacity, so a "low battery"
> indicator is about all that is useful on the AA battery powered cameras. A
> battery gauge on an AA powered camera using NiMH batteries isn't going to
> convey much useful information, since it'll show a full battery most of
> the time, even when the capacity is declining.



** And if it is calibrated to work with alkalines, it will say that NiMH
cells are near flat when they are not.



....... Phil


 
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ASAAR
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      12-07-2008
On Sun, 07 Dec 2008 14:30:17 -0800, SMS, the battery charlatan
wrote:

> Actually, a "dead" alkaline is about 1.0 volts, while a "dead" NiMH is
> about 1.15V, so it should be the opposite. That's the problem with
> metering the NiMH batteries, they have an extremely narrow voltage for
> most of their capacity, around 0.1V, while the alkaline have about a
> 0.5V range.


That shows how little you know about batteries. An alkaline
battery that appears to be "dead" with some digital devices is not
even close to being dead with others, especially analog devices such
as portable radios, clocks, etc. When they're nearly dead, some
radios can only play at low volume, others start to produce
distorted sound, and this is at or slightly below 0.5volts. You've
also got it wrong with respect to NiMH cells. There's still a
reasonable amount of capacity left at 1.15v, although some digital
devices are designed (intentionally or inadvertently) to shut down
near that point. Haven't you noticed that battery chargers that
have a discharge function as well as digital readout of cell
voltages continue discharging quite a while after 1.15v is reached?
They switch back to "charge" mode when the cells reach 1.0 volts.

 
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Phil Allison
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      12-07-2008

"SMS"
> Phil Allison wrote:
>
>> ** And if it is calibrated to work with alkalines, it will say that NiMH
>> cells are near flat when they are not.

>
> Actually, a "dead" alkaline is about 1.0 volts,



** That is only the battery maker's **opinion** - based on usage in
*voltage tolerant* devices like torches and toys.

Camera makers and most electronics device makers have a whole nuther point
of view !!!


> while a "dead" NiMH is about 1.15V,


** That is the actual voltage ( under load) at which the cell is near full
discharge - further discharge will result in the cell developing a high
internal resistance making it unusable in a camera.


> That's the problem with metering the NiMH batteries, they have an
> extremely narrow voltage for most of their capacity, around 0.1V, while
> the alkaline have about a 0.5V range.


** The narrow voltage range under discharge for NiMH is one of the issues -
the other is how the cells recover voltage during periods of non use.

Even a near flat NiMH *initially* shows virtually the same terminal voltage
as a near fully charged one - after an hour or two of non use. Confounds
any attempt to quickly determine remaining capacity from cell voltage.

Alkalines recover cell voltage during rest periods too, but not a fully as
NiMHs do.


> On the AA cameras I have, you wouldn't want to be using alkaline batteries
> because they have such high internal resistance.



** Internal resistance combines with actual load current to depress cell
voltage - but the thing that matters is whether the resulting voltage
remains above a critical threshold for the camera.

Fresh alkalines ( from one of the top brands) work fine until they have lost
about half their capacity - then the fall in cell voltage and simultaneous
rise in internal resistance puts them out of the game.

The other issue is that alkalines suffer a dramatic loss of capacity at high
discharge currents while NiMH cells do not.

The end up result is that a 2000mAH rated NiMH cell way outlasts a circa
3000mAH alkaline, when used in a typical camera.



...... Phil





 
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J. Clarke
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      12-07-2008
Phil Allison wrote:
> "J. Clarke"
> Phil Allison wrote:
>>
>>> ** The falsehood is that a battery voltage display shows (or even
>>> approximates) remaining capacity.
>>>
>>> Remember, we are considering only user replaceable AA cells - so
>>> AA
>>> cells of any type, condition or state of charge can be fitted to
>>> the
>>> device at whim.

>>
>> Do us a favor ..

>
>
> ** You do me one and go drop dead
>
> Nothing in some stupid user manual has any bearing on the FACTS of
> the
> matter.


I see. Canon's manual lies and there is no such indicator. I guess
that my eyes lie and there is no such on my Coolpix 990 either.

<plonk>

--
--
--John
to email, dial "usenet" and validate
(was jclarke at eye bee em dot net)


 
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Phil Allison
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      12-08-2008
"Jerk Clarke"
>> Phil Allison wrote:
>>>
>>>> ** The falsehood is that a battery voltage display shows (or even
>>>> approximates) remaining capacity.
>>>>
>>>> Remember, we are considering only user replaceable AA cells - so
>>>> AA
>>>> cells of any type, condition or state of charge can be fitted to
>>>> the
>>>> device at whim.
>>>
>>> Do us a favor ..

>>
>>
>> ** You do me one and go drop dead
>>
>> Nothing in some stupid user manual has any bearing on the FACTS of
>> the matter.

>
> I see. Canon's manual lies and there is no such indicator.



** What it REALLY indicates is another matter - fool.



...... Phil



 
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John Doe
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      12-08-2008
ASAAR <(E-Mail Removed)> wrote:

> John Doe wrote:


>> Name a camera that automatically detects whether you are using
>> disposables or rechargeables.


No answer, as expected.

Without being told, a camera cannot tell the difference between
disposables and rechargeables. That is exactly the point I was
making many messages above before Jack know-it-all butted into the
conversation.
 
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David J Taylor
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      12-08-2008
John Doe wrote:
[]
> Without being told, a camera cannot tell the difference between
> disposables and rechargeables. That is exactly the point I was
> making many messages above before Jack know-it-all butted into the
> conversation.


What about if the camera measured /both/ the voltage and the internal
resistance? Could it possibly make a good guess?

David

 
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Mark Thomas
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      12-08-2008
David J Taylor wrote:
> John Doe wrote:
> []
>> Without being told, a camera cannot tell the difference between
>> disposables and rechargeables. That is exactly the point I was
>> making many messages above before Jack know-it-all butted into the
>> conversation.

>
> What about if the camera measured /both/ the voltage and the internal
> resistance? Could it possibly make a good guess?
>
> David


Sony does this rather well with its chipped 'InfoLithium' batteries. I
was most impressed with the ones I used (in the f717 and f82, as they
gave very sensible estimates of remaining usage time - neither
optimistic nor pessimistic.

Perhaps you can do it with Lithium Ion, but not NiMh? The fact that
very few other people offer this feature would suggest that it is
difficult to implement (understandable in the case of AA's, where the
camera has no easy way of knowing the chemical formulation, capacity or
design characteristics).
 
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lens
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      12-13-2008
This thread has somewhat degenerated, but I would like to respond to
the OP. The newer hybrid NiMH cells (I like Sanyo Eneloop) transform
AA NiMHs from being completely useless to being an almost universal
replacement for alkalines. I have not purchased an AA alkaline cell in
almost a year since converting to Eneloops. With older NiMH, you would
charge them up, and then when it was time to use them they'd be dead.
Also, no one mentions that this subjects ordinary NiMH cells to many
more charge cycles (recharging cells that self discharge) than they
would otherwise need, and prematurely reduces their life.

With Eneloops I have two boxes labeled "good" and "bad". I have my
family take from "good" and put the dead ones in "bad". This never
worked before, because if the cells sat in the "good" tub for a month,
they would be way down. Now they can sit for a year if necessary. I
also try like hell to standardize everything on AAs: Mini Maglites,
wall clocks, remotes, cameras, etc. It helps that the video game
controllers my kids use are AA powered. Sure, a few things might be
better suited to alkalines (like clocks and remotes) but I still use
Eneloops in them because I'd rather not buy throwaways for anything. I
may have to replace the remote batteries a bit more often than with
alkalines, but the difference is not noticeable.

Hybrid NiMH have completely transformed the utility of rechargeable
AAs for me.
 
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default
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      12-13-2008
On Sat, 13 Dec 2008 00:47:10 -0800 (PST), lens <(E-Mail Removed)>
wrote:

>This thread has somewhat degenerated, but I would like to respond to
>the OP. The newer hybrid NiMH cells (I like Sanyo Eneloop) transform
>AA NiMHs from being completely useless to being an almost universal
>replacement for alkalines. I have not purchased an AA alkaline cell in
>almost a year since converting to Eneloops. With older NiMH, you would
>charge them up, and then when it was time to use them they'd be dead.
>Also, no one mentions that this subjects ordinary NiMH cells to many
>more charge cycles (recharging cells that self discharge) than they
>would otherwise need, and prematurely reduces their life.
>
>With Eneloops I have two boxes labeled "good" and "bad". I have my
>family take from "good" and put the dead ones in "bad". This never
>worked before, because if the cells sat in the "good" tub for a month,
>they would be way down. Now they can sit for a year if necessary. I
>also try like hell to standardize everything on AAs: Mini Maglites,
>wall clocks, remotes, cameras, etc. It helps that the video game
>controllers my kids use are AA powered. Sure, a few things might be
>better suited to alkalines (like clocks and remotes) but I still use
>Eneloops in them because I'd rather not buy throwaways for anything. I
>may have to replace the remote batteries a bit more often than with
>alkalines, but the difference is not noticeable.
>
>Hybrid NiMH have completely transformed the utility of rechargeable
>AAs for me.


Thanks. The stores where I am are just starting to stock the
"precharged" NiMH batteries. My wife has already abandoned all the
rechargeable's in favor of alkaline's (which she recharges until they
leak) because they hold a charge longer.


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