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Old Jun 11, 2007, 5:12 PM   #11
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mrc01 wrote:
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It's because even supposedly identical batteries have different capacities.
Yes, but using a battery tester to measure (a) the open-circuit voltage, and (b) the current delivered through a standard resistor will often show up differences in condition. My AA battery tester has a 37 ohm resistor, and its instructions suggest about 40mA for a good cell. It's usually about 37 or 38mA for a freshly-charged Ni-MH.

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Old Jun 11, 2007, 5:19 PM   #12
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SilverFoxCPF wrote:
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With flashlights we have found that the equal draw rule of series cells is bent a little. Often we find that the cell closest to the lamp empties first. Please note that we are beyond the normal low voltage cut off for secondary cells and are in over discharge territory now. This is an area where primary cells often find themselves, but the results are similar for both secondary and primary cells.

The theory is that the heat from the lamp warms up the cell that is closest to the lamp making it more "vibrant." This cell hold higher voltage under load and gives more power during the discharge. This results in it emptying before the other cells.

As far as TV remotes and radios go, the voltage of a cell can be raised simply by holding it in your hand.

Tom
Thank you for that explanation - I was confident that my observations on flashlight battery life were correct. However it is possible that extending that conclusion to remotes was premature - an easy extension to make. One must be careful not to get too much of one's exercize jumping to conclusions. In thecase of weakening batteries in remotes (and in radios) is it not also possible that increased resistance from light oxidation on the terminals could result in interruption of current that could be restored by removing and replacing the cells? Next time this happens I will try cleaning the contacts and replacing the batteries in the same sequence -- I have done this with flashlight cells often with no result, but remotes do not seem to run down as frequently and I don't recall if I have ever tried this with them.
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Old Jun 11, 2007, 5:27 PM   #13
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SilverFoxCPF wrote:
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...the heat from the lamp warms up the cell that is closest to the lamp making it more "vibrant."
Yes, I'll buy that.

More effective than swapping cells would be to warm them both, then. So 'position in the series'variation will apply only in cases with a significant temperature variation, and would apply regardless of connection type, and require a sgnificant heat source. Not LED flashlamps, then.Also swapping would have an effect only when there'd been enough 'on' time for significant differential warming of cells.

So the general idea we started with, of swapping cells around in a camera to revitalise the device would be somewhat hit & miss, and usually miss.

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Old Jun 11, 2007, 6:56 PM   #14
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Hello Mrc,

NiCd cells are much more tolerant of reverse charging, however if you push hard enough, it happens.

Tom
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Old Jun 11, 2007, 7:03 PM   #15
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Hello Alan,

Alan T wrote:
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SilverFoxCPF wrote:
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...the heat from the lamp warms up the cell that is closest to the lamp making it more "vibrant."
Yes, I'll buy that.

More effective than swapping cells would be to warm them both, then. So 'position in the series'variation will apply only in cases with a significant temperature variation, and would apply regardless of connection type, and require a sgnificant heat source. Not LED flashlamps, then.Also swapping would have an effect only when there'd been enough 'on' time for significant differential warming of cells.

So the general idea we started with, of swapping cells around in a camera to revitalise the device would be somewhat hit & miss, and usually miss.

Thanks,

Alan T
I must point out that not all LED flashlights are created equal...

Some of the more powerful ones see temperatures above 120 F during long runs. This is hot enough to warm things up.

Tom
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Old Jun 14, 2007, 4:23 PM   #16
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Alan T wrote:
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Over in the "Pentax / Samsung dSLR" forum...

http://forums.steves-digicams.com/fo...mp;forum_id=80......

penolta wrote: ..........Batteries arranged in series are also drawn down differently depending on their position, so changing their position on reinsertion can also make a difference (try reversing the sequence of the batteries in your flashlight, radio, or tv remote control the next time they run down, and you will see this pheomenon for yourself).............


This is rather a surprise to me. Would any experts care to comment? I'll have my say later.

Alan T
I had a good laugh when I saw that. What a load of b****. The only way that could happen would be if a lower voltage from one of the inter-cell connections was being used to power a separate circuit, and they just don't do that.
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