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'[ee]: AA Battery capacity'
2002\03\01@102413 by Graham North

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Hi,

Does anyone have a general rule of thumb (formula) to determine how long
an
Alkaline AA battery will last at a certain constant current drain?

I am actually using 6 Duracell Procell's in series, am I correct in
thinking that
the capacity will be the same, just with a higher voltage?

The design I have uses 400uA when turned off, and I am worried this will
drain
the batteries unacceptably if left for a long time.

Thanks

Graham North

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2002\03\01@105125 by NDuckworth

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Have a look on the Duracell web site, they have datasheets in PDF format for
download which contain discharge curves.


On Friday, March 01, 2002 3:10 PM, Graham North
[SMTP:.....grahamnorthKILLspamspam@spam@CASTLEGROUP.CO.UK] wrote:
{Quote hidden}

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2002\03\01@105828 by Jim

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The *rule of thumb* I've used for AA Alkaline batts
is around 3 AH (3 Ampere Hours) when discharged at
a slow rate ...

At 400 uA rate - this works out to around 7500 hours ...

Jim


{Original Message removed}

2002\03\01@110025 by Douglas Butler

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As battery manufacturers go Duracell provides some of the best data on
their web site.  But they don't go below 0.25A loads.  In the extreem
low load area data is hard to come by.  Somewhere I have some data taken
by the Woods Hole Oceanographic Inststute for instruments that would run
off batteries for several years on the bottom of the ocean, but that
data is from the 1960's and batteries have improved a lot since.
Generally if the batteries are cold (like the bottom of the ocean) they
are fairly ideal at low loads.  At higher loads internal series
resistance eats power.  At higher temperatures internal parallel
resistance causes self discharge.

I can look for the old data I have this weekend.

Sherpa Doug

> {Original Message removed}

2002\03\01@110956 by Eoin Ross
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Just a small thought here - why wouldn't they use two metal plates and use the sea as the battery? Unless the load would be too great of course.

>>> EraseMEdbutlerspam_OUTspamTakeThisOuTIMETRIX.COM 03/01/02 10:54AM >>>
<SNIP>  Somewhere I have some data taken by the Woods Hole Oceanographic Inststute for instruments that would run off batteries for several years on the bottom of the ocean,<SNIP>

Sherpa Doug

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2002\03\01@113520 by M. Adam Davis

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Corrosion.

-Adam

Eoin Ross wrote:

{Quote hidden}

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2002\03\01@114131 by Sergio Masci

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> Just a small thought here - why wouldn't they use two metal plates and use
the sea as the battery?
> Unless the load would be too great of course.

Bio mater buildup on the plates

> <SNIP>  Somewhere I have some data taken by the Woods Hole Oceanographic
Inststute for
> instruments that would run off batteries for several years on the bottom
of the ocean,<SNIP>

Regards
Sergio

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2002\03\01@114140 by Chris Loiacono

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Sonobuoys - disposable submarine detection units use salt-water batteries
that activate when dropped into seawater. As a bonus, when the battery power
drops below a certain level, a seawater valve is opened that scuttles the
units to keep them out of enemy hands...
Obviously not good for long-term applications though....

Chris

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2002\03\01@115706 by James Paul

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Graham,

Yes.  Go to Radio Shack and get a copy of their battery book.   It has
curves and charts in it that will allow you to get a good idea of what
to expect in battery lifetime(s).  They are geared to RS batteries in
particular, but I've found I get similar results using the charts with
other mfg's products also.  Actually, I usually get somewhat better
results with other mfg's.

                                               Regards,

                                                 Jim




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2002\03\01@122149 by Douglas Butler

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That is actually possible.  One company I have heard of (Sea Battery?)
makes power sources like that.  The problem is you only have one cell
that gives about 0.5V but at many amps.  They have a germanium
transistor startup oscillator that provides enough voltage to drive a
MOSFET power oscillator that then sustains itself.  The efficientcy is
bad but the input is free.  In their sales pitch they said it was a good
power source for navigational bouys.

I have never heard of anybody using it though.

Sherpa Doug

> {Original Message removed}

2002\03\01@134527 by Olin Lathrop

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> The design I have uses 400uA when turned off, and I am worried this will
> drain
> the batteries unacceptably if left for a long time.

400uA is awfully high for an "off" current.  Let's say, for example, that
you've got 2000mAH cells.  That means 400uA will drain the batteries to
oblivion in 2000mAH/400uA = 5000 hours = 208 days = about 7 months.  Of
course they may not be useable for the intended purpose during ON operation
well before that.  On the other hand, if normal operation would require the
batteries to be replaced every week, then 400uA is insignificant.


********************************************************************
Olin Lathrop, embedded systems consultant in Littleton Massachusetts
(978) 742-9014, RemoveMEolinEraseMEspamEraseMEembedinc.com, http://www.embedinc.com

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2002\03\04@045818 by Graham North

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Thanks to everyone who replied.

The instrument is only designed to last 8 hours on a set of batteries,
so guess this
is not such a bit deal. But as a dedicated engineer, I'll try to get the
off current down
a bit!

Thanks

Graham North

> {Original Message removed}

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