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Thread: Battery Capacity
www.piclist.com/techref/power/batterys.htm?key=battery
face picon face BY : email (remove spam text)(Olin Lathrop)



Tomás Ó hÉilidhe wrote:
>     Capacity = 1 Ahr = 3 Whr

There is one of your misconceptions.  Amp-hours do not equal Watt-hours.
The first is a measure of charge, the second a measure of energy.  You can
use the AH rating and the battery voltage to get a rough idea of energy, but
there are even more factors you have to take into account to get energy
actually delivered to a load than the charge delivered to the load.

> Therefore the Ahr for the battery, (i.e the amount of coulombs it has
> available), is 1 Ahr

Exactly.  Note that the internal or external resistance is irrelevant to
this calculation.

> (but this is figure is misleading if you don't
> know
> what voltage you have across the load).

It's not misleading if you know what AH are and how to use them.  You have
to understand that there is more to battery ratings than AH and that it only
gives you a rough guide to the total energy the battery can deliver.  AH is
still a useful rating because it is the closest simple value that describes
the battery independent of the external circuit, although it's not totally
independent and you have to understand how.


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