On 1 Mar 2001, at 19:33, Doug Franklin wrote:
> In _grossly_ oversimplified terms, the voltage a cell (battery) puts
> out is determined by its chemistry (alkaline, lead-acid, NiCd, NiMH,
> Mercury, etc.). The capacity (in current-hours) is determined by the
> volume of chemistry that it contains, the internal efficiency of the
> cell's construction, and probably other stuff.
>
> As Paul said, a 2 Ah (2000 mAh) cell will put out its voltage for about
> twice as long as a 1 Ah (1000 mAh) cell, but they'll put out the same
> voltage if they're the same chemistry.
>
> This is vastly oversimplified, too, since voltage produced graphed
> against remaining capacity is a curve. For example, a battery
> containing less than half its charge capacity might put out less
> voltage than the same battery when it's fully charged.
Capacity is easy to reconcile when you consider the units ie mAh ie a
1000mAh cell will theoretically deliver 1000mA of current (given an
appropriate load) for an hour until it is exhausted whereas a 2000mAh cell
will deliver 1000mA for 2 hours. Once you know the load characteristics you
can then estimate the time over which the cells will reliably supply power.
The construction and capacity is also often related to the internal resistance
of the cell, this resistance will be in series with any load and will therefore
effect the terminal voltage. Generally higher capacity cells will have a slightly
higher internal resistance and therefore may not be able to supply current
peaks as high as a lower capacity cell and obviously the terminal voltage will
be less regulated under high loads (this would effect motors more than
electronic flashes).
Cheers,
Rob Studdert
HURSTVILLE AUSTRALIA
Tel +61-2-9554-4110
Fax +61-2-9554-9259
UTC(GMT) +10 Hours
[EMAIL PROTECTED]
http://www.ozemail.com.au/~distudio/publications.html
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