Re: Reassure me.. please!


Rich Grise wrote:
On Tue, 25 Jul 2006 14:00:59 +0000, Puckdropper wrote:
me <me@xxxxxxxx> wrote in news:Xns980BAEBA396Fmeherenet@xxxxxxxxxxxxx:

yup. 12V is 12V no matter where you get it. Some 12V supplies can
deliver more current than others...

Correct me if I'm wrong, but aren't batteries of any type usually
considered infinite current sources? That seems to be what I remember
from some discussion a week or so ago.


They're modeled as a theoretically infinite current source, at a
specified constant voltage, in series with what's commonly known as
the internal resistance of the battery. You can't get infinite current
out of a physical battery, but that doesn't invalidate the model.
In the model, there is infinite current available at the source, but
because of the internal resistance of the battery, there is a practical
limit, which is when the internal resistance is dropping the whole
constant voltage that the current source is set at, leaving 0V at the
battery terminals.

But, to the OP - don't forget Ohm's law - the load only draws what
current it needs - if your little circuit needs, say, 100 mA, it will
get that from a 12V wall wart or a 12V golf cart battery. :-)

Hope This Helps!
Rich

Thanks all

I think for prototyping, I'll use a PC power supply with a fuse...
Needless to say, a car battery on my desk would be a little cumbersome.

.

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