Toralf Lund wrote:
Leon Altoff wrote:
Hi,
The R-CRV-3 batteries are not recommended for use in the Pentax
cameras. They supply too high a current that can cause motors to burn
out.
I'm not sure I understand how that can happen. Aren't batteries voltage
sources, not current sources?
- T
Well, with my rudimentary knowledge of D.C. theory, I've a problem with
that, too, Toralf...
A "load" (the camera body into which you install the battery) takes
whatever current it needs from the power source.
The voltage level (what I call the current 'vehicle') is essentially
fixed, as is the resistance of the load.
The result is a specific current DRAW, if the supply is capable of
supplying it.
A larger current capacity supply leads to a more stable supply, as it's
not straining to give out what's asked of it.
In other words, if you have a load that requires 1.0 amp of steady state
current, with only occasional spikes, a power supply only capable of
delivering 1.0 amps is going to strain if a 1.5 or 2.0 amp surge is
required. The 2.0 amp or greater supply will go along for the ride,
easily supplying what's been asked for.
I also think of amperage as a fixed reservoir of water.
Empty it with a 1/4" tube, and it supplies it readily.
Attach a 2" tube to the reservoir and it will deliver it much more
rapidly, and unless it's large enough, it might almost empty before the
need is met..
So, you increase the size of the reservoir, just in case. which provides
a margin of safety.
I've always believed this and it's never led me astray.
Now people talk of current as something that's "delivered", unbidden, to
some poor load that can't handle all that current.
Most perplexing!
At least that's the way I've been taught, but I'm a mechanical guy, not
an electrical one. Usually know just enough to get by...
If I'm wrong, one of your EEs out there will let me know! ;-)
keith whaley
