Date   : Fri, 14 Mar 2008 12:57:14 +0000 (WET)
From   : PCOGHLAN@... (Peter Coghlan)
Subject: Disc drive power

>
>I've run various things off old car batteries in the past.  Just
>remember that they aren't actually 12V - usualy 14V or higher on light
>loads.   I imagine that modern sealed bateries would be as good.  Just
>watch the current required.
>

Nominally 12V lead acid batteries are generally charged with just less
than 14V. So in a car, you get about 14V with the engine running,
dropping off to around 12V after a while with the engine stopped.

Please bear in mind that car batteries can be quite dangerous in a
number of ways. In particular, they can supply currents large enough
to heat power cables enough to cause burns or fires so suitable fusing
is highly recommended in case of even a very remote chance of an
inadvertent short circuit.

Rechargable batteries of all types and to a lesser extent, even
non-rechargable alkaline batteries can also supply surprisingly large
currents for a short time and suitable fusing is also a good idea.

Computer power supplies would have some sort of built in short
circuit protection and outlets in cars are protected by fuses in
the car. This, together with the low voltages involved, can make us
forget to think about this sort of thing when using unusual power
supplies such as direct connections to powerful batteries.

Regards,
Peter.