Date   : Tue, 02 Jul 2002 01:45:04 +0100
From   : "Richard Gellman" <r.gellman@...>
Subject: Re: Battery BBC

> > I'd be interested in hearing if anyone has tried running a BBC or
Master
> > from a external power source like a sealed lead acid battery (e.g. a
car
> > battery). The particular application I'm considering would do away
with the
> > Beeb's power supply (so no DC-AC inverters). Hence I need +5V, 0V
and -5V
> > (at whatever the current ratings are without looking them up).
>

A small power supply could be constructed with that lovely regulator series,
78xx.
These chips will provide stable voltage outputs, and the xx part is the
voltage you want.
e.g. for 5V use a 7805 and for 12V a 7812. All you need to surround them are
capacitors large enough to handle the current flow,
I'd suggest at least 2,700uF either side of the regulators to be safe. (The
BBC draws a suprising amount to keep all that stuff going..)
An idea might be seperate regulator circuits for each of the supplies.. (the
BBC Micro uses 3 +5v supplies I think). And I wouldn't
advise trying to run a floppy drive off the Aux power port in this
configuration either, not without some serious power supply circuitry
to drive the two motors inside such a device.

-- Richard Gellman

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