Re: Running Apple2e from a battery?

[dempson@atlantis.actrix.gen.nz (David Empson)]

In article <jknottDDuID2.6H0@netcom.com>, John Knott <jknott@netcom.com> wrote:
> I've got a couple of Apples lying around that I'd like to rip apart
> and turn into robots.  I was wondering if anybody out there has tried
> to run an apple from a battery, rather than from the power supply?

I just had a rather involved discussion with someone else in E-Mail
about a similar idea: powering a IIc+ from a battery.

In short: it is not possible to do this directly.  A battery only
provides a single voltage, which is not regulated and decreases as the
battery charge drops. 

All Apple II models require several voltage rails, which must be
regulated: +12V, +5V (both reasonably high current), -12V and -5V
(both low current).

The IIc is the only Apple II model that can easily be powered from an
external battery, as it has an internal voltage converter that takes
an unregulated DC voltage (9V to 20V, from memory) and generates the
necessary internal voltages.  A heavy duty battery (e.g. car battery)
should be used.

You could do it with other models by using an external "voltage
inverter", which regenerates mains AC voltage from a battery.

Another possibility would be to build or buy a voltage converter that
takes 10V to 15V unregulated DC input and generates the required IIe
power rails, with sufficient current capacity.

The IIc's voltage converter is not suitable, as it doesn't have enough
capacity.  In addition, it doesn't generate -5V (the IIc uses a 7905
regulator on the motherboard to generate -5V from the -12V rail).

> Is this possible?  What are the power requirements of a standard 2e
> motherboard, assuming no interface cards?

I don't think this is specified anywhere.  The total ratings for each
rail (including usage by cards in the slots) are:

+5V    (+/- 3%)  2.5A
+11.8V (+/- 6%)  1.5A continuous, 2.5A intermittent
-5.2V  (+/- 10%) 250 mA
-12V   (+/- 10%) 250 mA

The intermittent supply on the 12V rail is probably intended for
powering disk drives.  The IIe reference says that the internal power
supply can operate for up to 20 minutes at the higher rating, as long
as this is followed by at least 10 minutes at the normal load.

This sounds like a heating situation - two thirds duty cycle over any
reasonable period should be OK.

Taking the slot specifications into account, the implied motherboard
usage is:

+5V  2A
+12V 1.25A
-5V  50 mA
-12V 50 mA