PO> I've thought of a similar setup. Diodes to handle the
PO> current can be hard to find/expensive, so I thought of using
PO> a spdt relay with the coil connected to the AC that would
PO> connect the battery when the ac drops out. The advantage I
PO> see here is the circuit that connects the batteries uses no
PO> power and has no voltage drop while you are on batteries.
PO> I have been working on a similar system to keep my rig
PO> powered when I loose AC. I use the relay to connect the
PO> battery to the charger while the AC is on (actually while my
PO> 12v power supply is on since the relays I am using have 12v
PO> DC coils), and to the rig when the AC drops. The radio
PO> doesn't seem to mind the momentary power glitch when the
PO> relay drops.
First, I think you want to float the batteries on charge, which means that you
don't need much extra by way of diodes.
Second, bouncing computers up and down on relays is not a good idea.
-- Mike