Originally Posted by senormechanico
Sorry, but diodes don't play well together in parallel.
Minute differences in forward conduction make a big difference in which one does the heavy lifting.
In this case, it doesn't sound like that would be a problem as his load is supposedly small.
A battery combiner would be a better choice. Open circuit until the batteries are being charged, then virtually zero voltage drop between house and backup battery.
Well true on the parallel issue but for a small load and using schottky diodes I still think it would work as long as the total amps are oh 60% of peak for two. One might run more amps but the other would still take part of the load too. Putting both on a common heat sink would help some too
Oh you could get a pair that was grossly missmatched, and one could go into thermal runaway and die, but his load is probably less then 3 amps anyway. There are also 30 and 100 amp diodes also.
The problem I see with the battery combiner is that the house bank feeds the electronics and so would the backup. So they would be in the same circuit not on opposite sides of a combiner. In my mind the house is charging
the backup, where the .45v forward drop of the schottky would make it a fair match to keep the little battery at a good state of charge. When the house dies or is switched off the backup takes over with no loss of power.