Don, this could be of help..
I intend to run the my DreamC. setup 24/7, as I have no idea if downloads are start-stop plus I wouldn't like to continuously turn it off & on.
I power the DC like you do, 12v battery and DC-DC-buck converter (BTW, watch out for RFI "noise").
My readings tell me the DC+converter consume 300-400mA at 12v, that is say about 10Amps (120Watts) for the 24hrs period.
I currently connect the mains battery charger every 40hrs, mas o menos.
I use an old and tired 24Ah AGM battery. BTW, AGM batteries don't like being run down below 50%
Soon I will have:
- 3 or 4 12v 7Ah bricks in parallel (21-28Ah total). I like 7Ah AGM bricks because you can add/remove/swap them at will, as long as one is left to power your setup.
- 1x 30Watt solar panel plus a 5 or 10Amp PWM solar regulator (cheap from China).
During the day, this will put 7.5 Amps in the battery and power the DC (for 5 hour, being the conservative annual
average of sunny hours/day).
When the sun is gone, say for the next 16 hours (average) the DC will consume 6.4 Amps, about one third or quarter
of the battery's capacity... next day, the sun will hopefully fill the batt again. So, batt will fluctuate between say 90% and 60% day in and day out.
All of the above is obviously subject to all sorts of nuances like your local weather and actual amount of daily sunshine Example, you get 4-5-6 days of no sunshine and your battery goes flat (4-5-6 times 6.4A is 25.6-32.0-38.4 Amps out of your batt, right?), then you get a few sunny day and the batt will get SOME charge back, ONLY 7.5Amps/day which will be consumed at night and back to almost flat batt. Think backup, mains, genset, wind.
Sorry, I didn't mean to be so eloquent/boring but batteries and solar power are one big subject and a minefield of diff opinions