More to the point the original proposed 47000uF has more than ten times the required capacity - which sounds like a safe margin for a robust design.
-- Steve O'Hara-Smith | Directable Mirror Arrays C:>WIN | A better way to focus the sun The computer obeys and wins. | licences available see You lose and Bill collects. | http://www.sohara.org/
Not quite that bad
Hers a 10F 2.7v cap
Realistically you would need three or so to get to 7-8V
-- New Socialism consists essentially in being seen to have your heart in the right place whilst your head is in the clouds and your hand is in someone else's pocket.
But in series they'll only be 3.3F ...
Another point is that a moderately high voltage standard electrolytic can actually be your PSU *reservoir* cap, so no need for any fancy switching.
Just had a look for DC-DC converters:
-- W J G
Actually the easy way to do all this is a classic mains transformer, bridge rectifier, reservoir cap, 5V regulator, and then simply have a mains loss detector feeding some Pi pin.
If the 5V regulator is switched mode, well OK.
Or you can even go for mains->bridge rectifier->400V reservoir cap-> switched mode PSU->5V.
If you want best efficiency.
I am sure there are in fact wall warts or similar doing exactly that already. Just add mains fail detector
Or for a bit more DIY
-- Ideas are more powerful than guns. We would not let our enemies have guns, why should we let them have ideas? Josef Stalin
ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.