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> and a 3V to 5V step-up converter You may want to step it up to 3.3V only for the main power supply and do a little surgery on the Pi to feed it directly to i

by pflanze 12y ago

> and a 3V to 5V step-up converter You may want to step it up to 3.3V only for the main power supply and do a little surgery on the Pi to feed it directly to its 3.3V 'rail', foregoing the 5V->3.3V linear regulator. (I'm just saying this from reading the given page, I haven't done this myself, so YMMV.) http://www.bitwizard.nl/wiki/index.php?title=Reducing_power_consumption_of_a_raspberry_Pi http://www.bitwizard.nl/wiki/index.php?title=Reducing_power_... BTW it's not clear to me whether the Pi or the Beaglebone Black use less power [when idle]. The latter would provide more CPU power, which would make it more interesting for a general purpose solar computer. PS. I was thinking about the B+ when writing the above (stupid me, should actually read the article before posting). The A+ likely has lower power consumption than the Beaglebone (but also only 256 MB RAM, which is really going to be limiting for many tasks). Also, perhaps they have replaced the 5V->3.3V linear regulator with a step-down regulator which would be more efficient (still, doing only one transformation instead of two would give you a bit lower losses).

speeq 12y ago
Thanks! They seem to have replaced the linear regulator with a switching regulator (which is more efficient) on the A+ & B+ models. I agree though, doing only one transformation would be more efficient - but I'm not sure which USB devices would work on 3.3V - it depends on the individual use-case I guess.
- pflanze 12y ago
  I now noticed that the NCR18650B batteries are Li-ion batteries (i.e. 2.7-3.7V range for one cell; I was thinking NiMH which are below 1.5V per cell). This may be harder to regulate to 3.3V as you can't simply choose a step-up nor step-down circuit because the source voltage crosses the target voltage during operation; I think I've seen chips that claim to do this but I don't know how efficiently[1]. You may be better off with the original plan of converting to 5V after all. [1] well, actually an inverting buck-boost converter should be fine and seems like it should be as efficient as a step-up (https://en.wikipedia.org/wiki/Buck-boost_converter https://en.wikipedia.org/wiki/Buck-boost_converter). Whatever, my lack of enough experience in that area shows.

by pflanze 12y ago

speeq 12y ago

Thanks! They seem to have replaced the linear regulator with a switching regulator (which is more efficient) on the A+ & B+ models. I agree though, doing only one transformation would be more efficient - but I'm not sure which USB devices would work on 3.3V - it depends on the individual use-case I guess.

pflanze 12y ago
I now noticed that the NCR18650B batteries are Li-ion batteries (i.e. 2.7-3.7V range for one cell; I was thinking NiMH which are below 1.5V per cell). This may be harder to regulate to 3.3V as you can't simply choose a step-up nor step-down circuit because the source voltage crosses the target voltage during operation; I think I've seen chips that claim to do this but I don't know how efficiently[1]. You may be better off with the original plan of converting to 5V after all. [1] well, actually an inverting buck-boost converter should be fine and seems like it should be as efficient as a step-up (https://en.wikipedia.org/wiki/Buck-boost_converter https://en.wikipedia.org/wiki/Buck-boost_converter). Whatever, my lack of enough experience in that area shows.