I 'm working on a project that needs 1 5A of 5v (Arduino and some neopixels) and around 3A of 3...

[G+_Chris Kurtz]

I'm working on a project that needs 1.5A of 5v (Arduino and some neopixels) and around 3A of ~3v (vape atomizer, pump/fan, and speaker.)

 

To me it makes sense to power from as close in voltage to the largest draw as possible, so I'm thinking of powering from 4x 18650 batteries, arranged 1S4P, giving me 3.7v with around 10 AmpHours (4x 2500mAh)...

 

Several people have suggested that 7.4v (two pairs of 18650s in series, so 2S2P) makes more sense, theoretically because you have more C this way.

 

Doing that would require twice as many BECs (one to 5v and one to ~3v) instead of just one step-up BEC from 3v to 5v.

 

Thoughts and Comments?

[G+_Black Merc]

With the 1st(1s4p) setup, when the pack is near low charge level, will the high(3A) draw pull down the feed to the ubec(3v -> 5v) and cause the logics to reset?

[G+_Ben Reese]

I think the 2 in series for 7.4v would be your better option. If you don't want to use 2 UBECs, you could use a voltage regulator to step down the 5v to 3v. I'm not sure which would be more efficient. And in that case you'd probably need a 3+ amp UBEC.

[G+_Chris Kurtz]

Black Merc Hmm, if it got too low, likely, but with 4P I'd have so much capacity it would likely never reach that, but it's a good point to consider.

 

Ben Reese It seems less efficient to use 2 UBECs instead of one, but Black Merc's comment about low end dropouts bares thinking about.

 

Thanks all!

[G+_Peter Hanse]

I am not battery expert but can’t you run batteries both in parallel and in series by taping off connection between two packs.