You know I don't like to just buy someone else's stuff. All the fun is in building, but I get myself in over my head sometimes? Most of the time!
I could use some help with building a power bank for myself. I want to use it to power my Android tablet, or Kindle Fire. I am having a lot of excess time on my hands nowadays and I will for a long time to come, so I need to be mobile and without a plugged in charger for these things.
I figure a 5V USB style power bank would be good, or probably two of them, so one is charging while the other is being used.
I can get cells and solder cells to make a pack, but I need the electrical components, (Pre-made boards are fine, I don't need to build boards). I just want the boards to be good enough to take the load. I figure a max of 5 amps output to the tablets should be good and I want to charge the power banks at possibly 3-5 amps, to cut down on charging time, but I do not know if that is realistic.
So.... Guys, I need your electronics assistance here, on what to get. I am thinking of 26650 li-ion cells, for more capacity and I can come up with a housing home made out of aluminum, but component boards and switches, safeties, etc. are all beyond me.
I have found most of the “DIY powerbank circuity” to be sub-par when compared to those in built powerbanks. I have been trying to find a efficient board with correct output coding, but so far nothing. .
Things to consider for a DIY powerbank:
-Efficiency: >70% is minimal, >80% is good and >85% is excellent. Efficiency in DIY boards are usually around 75, mostly because the low voltage cutoff is too high for modern cells. Branded powerbanks can have LVP as low as 2.5V and up to 90 efficiency.
-Output coding: Different devices requires different output coding to charge at full speed, and this is controlled via a coding chip. Some circuity have fixed coding and will not charge all devices optimally.
-Input voltage: Powerbanks come in parallel battery configuration because charging the batteries this way is easier and safer, and they don’t need to implement a costly balance charging circuit. For a DIY pack you’re not limited to 1S, and a buck converter is most likely more efficient than a boost one.
I would not recommend most DIY powerbank board because most of them are old designs or doesn’t have auto coding, however since you’re not limited to parallel configuration, you can wire the batteries 3S/4S and use a 12V to USB circuit instead:
There are several brands of this same charger, externally not the same but you could assume it’s very similar inside: review by HKJ
This is a Matek DC-DC 4x USB adapter, total output 6A, coding is not auto but set to 2xAndroid 2xApple. Has programmable LVP but limited to 3.4V/cell.
Boost Setup:
There are also some specialized circuits for boosting 1S to USB with extrememely high efficiency, but they don’t come cheap and needs a USB port. These are not designed specifically for powerbanks, but for other DIY projects. They do come with D+ D- lines which are used to set charge coding, but until tested I cant say how good they are.
Another option, some good quality powerbanks are cheap enough to disassemble them and use the battery and board separately. But where is the fun in here right?
