Power bank design. LiPo vs Lithium ion. Single cell vs multiple

Thread Starter

kyleh04

Joined Jun 18, 2017
54
Hello all,

I'm working on prototyping a power bank, to be used for charging mobile devices, smart watches, ect.. It needs to be 10'000mAH.

My initial thought, was to use a single lithium polymer pack, 10'000mAH and at 3.7v. I would then use a boost regulator, to boost it to 5v, and use the 5v to charge the devices.

This approach is the simplest approach, and should work in theory.

I started looking at existing models, and >90% of power banks use cylindrical lithium ion cells, used in parallel and in series. The <10% that do use lipo's use them in series, at 7.4v or even higher. I assume they are doing this, because it is more efficient to reduce the voltage, than it is to increase it.

My thought with multiple cells, is that it will make it difficult for me, not controlling my battery sources, getting cells which match enough to use together.

Is my initial approach that wrong of an idea, and if so, what are your suggestions to use multiple cells (lipo or lithium ion)?

Thanks!
 

Dr.killjoy

Joined Apr 28, 2013
1,196
Power banks are a rabbit hole all there own..There are so many ideas and setups that can be used but you have to figure out where to stop which isn't always that easy..
Every design I have seen uses the batteries in parallel and not in series. I think that because it has a higher charge voltage with each cell added.. Also you can buy quality power banks alot cheaper then can be made..I would start with quality 18650 cells and go from there..
 

Thread Starter

kyleh04

Joined Jun 18, 2017
54
Power banks are a rabbit hole all there own..There are so many ideas and setups that can be used but you have to figure out where to stop which isn't always that easy..
Every design I have seen uses the batteries in parallel and not in series. I think that because it has a higher charge voltage with each cell added.. Also you can buy quality power banks alot cheaper then can be made..I would start with quality 18650 cells and go from there..
Thanks for the reply, was thinking nobody would!

Yeah it seems like there is a million ways to do it. My thought is to just use one of these: http://www.batteryspace.com/polymer...h-9a-rate---ul-listed-un38-3-passed-ndgr.aspx

I see how most do what you suggested, but I can't find a valid reason why my plan wouldn't work. It will be much easier, thinner, and safer (since I don't have to make sure the cells are perfectly balanced).
 
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