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4p battery pack
#1
hi, I need a relatively high capacity battery pack to power a 5v application. I want to have 4 x 18650 in parallel. Ideally I want to shrink wrap the whole thing. Do I need a BMS for this? I would like to make sure I don't over discharge the pack you see. Any advice welcome.

BTW I will use a boost converter to get 5v from the battery pack, so nominal voltage will do me fine.
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#2
(10-13-2020, 02:42 PM)crowhill67 Wrote: hi, I need a relatively high capacity battery pack to power a 5v application. I want to have 4 x 18650 in parallel. Ideally I want to shrink wrap the whole thing. Do I need a BMS for this? I would like to make sure I don't over discharge the pack you see. Any advice welcome.

BTW I will use a boost converter to get 5v from the battery pack, so nominal voltage will do me fine.
A BMS's primary function is to protect against overcharge and undercharge, then perhaps hi/low temperature extremes, and then perhaps balance in a multi-S (more than 1 cell in series).

Balance is not an issue. 

So, charge/discharge (limit) and temp would be the key issues in your case - and that depends on your situation.    
- Maybe you charge this battery manually? (e.g. not part of solar system for example) and if you have confidence in the charger - then there's no risk of overcharge.
- Maybe you can monitor discharge and the temperature manually?

There is such a thing as 1s BMS (just google lithium ion 1s BMS) and you could get one Smile
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#3
Use an DIY 18650 power bank it will have all the circuity needed to charge and output 5v if you need a different ouput jack I am sure they are around. this is listings of 18650 power bank on ebay https://www.ebay.com/sch/i.html?_from=R4...k&_sacat=0
later floyd
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#4
Hi,

Thanks for the info, I have been searching for 4p and not 1s instructions/ protection boards, DOH!

Basically yes, I do trust my charger, it is an intelligent RC charger, which will allow me to control the charge rate and all that good stuff. What confuses me is that if I have 4 cells in parallel, and I charge the unit, the charger should cut off at 4.2v, but I suspect it is possible that not all cells are at 4.2v, just the first one. So the charging will stop? Also the same with discharging, any discharge protection will only cut off the power when the last cell has reached 3.whatever volts? (faulty??) logic dictates that the first three batteries could possibly be discharged below the cutoff point. is this a correct assumption?

dave.
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#5
(10-13-2020, 04:11 PM)crowhill67 Wrote: Hi,

Thanks for the info, I have been searching for 4p and not 1s instructions/ protection boards, DOH!

Basically yes, I do trust my charger, it is an intelligent RC charger, which will allow me to control the charge rate and all that good stuff. What confuses me is that if I have 4 cells in parallel, and I charge the unit, the charger should cut off at 4.2v, but I suspect it is possible that not all cells are at 4.2v, just the first one. So the charging will stop? Also the same with discharging, any discharge protection will only cut off the power when the last cell has reached 3.whatever volts? (faulty??) logic dictates that the first three batteries could possibly be discharged below the cutoff point. is this a correct assumption?

dave.
Batteries in parallel act as ONE.   All 4 cells in parallel will have the exact same voltage *all the time* - its not possible for 1 cell to be more or less than the other 3 as voltage will flow back/forth between them instantaneously.     For your purposes -  just think of it as 1 larger cell instead of 4 separate smaller cells Smile
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