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making power bank with 18650

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Member level 3
Feb 9, 2010
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power bank related circuits are very less in net .
decided to make one

my 18650cells i bought 3year back
never used ...but they showed 3.7V when tested !

I kept for 10hour charge... the cell voltage is 3.82V now
current is 200mA

why so slow charge ?
can you suggest better circuit , "no special batt charger IC"


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There is a lot of information around on how to charge LiIon cells.There you find all about chemistry, charge current, charge voltage, lifetime....

In short: LiIon cells are very problematic when charged to a too high voltage. The voltage limit has small tolerance.
Especially to find the end of charge needs time with lowered charge current.


Why are you so averse to ICs? The TP4056, for example, is very cheap, compact, has all the components including the MOSFET and is very easy to use.

Why are you so averse to ICs? The TP4056, for example, is very cheap, compact, has all the components including the MOSFET and is very easy to use.

Oh that TP4056 seems good ... i thought it is 500mA !
even then they need to be ordered ..some pple cant .
My designs must serve lot many .

plan is
powerbank 1 : TP4056 based with 4cells like the 10400mah clones
will pull dcdc booster 1amp ckt from a cheapo power bank

powerbank2 : my charger ckt with opamp
the dcdc is same as above .

Main plan is to make a reliable 10400mAh
and help millions , to save from fake 10400mAH Pbs ...
I am getting good batteries

problem guys
the circuit charging cell too slow taking 10+ hours , need to measure the current ,
,the current control needs to be removed (the bc547 and resi 1.5E)

test setup
-3 year old 18650 (never used)
-sony 1.5AMP charger as input with this circuit (see post1)8-O
probable causes
--the cells 3year old never used , so may be 1st charge taking time
-- the current limiter is bugging the charging
--or the BD139 eating power

expert comments needed

tested the current ... 300mA! .. cells are not pulling enough current!
i am waiting for new cells


I felt it is better to adopt a cheap power bank than to make own circuit ...
Adoped a china 1$ PowerBank:roll: (with vry low Q cells )to house
(swapped the PBs cells) with 100% reliable new LITHIUM 18650 cells
for a test and they work nice

charged 2 cells indicating 3500mAH effective power

XPERIA Z 2300mAH phone : 1 time
SAmsung infuze 1750mAH : 68%

Pretty happy the 2 cells will charge any cell with 1500mAh TWICE !

Going to make a 4cell version now .
One issue is the highcut is not working for the adpted cheap PB

I will find a way


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I recommend mini360 board with MP2307 chip or some similar for better efficiency.

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