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Question about building a battery pack.
#1
Hi guys i'm still learning about batteries and i will appreciate you helping me i am thinking about this.

For example i have 4 cells and plan to make a 2S2P pack for my diy led lights
1st cell =Discharged capacity is 1850mAh@600mA and Charged Capacity is 2005mAh
2nd cell =  Discharged capacity is 1825mAh@600mA and Charged Capacity is 2015mAh
3rd cell = Discharged capacity is 1830mAh@600mA and Charged Capacity is 2010mAh
4th cell = Discharged capacity is 1845mAh@600mA and Charged Capacity is 2025mAh

what if i group them by discharged capacity?         What will be the problem here?
so if i will build 2S2P this is the arrangement:  

1st cell / 4th cell      1850mAh/1845mAh
3rd cell / 2nd cell     1830mAh/1825mAh        =2S2P(Discharged capacity Arrangement)

or grouping them in charged capacity is better?
4th cell / 2nd cell     2025mAh/2015mAh
3rd cell/ 1st cell       2010mAh/2005mAh        =2S2P(Charged capacity Arrangement)


Discharged Capacity - capacity measured in discharging the single cell
Charged Capacity - capacity measured in charging the single cell
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#2
You should use the Discharge capacity as it is more closely related to real world values. Charged based capacities also include heat dissipation caused by the cell warming, wiring heating, heat generated by the charger, or most likely a combination of all the above. Discharge testing eliminates a lot of the erroneous errors during testing.

In your above values, you didn't mention what the Charge testing amps were at, only your discharge. This can make a big difference on your results as well.

For LED lights, I would recommend 3s as you will have a better stable voltage to work with and longer duration the lights can be lit. Especially if the leds are wired in series, as each led will have a voltage drop and is cumulative. 3s would give you 8.4V (2.8V/cell absolute dead) to 12.6V (4.2V absolute full). That's a large working voltage range for led's. Then you could go with 1p as the current is very little, normally.
The led's will also pull higher amps at the lower voltage range, too, as they will try to run at a particular wattage
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#3
(05-09-2019, 12:26 PM)Korishan Wrote: You should use the Discharge capacity as it is more closely related to real world values. Charged based capacities also include heat dissipation caused by the cell warming, wiring heating, heat generated by the charger, or most likely a combination of all the above. Discharge testing eliminates a lot of the erroneous errors during testing.

In your above values, you didn't mention what the Charge testing amps were at, only your discharge. This can make a big difference on your results as well.

For LED lights, I would recommend 3s as you will have a better stable voltage to work with and longer duration the lights can be lit. Especially if the leds are wired in series, as each led will have a voltage drop and is cumulative. 3s would give you 8.4V (2.8V/cell absolute dead) to 12.6V (4.2V absolute full). That's a large working voltage range for led's. Then you could go with 1p as the current is very little, normally.
The led's will also pull higher amps at the lower voltage range, too, as they will try to run at a particular wattage

That's what i thought too. That's why i'm rebuilding and checking my 1kwh Powerwall and already found 6 weak cells that can't handle 600mA very long, at first i'm confused why my diy Powerwall voltages are drifting and goes unbalanced after a month of cycle with just 1.3A load every night for 12v bulbs, its because i group them in charged capacity and you just confirmed it thanks. btw my charge testing amps is 500mA im using XTAR VC4 how can this affect my results?
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#4
(05-09-2019, 07:00 AM)rhedbatt Wrote: so if i will build 2S2P this is the arrangement:  

1st cell / 4th cell      1850mAh/1845mAh
3rd cell / 2nd cell     1830mAh/1825mAh        =2S2P(Discharged capacity Arrangement)

+1 like Korishan suggests, use discharge capacity to decide.

Not sure how you have the cells above arranged but maybe below helps?
In your grouping above, you would want each parallel section to be close to the next parallel section in capacity.
So with the mAhrs you've shown it'd be better arranged
1850mAh +  1825mAh in parallel  (=3675mAhr)
in series with 
1845mAh + 1830mAh in parallel  (=3675mAhr, same!)
This is what the rePackr link (see site top right corner)
Running off solar, DIY & electronics fan :-)
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