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Using cells >1000mAh difference
#1
I have been building a power wall with a bunch of used laptop batteries that averaged out at 2000mAh each. I’ve used RePacker to create a 7S14P battery with an active balancer & 40Amp Chinese smart BMS w/ Bluetooth.

Recently, I came upon 120 lightly used LG 3200mAh cells (https://batterybro.com/products/lg-mh1-i...200mah-10a). I would like to incorporate these into my power wall to add capacity to the whole system. This system will see 250watts max load with an average load of about 100watts.

What are some strategies that I can use to accomplish this? any ideas would be greatly appreciated.
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#2
I run OK with a mix (by equal distribution) of used cells of a similar charge/discharge curve that vary by 5000mah... for example, for Panasonic 18650A(s) the nominal 'new' is 2950 or 3000 and I accept down to 2600 (85% of nominal) so my packs have cells from 2600mah to 3100mah - a 5000mah difference. However, note that the cells are same type and have same charge/discharge curve and IR characteristics.

Assuming your building a Xs set of packs - you have 3 choices
1) distribute evenly the 2000mah and 3200mah in each pack. This will create a 12,000mah difference, but I think this should work OK (same as my own 5,000mah differences)
2) create some packs with 2000mah and some with 32000mah - but make each pack have the same 'total' ah. 1 pack = 2000mah*100cells = 200.0ah and 1 pack = 3200*63cells = 201.6ah.
3) create 1 Xs battery with 2000mah cells and 1 Xs with 3200mah cells and hook them in parallel

In case #1 and #2 it would be best if the cells have a very similar charge/discharge and IR characteristics. If not, then I would do #3 for sure.

OK , that's my 2 cents, I'm sure you'll get other comments Smile
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#3
(10-12-2019, 03:05 AM)OffGridInTheCity Wrote: Assuming your building a Xs set of packs - you have 3 choices
1) distribute evenly the 2000mah and 3200mah in each pack.  This will create a 12,000mah difference, but I think this should work OK (same as my own 5,000mah differences)
if i m Reading it.right, there s a mistake.
you wrote One extra zero in differenze

(3200-2000=1200 mah)

btw general rules that i understand Is that mixing cells Is ok if Total Ah is same. but if you stay well far from both max and Min voltage, even a difference of 17ah on 150 Ah still keep cells balanced (seen on Peter videos)
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Building Lifepo4 Powerwall - atm 3400 cells growing
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#4
All cells will be discharge tested & matched with RePacker...
Battery A (~31Ah) 7S14P Sanyo UR18650FJ (2200mAh average, higher IR) from modem packs.
Battery B) (~31Ah) 7S10P LGEBMH11865 (3100mAh average, lower IR) from E-Scooter packs.

How will they behave when run in parallel? Do I need 2 BMS?
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#5
(10-12-2019, 07:22 AM)EnergyOasis Wrote: All cells will be discharge tested & matched with RePacker...
Battery A (~31Ah) 7S14P Sanyo UR18650FJ (2200mAh average, higher IR) from modem packs.
Battery B) (~31Ah) 7S10P LGEBMH11865 (3100mAh average, lower IR) from E-Scooter packs.

How will they behave when run in parallel? Do I need 2 BMS?

@emuland-metroman - yes, thank you for correcting 12,000 to 1200 (and 5,000 should have been 500)

>How will they behave when run in parallel? Do I need 2 BMS?
@EngeryOasis -   You must not hook a 7s14p (48v nominal) battery in parallel with a 7s10p  (36v nominal).    To hook batteries in parallel they must be the same voltage Smile    Before discussing BMS, can you clarify the battery/parallel plan you have in mind?
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#6
if you're building packs with cells in deviation of 3000mah or more, good 500mah 90% soh and 5000mah 90%soh..
And you divide them to get the same capacity in every pack, there is no reason i see a problem.
as long as your packs are in the same soh and capacity....
10 x 5000mah gives you 50 ah...thats one pack....100 x 500mah also gives 50 ah...thats pack two...ect
the real trick is to distribute all cells evenly among the number of packs you are creating...
credits go to daromer...workt perfect for me
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#7
(10-12-2019, 02:54 PM)OffGridInTheCity Wrote:
(10-12-2019, 07:22 AM)EnergyOasis Wrote: All cells will be discharge tested & matched with RePacker...
Battery A (~31Ah) 7S14P Sanyo UR18650FJ (2200mAh average, higher IR) from modem packs.
Battery B) (~31Ah) 7S10P LGEBMH11865 (3100mAh average, lower IR) from E-Scooter packs.

How will they behave when run in parallel? Do I need 2 BMS?

@emuland-metroman - yes, thank you for correcting 12,000 to 1200 (and 5,000 should have been 500)

>How will they behave when run in parallel? Do I need 2 BMS?
@EngeryOasis -   You must not hook a 7s14p (48v nominal) battery in parallel with a 7s10p  (36v nominal).    To hook batteries in parallel they must be the same voltage Smile    Before discussing BMS, can you clarify the battery/parallel plan you have in mind?

7S is 24v pack, whether it’s 10P or 100P. Parallel adds capacity, Series adds voltage.

My idea was to incorporate (35) 3200mAh matched LG cells with (91) 2000mAh modem Sanyo red top cells to make one big 24 Volt (7S18P) pack. My initial thoughts were to create two individual 24 V batteries of different capacities on 2 separate BMS’s and when the pack of lower capacity drops out the secondary pack will take over.

I would much rather mix the cells together and make one big battery. Will be utilizing RePackr to match my 7 strings up proper. My existing 7S14P battery that will be connected to this future [7S18P] (mentioned above) was matched to (6) 29527mAh strings & (1) 29526mAh string by RePackr.
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#8
(10-13-2019, 09:45 PM)EnergyOasis Wrote: 7S is 24v pack, whether it’s 10P or 100P. Parallel adds capacity, Series adds voltage.

Agreed - My bad i mis-read  Blush

(10-13-2019, 09:45 PM)EnergyOasis Wrote:
(10-12-2019, 02:54 PM)OffGridInTheCity Wrote:
(10-12-2019, 07:22 AM)EnergyOasis Wrote: All cells will be discharge tested & matched with RePacker...
Battery A (~31Ah) 7S14P Sanyo UR18650FJ (2200mAh average, higher IR) from modem packs.
Battery B) (~31Ah) 7S10P LGEBMH11865 (3100mAh average, lower IR) from E-Scooter packs.

How will they behave when run in parallel? Do I need 2 BMS?

@emuland-metroman - yes, thank you for correcting 12,000 to 1200 (and 5,000 should have been 500)

>How will they behave when run in parallel? Do I need 2 BMS?
@EngeryOasis -   You must not hook a 7s14p (48v nominal) battery in parallel with a 7s10p  (36v nominal).    To hook batteries in parallel they must be the same voltage Smile    Before discussing BMS, can you clarify the battery/parallel plan you have in mind?

7S is 24v pack, whether it’s 10P or 100P. Parallel adds capacity, Series adds voltage.

My idea was to incorporate (35) 3200mAh matched LG cells with (91) 2000mAh modem Sanyo red top cells to make one big 24 Volt (7S18P) pack. My initial thoughts were to create two individual 24 V batteries of different capacities on 2 separate BMS’s and when the pack of lower capacity drops out the secondary pack will take over.

I would much rather mix the cells together and make one big battery. Will be utilizing RePackr to match my 7 strings up proper. My existing 7S14P battery that will be connected to this future [7S18P] (mentioned above) was matched to (6) 29527mAh strings & (1) 29526mAh string by RePackr.

I also would go with 1 'big' battery with evenly distributed (mixed) cells - and this would only required 1 BMS (from your earlier comments).
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