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Lithium Phosphate (LiFePO4) Battery Pack

I have 96x2=192 cells

Assumptions

LiFePO4 26650 Battery Assumptions

SpecificationValue
Nominal Voltage3.2v
Max Voltage3.6v
Cutoff Voltage2.0v
Capacity2300mAh

Battery Spec 4S24P - 48Ah (based on salvaged batteries)

SpecificationValue
Nominal Voltage (4 x 3.2v)12.8v
Max Voltage (4 x 3.6v)14.4v
Min Voltage (4 x 2.0v)8v
Cells in Series for Voltage4

Parallel Cells to Get Capacity

48Ah/2.0Ah

24

Total Cells Required96

Dimensions (W x L x H)

1 cell: 26mm x 65mm

pack size: 26*4 x 26*24 x 65


104mm x   624mm x 65mm

Salvaged Batteries

Picked up a couple of BAE UPS battery packs.



SpecValues
MakeBAE
Model235C9387G1
Dimensions (WxLxH)31" X 6.5" X 3"
Weight19.55 lbs
Voltage40V
Configuration

12S8P

12*3.2v = 38.4v

Current

2250A

Watt Hours736 wH
Equivalent Ah for 12v=P/V = 736/12 = 61Ah
Battery26650 LiFePO4
Infohttps://secondlifestorage.com/showthread.php?tid=5451
Video - Teardownhttps://www.youtube.com/watch?v=AG36QB1WkuY


Cells A123

SpecValue
ModelANR 26650 M1B
ChemistryLiFePO4
Dimensions(DxH)  26mm(1.0") x 65.15 mm(2.6") 
Max Current50A
Nominal Voltage  3.25V +/- 0.05V Nominal, 3.2V Average
Nominal Capacity                 2500 mAh (at 0.2C rate, 3.65 +/-0.05V cut-off)
Charging current
  • Standard Charging: 2.5A, 1.0C rate 
  • Maximum Charging: 10.0A, 4.0C rate
Temperature Range
  • Charge and Discharge: -30°C to 55°C 
  • Storage:  -40 oC to 60 oC
Image


Observations:

Battery ConfigurationEstimated Capacity (~2Ah/cell)

4S8P

=2Ah * 8

= 16Ah

4S24P

=2Ah * 24

= 48Ah

Original Battery Confguration - 12S8P

New Configuration - 4S8P x 3 

Could use 3 BMSs for this configuration or just one.

Someone else's solution


Capacity Tests




Single Battery Tests

The rated capacity of these batteries is 2500 mAh. It appears that the average capacity seems to be around: 1186 mAh.

Cell Capacities
812
818
902
917
935
952
964
1017
1083
1087
1092
1095
1101
1109
1111
1119
1163
1187
1203
1213
1236
1255
1262
1277
1287
1332
1333
1431
1467
1478
1828
1891

Battery Pack Tests 4S8P

PackOriginal CapacityStarting VoltageFinal Voltage

Capacity

(mAh)

% Capacity ~Capacity/CellNotes
220Ah14.4 (3.6v/cell)8v 1015651%1270 mAh

BMS Added


2
14.0 ( 3.5v/cell)10.25993550%1241 mAh

Charged with Car Charger. Cells: 3.46, 3.48, 3.53, 3.53

Not a lot of time between charge and discharge test.


Discharged cells: 3.07, 3.01, 2.75, 2.73

2
13.5210.25968348%1210 mAh

Charged with Car Charger. Cells: 3.36, 3.38, 3.38, 3.39


Discharged cells: 3.02, 2.95, 2.51, 2.43

2





Using new tester. 5A load

Battery was charged a while ago and left to sit.









320Ah14.4 (3.6v/cell)8v 1092655%1366 mAhCould the battery be overcharged?
3

8v979149%1224 mAh
3

8.49v772739%965 mAhBMS Added. 
3

8.55v631532%789 mAh

Charging via power may be the issue?

Discovered that I had connected the cell voltage connectors in the wrong order.

3

13.91

(3.48/cell)

11.27?8123

Cells balanced before test to: 3.52, 3.58, 3.31, 3.32

BMS is attached.

Stopped at 11.27v because 1 cell voltage had dropped too low. Needs to be better balanced or taken apart and re-purposed.

3
All: 13.5211.13805240%1006 mAh

Before charge: Cells: 3.45, 3.47, 3.30, 3.30



3
13.27v

12.2??

Bounced back maybe?

7270 mAh/ 90.58 Wh

Using new tester. 5A load

Battery was charged a while ago and left to sit.









4

B-: 13.7

C-: 13.6

P-: 12.57

9.341092455%1366 mAh

BMS Attached.

Charged with C- using Car Lion Charger

Cells: 3.46, 3.43, 3.41, 3.42

@9500mAh:  12.5V on all -Terminals

Is there a voltage regulator on the output?

@10945mAh - V=9.34

Disconnected - Cells: 2.80, 2.85, 2.87, 2.89 Restarted discharge and it said v=11.4v.


4

13.62 

B-: 13.62

C-: 13.62

P-: 13.62

9.66

Read 10.6 after disconnect.

1120256%1400 mAh

Charged on C- using iMax B6 - Took 11845 mAh over 228min


4


10350mAh / 128.77Wh

Using new tester. 5A load

Battery was charged a while ago and left to sit.









5

13.49


B-: 13.49

C-: 13.49

P-: 13.49

11.54453723%567 mAh

BMS Attached.

Charged with C- using Car Lion Charger

Cells: 3.56, 3.32, 3.32, 3.32


After discharge:

Cells: 2.28, 3.16, 3.17, 3.16

5


4498

Garbage








6
All: 13.559.84943547%1179 mAh

Charged on C- using Auto Charger


6
12.21



Using new tester. 5A load

Battery was charged a while ago and left to sit.









3,6
13.2



Combined pack 3/6

Charged using battery charger to full

Discharged at 10A using new tester


2,4


20.20 Ah / 249 Wh

Combined pack 2/4

Charged using batter charger to full

Discharged at 10A using new tester

First Stop - 20Ah @10A, 

Second Stop -  @1A


.

Notes: 

Battery pack #1

  • was disassembled into singles in order to to test single batteries.

Battery Pack #3:

  • BMS will disconnect at 8.4v which is higher than what we tested at previously.


BMS


Size: 87*35*8 (MM)


Notes:

  • Will disconnect at 8.4v which is higher than what we tested at

Packaging Options


Example 4S20P 

Packaging


Packaged in 4S8P



Installed in a 50 Caliber Ammo Box (Inside Dimensions: 5.8" L x 11" W x 7.2" H)


I bought Plano 50 Cal Ammo Box, Black

Interior dimensions: 11.25" x 5.5" x 7" (Slightly thinner by 0.3" - Doh!)


References









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