Lithium Phosphate (LiFePO4) Battery Pack
I have 96x2=192 cells
Assumptions
LiFePO4 26650 Battery Assumptions
Specification | Value |
---|---|
Nominal Voltage | 3.2v |
Max Voltage | 3.6v |
Cutoff Voltage | 2.0v |
Capacity | 2300mAh |
Battery Spec 4S24P - 48Ah (based on salvaged batteries)
Specification | Value |
---|---|
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 Voltage | 4 |
Parallel Cells to Get Capacity 48Ah/2.0Ah | 24 |
Total Cells Required | 96 |
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.
Spec | Values |
---|---|
Make | BAE |
Model | 235C9387G1 |
Dimensions (WxLxH) | 31" X 6.5" X 3" |
Weight | 19.55 lbs |
Voltage | 40V |
Configuration | 12S8P 12*3.2v = 38.4v |
Current | 2250A |
Watt Hours | 736 wH |
Equivalent Ah for 12v | =P/V = 736/12 = 61Ah |
Battery | 26650 LiFePO4 |
Info | https://secondlifestorage.com/showthread.php?tid=5451 |
Video - Teardown | https://www.youtube.com/watch?v=AG36QB1WkuY |
Cells A123
Spec | Value |
---|---|
Model | ANR 26650 M1B |
Chemistry | LiFePO4 |
Dimensions(DxH) | 26mm(1.0") x 65.15 mm(2.6") |
Max Current | 50A |
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 |
|
Temperature Range |
|
Image |
Observations:
Battery Configuration | Estimated 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
First Discharge Test
Battery Pack | Configuration | Original Capacity | Starting Voltage | Final Voltage | Capacity (mAh) | % Capacity |
---|---|---|---|---|---|---|
1 | 4S8P | 20Ah | 12.94v (3.235v/cell) | 8v (2.0v/cell) | 3163 | 16% |
2 | 4S8P | 20Ah | 13v (3.5v/cell) | 8v (2.0v/cell) | 3234 | 16% |
3 | 4S8P | 20Ah | 13v (3.25v/cell) | 8v (2.0v/cell) | 3358 | 17% |
Thoughts:
- These batteries were not fully charged. They should have been closer to 14.4v. Need to charge and re-test.
- Did a balanced charge and they took in 11Ah (10.939 Ah) charge over 15 hours and finished at 14.4v. Once removed from the charger, they dropped to 13.9v.
Single Battery Tests
Battery | Original Capacity | Starting Voltage | Final Voltage | Capacity (mAh) | % Capacity |
---|---|---|---|---|---|
1 | 2500 | 3.6v | 1.99v | 1061 | 42% |
2 | 2500 | 3.6 | 1.99v | 1109 | 44% |
Out of 2 batteries, it appears that we have 42-44% capacity left.
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
Avg
Battery Pack Tests 4S8P
Pack | Original Capacity | Starting Voltage | Final Voltage | Capacity (mAh) | % Capacity | ~Capacity/Cell | Notes |
---|---|---|---|---|---|---|---|
2 | 20Ah | 14.4 (3.6v/cell) | 8v | 10156 | 51% | 1270 mAh | |
3 | 20Ah | 14.4 (3.6v/cell) | 8v | 10926 | 55% | 1366 mAh | Could the battery be overcharged? |
3 | 8v | 9791 | 49% | 1224 mAh | |||
3 | 8.49v | 7727 | 39% | 965 mAh | BMS Added. | ||
3 | 8.55v | 6315 | 32% | 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 | Cells balanced before test to: 3.52, 3.58, 3.31, 3.32 |
.
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
Reference | URL |
---|---|
Buying Used Batteries | https://batteryhookup.com/ |
A123 Spec | https://www.batteryspace.com/a123-lifepo4-26650-rechargeable-cell-3-3v-2500-mah-50a-rate-8-25wh-anr26650m1b---un38-3-passed-and-iec-listed.aspx |
Battery Pack Calculator | http://repackr.com/ |
LiFePower LiFePO4 Batteries | https://www.sawtechnology.com/solarengine-battery |
Building a pack in Ammo Boxes | https://www.youtube.com/watch?v=9CwnX9tovAM |