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 |
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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 | Expected Capacity | Starting Voltage | Final Voltage | Capacity (mAh) | % Capacity |
|---|---|---|---|---|---|---|
| 1 | 4S8P | 16Ah | 12.94v (3.235v/cell) | 8v (2.0v/cell) | 3163 | 20% |
| 2 | 4S8P | 16Ah | 13v (3.5v/cell) | 8v (2.0v/cell) | 3234 | 20% |
| 3 | 4S8P | 16Ah | 13v (3.25v/cell) | 8v (2.0v/cell) | 3358 | 21% |
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 | Expected Capacity | Starting Voltage | Final Voltage | Capacity (mAh) | % Capacity |
|---|---|---|---|---|---|
| 1 | 2000 | 3.6v | 1.99v | 1061 | 53% |
| 2 | 2000 | 3.6 | 1.99v | 1109 | 55% |
Out of 2 batteries, it appears that we have 50% capacity left. 
Battery Pack Tests
| Battery Pack | Configuration | Expected Capacity | Starting Voltage | Final Voltage | Capacity (mAh) | % Capacity |
|---|---|---|---|---|---|---|
| 2 | 4S8P | 16Ah | 14.4 (3.6v/cell) | 8v (2.0v/cell) | ||
| 3 | 4S8P | 16Ah | 14.4 (3.6v/cell) | 8v (2.0v/cell) |
Notes:
Battery pack #1 was disassembled into singles in order to to test single batteries.
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 |