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 |
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| 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
Single Battery Tests
The rated capacity of these batteries is 2500 mAh. It appears that the average capacity seems to be around: 1186 mAh.
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 | BMS Added |
| 2 | 14.0 ( 3.5v/cell) | 10.25 | 9935 | 50% | 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 | 13.52 | 10.25 | 9683 | 48% | 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. | ||||||
| 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 (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: 13.52 | 11.13 | 8052 | 40% | 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 | 9.34 | 10924 | 55% | 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. | 11202 | 56% | 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 | 11.54 | 4537 | 23% | 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: 13.55 | 9.84 | 9435 | 47% | 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
| 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 |