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.
Battery Pack Tests 4S8P
Battery Pack | Original Capacity | Starting Voltage | Final Voltage | Capacity (mAh) | % Capacity | ~Capacity/Cell | Comments |
---|---|---|---|---|---|---|---|
2 | 20Ah | 14.4 (3.6v/cell) | 8v | 10156 | 51% | 1270 mAh | |
3 | 20Ah | 14.4 (3.6v/cell) | 8v | 10926 | 55% | 1366 mAh | Overcharged maybe? |
3 | 8v | 9791 | 49% | 1224 mAh | |||
3 | 8.49v | 7727 | 39% | 965 mAh | BMS Added | ||
3 | 8.55v | 6315 | 32% | 789 mAh | WTF? - Charging via power may be the issue? |
Notes:
Battery pack #1 was disassembled into singles in order to to test single batteries.
Battery Pack #3:
Notes:
- BMS will disconnect at 8.4v which is higher than what we tested at previously.
- We are charging on the P- connection. Maybe this is causing some of the protection circuitry to activate.
BMS
Size: 87*35*8 (MM)
Notes:
- Will disconnect at 8.4v which is higher than what we tested at
- We are charging on the P- connection. Maybe this is causing some of the protection circuitry to activate.
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 |