Lithium Ion Battery Pack (18650)
Assumptions
18650 Battery Assumptions
| Specification | Value |
|---|---|
| Nominal Voltage | 3.7v |
| Max Voltage | 4.2v |
| Cutoff Voltage | 3.0v |
| Capacity | 2500mAh |
Battery Spec 3S24P - 60Ah
| Specification | Value |
|---|---|
| Nominal Voltage (3 x 3.7v) | 11.1v |
| Max Voltage (3 x 4.2v) | 12.6 |
| Min Voltage (3 x 3.0v) | 9v |
| Cells in Series for Voltage | 3 |
Parallel Cells to Get Capacity 60Ah/2.0Ah | 30 |
| Total Cells Required | 90 |
Dimensions (W x L x H) 1 cell: 18mm x 65mm pack size: 18*3 x 18*24 x 65 | 54mm x 432 mm x 65mm |
If battery stops being useful at 10.8 for some appliances (AC Inverter), then we would end up getting 50% the capacity of the 3S battery pack.
My solar battery charger supports the 3S configuration.
Battery Spec 4S20P - 40Ah
| Specification | Value |
|---|---|
| Nominal Voltage (4 x 3.7v) | 14.8v |
| Max Voltage (4 x 4.2v) | 16.8v |
| Min Voltage (4 x 3.0v) | 12.0v |
| Cells in Series for Voltage | 4 |
Parallel Cells to Get Capacity 40Ah/2.0Ah | 20 |
| Total Cells Required | 80 |
Would need to step down the voltage to 12v which may introduce some losses but would allow us to use the full capacity of the batteries.
Test Results of Batteries
Spreadsheet: 88af-18650.xls
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 (LxDxH) | 31" X 6.5" X 3" |
| 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 |
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| 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
Battery Charger
Solar Charger
ALLPOWERS 20A Solar Charge Controller Solar Panel Battery Intelligent Regulator with USB Port Display 12V/24V
What battery type is this controller supported?
A: (1)B-01=LEAD-ACID, 12V; B-02=LITHIUM ION 3s, 3*3.7V=11.1V; B03=LIFePO4 4s, 4*3.2V=12.8V. (B01 is the default type, If you would like to to switch to another 2 types, please select it manually.)
Could charge the battery with by adding a power supply to mimic the solar panel.
Max Input: 18V, 320W, 17A
Battery Examples
Tesla's Power Wall
| Capacity | Ah @12V | Cost |
|---|---|---|
| 7 Kwh | =7000/12 =583 Ah | $3,000 US |
| 10 Kwh | =10000/12 =833 Ah | $3,500 US |
Jehu's Power Wall
| Spec | Details |
|---|---|
| Capacity | 4.4Kwh |
| Ah @12V | 366 Ah |
| #cells | 600 |
| Cell | 18650 |