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We will be building a 100Ah LiFePO4 battery using cell modules we purchased from BatteryHookup.com.
Parts
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https://apps.apple.com/th/app/xiaoxiangelectric/id1576622653
Build
Battery Case
| Measurement | Width/Length/Height |
|---|---|
| Battery Cell | 7.5" X 3" x 5.5" |
| Battery Cells x 4 | 7.5" X 12" x 5.5" |
| Selected Box(Exterior) | 7.7" x 15.4" x 10.2" |
| Selected Box(Interior) | 7" x ? |
We couldn't find a box with the ideal interior dimension of 7.5" x 12", so we went with this bigger ammo box and placed the cells on their sides.
Cell Top Balancing
In order to ensure we get the max capacity out of our new battery, we need to top balance the cells.
See https://www.youtube.com/watch?v=x5ABvbbics8
Charge the battery in it's 4S configuration and then disassemble.
Connect all cells together in parallel and charge at 3.65v until very little current is flowing into the batteries.
Build Pictures
BMS Configuration
Capacity Tests
Battery 1 - 112 Ah
Battery 2 - 95Ah - Before Top Balancing
Battery 2 - 118Ah - After Top Balancing
Cost Breakdown
I ordered enough to build 3 batteries in order to save on shipping.
| Item | Cost | Currency | Exchange Rate | CA$ |
|---|---|---|---|---|
4 x 3.2V 100ah MODULES $240.00 US - 5% Discount | $228.00 | US | 0.750410380676933 | $303.83 |
Smart BMS $74.99.00 US - 5% Discount | $71.24 | US | 0.750410380676933 | $94.93 |
| Shipping ($68.35/3) | $22.78 | US | 0.750410380676933 | $30.35 |
| Duty ($145.41/3) | $48.47 | CA | - | $48.47 |
| My USAddress ($12.00/3) | $4.00 | US | 0.750410380676933 | $5.33 |
| Bluetooth Module | $10.16 | CA | - | $10.16 |
| Power Junction Post ($48.96/3) | $16.32 | CA | - | $16.32 |
| $509.39 |
Other Costs
| Item | Cost | Currency | Exchange | CA$ |
|---|---|---|---|---|
| Ammo Box ($16.99 + HST) | $19.19 | CA | - | $19.19 |
| 5x 5/16" Ring Terminal | ||||
| 10 AWG Red Wire | ||||
| 10 AWG Black Wire | ||||
| Solder | - | |||
| Strap | $3.00 | |||
| Heat Shrink Tubing | ||||
| 5/16 Nuts and Bolts | ||||
| Zip Ties | ||||
| Duct Tape | ||||
| Total |
Appendix
BMS Protocol
Command
Response
Baud Rate: 9600 bps
Sample - Read Info
Command
| StartBit | Read/Write | Command | Length | Data | Checksum | StopBit |
|---|---|---|---|---|---|---|
| DD | A5 | 03 | 00 | - | FF FD | 77 |
Checksum Calculation = (Command + Length + Data) XOR 0xFFFF + 1
= (0x03 + 0x00) XOR 0xFFFF + 1
= 0xFFFD
Response
| StartBit | Command | Status | Length | Data | Checksum | StopBit |
|---|---|---|---|---|---|---|
| DD | 03 | 00 | 1B | 17 00 00 00 02 D0 03 E8 00 00 20 78 00 00 00 00 00 00 10 48 03 0F 02 0B 76 0B 82 | FB FF | 77 |
Checksum Calculation = (Status + Length + Data) XOR 0xFFFF + 1
= 0x00 + 0x1B + data[] XOR 0xFFFF +1
= 0x0401 XOR 0xFFF + 1
= 0xFBFE + 1
= 0xFBFF
References
| Reference | URL |
|---|---|
| Smart BMS | https://batteryhookup.com/products/12v-lifepo4-smart-bms-w-low-temp-cutoff |
| 3.2V 100ah MODULES | https://web.archive.org/web/20210516124542/https://batteryhookup.com/products/new-battery-hookup-lifep04-32650-3-2v-5000mah-cells-1 |
| BMS Manual | |
| Xiaoxiang BMS Manual | https://github.com/smagicld/xiaoxiangBMS |
| Software | https://www.lithiumbatterypcb.com/smart-bms-software-download/ |
| OverkillSolar BMS Files | https://github.com/FurTrader/OverkillSolarBMS |
| Arduino Library | https://github.com/FurTrader/OverkillSolarBMS/tree/master/Arduino |
| Communication Protocol | |
Communication Protocol | |
Build Video $420 100AH LiFePO4 Build - BatteryHookup.com Modules - Super Easy Assembly! COMPLETE DIY GUIDE! | https://www.youtube.com/watch?v=uN1h0XIpfTg&t=1401s |
| DIY 100AH LIFEPO4 BATTERY PARTS LIST | https://jasonoid.com/diy100ahlifepo4/ |
| How to Top Balance LiFePO4 Battery Cells Quickly (and when you need to do it) | https://www.youtube.com/watch?v=x5ABvbbics8 |