Overview
We will be building a 100Ah LiFePO4 battery using cell modules we purchased from BatteryHookup.com.
Parts
| Part | Qty | Picture | URL |
|---|---|---|---|
| 3.2V 100ah MODULES | 4 |
| https://web.archive.org/web/20210516124542/https://batteryhookup.com/products/new-battery-hookup-lifep04-32650-3-2v-5000mah-cells-1 |
| 100A Smart LiFePO4 4S BMS | 1 |
| https://batteryhookup.com/products/12v-lifepo4-smart-bms-w-low-temp-cutoff |
Bluetooth Module (Optional) | 1 |
| https://batteryhookup.com/collections/accessories/products/bluetooth-module-for-battery-hookup-bms https://www.aliexpress.com/item/4000546700379.html?spm=a2g0o.order_list.0.0.21ef1802QOiBrg |
| 50-Cal Black Ammo Box with Tray | 1 |
Dimensions: 15.4 x 10.2 x 7.7 in. | https://www.princessauto.com/en/50-cal-black-ammo-box-with-tray/product/PA0008985962?skuId=8985962 |
| Carkio 8mm (5/16") M8 Stud Premium Remote Battery Power Junction Post Connector Terminal Kit 2pcs | 1 |
| https://www.amazon.ca/gp/product/B08J7TGPK5/ref=ppx_yo_dt_b_asin_title_o08_s00?ie=UTF8&th=1 |
| 5/16 Ring Terminals | 5 |
| |
5/16 bolt and lock nut | 7 |
| |
| 10 AWG Wire (red and black) |
| Princess Auto | |
| Strap | 1 |
| Princess Auto |
Modules
These modules were built specifically to handle up to 100a (1c) charge and discharge continuous. Standard lithium ion capacity tests are done at 0.2c which would be 20a continuous. The cells can handle up to 3c but the nickel and wiring was sized to handle 1c loads which is realistically where you want to be.
| NOMINAL VOLTAGE | 3.2V |
|---|---|
| CAPACITY | 100ah (105ah+ is being reported by customers) |
| WATT HOURS | 320 |
| FULLY CHARGED VOLTAGE | 3.65V |
| FULLY DISCHARGED VOLTAGE | 2.5V |
| MAX CONTINUOUS CHARGE | 100A (1C) |
| MAX CONTINUOUS DISCHARGE | 100A (1C) |
| MAX PULSE DISCHARGE (10 SECONDS) | 200A (2C) |
| MODULE WEIGHT | 6.5 lbs |
| MODULE DIMENSION | 7.5" X 5.5" X 3" |
BMS
LiFePO4 4S 100a BMS W/ LOW TEMP CUTOFF
Connections
Specifications
| Manufacturer | Xiaoxiang |
|---|---|
| Model | SP04S020A |
| Configuration | 4S 100A |
| Chemistry | Lifepo4 3.2V |
| Configuration | Common port with balance |
| Part Number | 16270007 |
Settings
| Overcharge Voltage per Cell | 3.65 |
|---|---|
| Over Discharge Voltage per Cell | 2.5 |
| Discharge Continuous Amps | 100A |
| 10 second Discharge Burst | 200A |
| Charge Continuous Amps | 60A |
| Balancing Current | 60mA |
| Low temp cutoff | 32° F (0° C) |
| High temp cutoff | 167° F (75° C) |
Bluetooth Module
The Bluetooth module is an optional accessory that may be used to configure and monitor the BMS.
To use, simply plug the 4-pin connector into the BMS. The BMS must be connected to the battery, with the balance lead connected in order for the Bluetooth module to operate.
Note that other Bluetooth modules are not compatible.
For best reception, mount the module high, ideally away from metal. Do not mount it inside of a metal enclosure. The Bluetooth module may be left connected to the BMS for long periods of time. It will go into a deep sleep mode when not in use.
Software (Requires Bluetooth Module)
XiaoXang BMS
https://apps.apple.com/us/app/xiaoxiang-bms/id1375405426
Big Battery
https://apps.apple.com/us/app/bigbattery-com/id1576090574
XiaoXiang Electric
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 |