This battery was a design conceived by KE6MT after he received the Mk IV battery from me. Rex drew up a flat pack 4S2P design that I would spot weld for him, and he would complete.
Rex later went on a deep dive creating an Arduino-based cell monitor showing each 2P combination’s voltage for the 4 in series.
General Specs:
Created: November 2019.
Cells: LiitoKala 32700 7Ah 3.2v LiFePO4.
BMS: HX-4S-F100A.
Configuration: 4S2P.
New since last make: Flat unfinished build, only connections spot-welded, and parts provided (BMS).
Current Owner: KE6MT Rex.
Cell specs:
LiitoKala 32700 cells
Nominal Capacity: 7Ah (6.5Ah in practical use)
Nominal Voltage: 3.2V per cell
Dimensions: 32mm x 70 mm
Weight: 145g per cell
Internal resistance: less than 8 mΩ
Cycle life: > 2000 cycles, DOD at 80%
Input charging voltage: 3.65v/cell
Input charging current: 3A
Continuous discharge current: 30A
Max discharge current (pulse): 6C
Discharge cut-off voltage: 2.5V
Charging temp: 0-45°C
Discharge temp: -20°C – 60°C
Storage temp: -20°C – 45°C
BMS Specs:
HX-4S-F100A BMS
1. Continuous discharge current: 100A
2. Instantaneous discharge current: 120A
3. Charging Voltage: Iron lithium charger 14.8V (Switching power supply: 15V-16V)
4. Charging Current: 10A(Max)
5. Overcharge detection voltage: 3.75V±0.05V
6. Over charge detection delay time: 1300 ms
7. Over charge release voltage: 3.6V±0.05V
8. Electricity equalization detection voltage: 3.6V±0.05V
9. Electricity equalization release voltage: 3.59V±0.05V
10. Electricity equalization current: 58mA
11. Over discharge detection voltage: 2.1V±0.08V
12. Over discharge detection delay time: 145s
13. Over discharge release voltage: 2.30V±0.1V
14. Over current detection voltage: 200mV
15. Over current detection delay time: 20mS
16. Over current protection current: 120A±10A
17. Over current protection release: Cut off the load
18. Detection condition: Exterior load short circuit
19. Detection delay time: 300us
20. Over current protection: Cut off the load
21. Temperature Protection: Can use an external temperature switch
22. Main circuit conduction resistance ~20mΩ
23. Working current: ~30uA
24. Working Temperature: -20°C to 80°C
25. Size: 70 x 60 x 8.5mm
