tailieunhanh - Lightweight Electric Hybrid Vehicle Design Episode 4

Tham khảo tài liệu 'lightweight electric hybrid vehicle design episode 4', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 32 Lightweight Electric lybrid Vehicle Design Ni-Cad cells BatteryType RR C Sub D D Cell capacity Ah Int. resistance milliohms Cell dimensions DxL mm 22x34 22x56 32x42 32x56 Weight gm 42 65 130 200 Int. Resistance of 4 Ah milliohms Internal Resistance is at 20 C and 50 state of charge. Fig. Typical Ni-Cad packages and capacities. INTERNAL RESISTANCE PERFORMANCE OF FAST-CHARGE NI-CAD CELLS The results discussed here are based on Sanyo products but the same trends are seen in Varta Panasonic and Saft cells. See Fig. . Why does internal resistance matter so much This is because at 25 C discharge rate the voltage drop on a V cell is as tabulated below Voltage drop on a V cell at 25 C discharge rate RR C Sub D D mV 160 mV 250 mV 280 mV The V cell is thus no longer a V cell but closer to 1 V at 20 C. Why does the 1 Ah cell win It is because it is short and fat - the others are long and thin. Cell geometry is the decisive factor for low internal resistance. Viable energy storage systems 33 Fig. Discharge test rig. To test the performance of individual cells Polaron built a string of six and charged discharged at 24 C that is 24 amps on1 Ah cells. After five cycles discharge time increased to 130 seconds and temperature rise was about 10 C. It ran for several hundred cycles with virtually no change in characteristics. This is very severe compared to the true operating conditions where the cells will have to supply 24 amps for perhaps 10 seconds under real world conditions Fig. . B UILDING A STRING OF CELLS To achieve 70 kW for 2 minutes will require ten strings of260 cells at l Ah. This is economical but not optimal. Three strings of Ah would be optimal. This corresponds to using short D cells. The use of l Ah packages does have some benefits. Spot welded connections can handle the current without special packaging. The key problem is that of automatic assembly with so .