64
ELECTRIC VEHICLE BATTERY CAPACITY
Figure 3β11
Change in resistance with discharge.
Change in Resistance (milliohms)
16 14 12 10 8 6 4 2 0 4
10
20
30
40
50
60
70
80
90
98
% DOD 0-10 W/kg
10-79 W/kg
79-50 W/kg
50-20 W/kg
Identical to the VRLA battery, a 90-Ahr NiMH battery undergoes a similar change in the battery resistance. The discharge variation is the worst-case resistance calculated for the performance of the battery pack when the EV goes from a cruising speed of approximately 30 mph (20 A) to a hard acceleration of 60 mph (170 A). Figure 3β12 illustrates a change in the battery resistance for a regenerative charge applied during the driving at 15 W/kg and 60 W/kg, respectively.
ENERGY BALANCES FOR THE ELECTRIC VEHICLE Several factors influence the EV energy balance. The energy removed from the traction batteries, defined as a positive power gain is expressed in kilowatts (kW). The energy consumption during the time interval is calculated as the total power loss multiplied by the time increment and is termed as a negative power gain expressed in kilowatts (kW). The factors influencing the energy balance of the EV include: β’ β’
Aerodynamic drag losses Rolling resistance losses
