Evaluation of Electric Vehicles as an Alternative for Work Trip and ...

of discharge (DOD) of the ALAB. The drive utilized only fifty percent
of the battery capacity (50% DOD).
The upper half of the graph records battery cell voltage during
the entire discharge. The voltage values are reported as a cell voltage
in a six-cell battery. Each cell has a nominal two volts, so six cells
combine to produced the nominal 12-Volt battery. Cell voltages are
reported in three lines for the highest, lowest and average batteries in
a 13-battery pack. The two lines representing batteries with highest
and average voltage are very close to each other on the graph. At fifty
percent DOD, average voltage is approximately 1.95 V., very close to the
nominal value. Only battery #4 had low voltage. It is represented as
the lowest-voltage line on the graph. From 44 percent to 49 percent
DOD, voltage of battery #4 plunges from 1.9 V to 1.7 V, below the 1.8-V.
limit, indicating permanent capacity loss has occurred in that battery
(#4). The ALAB car was taken out of service in August for replacement
of battery #4. Data from the 68 single-charge drives with the original
13-battery pack is presented in Figure 9.
Distance (miles)
70
60
50
40
30
20
10
0
1
4
7
10
13
16
19
22
25
28
and work trips shows that the majority of drives were accomplished
26
31
34
37
40
Drives (sorted by length)
FIGURE 9 Single-charge distances from 68 commuting and work-trip drives
in ALAB Car during 1998 before Battery #4 failed and was
replaced
The distribution of single-charge distances driven in commuting
43
46
49
52
55
58
61
64
67