Environmental Engineering Reference
In-Depth Information
oxidation-reduction reactions, which convert chemical energy to electrical energy
(see
Sect. 3.1
). They consist of one or more cells joined together and generally
connected in series, depending on the voltage or capacity required by the designer
[
13
]. After their discharge, batteries are recharged electrically to their original state
by passing a controlled current through them in the reverse direction to that of
discharge. The term battery pack is often used by electric vehicle designers to refer
to the overall storage system composed by more batteries connected in series or
parallel, with the function of supplying the electric drive.
Next sub-sections report the definition of the main operative parameters that
characterize the battery working and some details about the electrochemistry of
different types of batteries.
5.3.1 Main Operative Parameters of Batteries
5.3.1.1 Battery Voltage
The battery voltage is the voltage value measured at the battery terminals when the
battery is delivering energy. The nominal voltage for a battery is a voltage ref-
erence value which the battery is referred to and it gives approximately the voltage
when the battery works properly in the working range defined by the manufacturer.
Traction batteries are usually referred as 6 or 12 V nominal voltage batteries, and
these units are connected in series to produce the required voltage. In practice, this
voltage changes as a function of the battery current: the voltage falls when the
current is given out and rises when the battery is being charged. For example,
Figs.
5.9
and
5.10
show the lead-acid cell voltage as a function of time for a
constant current charge and discharge.
The voltage drop observed in
5.10
, typically 0.02-0.03 V, at the beginning of
discharge, is related to the delay of the anodic discharge reaction (see
Sect. 5.3.2
),
due to the electrolyte saturation with lead ions.
Fig. 5.9 Lead-acid cell
voltage charge for a constant
charge as a function of time
3
2.6
2.2
1.8
0
2
4
6
8
10
Charging time [h]
