Environmental Engineering Reference
In-Depth Information
Figure 4.41
Charging and Discharging a Lead-Acid Battery
density changes with the temperature and charge state. An acid density meter
or a voltmeter can indicate the charge state of a battery. Since the nominal
voltage of one lead-acid battery cell is 2 V, six cells are connected in series to
get the common operating voltage of 12 V. The number of cells can be adapted
for other voltage levels.
Figure 4.41 illustrates the chemical reactions inside the lead-acid battery;
they are represented by the following equations:
Negative electrode:
(4.92)
(4.93)
(4.94)
When discharging a lead-acid battery, the electrode material and the
electrolyte react to form lead sulphate (PbSO
4
). This reaction releases
electrons that can be used as electrical energy by the consumer. Electrical
energy must be fed into the battery for charging. The PbSO
4
at the electrodes
transform to Pb and PbO
2
again. The charging process needs more energy
than is set free during discharging. The charge efficiency is the ratio of the
discharge over the charge. For the charge efficiency, a distinction is made
between the
Ah efficiency
η
Wh
. The Ah efficiency is
calculated on the basis of integrated currents; the Wh efficiency considers
currents and voltages during the discharge and charge periods needed to
regain the same charge level as follows:
η
Ah
and the
Wh efficiency
