Environmental Engineering Reference
In-Depth Information
Figure 4.43 Battery Voltage as a Function of Discharge Time and
Discharge Current
If the lead-acid battery is continuously charged, it starts to produce gas at
a voltage of 14.4 V; the electrolysis decomposes the water within the electrolyte
into hydrogen and oxygen and these gases escape from the battery. Therefore,
the battery must be refilled with water from time to time. Continuous strong
gassing can damage a battery. To protect the battery, charging should be
stopped at voltages between 13.8 V and 14.4 V. However, it is advisable to
charge lead-acid batteries until they begin gassing from time to time to mix
the electrolyte thoroughly.
The batteries should be placed in a dry room at moderate temperatures.
Battery gassing can produce explosive oxyhydrogen, so good ventilation of
battery rooms is essential.
An equivalent circuit that describes battery behaviour is essential for exact
simulations. However, an equivalent circuit that describes the battery perfectly
is difficult to find, because many parameters such as temperature, current,
state of charge (SOC) or state of health influence the operation. A standing
joke is that a perfect model for a rechargeable battery is a black bucket with
hole. However, several battery models have been developed over recent
decades. One of these models, the Gretsch equivalent circuit, is described here
as an example (Gretsch, 1978).
Table 4.9 State of Charge Estimation for a 12-V Lead-Acid Battery Based on
Measured Operating Voltages
Voltage range (V)
State of charge (SOC)
>14.4
Stop charging, battery is full
13.5-14.1
Normal voltage range during charging without load
12.0-14.1
Normal voltage range during charging with load
11.5-12.7
Normal voltage range during discharging
11.4
Disconnect load, start charging
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