Environmental Engineering Reference
In-Depth Information
is a direct measure of available plate surface area and it relates directly to the
batteries' ability to produce power. Conductance also has a direct proportionality to
cold cranking amperes, and the higher the conductance, generally the healthier the
battery is. As batteries age, the conductance decreases due to sulphation of the
plates. The battery immittance method is repeatable and accurate across a range of
batteries. It is immediately capable of detecting defective cells and cell inter-
connector integrity. When several discrete frequencies (
N
) are used to characterize
the battery in discrete immittance spectroscopy (DIS), the results can be expressed
as a 2
N
element circuit model. A representative model is shown in Figure 10.45.
G
2
G
N
G
1
L
1
C
N
V
o
C
2
Figure 10.45 Discrete immittance spectroscopy battery characterization model
The measured admittance of the battery using DIS techniques reveals that
conductance increases with increasing frequency, whereas immittance starts as a
capacitive value and decreases through zero (approximately when conductance
maximizes and flattens out or declines again), then becoming progressively more
negative as frequency is raised further. The
N
discrete frequencies used are related
to the battery capacity, but in general are low hertz to 1 kHz. At very low fre-
quencies the conductance is low and immittance is high, revealing the capacitive
nature of the battery, but with low available area to deliver power. For higher
frequencies the conductance is higher.
A more recent model of the lead-acid battery is based on measure of available
energy [31]. This method is consistent with hybrid vehicle needs of ESS available
energy and SOH rather than a crude estimate of SOC. With the available energy
model, the battery's characteristics are again modelled with lumped parameter
values, but in this case a very accurate dynamic model is described with 16 indi-
vidual parameters. In this model, deliverable energy is characterized by parameters
that are only functions of voltage, current, temperature and time. The basic premise
of the available energy model is that SOC is a measure of relative capacity under
nominal conditions and reflects only average performance based on ampere-hours
removed and it does not characterize the battery power delivery capability. The
available energy model is based on two words: Word 1 are essential parameters for
