Operator`s manual
o 12.4
12.2
5
State of Charge i%1
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36
Installation, Operation and Maintainance of Buoy Operated Automatic Meteorological Stations
Power Supply
4.2.3 State of the Battery
To avoid either deep discharge or overcharge, the amount of energy in the battery needs to be monitored. The State
of Charge (SoC) is a good indicator for this. Table 2 presents the SoC for the Yuasa 24AH sealed lead-acid battery as
function of the voltage, for a situation when no load is attached. This is called the Open Circuit Voltage (OCV). Obvi-
ously, actual performance varies per individual battery, and therefore a lower and upper limit for the OCV has been
defined.
State of Charge[%]
100
90
80
70
60
50
40
30
20
10
0
Open Circuit Voltage(lower limit [V]
12.80
12.65
12.50
12.35
12.20
12.05
11.90
11.75
11.60
11.45
11.30
Open Circuit Voltage(upper limit) [V]
12.80
12.65
12.50
12.35
12.20
12.05
11.90
11.75
11.60
11.45
11.30
Table 2: SoC Versus Open Circuit Voltage for a Yuasa 7 Ahr Lead Acid Gel Battery
As indicated in Table 2, lead-acid rechargeable batteries have no uniform characteristics. This is partly because
of the intrinsic behavior of batteries, but also a result of the individual history of a battery. A single deep discharge
event will certainly change the performance of a battery.
It is for these reasons that we cannot define a clear, univocal relation between State of Charge and Open Circuit
Voltage. Instead, such a relation falls within a band defined by a known upper and lower limit (see figure 14). However,
one can obtain a good indication of the behavior of a battery by knowing the voltage in the fully charged state (SoC
100%), and presuming a straight line downwards from this point interpolated between the upper and lower limits.
The user should follow the below guidelines to construct the relation ‘State of Charge versus Open Circuit Voltage’
for an individual Yuasa 24AH battery:
• Makesurethebatteryisfullycharged(tothisend,chargethebatteryfor48hoursusingtheCH12Rcharging
unit; see paragraph 4.2.4 for detailed instructions on recharging a battery)
• Contactthevoltmeter’sleadtothepositiveandnegativebatteryterminals,andreadthevoltage;
• PresumethisvoltagecorrespondswithSoC100%;henceastartingpointofthecurveisobtained;
• Drawastraightlinestartingfromthispointinterpolatedbetweentheupperandlowerlimits.
Figure 14 presents an example of this procedure. It presumes a SoC 100% voltage of 12.9 V.