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FIAMM Energy Technology S.p.A
Installation & Operating Instruction -Technical Manual
Edition 03/2018 Rev.7
these instruments will be
different to the values
stated in FET Product Sheet.
2.6.
Service life
According to the main international standards a battery is
considered at the end of its service life whenever
delivering less than 80% of its nominal capacity. The
recommended operating temperature range is between
10°C to 30°C (FHT range peaks up to 45°C). FET
VRLA batteries can operate over a temperature range of
–20 to +50°C and higher; operation at temperature higher
than 20°C reduces life expectancy according to the graph
in figure 4.
Fig. 4: Expected service life vs. working temperature
2.7.
Gassing
All Lead Acid Batteries emits gases during the charge
process. FET VRLA batteries have a high recombination
efficiency (>98%) and for cells operated at 20°C under
normal operating conditions venting is virtually
negligible. Laboratory test measurements show the
following gassing rates:
2 ml/Ah/cell/month at a float voltage of 2.27 V/cell
10 ml/Ah/cell/month at a recharge voltage of 2.40
V/cell.
The quantity of gas given off in the air (it basically
consists of 80-90% hydrogen) is very low and thus it is
clear that FET VRLA batteries can be installed in rooms
containing electric equipment with no explosion danger
or corrosion problems under normal conditions. In any
case these rooms or cabinets must have natural or forced
ventilation and not be fully sealed. Please refer to
“VENTILATION” for information on required air
exchange.
2.8.
Operation of batteries in parallel
When the required capacity exceeds the capacity of a
single string of batteries, it is possible to connect more
strings in parallel paying attention to the following
guidelines:
in each string only cells or monoblocs of the same
type, model, manufacturing date and quantity
should be used;
a symmetrical layout of the batteries should be
designed (i.e. length and type of connector) to
minimize possible resistance variations;
the quantity of strings in parallel should be
reasonable in terms of layout and application.
Usually 4 strings could be connected in parallel.
However, depending on strings voltage and
cables length, a higher number of strings could be
safely connected to reach required total capacity.
2.9.
Open circuit voltage - State of charge
The measurement of the open circuit voltage (battery has
to be disconnect from charger system for at least 24
hours) provides an approximate indication of the state of
charge of the cells.
Fig. 5: Approximate state of Charge versus Open circuit cell voltage
20
30
40
50
TEMPERATURE [°C]
0
20
40
60
80
100
120
B
a
tt
e
ry
L
if
e
(
%
)
1.95
2.00
2.05
2.10
2.15
0%
20%
40%
60%
80%
100%
O
pe
n
C
ir
cui
t
V
ol
ta
ge
[
V
/c
e
ll.
]
State of Charge [%]