User manual

The impact of undercharging is felt much earlier than that of
overcharge. Hence, for cyclic applications, where the calendar life
is relatively short, it is very important to ensure that the batteries
are not undercharged. For cyclic applications, it is preferable to
err on the side of overcharge than on the side of undercharge.
The recommended charge voltage for cyclic applications is
higher than that for float applications. This is due to the fact
that in cyclic applications the time available for a recharge is
substantially less than that for float applications. To compensate
for the shorter recharge time, the charging voltage, and thereby
the charging current, in cyclic applications is raised so that more
ampere-hours can be supplied to the battery in a given time.
7.3 Float Life
The design float life of CYCLON
®
batteries is up to eight (8) to
ten (10) years at room temperature (25°C/77°F) and under proper
charging conditions. This design life has been confirmed by the
use of accelerated testing methods that are widely accepted
by both manufacturers and users of sealed-lead batteries. High
temperatures are used to accelerate the aging process of the
battery under test.
The primary failure mode of CYCLON batteries can be defined
as positive current collecting grid corrosion and growth. Because
this corrosion and growth are the result of chemical reactions
within the cell, the rate of corrosion and growth increases with
increasing temperature as expressed by the widely-accepted
Arrhenius equation, which shows that the float life of a VRLA
cell is cut in half for roughly every 8°C (14.4°F) rise in ambient
temperature. Figure 7-2 shows this relationship between ambient
temperature and float life for CYCLON single cells that have a
float life of ten years at 25°C (77°F).
Figure 7-1: Cycle Life and DOD for CYCLON
®
Battery Cells
A ten year battery, such as a CYCLON battery single cell pack
will last for five years at 33°C (91.4°F) and only 2 1/2 years at
41°C (105.8°F).
8.1 Introduction
There are two main considerations relative to the application of
CYCLON cells and batteries that should be recognised to assure
that the usage is safe and proper. These are gassing and shorting.
8.2 Gassing
Lead-acid batteries produce hydrogen and oxygen gases
internally during charging and overcharging. The gases
released or diffused must not be allowed to accumulate.
An explosion could occur if a spark were introduced.
During normal charging operation, some hydrogen gas is
released (vented) or diffused through the container walls. The
pure lead-tin grid construction as well as the extremely high
purity of lead oxides and sulphuric acid used in the manufacture
of the CYCLON battery cell all serve to minimise the amount of
hydrogen gas produced.
The minute quantities of gases that are released or diffused from
the CYCLON battery cell with recommended rates of charge and
overcharge will normally dissipate rapidly into the atmosphere.
Hydrogen gas is difficult to contain in anything but a metal or
glass enclosure. It can permeate a plastic container at a relatively
rapid rate.
Table 8-1 illustrates how little gas is generated by CYCLON
battery cells when they are under charge. The chart also shows
how much ventilation is needed to keep hydrogen gas below 1%,
2% and 4% concentration levels.
The use of this table can be understood by an example. Suppose
you have a 120V CYCLON pack using ten of the 12V, 25Ah BC
cells packs and these batteries are in a float application with the
charger set at 2.27 VPC. As a safety measure you want to design
a ventilation system that will keep hydrogen gas accumulation to
less than 1%.
Looking at the 1% cell under the 2.27 VPC column (shaded and
boldfaced), each 12V BC pack will require 0.0032 cubic feet of
airflow per hour to limit the concentration of hydrogen to 1%.
Since there are ten 12V packs, the ventilation system should be
designed for an airflow of 0.032 cubic feet per hour. This is a very
small amount of airflow.
Because of the characteristics of gases and the relative difficulty
in containing them, most applications will allow for their release
into the atmosphere. If any CYCLON batteries are being designed
into a gas-tight container, precautions must be taken so that
the gases produced during charge can be released into the
atmosphere. If hydrogen is allowed to accumulate and mix with
the atmosphere at a concentration ranging from 4% to 75% by
volume, an explosive mixture is formed that would be ignited in
the presence of a flame or spark.
0
1
2
3
4
5
6
7
8
9
10
25 35 45 55 65 75 85
Ambient temperature °C
Years to 80% of rated capacity
50% drop in float life for 8°C rise in
temperature
33°C
Chapter 8:
Safety Issues
16
Publication No: EN-CYC-AM-007 - December 2008
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