Handbook of Electrical Installation Practice - BeKnowledge

144 Handbook of Electrical Installation Practice
Set
point
Series
regulator
Regulator with
battery voltage
sensing
the boost charge position, enables positive action to be taken to prevent possible
permanent damage to the battery.
Boost charging is not usually required with sealed lead-acid cells. However, if
external requirements call for this facility, care should be taken to follow the battery
manufacturer’s specifications.
A low-voltage alarm, set at a level towards the end-of-discharge voltage, reveals
that the battery is approaching the end of its design performance. Other alarms
that may be useful are an earth-fault alarm, and for flooded cell type batteries
an electrolyte level-low alarm, which indicates that the electrolyte needs topping up.
As far as meters are concerned, a voltmeter indicates that the system is operating
correctly; an ammeter, however, is an unnecessary expense in most cases.
Current levels in constant-voltage chargers are factory preset, and in any case during
the final float stage, the current would typically be only 0.005 the rated capacity of
the battery.
Charger techniques for regulated d.c. loads
Where the load includes telecommunications equipment and instrumentation, and
the d.c. standby supply must be regulated to within 5–10% of the nominal voltage,
problems may arise unless precautions are taken to boost charge the battery in such
a way that the system voltage does not rise to an unacceptable level.
+ –
regulator
Fig. 6.10 Circuit and waveform of a typical transistor constant-voltage charger.