User Manual

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Charge Output Regulation and Accuracy
To ensure the correct voltage is set accurately, when
adjusting the output voltage of a constant voltage charger,
all adjustments must be made with the charger “ON
LOAD”. Adjusting the output voltage with the charger in
an “OFF LOAD” condition may result in undercharging.
The constant voltage range required by a battery is always
defined as the voltage range applied to a battery which is
fully charged. Therefore, a charger having the output
characteristics illustrated in Figure 27, should be adjusted
with the output voltage based on point A. The most
important factor in adjusting charger output voltage is
the accuracy at point A, which should be in the range of
2.275vpc ± 0.005 volts per cell; however this accuracy is not
normally required over the entire range of the load. A
charger adjusted in accordance with Figure 27 will never
damage a battery, even if the charger has the
characteristics shown by the broken line in Figure 27.
Initial Charge Current Limit
A discharged battery will accept a high charging current
at the initial stage of charging. High charging current can
cause abnormal internal heating which may damage the
battery. Therefore, when applying a suitable voltage to
recharge a battery that is being used in a recycling
application it is necessary to limit the charging current to
a value of 0.25C Amps. However, in float/standby
use, Yuasa NP batteries are designed so that even if the
available charging current is higher than the
recommended limit, they will not accept more than 2C
Amps and the charging current will fall to a relatively
small value in a very brief period of time.
Normally, therefore, in the majority of float/standby
applications no current limit is required. Figure 26 shows
current acceptance in NP batteries charged at a constant
voltage of 2.30 vpc without current limit.
When designing a charger, it is recommended that suitable
circuitry is employed to prevent damage to the charger
caused by short circuiting the charger output or
connecting it in reverse polarity to the battery. The use of
current limiting and heat sensing circuits fitted within the
charger are normally sufficient for the purpose.