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Section 5 |
5.1 oPeration
!
caution!
P lease ensure that the rated output current of the 12VDC or 24VDC power
supply is only up to 25A.
As already stated at in Section 3.1, this unit is a passive device and functions only as an
interface between the external power supply, the battery and the DC load.
Switch ON the external power supply to power on the load and also to start charging
the battery. If the power supply fails or is switched OFF, the load will be immediately fed
by the battery. When the load is supplied by the battery, the battery will start draining
and its voltage will continue to drop. During this time, the voltage at the Load Terminals
(4&3, Fig 2.2) will be up to 0.5V lower than the voltage at the Battery Terminals (5&3,
Fig 2.2) due to the Forward Voltage Drop across the internal Schottky Diode D2.
5.2 Protecting the batterY against DeeP Discharge
For longer life, Lead Acid Batteries should not be allowed to discharge more than
80%. For example, a 12V / 24V loaded battery at load current of C/10 Amps (C is the Ah
capacity) will be 100% discharged at around 11V / 22V and 80% discharged at 11.5V / 23V.
It is recommended that a suitable "Low Voltage Disconnect Device", also called "Battery
Guard", may be used in series with Positive line of the load for protection against deep
discharge of the battery. battery guard, Model no. bg-40, made by samlex america, inc.
may be considered.
5.3 oVerLoaD anD short circuit Protection
i
inFo
E xplanation given below is based on use of external power supply with
"Constant Current Limit" value of 25A. In a Constant Current Limited Power
Supply, when the Current Limit value is reached, the output voltage will not be
regulated and will drop.
If the load tries to draw current higher than the current limit value of the external
power supply (25A), the output voltage of the external power supply will not be
regulated and the voltage at the Load Terminals (4&3, Fig 2.2) will drop. Portion of
overload current beyond the current limit value of the external power supply (25A)
will now be fed from the battery and the battery will start draining at this differential
current. The voltage at the Battery Terminals (5&3, Fig 2.2) will start dropping and will
be equal to the voltage corresponding to state of discharge of the battery. The voltage
at the Load Terminals (4&3, Fig 2.2) will be up to 0.5V below the voltage at the Battery
Terminals (5&3, Fig 2.2). External 25A Fuse (F2) on the load side will blow.
operation and Protections
SAMLEX AMERICA INC. | 9
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