Samlex America SEC-4825BRM - Manual (Page 8)

8 | SAMLEX AMERICA INC. SAMLEX AMERICA INC. | 9
Section 3 | Design & Principle of operation
* NOTE: It is likely that due to drift in the pre-set values of components, the minimum
internal preload current may not be suffi cient to provide adequate feedback signal
strength resulting in shut down of one or more modules when no external load is
present (The associated PSM Status LED will fl ash and also, the associated signal for
remote indication will oscillate between High and Low). As soon as external load is
applied to the unit, the feed back signal strength will increase and the PSM(s) that
were shut down will also operate normally.
The output is delivered through an isolating Schottky diode to enable connection of
external 48V battery (not supplied) for un-interrupted DC power output. The external
backup battery is kept charged by “Taper Type of Float Voltage Charging” through a
current limiting series resistor that limits the maximum charging current to 2A when the
battery is completely discharged.
The SMPS Section along with the Battery Backup and Charging Section work as a DC
Uninterruptible Power Source (DC UPS) in conjunction with an external 48V, Lead Acid
backup battery (battery is not supplied). As long as 120VAC input power is available,
the unit will put out 54.8VDC to 54.2VDC at the Load Terminals (7A, 7B - Fig 2.1). At
the same time, charging current of up to a maximum of 2A (when battery is completely
discharged to Standing Voltage of 42.8V) will be fed through the Battery Terminals (8A,
8B - Fig 2.1) to charge the external battery. The voltage at the Battery Terminals (8A, 8B
- Fig 2.1) will always be clamped to the actual voltage of the battery corresponding to its
State of Charge. If AC input power fails, the DC load will be instantaneously transferred
to the external 48V backup battery and the battery will start discharging. When AC
input power is restored, the DC load will once again be transferred instantaneously to
the Power Supply Section and the external backup battery will be recharged and kept in
charged condition all the time at fl oat Voltage of 54V to 54.6V (when fully charged). If
battery backup function is not used (external 48V backup battery is not connected), the
unit will work as a normal 48V nominal Power Supply.
N+1 Redundancy
5 Power Supply Modules operating in parallel with equal current sharing provides
redundancy. Chance of failure of all the 5 modules is reduced tremendously. If say one
module fails, the remaining 4 modules will share the load current equally. Such re-
dundancy is also called N+1 redundancy i.e. if “N” number of paralleled modules are
required to service a certain load, the unit should have 1 additional module (total “N+1”
modules) to provide redundancy. For example, if the rated load drawn from this unit is
20A, 4x5A modules will be required. Using 1 additional 5A module (total 25A) will have
the capacity to service the full load of 20A even if 1 module fails.
OPERATION OF BATTERY BACK-UP AND CHARGING SECTION
Please refer to the schematic at Fig 3.1 (page 9).
Regulated output voltage of 55VDC from the modules (measured at screw terminals
S5 and S6 (Fig. 3.4) is fed to the Positive and Negative DC bus bars and from there to
the output terminals LOAD (+) and LOAD (−) through the isolating Schottky Diode D1.
Although the output voltage at the module terminals S5 and S6 (Fig.3.4) or at the
11001-SEC-4825BRM-0114.indd 8 14-01-07 1:15 PM