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SECTION 3 |
PSMs deliver equal output current. Typically, the output currents of the paralleled PSMs
will be within 10% of each other at full output current. One of the modules automati-
cally assumes the role of a master and the others operate as slaves. Each PSM is required
to be interconnected with one another to a common "SHARE BUS" through a pair of
parallel pins marked "Jump 1" and jumper wires ( Fig.1 and 2).
For proper operation of the current share control circuitry, a minimum load current is
required to flow through each PSM to produce adequate feed back signal. This mini-
mum pre-load current is provided by the sum of the currents drawn by the fans and by
an internal static load resistor connected across the load output terminals. This internal
pre-load current* is kept to the minimum to reduce dissipation.
NOTE:
It is likely that due to the drift in the pre-set values, the minimum internal preload
current may not be sufficient 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 flash and also, the associated signal for remote indication will oscil-
late 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 battery for un-interrupted DC power output. The external backup battery is
kept charged by taper charging through a series resistor.
• SEC-2450BRM has 5 PSMs of 10A each providing a total of 50A
• SEC-2440BRM has 4 PSMs of 10A each providing a total of 40A
• SEC-2430BRM has 3 PSMs of 10A each providing a total of 30A
SECTION 4 |
The heat generated due to internal power dissipation is removed by forced cooling
through two high power D.C. Fans mounted at the back of the unit which suck air from
the vents on the sides of the unit & blow outwards from the rear of the unit. It is
extremely important that the discharge side of the fans and the suction sides of the
vent slots are not blocked.
A warning circuit monitors the operational condition of the fans. In case of a fan failure,
a buzzer will sound and the red LED indicating "FAN FAILURE" will light up. The unit
should be switched OFF immediately and the defective fan should be replaced. Never
load the unit when there is an audible alarm and the fan failure LED is illuminated.
The 2 fans are rated for 24V nominal and are powered from the output voltage of the
modules. A small printed circuit board (PCB) located on the right corner towards the
back of the unit is used to monitor the fans for abnormal operating conditions viz. open
circuit or overload condition due to obstructed rotor.
Design & Principle of Operation
Cooling & Warning for Fan Failure
SAMLEX AMERICA INC. | 7
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