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OM-2010
(4) Overload Trip Light (4, Fig. 4)
The overload trip light glows whenever the solid state printed circuit board turns off the power sup-
ply output due to output voltage exceeding 31.5 V DC, output current surge exceeding 2200-A
DC.
H.Main SCR Heat Sink Assembly (See Fig. 5)
The main SCR heat sink assembly is mounted on the front of the rear panel. It surrounds the 115 V
AC cooling fan assembly for optimum cooling efficiency. The SCR heat sink (2, Fig. 5) consists of a
formed aluminum heat sink with 6 "hockey puck" silicon controlled rectifiers held by 6 insulated com-
pression spring assemblies held against it by 6 U-shaped aluminum heat sinks for the "hockey puck"
device cooling, two snubber pc board assemblies for SCR gate signal control and protection (1, Fig.
5), the associated insulators, thermostats and hardware.
The solid state printed circuit board (13, Fig. 3) described later provides a properly timed and se-
quenced turn on signal to the silicon controlled rectifiers that must conduct to provide the desired out-
put. If the output voltage is too high or if the output current is above the limit set by controls such as
the R13 starting potentiometer, the "pcb" control delays the SCR turn-on signal to allow less SCR de-
vice conduction time for a correspondly lower output. Conversely, if the output voltage is too low, the
SCR turn-on signal is delivered earlier in the possible conduction time for each SCR thereby allowing
more power to be supplied because of the longer conduction time. Proper operation of the SCR de-
vices requires phase sequence and presence of all 6 voltage sensing signals, proper phase se-
quence and presence of the output voltage to the SCR devices and the proper magnitude and
sequence of the SCR turn-on signal to the SCR gate leads.
J. Solid State Printed Circuit Control Board (13, Fig. 3)
The printed circuit board is located in a steel box behind the front access door on the power supply
right side panel (2, Fig. 3). This large printed circuit board is the "brains" or electronic control for the
following functions:
(1) Electronic Overvoltage/Overload Trip Circuit
The "pc board" trips the power supply off and turns on DS-2 red overload trip light (4, Fig. 4) on
the front panel if more than 31.5 V DC or 2200 A overload exists. To reset, correct the cause of
the condition and then turn the input switch off and back on.
(2) Electronically Controlled Current Limit
The starting current or output surge current is selected by adjusting R13 starting current control
(8, Fig. 4) on the front panel from the minimum 250 A DC to the maximum 2000 A DC.
CAUTION: EXCESS STARTING CURRENT MAY CAUSE DAMAGE TO LOAD, BLOW FUSES OR
DAMAGE POWER SUPPLY. CONTACT FACTORY IF YOU REQUIRE A CURRENT LIMIT LOWER
THAN THE 250 A DC STANDARD MINIMUM LIMIT.
(3) Regulated DC Output Voltage
The voltage value is continuously compared to the actual output. If adequate input voltage exists,
deviation from the desired voltage output is corrected by the change in SCR conduction time set
by the printed circuit board firing pulse output. This corrective action is done quickly because the
control is done electronically with only limited stored energy in the circuitry. Typical response time
is about 25 milliseconds.
2-1
Page 10
April 10/89 Revised
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Troubleshooting
