Hobart 6T28-600CL Operation And Maintenance Manual page 23

OM-2244 / Operation and Maintenance Manual
DCS-600 / Series 500082 / Solid State Transformer-Rectifiers
CAUTION
Capacitor charge can injure. Be sure capacitors are discharged before touching.
The CR7 flyback diode (9, Figure 7) acts to facilitate discharge of the output filter circuitry as well as
to protect the main SCR rectifier assembly from damaging reverse voltage spikes.
h) Main SCR Heat Sink Assembly (See Figure 7)
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 consists of a formed
aluminum heat sink with 6 "hockey puck" silicon controlled rectifiers (3, Figure 7) held by 6 insulated
compression spring assemblies (2, Figure 7), held against it by 12 U-shaped aluminum heat sinks (4,
Figure 7) for the "SCR" device cooling. There are two snubber pc board assemblies for SCR gate
signal control and protection (10, Figure 7), and the associated insulators, thermostats and hardware.
The solid-state printed circuit board (9, Figure 5) provides a properly timed and sequenced turn on
signal to the silicon controlled rectifiers that must be conducted to provide the desired output.
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 control board delays the SCR turn-on signal to allow less SCR device
conduction time for a corresponded 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 devices requires phase sequence and presence of all 6 voltage sensing signals, proper phase
sequence 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.
i) Thermostatically Controlled Fan
The 115 V AC fan motor ( Figure 5 Item 15) does not run until the SCR heat sink gets hot enough to
turn on the S4 thermostat ( Figure 7 Item 6). This feature can reduce the need for internal power
supply cleaning and the use of electricity.
December 15, 2014
( Normally open closes on rise of temperature)
Chapter 1-1
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