Hobart 6T28-600CL Operation And Maintenance Manual page 19

OM-2244 / Operation and Maintenance Manual
DCS-600 / Series 500082 / Solid State Transformer-Rectifiers
b) Control Board ( Figure 5 Item 9)
The control board mounts inside the GPU, on a steel panel behind the left side panel. This circuit
board controls for the following functions:
(1) Electronic Overvoltage/Overload Protection Circuit
The control board turns off the power supply and turns on the DS2 red overload trip light on the
front panel if more than 31.5 V DC or 2125 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
on the front panel from the minimum 200 A DC to the maximum 2000 A DC.
CAUTION
Excess starting current may cause damage to load, blow fuses or damage the power
supply. Contact the factory if you require a current limit lower than the 150 A DC
standard minimum limit.
(3) Regulated DC Output Voltages
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.
(4) Thermal Overload Protection
Normally Closed, open on over temperature.
The control board turns off the SCR firing or gate pulses when the S5 overload thermostat (item
18 in Figure 5) opens. The power supply cannot produce any DC output until the S5 thermostat
cools enough to automatically reset (close).
c) Main Transformer ( Figure 5 Item 1)
The main power transformer is a forced air-cooled, core-type, three-phase unit that reduces the rated
input voltage or voltages to a voltage somewhat higher than the maximum rated output voltage. The
extra voltage for the output provides a reserve capability to compensate for under voltage on the input
circuit, for the higher IR voltage drop found as the transformer, cables and other components heat up
with load and ambient temperature rises.
The main transformer in the GPU supplies power for the DC output and powers the auxiliary output
receptacle and the fan. The main transformers for the 60 Hz. units have windings to provide 115 VAC
for the auxiliary power receptacle and fan motor. The main transformers for the 50 Hz. units have
windings to provide 220 VAC winding for its auxiliary power receptacle and a 110 VAC winding for the
fan motor.
The main transformer has a center tapped coil on each phase that provides six fused (F2-F7) sensing
or synchronizing voltage signals to the solid state printed circuit control board ( Figure 5 Item 9). Be
certain to follow the changeover diagram for both the main transformer and the control transformer (
Figure 5 Item 6) for the input voltage you have available.
December 15, 2014 Chapter 1-1
Page 7