Theory Of Operation; Detailed Description Of Gpu-600 Components - Hobart 6T28-600CL Operation And Maintenance Manual

OM-2244 / Operation and Maintenance Manual
DCS-600 / Series 500082 / Solid State Transformer-Rectifiers

6) Theory of Operation

The GPU provides regulated 28.5V DC. Power to the GPU is provided from the local utility company,
through the input contactor. The output contactor, controlled by the Output Switch, connects DC power to
the load.
The 28V DC power supply consists of a simple and reliable step-down transformer (1, Figure 5) whose
output is rectified by six silicon-controlled rectifiers (SCRs) (3, Figure 7) in a full-wave, center tapped
configuration. A filter consisting of an inductor and capacitors produces a low ripple DC voltage.
The printed circuit board (PC Board) (9, Figure 5) regulates the output voltage by controlling the SCR
turn-on. It does this via the phase control method; which uses the SCRs to select the desired portion of
the voltage that has been stepped down by the main transformer to produce the DC voltage. The PC
Board also provides current limiting, over-voltage and overload protection for loads connected to the DC
output. This output is floating (isolated from chassis ground), eliminating any grounding problems
between the load and the chassis ground.
CAUTION
Capacitor charge can injure! Allow capacitors to discharge fully and verify capacitor
discharge with voltmeter before touching the capacitor circuitry.

7) Detailed Description of GPU-600 Components

a) Front Panel Control Components (See Figure 4)
(1) Front Panel
The GPU operator controls mount directly to the front panel.
(2) Convenience Receptacle ( Figure 4 Item 2)
The convenience provides AC power from a secondary winding on the transformer. The output
voltage is 115 VAC for the 60 Hz units and 220 VAC for the 50 Hz units. The receptacle has a
weather cover and an MOV surge suppressor.
(3) Starting Current Control (Figure 4 Item 3)
The R13 starting current potentiometer can select any initial or starting current from 200 amperes
to a maximum of 2000 amperes. The GPU limits the output current by lowering the output voltage
for loads that draw more than the specified current.
(4) Receptacle Fuse (Figure 4 Item 4)
This front-panel fuse protects the convenience receptacle. It is rated at 10 amps.
(5) DC Voltmeter
The M2 output voltmeter ( Figure 4 Item 5) measures the DC output voltage across the main filter
capacitors. The scale has a 50 V DC maximum reading.
December 15, 2014 Chapter 1-1
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