Hobart 120CU20, Operation And Maintenance Manual With Illustrated Parts List

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OM-2228 / Operation and Maintenance Manual
120CU20 / Series 500120 / 400 Hz. Generator Set
October 15, 2013 Chapter 1-3
Page 6
3) DC Operating Procedure (optional).
This section describes the operation of the optional DC unit. The DC output voltage value, which is
controlled by a potentiometer on the Transformer-Rectifier Board (TRB), need only be set once. The
voltage level will remain the same for all future operations, even when the unit is shut down or the battery
is disconnected. It may, however, be changed as often as desired.
Note: The DC output voltage is only regulated when operating DC alone without an AC output. If AC
and DC are operated together, only the AC voltage is regulated.
a) Normal Power Delivery.
(1) Connect the output cable plug connector to the aircraft receptacle. Be sure connector is mated
fully and securely.
(2) The engine should be running at rated speed (2000 RPM) and generating 115/200 VAC. If not,
reference the engine starting procedure above.
(3) Press “ DC OUTPUT ” push button to close the DC output contactor. The blue “ DC OUTPUT ”
lamp glows to indicate that DC power is being delivered to the aircraft.
b) Current Limiting Power Delivery.
If current limiting is required for starting an aircraft, set the current limit as follows:
(1) Press the “ STARTING CURRENT ” push button to activate and view the present current limiting
value. Continue to hold the button down to increase the setting.
(2) Each time the “ STARTING CURRENT ” push button is pressed the current limiting will be viewed
and increased by 100 A until it reaches the maximum setting of 2500 A. At that time the current
limiting will reset to the beginning and start the 100 A increments again. Set the current limit to
the desired setting.
c) Discontinue Power Delivery.
(1) Press “ DC OUTPUT ” push button to open the DC output contactor. The blue “ DC OUTPUT ”
lamp turns off to indicate that DC power has been removed from the aircraft.
(2) Disconnect the output cable connector from the aircraft receptacle and store properly in the
GPU’s cable tray.
4) Simultaneous AC and DC Operation.
If both 28.5 VDC and 400-Hz AC power must be delivered at the same time, the operation of the controls
remains the same. However, the DC output voltage will not be regulated when the AC voltage contactor
is closed and is supplying power.
When both AC and DC are being used and a fault condition occurs, the system’s response to the fault is
given priority over all operations.