Lincoln Electric SVM118-A service manual Theory of Operation, Input Power Circuit

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E-2 E-2

THEORY OF OPERATION

FIGURE E.2 – INPUT VOLTAGE, CONTACTOR, RECONNECT PANEL, PILOT TRANSFORMER, CONTROL TRANSFORMER, POWER FACTOR CAPACITORS AND MAIN TRANSFORMER

HIGH FREQUENCY SPARK

ELECTRODE SENSE

PANEL	UPPER		LOWER	DISPLAY	STATUS
	CONTROL	CONTROL
SWITCHES				BOARD	BOARD
	PANEL		PANEL

			ELECTRODE		SCR GATE COMMANDS
HIGH VOLTAGE	115VAC		SENSE		15VDC
TRANSFORMER	REMOTE
CIRCUIT		FEED - THRU		CONTROL		POWER
	RECEPTACLE
		BOARD	TRIGGER	BOARD		BOARD
GAS/WATER			REMOTE		INTERLOCK
SOLENOIDS	115VAC		COMMANDS
					HI-FREQ/ WATER/GAS
	INTERLOCK				COMMANDS
			INTERLOCK
			115VAC -HI-FREQ AND GAS/WATER
	FANS 115VAC	115VAC				SNUBBER
	RECEPTACLE	CONTROL TRANSFORMER				BOARD
			115VAC

INPUT	R		AC	DC-
CONTACTOR
	E
					C
	C
			AC	DC+	H
	O				O
	N				K
		POWER			E	BY-PASS
	N						WORK
	E	FACTOR				BOARDS
		CAPACITORS	POLARITY
	C
	T		SWITCH
						SHUNT
	START/	MAIN					ELECTRODE
	STOP
		TRANSFORMER
							HI-FREQ
	PILOT						TRANSFORMER
	TRANSFORMER

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GENERAL DESCRIPTION

The Square Wave TIG 355 is a constant current, single range square wave AC/DC TIG (GTAW) arc welding power source with built-in high frequency stabilization. It also has stick (SMAW) capability. The Square Wave TIG 355 gives the operator full control of the welding current plus the ability to preset weld and start cur- rents. Preflow and postflow timers are included for shielding gas and cooling water control. Altogether the many features of the machine allow part or all of a weld cycle to be preset or “programmed,” which sim- plifies the TIG welding process.

INPUT POWER CIRCUIT

The desired single-phase input power is connected to the TIG 355 through an input contactor located in the rear of the machine. The input power is also con- nected directly to the pilot transformer, which supplies 115VAC for the input contactor interlock and start/ stop circuits.

A reconnect panel allows the user to configure the pilot transformer, the power factor capacitors, and the main transformer for the desired input voltage. This AC input voltage is applied, through the input contac- tor, to the primary of the main transformer. The power factor correction capacitors are incorporated in the primary circuit of the main transformer to help balance the inductive nature of the TIG 355. The main trans- former changes the high voltage, low current input power to a low voltage, high current output.

In addition, the main transformer also has an isolated 115VAC auxiliary winding that supplies power to oper- ate the cooling fans and offers 15 amps of auxiliary power at the 115VAC receptacle. This 115VAC is also applied, through the feed-thru board, to the power board for high voltage and gas/water solenoid opera- tion.

The control transformer primary is also powered by the 115VAC winding in the main transformer. The sec- ondary voltages that are developed in the control transformer supply power to the control and power boards.

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NOTE: Unshaded areas of Block Logic Diagram are the subject of discussion.

SQUARE WAVE TIG 355