Lincoln Electric SVM118-A service manual Figure E.5 DC Welding Output Circuit

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E-5 E-5

THEORY OF OPERATION

FIGURE E.5 – DC WELDING OUTPUT CIRCUIT

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

DC WELDING OUTPUT

When the polarity switch is placed in either DC posi- tion, the AC voltage from the main transformer sec- ondary is applied to the SCR bridge. The SCR bridge and choke circuits are connected in a conventional full wave bridge and filter configuration, resulting in a con- trolled DC output. Since the choke is in series with the negative leg of the bridge and also in series with the welding load, a filtered DC is applied to the machine output terminals.

FIGURE E.5a – SCR BRIDGE AND CHOKE CONFIGURATION FOR DC WELDING

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

SQUARE WAVE TIG 355