Lincoln Electric SVM144-B service manual Theory of Operation, Input Line Voltage, Main Transformer

E-2 THEORY OF OPERATION E-2

TOC	TOC	FIGURE E.2 — INPUT LINE VOLTAGE AND MAIN TRANSFORMER.
Section	Master		GAS	FAN
			SOLENOID	MOTOR		WIRE
						DRIVE
						MOTOR
to	to	WIRE
		SPEED
Return	Return
		ARC	CONTROL
		VOLTAGE	BOARD
						TACH
		115 VAC					GUN TRIGGER
			RECTIFIER
			DIODE	G			FEEDBACK
			BRIDGE
				A
		30 VAC		T
				E
		LINE	SNUBBER	S
			BOARD
		SWITCH		I
				G
				N
TOC	TOC			A
				L
Section	Master			POWER	C	F	OUTPUT	POSITIVE
		RECONNECT		ENHANCEMENT	A		CHOKE
								TERMINAL
		MAIN		CHOKE	P	E
		TRANSFORMER	SCR		A	E
to	to				C	D
			RECTIFIER		I	B
Return	Return				T	A
					O	C		NEGATIVE
					R	K
								TERMINAL
					S
					SHUNT

		INPUT LINE VOLTAGE	gate drive circuitry. The weld power windings connect
		AND MAIN TRANSFORMER	to the main SCR Rectifier and via the Snubber Board
			to the Rectifier Diode Bridge. This AC voltage is recti-
		The desired single phase input power is connected to	fied and then regulated by the control board. The
			resultant +15 VDC and +5 VDC voltages supply power
TOC	TOC	the POWER MIG 255 through a line switch located on	to the control board circuitry. The 115 VAC winding (X8
		the front panel.	and X9) supplies power, through the control board, to
Section	Master	A reconnect panel allows the user to configure the	the thermostatically controlled fan motor.
		machine for the desired input voltage. This AC input	The fan is designed to come on automatically when
to	to	voltage is applied to the primary of the main trans-	weld arc is established. The fan will stay on for a mini-
		former. The main transformer converts the high	mum of six minutes after the weld arc is terminated.
Return	Return
		voltage, low current input power to a low voltage, high	The fan will also stay on when the machine’s welding
		current output. In addition, the main transformer also	and feeding are disabled during thermostatic over-tem-
		has an isolated center tapped 30 VAC auxiliary winding	perature protection. (See Thermal and Overload
		that supplies power to the Control Board for the SCR	Protection.)

Section TOC	Master TOC
to	to	NOTE: Unshaded areas of Block Logic
		Diagram are the subject of discussion
Return	Return
		POWER MIG 255