Lincoln Electric SVM170-A service manual 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	SPOOL
			SOLENOID	MOTOR		GUN	WIRE
							DRIVE
							MOTOR
to	to	WIRE
		SPEED
Return	Return	ARC	CONTROL
		VOLTAGE	BOARD
		AUX					TACH
		115 VAC						GUN TRIGGER
			RECTIFIER
			DIODE	G				FEEDBACK
			BRIDGE
				A
		30 VAC		T
				E
		LINE	SNUBBER	S
			BOARD
		SWITCH		I
				G
				N
TOC				A
	TOC			L
Section	Master			POWER		C	F	OUTPUT	POSITIVE
		RECONNECT		ENHANCEMENT		A		CHOKE
									TERMINAL
		MAIN		CHOKE		P	E
		TRANSFORMER				A	E
			SCR			C	D
to	to
			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 255C through a line switch located	to the control board circuitry. The 115 VAC winding
		on the front panel.	supplies power, through the control board, to the ther-
Section	Master	A reconnect panel allows the user to configure the	mostatically controlled fan motor and also provides
			voltage for the auxiliary receptacle
		machine for the desired input voltage. This AC input
to	to	voltage is applied to the primary of the main trans-	The fan is designed to come on automatically when
		former. The main transformer converts the high	weld arc is established. The fan will stay on for a mini-
Return	Return
		voltage, low current input power to a low voltage, high	mum of six minutes after the weld arc is terminated.
		current output. In addition, the main transformer also	The fan will also stay on when the machine’s welding
		has an isolated center tapped 30 VAC auxiliary winding	and feeding are disabled during thermostatic over-tem-
		that supplies power to the Control Board for the SCR	perature protection. (See Thermal and Overload
			Protection.)

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