Lincoln Electric SVM136-A Protective Devices And, Circuits, Theory Of Operation, Section, Master

E-4 E-4

THEORY OF OPERATION

TOC	TOC	FIGURE E.4 – CV-400 TRIGGER AND THERMAL LIGHT CIRCUIT
Section	Master		THERMAL
			LIGHT
		#42	#240
to	to
Return	Return				TERMINAL
					STRIP
		# 42A	#241	#2	#2
		CIRCUIT	SECONDARY	PRIMARY
		BREAKER	THERMOSTAT	THERMOSTAT
				#4
TOC	TOC
Return to Section	Return to Master	#41			#240
				#41
					CONTROL BOARD

TOC	TOC	PROTECTIVE DEVICES AND
		CIRCUITS
Section	Master
		Two thermostats protect the CV-400 from excessive	The power source is also protected against overloads
		operating temperatures and overload conditions.	on the SCR bridge assembly through the solid state
to	to	Excess operating temperatures may be caused by	fault protection circuit. This circuit senses an overload
		insufficient cooling air or by operating the machine	on the power source and limits the output to approxi-
Return	Return
		beyond the duty cycle and output rating. The primary	Protection is also provided to protect the circuitry from
			mately 550 amps by phasing back the SCRs.
		thermostat is located on the nose of the center bottom
		primary coil. The secondary thermostat is attached to	accidental grounds.	If the customer accidentally
		the lead connecting the secondaries. Both thermostats
			"grounds" 75, 76, or 77 to the positive output lead, the
		are connected in series with the trigger circuits. If the
			CV-400 output will be reduced to a very low value, thus
		machine is over-heated, the thermostats will open and
			preventing any damage to the machine. If the ground
		output will be zero. The thermal protection light will
			occurs between 75, 76, and 77 and the negative output
		glow and the fan will continue to run. See Figure E.4,
			lead, one of the PC board electronic "self-restoring"
		CV-400 Trigger And Thermal Light Circuit. Under nor-
			fuses will blow, preventing any machine damage. After
		mal conditions the Thermal Light is "shorted out" by
TOC			the ground is cleared,	the fuses automatically reset
	TOC	the circuit breaker and thermostat circuit. If the ther-
			within a few seconds.
		mostats or the circuit breaker opens, more current will
SectiontoReturn	MastertoReturn	flow through the Thermal Light circuit, and the light will
		glow.
		IDEALARC CV-400