ESAB EPP-400 Manuel D'instructions page 307

section 6 troubleshootinG
6.6 auxiliary main contactor (k3) and solid state contactor circuits
K3, activated by supplying a Contactor Signal, initiates and controls the operation of K2 (Starting Contactor) and K4 (Pilot
Arc Contactor). K3 is called the Auxiliary Main Contactor because it must be activated before the Main Contactor (K1)
power-up sequence can occur. The Contactor Signal is supplied through a remote contact connecting 115VAC from J1-F
to J1-E. If K6-2 is closed (no fault) and the Emergency Stop loop is closed, K3 will activate. The closing of K3-3 activates K2,
the Starting Contactor, and K4, the Pilot Arc Contactor, provided the power source is not over heated. See Subsection 6.7,
Main Contactor (K1A, K1B and K1C) Activation Circuit for more information on the operation of K2. K4 is turned off when
the Current Detector senses arc current and opens the contact connecting P2-5 to P2-6 on the Control PC Board.
In addition to operating K3, the Contactor Signal also activates the Solid State Contactor. The Solid State Contactor is a
logic and interlock circuit permitting the IGBT's to conduct whenever the remote Contactor Signal is present. The 115V
AC Contactor Signal is fed to TB1-9, TB7-8, and resistor, R45. R45 reduces the 115V to approximately 10V AC fed into the
Control PC Board at P6-1 and P6-2. The Control PC Board sends a signal to both the Left and Right PWM / Gate Drive PC
Boards mounted directly on the IGBT's. Illumination of LED3 on both of the PWM / Gate Drive PC Boards is indication that
the Solid State Contactor is functioning.
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