ESAB Caddy Tig 1500i TA34, Service Manual

Page: 19 / 50

DESCRIPTION OF OPERATION
0740 800 186 - 19 - © ESAB AB 2016
The processor on circuit board 20AP1 controls the HF generator and gas valve.
HF generator
When the welding torch switch is operated, and the open-circuit voltage is over 50 V, relay
RE2 closes and turns on the HF generator, TR2. It remains activated until the arc strikes, or
for a maximum of 0.5 seconds.
The voltage on the primary side of HF transformer 10TV1 is about 550 V. The secondary
voltage is about 11 kV if a 4 metre long welding torch is connected. If the welding torch is 16
metre long, the HF spark is about 8 kV.
Due to electromagnetic interference regulations, the energy in the HF ignition spark is
limited, and so the HF spark weakens with increasing length of the torch. The HF ignition is
satisfactory for welding torches up to 16 metres.
Gas valve
When the torch switch is operated, relay RE1 closes and energizes the gas valve.
When the torch switch is released and the gas post-flow time has elapsed, the gas valve is
deactivated.
TIG torch switch
The secondary windings of transformer TR1 and rectifier bridge D3-D6 produce 24 V DC.
This voltage energizes relay RE3 when the torch switch is closed.
10AP1 Component positions
WARNING!
Dangerous voltage - mains voltage.