ESAB Caddy Tig 1500i TA34, Service Manual

Page: 31 / 50

DESCRIPTION OF OPERATION
0740 800 186 - 31 - © ESAB AB 2016
20AP1:7 Arc voltage feedback
This circuit measures and scales the arc voltage to a suitable level for the processor. 64 V
arc voltage produces a voltage signal of 5.0 V at the cathode of diode D13.
Open-circuit voltage control
Version 1 of 20AP1:
The open-circuit voltage control holds the voltage at about 70 V.
Version 2 of 20AP1:
The open-circuit voltage control holds the voltage at 46 - 60 V.
When the VRD (voltage-reducing device) function is active, the open-circuit voltage is < 35 V
(19 - 26 V). The VRD function can only be activated or deactivated by the ESAT, see chapter
"Service Instructions".
NOTE!
Spare part boards are delivered with the VRD function deactivated.
See the component positions diagram in section "Component Positions" of this chapter for
identification of circuit board versions.
TIG
• The open-circuit voltage is about 90 V. Arc voltages above 45 V are defined as no
welding.
• Output voltage is produced only when TIG welding is in progress. If the open-circuit
voltage/arc voltage is above 45 V for more than 100 milliseconds the open-circuit voltage
control is activated and then the output voltage is shut down.
MMA
• The power source generates the actual open-circuit voltage, see: "Open-circuit voltage
control" above.
• Touch the electrode on to the workpiece. When the open-circuit voltage goes below 45 V
(16 V when VRD is active), the open-circuit voltage control is disabled.
• When the current exceeds 8 A the hot start current is activated.
• When the arc voltage exceeds 52 V, welding stops and the open-circuit voltage control is
activated.