Diagnostic workflow
Rotary DC Arc Welder Common Fault Routing
Use this workflow for older motor-generator DC arc welders before treating weak output or no output as a generator failure.
Fault-routing map
Symptom routing table
| Symptom | First checks | Likely section |
|---|---|---|
| Motor does not run | Input supply, switch, fuse, starter/contact, motor winding and mechanical lock. | Input / motor section. |
| Motor runs but there is no welding output | Field continuity, field resistor, brush contact, open-circuit voltage at output terminals. | Field excitation or generator output. |
| Weak weld current | Current-control rheostat, output cable, holder, work clamp, brush pressure and generator load response. | Field control or output circuit. |
| Current cannot be adjusted | Range switch, rheostat, field-control path and mechanical linkage. | Current-control section. |
| Arc is unstable | Brush sparking, commutator contamination, cable connection, electrode holder and work return. | Brush/commutator or external output path. |
| Brushes spark heavily | Brush wear, spring force, holder position, commutator surface and overload condition. | Brush / commutator maintenance fault. |
| Machine overheats | Cooling fan, ventilation, bearing friction, overload duty and field/armature temperature. | Mechanical cooling or electrical overload. |
Stop conditions
- Stop load testing if brush sparking becomes heavy or the commutator surface burns rapidly.
- Stop if the motor slows severely under load, vibrates abnormally or produces smoke.
- Do not keep increasing current when output terminals, cables or clamp connections overheat.
- Do not clean or adjust brushes while the machine is energized.
Repair record template
| Record field | Example evidence to write down |
|---|---|
| Motor state | Starts / does not start, reaches speed, noise, vibration, fan. |
| OCV | Measured open-circuit voltage at output terminals. |
| Field path | Field continuity, rheostat position, range switch condition. |
| Brush/commutator | Brush length, spring pressure, sparking, carbon dust, commutator surface. |
| Output path | Welding cable, holder, clamp, work return and heat marks. |