Practical answers on choosing and fitting internal and external spares for an arc welding power source.
What can I read from the rating plate that helps me choose a spare part?
The rating plate on the power source gives the maker, the supply it needs and its performance. Typical entries include the input voltage and current and the duty cycle shown as a percentage.
Note the full type designation and serial number exactly as printed. Spare parts such as mains cables, circuit boards, switches and chokes are usually matched to a specific type or version of machine, so the plate is the first thing to check before ordering. If the plate is unreadable, the manual or the maker's parts list is the next step.
What does duty cycle mean and why does the machine cut out?
Duty cycle is shown on the rating plate as a percentage and is commonly expressed over a 10 minute period, so a rating of 30 percent at a given current means about 3 minutes of welding followed by about 7 minutes of cooling. It usually rises as the welding current is lowered, so read the figure at the current you actually use.
If you reach the limit, a thermal protection system stops the welding and normally lights an indicator until the machine has cooled. Some machines also stop if the supply voltage is too low or too high. Keep the vents clear and follow the manual before suspecting a faulty part.
Can I fit an internal spare part myself?
Only if you are trained and competent for the task. Welding power sources contain mains voltage and electronic circuits, and HSE guidance says electrical supplies should be made dead and proved dead before work starts, with the method of isolation preventing accidental re-energising.
Unplug the machine, follow the maker's instructions for removing covers, and leave the case closed if you are not sure what you are doing. Makers generally state that servicing should be done only by qualified people, and some internal capacitors need discharging before work. Your risk assessment and the manual should decide who does the work.
How do I tell that a mains connection cable or plug needs replacing?
Look at it before every use, with the machine switched off and unplugged. HSE user-check advice is to look for damage to the lead such as fraying or cuts, a damaged plug or bent pins, tape used to join or patch the lead, coloured wires showing where the lead enters the plug, and signs of overheating.
Damaged equipment should be taken out of use until it is repaired by a competent person or replaced. A replacement cable and plug must suit the machine, so check the data plate and manual rather than guessing from the old cable. Fitting a mains cable or plug is normally a job for a competent electrician, and many manuals say so.
Does the welder need inspecting and testing after a repair?
Often it is sensible. The HSE says the law requires electrical equipment to be maintained to prevent danger but does not say exactly what must be done or how often. It describes brief user checks as useful, with more formal inspection and testing by a competent person where the equipment and its environment call for it.
There is also an arc welding standard that sets out test procedures for periodic inspection and for testing after repair to ensure electrical safety. A competent person can test to it. The maker's manual and your risk assessment should set the routine, and a simple record of what was replaced is worth keeping.
How do I identify the right spare part for my machine?
Start with the data plate: record the type designation, version and serial number. Then match the spare to the part number or code on the old part, or to the exploded drawing in the manual.
Be careful with parts that look alike. Circuit boards, switches, fans and chokes often differ between versions of the same machine, and the difference may only show in the part number. Take clear photographs of the old part and where it sits before removing it. If you cannot find a reference, our team can help you match it from the details on the plate.