WELDING EQUIPMENT

Welding duty cycle ratings: what the percentage and current tell you

How to read 40 °C, ten-minute duty points, find the continuous current and spot ratings that need a question before you compare machines.

By WeldOrigin Editorial · Published · Updated

A percentage is only half of the rating

A duty cycle figure states how much of a fixed period a power source can deliver a given current before it has to rest. Since the 2012 edition of IEC 60974-1, the heating test behind the rating has been run at 40 °C ambient, and ratings are conventionally expressed over a ten-minute cycle, so 60% means six minutes of arc time followed by four minutes of cooling, at the stated current and no higher.

The current is the part buyers most often lose. The Dabu MIG-180 wire welder listing gives 10% with no current, ambient temperature or test convention beside it, so the figure cannot be checked against anything. The Dabu MMA-140 table prints 60% the same way, and the Dabu MMA-400 table also shows 60% without naming the current it belongs to.

Ask for each rating as a complete statement: percentage, current, ambient temperature and cycle length. Record any missing item as an open question rather than borrowing it from another catalogue.

Intermittent point and continuous point

Well-documented industrial sets publish at least two points. The Linlong MIG400GFW and MIG500GFW guide records 60% at 400 A with 100% at 310 A, and 60% at 500 A with 100% at 387 A, both referenced to 40 °C and ten minutes. The Dabu Split MIG500 SiC page gives the same 500 A and 387 A pair but leaves the ambient temperature out, which matters when you set it beside the Linlong figures. The Dabu All-in-one MIG350 shows 350 A (60%) and 271 A (100%), again without reference conditions.

The 100% figure is the current the machine can hold indefinitely under the test conditions. For long seams, mechanised travel or shift work it is the number to compare. The intermittent figure says more about short bursts: tacking, short runs between fit-up and repositioning.

Some machines publish only the intermittent end. The Linlong MIG90 lists 25% at 90 A and no continuous current at all. The Linlong OMNI210 gives duty points per process and per supply voltage, and MMA at 120 A is rated 20% on 110 V while MIG at the same current reaches 30%. A multi-process machine can therefore carry several different ratings, and none of them shows what the set will sustain all day.

How current and duty trade off

Heating in the power source rises roughly with the square of current, which is why a lower setting buys a longer arc-on time. A formula reproduced from the AWS Welding Handbook estimates the current at a different duty cycle as the rated current multiplied by the square root of the rated duty divided by the required duty. Its worked example takes a 200 A source rated at 60% and estimates about 155 A at 100%.

Several published tables follow this relationship closely. The Dabu MIG160 LED, rated 35% at 160 A, also lists 60% at 122 A and 100% at 94 A, and those figures sit almost exactly on the square-root curve. Each column of the Linlong G-series MMA comparison halves the current between 25% and 100%, which is the same rule.

Other tables depart from it. The Linlong TIGACDC200GD publishes 76 A at 100% against 120 A at 25%, higher than the estimate would give. In the Linlong TIG200PGD / TIG250PGD table, stick mode on the 250 model shows 220 A at both 30% and 100%, which suggests a printing error. Use the formula to spot figures that need a question, never to replace a rating the manufacturer has not published.

Matching the rating to how your shop actually welds

In real work, TWI gives typical figures of about 25% for manual metal arc, around 45% for semi-automatic MIG/MAG and about 90% for automatic MIG/MAG, with wide ranges. Slag removal and electrode changes interrupt stick welding; mechanised travel removes most pauses.

So a set for occasional MMA / stick repair work can live comfortably with a modest intermittent rating, while a power source feeding a robot in a welding automation cell should be judged on its continuous figure at the current your procedure needs. The same logic applies to semi-automatic MIG / MAG fabrication where long fillets run back to back. Kaierda, which publishes both robots and arc welding power sources, is an example of a supplier where this question belongs in the first technical conversation.

Ambient temperature works in the other direction too. A rating established at 40 °C leaves margin in a cool building, while a hot, poorly ventilated bay may erode it. Note the conditions in your enquiry rather than assuming either case.

The weakest component sets the limit

The power source is only one part of the welding circuit. The torch, interconnecting cables, wire feeder and return lead each carry their own current and duty ratings, and an air-cooled torch rated below the power source will limit sustained output. When comparing a supplier such as Keyue Welding, whose range runs from portable stick sets to MIG and submerged-arc power sources, ask for the duty rating of every item in the offered package at your working current, not just the headline on the power source.

Thermal protection is not a capacity guarantee: a machine that trips and recovers is protecting itself, not proving your production pattern fits the rating.

Writing duty cycle into an enquiry

Describe the work rather than asking for a percentage: typical current, longest continuous seam, pauses between parts and shifts per day. Ask the supplier to show which published rating covers that pattern and at what ambient temperature. Request the rating plate data for the exact model and supply voltage; the companion piece on reading welding power source nameplates shows where those values sit.

Linlong Welding publishes 40 °C, ten-minute references on most of its tables, which makes its machines easier to compare than listings without conditions. Even so, confirm the figures on the delivered unit. A run at your continuous current during welding sample trials and acceptance is the practical check, and comparing welding equipment quotations is far easier once every offer states its ratings in the same terms.

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