How to use this calculator
- Enter the rating point. Use the rated current and duty cycle from the welder nameplate or manual.
- Enter target current. Set the amperage and duty cycle you want to check.
- Enter cycle timing. Use the duty-cycle time base and planned arc-on time for the weld segment.
- Read current and cooldown. Compare target current with the allowable current and use the required idle time for planning.
How it works
Welder duty-cycle ratings are thermal limits. This calculator starts from the rated current and duty cycle, then holds the heating term constant:
I^n x D = constant
With the default current-squared model, n = 2. Allowable current
at a target duty cycle is:
I_allowed = I_r x (D_r / D_target)^(1/n)
Duty cycle at a target current is:
D_allowed = D_r x (I_r / I_target)^n
Planned duty cycle is simply arc-on time divided by the cycle length:
D_planned = t_arc / T_cycle
Worked example
Verified against the live calculator
A welder rated 200 A at 60% duty can be screened at
250 A with n = 2. The allowable duty is
60 x (200 / 250)^2, or 38.4%. A
3 min arc-on run therefore needs a total cycle time of about
7.8 min, leaving roughly 4.8 min of idle
cooldown before repeating at the same current.
Frequently asked questions
How do you calculate welding duty cycle by amperage?
Use the machine rating as a thermal point and keep I^n x duty approximately constant. With the common n = 2 screen, duty at a new current is rated duty times (rated current / target current) squared.
Why does the calculator use a 10 minute cycle by default?
Many welder ratings are stated over a 10 minute duty-cycle period, such as 60% at 200 A. Change the cycle length if your machine manual uses a different basis.
What does required cooldown mean?
It is the idle time needed after the entered arc-on time so the target current stays within the estimated duty-cycle rating.
Does this override the welder manual?
No. It is a first-pass thermal interpolation only. The manufacturer rating, ambient derating, process mode, input voltage and thermal shutdown behavior control real equipment use.
Method & assumptions
- Uses an interpolation screen between current and duty cycle; it is not a certified machine rating.
- The default exponent is 2 for current-squared heating. Change it only when you have a defensible equipment basis.
- Ambient temperature, fan condition, process mode, input voltage, cable losses, generator supply, enclosure ventilation and machine thermal protection are not modeled.
- Use welding amperage, welding heat input, wire feed speed, weld deposition, weld cost per inch and groove weld area for adjacent setup, estimating and production planning.