Formula to Convert 25A @ 25% duty cycle to lower constant amperage?

Is there a formula to convert duty cycle at a certain amperage to a lower constant amperage?

I have a heat rise test that I need to do on a conductor that will have a 25A DC @ 25 Duty Cycle. I'd like to figure out what lower constant amperage I can run it at that would give me an equivalent average temperature.

I can do 25 * .25 = 6.25 but that seems to easy and doesn't take in to account heat dissipation.

On a side note: if I ran the test using AC rather than DC it would give me different results correct?

You can perform an RMS calculation on the waveform. RMS is to take the square root of the sum of the squares of small time slices of the current.

If the waveform is a squarewave the RMS is found by the square root of the duty cycle times the peak current. For your 25% duty cycle waveform this is (0.25)^0.5 x 25A =12.5 amps RMS.

I think the first question should be whether the device you are operating can run at a reduced amperage. Some devices cannot run at lower power inputs and still do the job; ie a small water pump. you mat be able to shorten the cycle or increase frequency and achieve a lower overall power input but not necessarily amperage. If you are trying to reduce the size of the conductors remember that smaller conductors heat more rapidly for a given amperage and that heat dissipation is affected by the wire routing, free air, in conduit etc.

As a side note, yes AC will tend to run cooler and high frequency AC (400 hz)will run cooler still.