Littlefuse Spec Error

Summary

The specification for " i^2 t " has units of Amps squared times seconds. Th ere is a spec to test fuse blowing performance which uses i squared t. In t he spec, that "iit" uses a current i in a fuse for a time t of 8ms. The err or is that Littlefuse calls (i^2 t) energy. But it is not Joules, it is Jou le seconds.

iit = Joule Seconds, not energy as Littlefuse claims.

Details

Joules = distance*force = meters*kilogram*meters/second^2

Ampere = Coulomb/second

Ampere^2 = Coulomb^2 / second^2

iit = Coulomb^2 / second

The ERROR is there. The denominator has second, but energy has second^2 in the denominator. I call upon Littlefuse to notify all of its distribution c orporations to correct their documentation. It is not energy, Joule Seconds is Action.

Joule Seconds = angular momentum, and was called Action by Planck.

Joule = energy = meters*kilogram*meters/second^2

iit = Coulomb^2 / second

Reference Specs:

Littlefuse Error Spec: "This energy is described as nominal melting I^2 t a nd is expressed as ?Ampere Squared Seconds? (A^2 Sec.). A p ulse of current is applied to the fuse, and a time measurement is taken for melting to occur."

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Mersen: "AMPERE SQUARED SECONDS, I^2 t It is the measure of heat energy dev eloped within a circuit during the fuse's clearing. It can be expressed as "melting I^2 t", "arcing I^2 t" or the sum of them as "Clearing I^2 t ". "I " stands for effective let-through current(RMS), which is squared, and "t" stands for time of opening, in seconds. The use of I^2 t values to determin e proper fuse typing/ rating is only valid under adiabatic conditions, wher e there is no external heat transfer."

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Alan Folmsbee, MSEE

Reply to
omnilobe
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** "I squared T" is an engineering term that characterises a particular fuse type. It is proportional to energy, NOT a direct measure of energy like Joules.

The resistance of the fuse and how it changes with temperature must be taken into account to know the *energy* required to melt the metal link.

I squared R times T gives Joules, but R varying with T makes computation messy.

Using "I squared T" instead solves that problem, in the case of fuse links.

.... Phil

Reply to
Phil Allison

No, iit = I^2 * T is not joule seconds.

I^2 * R * T is joules.

The fuse has some implicit resistance R, and some amount of quickly-delivered joules will melt the element.

Relax. This is electronics, not physics.

--
John Larkin         Highland Technology, Inc 

lunatic fringe electronics
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Reply to
John Larkin

i^2 t is Joule seconds? I think not. If i^2 t were Joule seconds then i^2 would be Joules. Joules is energy; i^2 r is power; i^2 r t is energy (Joules)

"MSEE"? What school was that?

Reply to
Bob Engelhardt

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