Hot resistor questions

[brianp]

When a resistor is driven near its power limit, and it heats up, does its resistance rise with temperature? If so, by approximately what percentage of its nominal value?

[Pete Schumacher ®]

When a resistor is driven near its power limit, and it heats up, does its resistance rise with temperature? If so, by approximately what percentage of its nominal value?

Thermal coefficients vary with resistor type. 100ppm/degC would be a reasonable guess. In other words, the value won't change appreciably.

[Hackomatic]

Thermal coefficients vary with resistor type. 100ppm/degC would be a reasonable guess. In other words, the value won't change appreciably.

I agree . . until it burns on two! Expect a substantial rise in impedance at that point!

I suppose a test could be done to measure a wire wound at ambient room temp, then place the thing on a stove burner, turn it on high and see what happens as she heats up.

Let us know how it turns out!

[Pete Schumacher ®]

I agree . . until it burns on two! Expect a substantial rise in impedance at that point!

I suppose a test could be done to measure a wire wound at ambient room temp, then place the thing on a stove burner, turn it on high and see what happens as she heats up.

Let us know how it turns out!

Once you let the smoke out of the part, it stops working.

Magic smoke . . . isn't that what Michael Phelps was trying to inhale?

[Hackomatic]

Once you let the smoke out of the part, it stops working.

Magic smoke . . . isn't that what Michael Phelps was trying to inhale?

Um . . I think he more than tried!

Maybe in his quest to become an Olympic star he consumed too many Weedies.

[billfitzmaurice]

When a resistor is driven near its power limit, and it heats up, does its resistance rise with temperature?

Yes. That's how tweeter protection lamps work, and what causes thermal power compression in drivers. A good rule of thumb is to use a resistor that's rated for at least twice the power that will actually pass through it.

[daryl]

Yes. That's how tweeter protection lamps work, and what causes thermal power compression in drivers. A good rule of thumb is to use a resistor that's rated for at least twice the power that will actually pass through it.

As per usual bilf is replying to a question when he should not.

The first answer (from Pete Schumacher) is absolutely correct.

Resistors are temperature compensated and relatively stable with temperature.

There are low temperature coefficient types and low noise types neither of which are ever necessary for a crossover.

The voice coils in your drivers on the other hand are simply coils of copper or aluminum which will exhibit large swings in resistance with temperature.

So your systems characteristics will vary considerably but because of voice coil temperature not resistor temperature.