Cooked fan timers

[JohnW2]

1W or so isnt exactly a lot of power.

It's enough to raise the temperature of 10-12mm² of the sole plate of a normal domestic clothes iron to over 200°C....

Really? How to you calculate this ....bearing in mind that dividing the wattage of of the iron by its surface area is flawed maths....... I suggest that 1W won't raise a piece of steel of even that kind of small surface area by anything like 200 degress in free air....

I'm sure you're right. BAS's arithmetic would tell us that even a microwatt would raise the temp of a small enough object to over 200 degrees - but, as you say, that certainly would not be the case if it were an isolated object in free air! Now, if we are talking adiabatic, that's a whole different matter!

Kind Regards, John.

 

[JohnW2]

dividing the wattage of of the iron by its surface area is flawed maths

Why?

Because your tiny part of the iron plate is surrounded by other parts at 200 degrees, thereby minimising heat losses. If the resistor we were talking about were part of a mega-resistor (rather than being an isolated object, surrounded by air), then the same would apply.

Kind Regards, John.

 

[ban-all-sheds]

Sadly I wasn't quick enough with my edit about the soldering iron.

I don't see how there's any getting away from the fact that the average power dissipation of a clothes iron is approximately 10w/cm².

I wonder what the length of nichrome wire in a 1kW electric fire element is? 10m? Show me why 1W could not make 10mm of it glow a bright orange colour.

 

[JohnW2]

I don't see how there's any getting away from the fact that the average power dissipation of a clothes iron is approximately 10w/cm².

One can't get away from that fact. However, nor can we get away from the fact that if you cut up the baseplate of the iron, and the element, into 1000 pieces and fired them up (separetely in free air) such that they were not within each other's thermal influence, that none of them would get anywhere near the same temperature.

However, before this tangential discussion gets silly and destroys the thread, I'm quite happy to concede that, under the right circumstances, 1W or so is quite capable of resulting in high temperatures and appreciable thermal damage - as witness the very damage to the PCBs of timer modules that this thread is meant to be about.

Kind Regards, John.