Calculating Current Heat

[mishimaBeef]

Hi guys, I was wondering if anyone could shed some light on a topic that I feel is overlooked in my school's electrical engineering curriculum (at least thus far): current heat calculations.

If I have 15 A flowing through a copper wire, how can I calculate the temperature the copper will rise to? Does this involve looking at heat dissipation curves for the grade of wire being used? Some people have said that Watts*seconds = Joules (heat) but I understand that there is a process creating heat and a process dissipating heat. Or is there something I'm not considering?

Insight greatly appreciated,
EE Student

[Bored@Work]

There is this guy with a squeaky voice who occasionally does some electronics video. He did one about heatsink design. The principles are the same, thermal resistance and all that:

[Simon]

There is this guy with a squeaky voice who occasionally does some electronics video. He did one about heatsink design. The principles are the same, thermal resistance and all that:

I can't possibly think who that may be 

[ejeffrey]

You will need some numbers for the cooling rate.  There are two processes, cooling through the ends of the wire to the terminal, and cooling into the air.  You will need some estimates of these effects for your particular wire before you can do the thermal impedance calculations.  You can also just check:

http://www.powerstream.com/Wire_Size.htm

Which are conservative current capacity guidelines for various wire sizes.  It doesn't give temperature rise vs. current, only minimum conductor size for a given current load.  Obviously they cannot be one-size-fits-all, and they are fairly conservative in an attempt to be one-size-fits-many.

[mishimaBeef]

Oh sorry guys I didn't see that video there! Will check it out when I have some time.

[Neilm]

Try this http://www.miscel.dk/MiscEl/miscel.html. It is a free programme that I find very useful. It calculates heat in PCBs and wires as well as very many other things.

Neil

[mishimaBeef]

Post removed

Reason: Oversight

Lesson Learned: Junction to Ambient (diode without heatsink) >> Junction to Case (diode with heatsink). Had forgotten there was this type of distinction in thermal resistance.

[qno]

You need to calculate the resistance of the wire.
Look for the fomulae on google

It is the specific electrical resistance, or volume resistivity divided by the cross section of the wire times the length.

When you calculated the resistance of your wire you can calculate the power dissipated, like a resistor.
When the wire is insulated you should check the manufacturers data for the heat resistance of the insulation.

Normally the max current is defined by the insulation material. vinyl is usually 70 °C Teflon or silicone is a bit higher.

[Zero999]

Off topic I know but my favourte type of wire is silicone because it's resistant to high temperatures and when overheated it doesn't burn or release any nasty gasses, it just looses its flexiblity and forms an insulating glass. Chlorine containing plastics such as PCV release corrosive gasses such as HCl which burn the lungs and damage other components.