Calculating Current Heat - Page 1
Forum section: electronics / beginners

author: mishimaBeef
author_rank: Contributor
timestamp: July 05, 2011, 01:45:16 am
content: 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

author: Bored@Work
author_rank: Super Contributor
timestamp: July 05, 2011, 06:08:46 am
content: 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:

author: Simon
author_rank: Unknown
timestamp: July 05, 2011, 06:42:28 am
content: Quote from: BoredAtWork on July 05, 2011, 06:08:46 amI can't possibly think who that may be

author: ejeffrey
author_rank: Super Contributor
timestamp: July 05, 2011, 08:02:41 am
content: 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.htmWhich 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.

author: mishimaBeef
author_rank: Contributor
timestamp: July 05, 2011, 10:16:21 am
content: Oh sorry guys I didn't see that video there! Will check it out when I have some time.

author: Neilm
author_rank: Super Contributor
timestamp: July 05, 2011, 06:59:17 pm
content: Try thishttp://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

author: mishimaBeef
author_rank: Contributor
timestamp: July 09, 2011, 08:51:39 pm
content: Post removedReason: OversightLesson Learned: Junction to Ambient (diode without heatsink) >> Junction to Case (diode with heatsink). Had forgotten there was this type of distinction in thermal resistance.

author: qno
author_rank: Frequent Contributor
timestamp: July 09, 2011, 09:52:43 pm
content: You need to calculate the resistance of the wire.Look for the fomulae on googleIt 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.

author: Zero999
author_rank: Super Contributor
timestamp: July 10, 2011, 11:26:03 am
content: 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.