Please help me calculate the wire temperature due to this current

[Rubbu22]

TL;DR Summary

I need to calculate the temperature of a copper thread due current, in order to buy an equipment for a device that I want to build.

Hi,

I need to calculate the temperature of a wire, due electric current passing through, and I have no idea how to do that. I need it for a device that I want assemble.

I'm using one single thread (strand) of speaker cable, like you can see in this picture:

Again, Just a single thread that I'm pulling out of the cable.

The length of the wire will be about 50 cm, and I'll connect it to a power supply of 12V DC, and 2A current.

(I think that it's copper, and I estimate that it's about 1-2mm thick)

What will be the temperature of the thread after about 1 minute?

Will it reach 60°C ?

I tried to look up for it at Google but the calculations are too complicated for me :-(

Please help me figure this out, if possible also show me the calculation so I can calculate it for other currents.

Thanks very much.

(It's not a homework question)

 

[Drakkith]

Again, Just a single thread that I'm pulling out of the cable.

A quick google tells me that most speaker wire handles about 12-20 amps depending on gauge. I can't tell exactly how many strands are in the cable but it looks like more than ten, so I would venture a guess and say that no, a single strand of this speaker cable cannot handle 2 amps.

 

[Borek]

This is not trivial, as it is about estimating heat transfer to the surroundings - which depends on both radiation and convection. I am not surprised you find the math intimidating (I do).

Actually I think it be much easier to check the temperature experimentally, probably using some kind of a pyrometer.

 

[Rubbu22]

A quick google tells me that most speaker wire handles about 12-20 amps depending on gauge. I can't tell exactly how many strands are in the cable but it looks like more than ten, so I would venture a guess and say that no, a single strand of this speaker cable cannot handle 2 amps.

Does it mean that it will Exide 60°C ?

Will it burn?

 

[Rubbu22]

This is not trivial, as it is about estimating heat transfer to the surroundings - which depends on both radiation and convection. I am not surprised you find the math intimidating (I do).

Actually I think it be much easier to check the temperature experimentally, probably using some kind of a pyrometer.

Yes I can do experiment... but it will cost me more money... I want to know in advance if I have to buy a 12V, 2A Power Supply, or do I have to buy a 12V, 4A Power Supply... I don't want to waste too much money on this.

I need the thread to heat to about 60°C.

So I want to know if 2A is enough.

 

[Drakkith]

Does it mean that it will Exide 60°C ?

Will it burn?

I don't know.

I suppose you could try connecting a car battery to it to do a simple test. Just remember your safety.

 

[Rubbu22]

I don't know.

I suppose you could try connecting a car battery to it to do a simple test. Just remember your safety.

I don't want to do experiments on my car... I need to know if I have to buy at the electronic shop a 12V (DC) 2A power supply? or a 12V 4A power supply? or a 12V 6A power supply...?

All I want is that the thread will heat to at least 60°C, it will be enough for what I need.

 

[Borek]

Tables like this: https://www.powerstream.com/Wire_Size.htm should give you some idea about whether the wire can survive. They don't say anything about the temperature though. You need to use the gauge of the single strand.

I need the thread to heat to about 60°C.

So I want to know if 2A is enough.

And you won't know without tons of additional information. Think about it this way: the final, equilibrium temperature is a function of two processes - heating and cooling. Heating is reasonably easy to estimate from known wire resistance and current. Cooling is not that easy, as it depends on how fast the air is moving around the wire, and what is the air temperature. Do you want it to use indoor, or outdoor? Is it enclosed in some larger box, where the air is stable and only convection is at work? Is the wire in the area that is well ventilated, with forced air movement? If it is inside just opening the window or door can produce enough draft to change the temperature of the wire by several degrees. Is it OK with you?

Note: I can't answer your question about wire temperature even if you will be able to provide all details - I am just trying to show you why it is a difficult question, and why your attempts at finding the theoretical answer can be futile. I suppose there can be some rule of thumb way of estimating the temperature, but these estimates will be crude and can prove useless.

 

[Rubbu22]

Tables like this: https://www.powerstream.com/Wire_Size.htm should give you some idea about whether the wire can survive. They don't say anything about the temperature though. You need to use the gauge of the single strand.And you won't know without tons of additional information. Think about it this way: the final, equilibrium temperature is a function of two processes - heating and cooling. Heating is reasonably easy to estimate from known wire resistance and current. Cooling is not that easy, as it depends on how fast the air is moving around the wire, and what is the air temperature. Do you want it to use indoor, or outdoor? Is it enclosed in some larger box, where the air is stable and only convection is at work? Is the wire in the area that is well ventilated, with forced air movement? If it is inside just opening the window or door can produce enough draft to change the temperature of the wire by several degrees. Is it OK with you?

Note: I can't answer your question about wire temperature even if you will be able to provide all details - I am just trying to show you why it is a difficult question, and why your attempts at finding the theoretical answer can be futile. I suppose there can be some rule of thumb way of estimating the temperature, but these estimates will be crude and can prove useless.

I understand... I didn't thought that it's so complicated. I thought that it's a standard question in physics class...

By the way it's indoor, and regular room temperature (25°C).

 

[Drakkith]

I don't want to do experiments on my car... I need to know if I have to buy at the electronic shop a 12V (DC) 2A power supply? or a 12V 4A power supply? or a 12V 6A power supply...?

All I want is that the thread will heat to at least 60°C, it will be enough for what I need.

Like I said, I don't know, and based on what Borek has said I don't know how much help you can find here. Even professionally designed and manufactured equipment usually has to undergo a lot of testing just to make sure the engineers designed it correctly. And they actually know how to do the math.

I understand... and I didn't thought that it's so complicated. I thought that it's a standard question in physics class...

Unfortunately nothing in physics class translates to the real world in a simple way. If it did, engineers and architects wouldn't design bridges that fall, walkways that collapse, or buildings that topple over in the wind.

 

[Rubbu22]

Like I said, I don't know, and based on what Borek has said I don't know how much help you can find here. Even professionally designed and manufactured equipment usually has to undergo a lot of testing just to make sure the engineers designed it correctly. And they actually know how to do the math.Unfortunately nothing in physics class translates to the real world in a simple way. If it did, engineers and architects wouldn't design bridges that fall, walkways that collapse, or buildings that topple over in the wind.

OK thanks.

 

[AZFIREBALL]

Why don’t you use a small 12 volt smoke detector battery for a test?

Just place the wire across the terminals and see how hot it gets.

CAUTION! IT WILL BE VERY HOT!
CAUTION! IT WILL BE VERY HOT!
Add resistance in series with the wire to reduce the current/temperature.

Adjust(add/remove) the amount of resistance to get the temperature you desire.

 

[Dullard]

You don't say what you're up to, but it sounds like you might want to investigate nichrome wire. Intentionally heating copper wire (but not melting it) is challenging. Nichrome is a lot easier to manage.

 

[alan123hk]

I don't know why your application needs to heat the wire to 60 C and what temperature tolerance you accept. But anyway, I think the actual temperature of the wires at a fixed supply voltage will be affected by the ambient temperature, so an adjustable voltage supply might be suitable for your application. A little more complicated, you can also consider adding a sensor to detect the temperature of the wire, and then control the current of the wire to keep the temperature at about 60 C.

 

[Rubbu22]

You don't say what you're up to, but it sounds like you might want to investigate nichrome wire. Intentionally heating copper wire (but not melting it) is challenging. Nichrome is a lot easier to manage.

Thanks very much!

Sorry for not replying, I forgot the password. By the way my Nickname should be Rubby22, I wrote 'Rubbu22' by mistake and now I can't change it anymore.

I never heard of this, but now I read a little about it and it sounds like a piece of Nichrome thread will be perfect for what I need!

The only question is will current of 2A be enough for heating this wire to about 40-60°C ? which I estimate that it's exactly what I need.

I'll be happy if someone can calculate it and tell me (again, room temperature (about 25°C), indoor, and a Nichrome thread of about 0.1mm (or 0.2mm, or 0.5mm) and about 50cm length).

I really like this new direction, and I already started to check where can I buy this wire.

Again, I'm going to limit the current to 2A (using resistors) in order to prevent damage to the power supply.

So 2A will be the maximum current through the wire.

 

[DaveE]

There is a persistent myth out there that the wire gauge determines the amount of current that can be carried. In the real world, this is a complex thermal problem. Wire gauge is only one of the significant variables.

The current capacity (ampacity) is dependent on the temperature rating of the wire insulation as well as other construction and environmental variables. Any ampacity table that doesn't have the insulation temperature rating included is useless, IMO. As others have said, the wire temperature also depends on the environment it's in. For example, good ampacity tables also account for multiple current carrying conductors routed together, like in a conduit. They also have an assumption about the maximum ambient temperature.

There are several ampacity tables available on the web. If you can't research this further and find an answer, it may be best to seek the help of a professional.

https://diysolarforum.com/media/albums/nec-2017-ampacity-tables.3/

 

[Rubbu22]

There is a persistent myth out there that the wire gauge determines the amount of current that can be carried. In the real world, this is a complex thermal problem. Wire gauge is only one of the significant variables.

The current capacity (ampacity) is dependent on the temperature rating of the wire insulation as well as other construction and environmental variables. Any ampacity table that doesn't have the insulation temperature rating included is useless, IMO. As others have said, the wire temperature also depends on the environment it's in. For example, good ampacity tables also account for multiple current carrying conductors routed together, like in a conduit. They also have an assumption about the maximum ambient temperature.

There are several ampacity tables available on the web. If you can't research this further and find an answer, it may be best to seek the help of a professional.

https://diysolarforum.com/media/albums/nec-2017-ampacity-tables.3/

Actually I'm very optimistic now, I found lots of stuff about this Nichrome wire and I think that I can heat it for what I need even with 5V 1A power supply... Here are only few of the things I found:

 

[berkeman]

Actually I'm very optimistic now, I found lots of stuff about this Nichrome wire and I think that I can heat it for what I need even with 5V 1A power supply

I may have missed it, but I don't think you've described your application. It's one thing (still very complicated) to calculate the temperature of an isolated bare wire in the air from some current flowing through it. It's a very different calculation (and actually a bit easier) if that heat is being used to heat something up (like a pot of water).

What are you trying to use this 5 Watt power supply for? Why is 60C such an important number for you?

 

[Rubbu22]

I may have missed it, but I don't think you've described your application. It's one thing (still very complicated) to calculate the temperature of an isolated bare wire in the air from some current flowing through it. It's a very different calculation (and actually a bit easier) if that heat is being used to heat something up (like a pot of water).

What are you trying to use this 5 Watt power supply for? Why is 60C such an important number for you?

I prefer not to say what it is about because I may want to write a patent on this. But I tried to be very clear about what I want to achieve, I said that I want the wire to get warmed to at least 60°C in about one minute or less, indoor, in a room temperature of about 25°C.

Why isn't that enough?

Edit: I showed a picture of the wire and I said that I'll use one single strand that I will pull out of this wire... so obviously it's not isolated.

 

[berkeman]

I prefer not to say what it is about because I may want to write a patent on this. But I tried to be very clear about what I want to achieve, I said that I want the wire to get warmed to at least 60°C in about one minute or less, indoor, in a room temperature of about 25°C.

Why isn't that enough?

Well, because it doesn't include any details about what-all is cooling the wire. If it is just bare wire in air not touching anything, that's one situation (but also a bit baffling what the use is, since a warm wire just hanging in the air would not seem to be doing anything useful and patentable). If it is heating a strip of something, then that draws heat energy away from the wire, so you need more energy input to keep the wire+strip at 60C (so that changes the power input calculation). If you are warming something up that has a high specific heat and heat conductivity, then it will be very hard to put enough power into the system to heat it to 60C (especially with only a 5 Watt power source)...

 

[Rubbu22]

Well, because it doesn't include any details about what-all is cooling the wire. If it is just bare wire in air not touching anything, that's one situation (but also a bit baffling what the use is, since a warm wire just hanging in the air would not seem to be doing anything useful and patentable). If it is heating a strip of something, then that draws heat energy away from the wire, so you need more energy input to keep the wire+strip at 60C (so that changes the power input calculation). If you are warming something up that has a high specific heat and heat conduction, then it will be very hard to put enough power into the system to heat it to 60C (especially with only a 5 Watt power source)...

Thanks, but I already got to a conclusion that it will be much faster and easier for me to do that through Trial and error.

 

[DaveE]

I said that I want the wire to get warmed to at least 60°C in about one minute or less, indoor, in a room temperature of about 25°C.

You'll want to use feedback then. This is a relatively simple control system problem. The TCR of the resistor is your sensor (especially good for resistive wires like nichrome). You'll apply the voltage required to get the resistance you want, which is, of course, a function of the wire temperature. Look into the wheatstone bridge for starters.

Controlling the temperature of the heater is easy. The more common "oven problem" is controlling the temperature of what you want to be heated.

 

[Babadag]

In my opinion, if air temperature is not more than 40oC then conductor temperature at 2 A will be 45oC.
If you may measure the d.c. resistance of one conductor , the approximate stranded conductor diameter and the insulated core diameter of one of two cables [I considered it 0.8 mm conductor and 2.2 mm overall diameter of one insulated core [one of two].The resistance of 50 cm conductor at room temperature [30oc] has to be 0.04 ohm.