#### Robby2022

Joined Jan 18, 2022
11
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.

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.

#### SamR

Joined Mar 19, 2019
4,118
First you will need the gauge of the wire to calculate.

#### Robby2022

Joined Jan 18, 2022
11
First you will need the gauge of the wire to calculate.
I have no idea what this means... isn't it possible to estimate it from the picture?

It's a standard speaker cable (like you can see in the picture on my first post) and I'm using just one thread that I'm pulling out of the cable. I think that it's copper... maybe 1-2mm.

#### Ian0

Joined Aug 7, 2020
4,824
I have no idea what this means... isn't it possible to estimate it from the picture?

It's a standard speaker cable (like you can see in the picture on my first post) and I'm using just one thread that I'm pulling out of the cable. I think that it's copper... maybe 1-2mm.
Either measure it with a micrometer, or get it from the spec of the cable.
if the cable spec says 79/0.2 then each strand is 0.2mm diameter and there are 79 strands.
Failing that, if you know the cross sectional area, then divide it by the number of strands (you’ll have to count them).
Then you will need to know the current through the wire, the air temperature and the rate of air flow over the wire.
And is your cable genuine copper, or, if you bought it from some dubious supplier, is it brass or copper plated steel?

#### Marley

Joined Apr 4, 2016
468
Generally, for a simple application like this, you would choose a CSA (cross-sectional-area) dependent on the current flow with a large safety margin. So for 2A, between 0.5mm2 or 0.75mm2 would be OK. In the USA I think this is specified as a wire gauge - look -up tables are online.

If it was a longer length, where voltage drop would be an issue or cost of the cable - you might have to do some calculations! Normally no need.

#### ericgibbs

Joined Jan 29, 2010
15,338
hi Robby.
Is this a Homework question.?

Why not do a test, cut the wire strand to length, use drawing pins at the ends to keep it in say a line, use a wooden base of course.
Power to the wire and measure the wire temperature, what measuring devices do you have.?

Also note the ambient temperature and the heat up time.

E

#### Alec_t

Joined Sep 17, 2013
12,732
Unless the power supply has built-in current-limiting it may well try to pass more than 2A through the wire strand. Is 2A the rated current or a current limit? I suspect 50cm of a single strand of that sort of cable will have such a low resistance that your power supply will see it as almost a short-circuit.
Do you have a multi-meter?

#### MisterBill2

Joined Jan 23, 2018
11,579
If the TS is able to separate one strand of that cable and then accurately measure the resistance, then the power can be easily calculated when the voltage is known. If the single strand will be in open air the heat lost thru radiation can be calculated since the surface area of the wire can be calculated.
Without the ability to accurately measure the wire diameter or the wire resistance there is no way to accurately calculate the temperature. that the wire will reach.
The maximum power that can be delivered to the wire is 24 watts, presuming that the power supply is able to hold up the 12 volts at a current of 2 amps. temperature rise will be due to the difference between heat input, (24 watts) and the heat lost through radiation and conduction into the surrounding air. It is not likely that the temperature will be below the melting point of whatever copper alloy the wire is,and so the wire will melt at some weakest point, much like a fuse.

So don't waste your time because the wire will quickly heat up and glow, and then fail at a weak spot where the cross section is a bit less, and the temperature will thus be a bit hotter.

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#### BobaMosfet

Joined Jul 1, 2009
1,942
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:

View attachment 258135

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.

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.
A single strand can't handle 2A and stay within NEC safety guidelines. I don't know where you are, but 14ga speaker wire in the USA is rated for about 5.8A at 30C dissipating into ambient 25C, no matter what the wire is (stranded, composited, alloy, etc).

#### Wendy

Joined Mar 24, 2008
22,776
Are you trying to heat the wire?

#### Robby2022

Joined Jan 18, 2022
11
Unless the power supply has built-in current-limiting it may well try to pass more than 2A through the wire strand. Is 2A the rated current or a current limit? I suspect 50cm of a single strand of that sort of cable will have such a low resistance that your power supply will see it as almost a short-circuit.
Do you have a multi-meter?
Sorry for not being clear enough about that, Yes I'm going to limit the current to 2A (using resistors) in order to prevent damage to the power supply, and yes I have a multi-meter.

Can you estimate (roughly) what will be the temperature of the thread (single stand) after about 1 minute, indoor, in a room temperature of about 25°C ?

#### djsfantasi

Joined Apr 11, 2010
8,255
Sorry for not being clear enough about that, Yes I'm going to limit the current to 2A (using resistors) in order to prevent damage to the power supply, and yes I have a multi-meter.

Can you estimate (roughly) what will be the temperature of the thread (single stand) after about 1 minute, indoor, in a room temperature of about 25°C ?
Yes, you can if you read and follow the previous posts in this thread. But first you will have to know or be able to measure several things. Which you have to learn how to do. If something is unclear, let us know.

Edit: changed wording

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#### Wendy

Joined Mar 24, 2008
22,776
Be kind, it is obvious the OP is new to electronics. Unless you are aiming for a specific temperature, you will not be able to do what you are trying to do. If you are aiming for a specific temperature you will need some kind of sensor to measure this temperature. All wires heat up a little when they conduct electricity the idea is to keep them from not healing up by overrating the wire for the current it will carry.

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#### Robby2022

Joined Jan 18, 2022
11
Be kind, it is obvious the OP is new to electronics. Unless you are aiming for a specific temperature, you will not be able to do what you are trying to do. If you are aiming for a specific temperature you will need some kind of sensor to measure this temperature. All wires heat up a little when they conduct electricity the idea is to keep them from not healing up by overrating the wire for the current it will carry.
Thanks!

Using sensor is too complicated for what I need, I want a very simple device.

I checked a little more, and someone suggested me to use a Nichrome heater wire, and it's sound 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.

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#### Robby2022

Joined Jan 18, 2022
11
Yes, you can if you read and follow the previous posts in this thread. But first you will have to know or be able to measure several things. Which you have to learn how to do. If something is unclear, let us know.
Thanks, and I meant "Strand" (Not 'Stand').

#### djsfantasi

Joined Apr 11, 2010
8,255
Do you want to raise the temperature of the wire or the air around the wire (like an electric heater)?

#### Wendy

Joined Mar 24, 2008
22,776
Are you trying to cut Styrofoam? Or what? You can adjust the temperature of the wire by adjusting the current. But it would help if we knew what you were trying to do with it.

I have been known to cut Styrofoam with a conventional wire just by adjusting current from a high power power supply.

#### Robby2022

Joined Jan 18, 2022
11
Are you trying to cut Styrofoam? Or what? You can adjust the temperature of the wire by adjusting the current. But it would help if we knew what you were trying to do with it.

I have been known to cut Styrofoam with a conventional wire just by adjusting current from a high power power supply.
Sorry I can't tell, but 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:

#### Sensacell

Joined Jun 19, 2012
2,985
The temp of the wire can only roughly be calculated, it depends on so many difficult to predict factors.
All of this around in circles stuff can be reduced if you just tell us what you are trying to do with this heated wire?

Edit- Ok, I read that you "cannot tell" - at that exact moment, 90% of the smartest people left the room.
It's so not interesting to play 20 questions about some secret project ... yawn.