Electric resistance of Nichrome wire for heating?

[Ahmad.khd]

Hello,

I have an 80-meter nichrome wire and I want it to heat up to 40 degrees Celsius maximum (30 to 40 is ok). I want to connect it to a battery that is enough to make it hot for at least 10 hours.

The ambient's temperature is negative 15 degrees Celsius.

What is the diameter for this wire? what is the resistance? 

What are the spec of that battery in this case?

[Pres]

Ahmad, I edited your title for better response from the community. Hopefully others will horn in on this one.

 

best,

Pres

[Bill Kielb]

6 hours ago, Ahmad.khd said:

Hello,

I have an 80-meter nichrome wire and I want it to heat up to 40 degrees Celsius maximum (30 to 40 is ok). I want to connect it to a battery that is enough to make it hot for at least 10 hours.

The ambient's temperature is negative 15 degrees Celsius.

What is the diameter for this wire? what is the resistance? 

What are the spec of that battery in this case?

My thought is first work out the total heat needed which goes to what are you trying to heat up and what are the losses. Once you know the losses in watts we can figure out how to replace those watts with available nichrome wire (Diameter and resistance using your 80 meter length) and available batteries. It’s actually a very significant problem in my mind where no simple answer comes to mind. Perhaps a bit more description of what you are trying to heat would be helpful here.

Edited July 29, 2023 by Bill Kielb

[Ahmad.khd]

2 hours ago, Bill Kielb said:

My thought is first work out the total heat needed which goes to what are you trying to heat up and what are the losses. Once you know the losses in watts we can figure out how to replacer those watts with available nichrome wire (Diameter and resistance using your 80 meter length) and available batteries. It’s actually a very significant problem in my mind where no simple answer comes to mind. Perhaps a bit more description of what you are trying to heat would be helpful here.

I think the loss is going to be small since I am trying to heat up a sheet of woven polyester that will sit on a wall to prevent it from getting frozen.

it's whole purpose is to melt the snow off that sheet

[Bill Kielb]

Knowing that, I would suggest a carbon fiber heating element or flexible element often used in heated clothing. 80 meters of Nichrome is a very long distance so not sure what area you plan to heat or how you intend to distribute the heat from a single wire. My first instinct is to enclose or protect from snow, maybe move energy with air, but that may not fit your use. Maybe a full description here will sparks some ideas from others.

Just to add a bit to this we are talking about raising some area from -15c to above 0c with only still air (undisturbed layer of air near the fabric) as an insulator. The slightest breeze makes that layer go away. This can become a very large loss of heating in a hurry. Maybe insurmountable wattage actually, when we look at available batteries and storage.

I think the more accurately you can describe here it likely will improve your chances of suggestions by others.

@Ahmad.khd Just looking at this further, car mirror heaters might give us an idea of the energy required. If my quick math is right - temperature dependent - it looks like on the order of 1-2 watts per square centimeter. Likely not trivial depending on how large an area you are trying to defrost. Cold climate Heat pump technology could produce this at 1/2 to 1/4 the electrical energy vs resistance heat. 

Assuming the above is correct my thoughts go to dark minimal awning, maybe using the existing sun as practical and a ducted heat pump only when essential. Maybe even automotive heat pump.
 

Edited July 30, 2023 by Bill Kielb

[Ahmad.khd]

On 7/30/2023 at 12:39 AM, Bill Kielb said:

Knowing that, I would suggest a carbon fiber heating element or flexible element often used in heated clothing. 80 meters of Nichrome is a very long distance so not sure what area you plan to heat or how you intend to distribute the heat from a single wire. My first instinct is to enclose or protect from snow, maybe move energy with air, but that may not fit your use. Maybe a full description here will sparks some ideas from others.

Just to add a bit to this we are talking about raising some area from -15c to above 0c with only still air (undisturbed layer of air near the fabric) as an insulator. The slightest breeze makes that layer go away. This can become a very large loss of heating in a hurry. Maybe insurmountable wattage actually, when we look at available batteries and storage.

I think the more accurately you can describe here it likely will improve your chances of suggestions by others.

@Ahmad.khd Just looking at this further, car mirror heaters might give us an idea of the energy required. If my quick math is right - temperature dependent - it looks like on the order of 1-2 watts per square centimeter. Likely not trivial depending on how large an area you are trying to defrost. Cold climate Heat pump technology could produce this at 1/2 to 1/4 the electrical energy vs resistance heat. 

Assuming the above is correct my thoughts go to dark minimal awning, maybe using the existing sun as practical and a ducted heat pump only when essential. Maybe even automotive heat pump.
 

Thanks for your suggestion, I will definitely look into it.

and I was wondering, what if I reduce the length to 10 meters instead? could you tell me the specs of the wire in that case?

[Bill Kielb]

38 minutes ago, Ahmad.khd said:

and I was wondering, what if I reduce the length to 10 meters instead? could you tell me the specs of the wire in that case?

I think we can tell you more but you will need to tell us how big will this be …….  Tell us as much as practical. To be effective, I believe we are just going to need the potential load in watts which is affected by size and enclosure or lack there of.

Sorry, the above is the best thoughts that come to mind to address the potential load. Maybe others will have more insight here. I would suggest describing what you envision as completely as practical though.

[PeterH]

On 7/29/2023 at 4:29 PM, Ahmad.khd said:

Hello,

I have an 80-meter nichrome wire and I want it to heat up to 40 degrees Celsius maximum (30 to 40 is ok). I want to connect it to a battery that is enough to make it hot for at least 10 hours.

The ambient's temperature is negative 15 degrees Celsius.

What is the diameter for this wire? what is the resistance? 

What are the spec of that battery in this case?

First a few caveats.

1) As you ask what is the diameter of the wire I assume that you haven't got it yet. If so, why use expensive nichrome when you are operating it at such a low temperature? Oxidation of the conductor isn't going to be an issue, so nichrome's big selling point doesn't apply.

2)  At the temperature you mention the wire looses heat  mainly through conduction and convection rather than radiation. These are very dependent on the (changing?) surroundings of the wire. 

3) The amount of heat required to melt snow off the wall (I'm assuming the fabric is inside the wall) may significantly exceed that required when the outside conditions are dry. Do you have any guestimate of the weight of water that might need to be unfrozen? (It takes about 0.1 Kwh to melt 1Kg of ice once it's at 0C.)

4) While it still needs careful engineering, I suspect that a thermostat-based solution would handle the wide range of conditions better.

Then a reference from the Electrical Engineering section of a Q&A site
How do i find nichrome temperature
https://electronics.stackexchange.com/questions/84516/how-do-i-find-nichrome-temperature
... I rather go with the second answer

You can't. Sorry.

The temperature of the wire depends not only on the electrical power on this wire, but also on the ambient conditions - i.e. how the heat is dissipated. This way, the temperature of the wire will not be constant in time, but will change depending on the air temperature and movement, materials that are in contact with the wire and so on.

In order to make the temperature constant you will need to make the ambient conditions pretty stable, or to use temperature regulator that to regulate the electrical power on the wire in order to get the same temperature in different conditions.

As long as the theory behind such phenomenons is too complex, the calculations are actually possible, but very complex. In most cases, experimental way is much more reliable and useful.

Simply use regulated power supply and change the wire current until the temperature becomes what you need. But always remember that in other conditions it will be different.

PS I see that StackExchange have tags that direct heating questions to interested readers. Maybe posting there would give you a better answer.
https://diy.stackexchange.com/questions/tagged/heating
https://diy.stackexchange.com/tags/heating/info

I've almost no personal experience with StackExchange, other than it's software section which is always informative.

Edited August 3, 2023 by PeterH

[Bill Kielb]

On 8/3/2023 at 4:22 AM, PeterH said:

Do you have any guestimate of the weight of water that might need to be unfrozen? (It takes about 0.1 Kwh to melt 1Kg of ice once it's at 0C.)

The density of snow varies significantly. I kind of really liked the heated mirrors above  for approximate established data. I think we really need more of a description as much as practical as the mounting and what it is mounted to could significantly affect the required energy as well. Gotta start somewhere so maybe size, mounting, materials ….. Maybe a display case in the end is practical.

Edited August 4, 2023 by Bill Kielb

[PeterH]

On 7/29/2023 at 11:39 PM, Bill Kielb said:

Just looking at this further, car mirror heaters might give us an idea of the energy required. If my quick math is right - temperature dependent - it looks like on the order of 1-2 watts per square centimeter.

Just another data point: electrical heating film for underfloor or sauna heating @ 440w/sq meter.  https://tinyurl.com/2abs2xdf

Didn't quite believe the difference in the wattage figures, so checked my maths.

The rather large difference maybe related to the speed of response required?

[Bill Kielb]

10 hours ago, PeterH said:

The rather large difference maybe related to the speed of response required?

No, I think my math. Assuming 8”round prox. 20.32 cm so area should by 3.14x((20.33/2)^2 ) = Prox 324 sq cm. So 22W (from above)/ 324= ..068W per sq cm. A bit more than your floor heater ought to melt ice off your mirror as opposed to heating a floor to comfort temps.. I think you are in range and my quick calcs are wrong above.

All done flipping back and forth on this iPad, but seems right. Someone should triple check all the calcs if the OP does want to do this in some fashion, I think we can sneak up on a real potential load.

Edited August 4, 2023 by Bill Kielb