How to build a heater?

[J_Nichols]

Hello to all, I want to build an electronic controlled warmer/heater as easier as possible because I know very little about electronics.

The device must consist in a regulated constant (not on for a while and then off for a while) heat source (nichrome wire? copper wire? peltier module?). I want to control very exactly the temperature emitted, 0.1 degrees Celsius / 0.18 degrees Fahrenheit. Maximum temperature around 150 degrees Celsius / 302 degrees Fahrenheit.

I've thought about using pwm or maybe some resistances to select exactly the temperature I want.

What do you recommend to use and what circuit you suggest? If it can be possible I prefer to use copper wire to produce the heat. The nichrome wire I've is very thick and it's more difficult to manipulate.

 

[alec_t]

Welcome to ETO!
What is it you need to heat?
How evenly distributed must the heat be?
What power source do you want to use?
Control to within 0.1C will not be "as easier as possible".
Copper wire doesn't make a good heating element.

 

[Sean the Nailer]

Would not a "Cartridge heater" do the task you are asking?

 

[Tony Stewart]

The challenge is that there is always thermal resistance in conductors and thus a a temperature drop from one location to another. This is affected by the thickness, mass, dimensions, power available, thermal conductivity , temperature difference, thermal insulation and quality of assembly.

Ideally it can be as accurate as it is calibrated. In practice there are both the above mechanical and also electrical errors.

Do you want to understand how to design one, or just copy an existing one?

 

[KeepItSimpleStupid]

What is your intended power source/voltage?

 

[Tony Stewart]

The thermal properties are the most important. I would suggest an oil thermal conductor between two pots like a sealed doubler boiler and regulate the oil temperature with any external heater. Then have excellent insulation to retain the heat. The heater, thermal sensors and regulator would then be possible to obtain this precision for cooling. It can be calibrated for gain and offset with ice water and boiling water.

 

[tcmtech]

Given that any type of heating element is going to exhibit some amount of thermal lag on the heat up and cool down rates VS the electrical power, air flow rates, incoming air temperature and humidity and so forth flowing though and across it you will likely need a PID control of some sort.

Also a .1 C tolerance on a 150 C output air temp (+- ~.06%) is going to be darn near impossible unless you have some very high degree of control over the air and the electrical power sources as well meaning the incoming air will need to stay within a very limited range of temperature and humidity and the electrical power source will also have to have a fairly high degree of stability as well.

 

[ChrisP58]

Well, just to ask a few more questions that need answers:

• What are you trying to heat?
• What is its volume and thermal mass?
• Are you heating it directly, or through some other medium like air or a liquid?
• What is the ambient temperature range?
• When you start heating, how fast do you need to go from ambient to target?

 

[J_Nichols]

Welcome to ETO!
What is it you need to heat?
How evenly distributed must the heat be?
What power source do you want to use?
Control to within 0.1C will not be "as easier as possible".
Copper wire doesn't make a good heating element.

Thank you!
I need to heat a small piece of metal (around 1 cm width x 1 cm height x 0.3 mm deep / 0.393 inches x 0.393 inches x 0.118 inches). The metals each time can be a different one. They're not alloys.
The heat must be the same in all the piece and not hotter in some areas and colder in others.
I've an AC to DC transformer from an old electronic device. The output is 42 watts 12 VDC 3.5 amperes/hour. Maybe to reach 150 degrees Celsius is not enough but maybe it's ok to heat the metal below 80 degrees Celsius.
If it's a little more complex it's ok.
Maybe a peltier module would be a better option?

 

[J_Nichols]

Would not a "Cartridge heater" do the task you are asking?

I didn't know about a cartridge heater. I've seen it and it seems ok, but I don't know if the heat distribution would be ok for a piece of around 1 cm width x 1 cm height x 0.3 mm deep / 0.393 inches x 0.393 inches x 0.118 inches.

 

[J_Nichols]

The challenge is that there is always thermal resistance in conductors and thus a a temperature drop from one location to another. This is affected by the thickness, mass, dimensions, power available, thermal conductivity , temperature difference, thermal insulation and quality of assembly.

Ideally it can be as accurate as it is calibrated. In practice there are both the above mechanical and also electrical errors.

Do you want to understand how to design one, or just copy an existing one?

I'm interested in copying one. I know I should know something about the design to better select the components to build the device, but I ask here this questions because I know very little about electronics. So basically I'm looking for advice to build/copy the correct one.

 

[J_Nichols]

What is your intended power source/voltage?

I've an old transfomer and its output is 12 VDC, 3.5 amperes hour. I don't know if this is ok, but at least I want to reach 80 degrees celsius heating a small piece of metal.

 

[J_Nichols]

Given that any type of heating element is going to exhibit some amount of thermal lag on the heat up and cool down rates VS the electrical power, air flow rates, incoming air temperature and humidity and so forth flowing though and across it you will likely need a PID control of some sort.

Also a .1 C tolerance on a 150 C output air temp (+- ~.06%) is going to be darn near impossible unless you have some very high degree of control over the air and the electrical power sources as well meaning the incoming air will need to stay within a very limited range of temperature and humidity and the electrical power source will also have to have a fairly high degree of stability as well.

I've thought about covering the small piece of metal with sand to protect from the wind and humidity and help to better stabilize the temperature.
I've this PID controller: d1s-2r-220 from sestos.

 

[J_Nichols]

Well, just to ask a few more questions that need answers:

• What are you trying to heat?
• What is its volume and thermal mass?
• Are you heating it directly, or through some other medium like air or a liquid?
• What is the ambient temperature range?
• When you start heating, how fast do you need to go from ambient to target?

• A small piece of metal
• Around 1 cm width x 1 cm height x 0.3 mm deep / 0.393 inches x 0.393 inches x 0.118 inches. I don't know about thermal mass. The first metal will be silver.
• I want to heat it introducing the metal in a small metallic container. Then add some sand to stabilize the temperature as maximum as possible.
• If you are asking about air temperature (weather) at the moment is about 23 to 28 in celsius and 73 to 82 in Fahrenheit.
• That is no problem. It's not a critical factor. It can take some minutes or some hours.

 

[alec_t]

Ok, so you have your metal square in a sand-bath at, say, 80C. Why? What next? You won't be able to see the square, and if you attach a probe to it (for whatever reason) you will likely upset the heat distribution.

 

[tcmtech]

Heating a 1 cm square of metal to 150 C under sand will take about 2 - 3 watts so yes your transformer is more than adequate.

 

[J_Nichols]

Ok, so you have your metal square in a sand-bath at, say, 80C. Why? What next? You won't be able to see the square, and if you attach a probe to it (for whatever reason) you will likely upset the heat distribution.

I've thought about the sand after reading some comments here in this thread about preventing that the air and changes in humidity affects the temperature. I thought, it could be a good idea to cover the piece of metal with sand to insulate it from the ambient. If I attach a temperature probe to it I will upset the heat distribution? So it would be better to prevent to use the sand and close the metallic container with a plastic lid?

 

[J_Nichols]

Heating a 1 cm square of metal to 150 C under sand will take about 2 - 3 watts so yes your transformer is more than adequate.

Thank you. It will take 2 or 3 watts using what kind of heater? Peltier module? copper wire? nichrome wire? other?

 

[Tony Stewart]

At first I thought this was a cooking project, now some science project. Since you are not familiar with the thermal properties, I am wondering what is the purpose?

 

[Sean the Nailer]

Instead of sand, I would use oil. That is the medium we used in industry for evenly 'pre-heating' bearings for mounting onto shafts or into bosses in some delicate and particular situations. Since you're using such low temperatures, simple/common engine oil will be more than sufficient. And most oils are non-conductive too, so that should help.