# Heating up a container - most efficient

I got a container that must be heated up to atleast 250 celsius, but I don't have alot of space to work with and I am also not so familiar with this kind of topic.

So I've attatched an image which shows my design. Everything in the color dark blue or red will be in iron or steel or even stainless steel, the red container will be in the same material as the blue discs, but I've colored them to visualize what that will be going to 250 celsius and what that should not be heated at all.

I was thinking about heating it up by using the container as a resistor, shown on the second image I would have a circuit of a copper cable going into red through the container out from green and then to a power supply unit (400W, same thing that powers most stationary computers) which leaves me at 12V and X amps. I do have an N-Channel MOSFET 60V 30A and an arduino and a Thermocouple Type-K for controlling the heating.

So my question to you is: Will it even work having the container as a heater? Or do I need some heating-resistors?

On the image below I've shown the diameter for calculation purposes. The resistance got something to do with the area through the material, and I'm sadly not sure how to exactly calculate it since it's going sideways rather than vertical.

I will be checking out this topic about once per day so if there's any extra information you need or even the model itself then I'm happy to give it to you, but since it's a blueprint of something very valueable to me I don't want to give it away unless it's necessary.

The problem with using the container as a resistor is that it's actually a very good conductor. Your wires will have more resistance, and will therefore get hotter than the container.

What would be amazing is if somehow you could deliver a very high current to the container, using a lower current flowing in the wires. Well, you can!

A very efficient way to heat an iron or steel object is by Induction Heating. It's used a lot in industry for heating bearings and things. It's also quite possible to do it yourself. Many people do.

It works by inducing an alternating current in the object to be heated. Essentially you're creating a transformer, where your object is the (single turn) secondary coil. Much more current can be made to flow in the secondary coil simply by using many turns in your primary.

An induction heater can get things really hot if you want:

And you can even use it to heat large containers:

• This sounds like something definitely doable, getting the coil is very easy to get, I have the power (400W 12v), the thing I don't have is alternatic current. As I said I do have an arduino(nano to be precise). So how am I going to get AC up to the 200-300 khz range? – Harry Svensson Oct 16 '12 at 20:52
• Look around for some projects people have done. Basically you would need to make an H-bridge to allow you to drive the current in both directions. Use the Arduino to switch the current. You'll either have to tune the frequency to achieve maximum efficiency, or create an auto-tuning circuit. – Rocketmagnet Oct 16 '12 at 21:05
• Okay, I've made the circuit you told me about and I understand it. Last question then I suppose - a tough one. Will 12v X 30 amps(if I even can draw that much power from the psu) with 200khz be enough to heat the container? This question is aimed to everyone, not just rocketmagnet ;) – Harry Svensson Oct 16 '12 at 22:41
• @HarrySvensson there is an easy way to find out, sorta. Test it! – Kortuk Oct 16 '12 at 22:56
• Alright I've looked into this and to use this I'll have to move the motor or use some mumetal to keep the magnetic flux away from the motor so it doesn't melt down. I'd also have to use some kind of copper pipes with water flowing through them as a cooling effect because I plan on having this on for a long time, and "eventually" the coil will melt down if it's on for X mins. This is a real overkill for something that is this small. – Harry Svensson Oct 17 '12 at 12:36

I'm not sure this is entirely an Electrical question, but I will give it my best effort.

"Will it even work having the container as a heater?"

My answer is 'probably not' whatever material you use in the construction of this container will most likely not be ideal for direct heat production. For example, while these materials may have good thermal conductivity properties, and may even heat up sufficiently, they are also fairly electrically conductive so you will be wasting a large amount of power.

"Or do I need some heating-resistors?"

The answer is yes. I would suggest finding a material or device that can wrap around your container and use that to heat the container. Then just make sure your container is made out of a sufficiently thermally conductive material (e.g. Copper or Aluminum) as you can see from this image from Wikipedia These materials offer the best conductivity properties which will ensure the entire container (and whatever is in it) will be properly heated.

Let me know if you have any further questions or if I misunderstood what you were asking, and best of luck to you!

Edit: Rocketmagnet and I were apparently working on our answers at the same time. His solution appears to be a very good solution as long as your device is not magnetically sensitive and you have the space to wrap an inductive element around the container.

Edit2: After looking into more solutions, I really think wrapping your container in Nichrome wire would be a very viable solution. For maximum efficiency, if it is practical, I would wrap the container in wire, then wrap the wire in thermal insulation. This website seems like a good place to go to get a better idea of what the wire is capable of and how much power you will need to supply. Let me know if you have any more questions and I will do my best to answer them. Upon further research, it seems I made one assumption that I shouldn't have. The nichrome wire is of course conductive, so putting it in direct contact with the container will most likely cause it to not work. So you would need to electrically isolate it somehow, but that really seems like a question better suited to a materials specialist.

• "The answer is yes. I would suggest finding a material or device that can wrap around your container and use that to heat the container" - Got any example for the material to be used as heater? – Harry Svensson Oct 16 '12 at 20:54
• Most heaters today use Nichrome as the heating element. I would think that it would be fairly efficient (both electrically and financially) to just wrap the container in Nichrome wire. Check out this forum for a discussion on using Nichrome. From what I can tell this stuff get HOT, so it would work well. – Michael Leonard Oct 17 '12 at 13:55

The easiest way (and by no means the cheapest!) would be to use a high temperature heating blanket (common in the composite industry). This allows you to cover only the area you wish to heat and have the benefit of precise temperature control as well.