Heating an object with a circuit

Question

I would like to make a circuit that can heat up an object to a very high temperature, similar to an electric griddle or coffee cup warmer. What kind of heating elements do they typically use and where can I buy them? They should be pretty easy to power with 120VAC right? I just need to be able to switch it on and off from an MCU.

Target temperature is ~200°C

about 200C. I want to heat up a thin rectangle of aluminum about 3" x 5" and .25" thick. — PICyourBrain, Feb 09 '11 at 20:51
is that temperature for the heating element or the heating target? And what is the allowable variance for the temperature of the target? I think you'll find that this will have a massive influence on your design as heating up a block the size your talking around to a uniform temperature, even maybe +-10 degC is a more difficult task than getting the heating element to a particular temperature. Although a heating element of that size is likely going to have to be segmented with independent monitoring of segments to approach uniform heating over that area. — Mark, Feb 10 '11 at 00:44
Just so we're clear, you are going to run this off a relay right? — drxzcl, Feb 11 '11 at 09:38
@Mark: Thanks for the heads up. Ideally I want to heat the target to 200ish °C. Perfect uniformity is not necessary but the closer the better, as always! I don't have any quantitative numbers yet but some testing will prove if it's good enough or not. — PICyourBrain, Feb 11 '11 at 14:08

score 11 · Accepted Answer · answered Feb 09 '11 at 21:42

11

Resistance wire is what you want. This is used in (at least older) space headers. But make sure you have a fail-safe.

answered Feb 09 '11 at 21:42

Brian Carlton

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Where can you get resistance wire? – PICyourBrain Feb 09 '11 at 22:14
Look for something like Nichrome 60 – Dave Feb 10 '11 at 00:42
I think I am going to use this approach. It seems to be the most cost effective way of getting a lot of heat. – PICyourBrain Feb 17 '11 at 00:24
@PICyourBrain, The main reason it was such a commonly used product, cheap and effective! – Kortuk Mar 10 '11 at 01:24

score 6 · Answer 2 · answered Feb 09 '11 at 22:58

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A metal-clad wirewound resistor makes a pretty good ready-made heating element enter image description here

answered Feb 09 '11 at 22:58

mikeselectricstuff

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Hmm, now let's work out how we can make an 8K2 wirewound resistor very hot....!! – Linker3000 Feb 10 '11 at 20:10
Lol. Right now, my most viable option is using these resistors. I found some 50Watt, 20 ohm-ers for a couple bucks each. If I run 120VAC through four of them that should give me some pretty good heat. We'll see..... – PICyourBrain Feb 11 '11 at 14:09
That's the other nice thing - they are available for pretty much any supply voltage and output power you need! Just don't be tempted to thinking that as they are metal you can very grossly overload them - I've seen taser-like failure modes where the end blows off pulling a trail of live wire behind it! – mikeselectricstuff Feb 12 '11 at 23:50

score 6 · Answer 3 · answered Feb 10 '11 at 00:02

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You want a cartridge heater.

enter image description here

Fortunately, cartridge heaters are very cheap.

McMaster Carr Cartridge Heaters
Google Shopping

answered Feb 10 '11 at 00:02

Connor Wolf

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score 3 · Answer 4 · answered Feb 10 '11 at 00:25

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I would recommend looking at silicone heater pads, which take 120VAC. McMaster is one place that has them. http://www.mcmaster.com/#silicone-heaters/=aypumy. You can pair them with a thermocouple and inexpensive PID controller to regulate the temperature.

answered Feb 10 '11 at 00:25

Dave

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only thing is, these run on DC – Matt Williamson Feb 14 '11 at 05:22
@Matt that's true if you click on the DC silicone pad link. But if you click on every other link on the page, you'll see that they take 120VAC. – Dave Feb 14 '11 at 14:28
sorry, I clicked the first one. good heads-up for the op then – Matt Williamson Feb 14 '11 at 14:42

score 3 · Answer 5 · answered Feb 10 '11 at 02:44

Any electronic item can dissipate heat. The temperature achieved depends on the thermal resistance to ambient. Usually the temperature will rise linearly at a certain number of degrees per watt. This is determined almost entirely by the load, and not by the element you are using to heat the load. For further reading look at heatsinking app notes.

Notice that heat rise is above ambient. If you care about the exact temperature you should plan to have some kind of feedback system to measure the temperature and turn the heating element on / off.

200C is hot! Most electrical components will be damaged by such heat. Look for cartridge heaters as mentioned in other answers. You can buy replacement electric range heating elements in an appliance store. A complete electric heating plate is about $20 at discount stores. These wirewound resistors are spec'ed up to 250C: http://www.mouser.com/catalog/specsheets/rhnh.pdf

score 2 · Answer 6 · answered Feb 12 '11 at 20:13

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I've seen a heater design that used fat-ish PCB traces as a resistive heating element.

answered Feb 12 '11 at 20:13

XTL

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plus one for the interesting idea! I doubt it would be able to handle the power though... – PICyourBrain Feb 17 '11 at 00:21

score 1 · Answer 7 · edited Mar 09 '11 at 23:51

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Peltier Junction is a thermoelectric device, which is a kind of an electronic heat pump.

When you input DC, peltier element transfers heat from one side to another one. Turn the DC around, and hot/cool change sides. Just don't change polarity when it is very hot, this will stress the device and blow it up. Also it is a good idea to monitor the device and regulate current accordingly.

One cool fact, if you heat it up on one side and keep the other cool, it will generate a current..

edited Mar 09 '11 at 23:51

Olli

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answered Feb 09 '11 at 21:58

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I can't seem to find one that can go hotter than 200F, I need 200C – PICyourBrain Feb 09 '11 at 22:24
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also don't forget that with peltiers, you could end up with a condensation issue on the cold side, which might be an undesirable effect. I've encountered unpleasant situations like this before. – Dave Feb 10 '11 at 00:43
the system supports adding a link to text so that someone can click on what the link relates to and get more information rather than just knowing the links are related. – Kortuk Mar 10 '11 at 01:26

score 0 · Answer 8 · answered Feb 12 '11 at 22:28

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I would like to make a circuit that can heat up an object to a very high temperature, similar to an electric griddle or coffee cup warmer.

If this is a hobby project or other one-off, why don't you repurpose an electric griddle or coffee cup warmer or iron or...? Your local thrift store has a ready-made supply of these.

answered Feb 12 '11 at 22:28

John Lopez