Calculate how many Watts i need in an electric oven?

samsagaz said:
how can i calculate the stretch of the coil? :S
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About 3x to 5x longer than unstretched coil, depending on how much you stretch them. You can either buy the pre-coiled Kanthal wire or the bare wire and coil them yourself. I never did the calculations, just bought random parts and it all worked out perfectly. I also randomly decided to buy 16 firebricks, which also worked out perfectly. And I bought micarta slabs for my knife handle, which I never used, which was also perfect, as it served as an insulator for the coil connections to the power cable for the oven. Also perfect was the fact that my dad's company manufactures PID temperature controllers for heat treat ovens, and he had a spare that day. And that I had a 240V wall outlet right where I wanted to place the oven, which I never knew existed. =)

Total, I spent about $130 for the oven, but a lot of it was just luck.
 
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Ok so I'm building a small heat treating oven that's long out of k23 for brick. It'll be 50 inches long, buy 6 inches tall and 9 inches wide.. how much wattage would I need to power it. I'm trying to do it on a 120 if possible but can move to 220 just need to know what will and won't work. I'm using kenthal wire or a couple cartridge heaters cause there a little easier to to exactly what there ranges are and how much there pulling and resistance there is but I figured best to ask you guys cause you'd know far more than I do
 
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You won't do it with 110v. My oven is smaller then that at 5x5x32 and it's just over 4000W. I would not want to go any less in my oven. Also this is a very old thread. You need to start a new one about your question.
 
I built a longish oven a while back. 6 kW of elements for a chamber 9" wide, 6" high and 42" long. It was very much an el-cheapo project, built using stuff I already had, and involved some very cheap IFBs that weighed about twice as much as the JM23s I usually use and therefore had about twice the thermal mass and less insulation value. They were 9" x 4.5" x 3" and I used them for the floor and walls. With a 9" width, it would have been difficult to roof it with bricks, so I used 1" of Ceramic Fiber board backed with 2" of Calcium Silicate board. I used the same construction for the door. I know I could have used a lot less power, but I don't know how much less.

Given that sword-length generally means Carbon steel and therefore needs hardening temperatures under about 1800 degF, even for EN45. For most other Carbon steels, 1600 degF would have been enough and I suspect it would have worked fine on 3 kW. If it will need to handle stainless temperatures, the higher wattages are required.

I also built a pair of ovens, 28" x 7" x 6" internally, each with 3 kW of elements that would reach 1300 degC, 2372 degF (and rising: the thermocouple/controller combination would only read to 1300 degC). They were built to be coupled together for swords and would cope with a 56" workpiece when combined. Power for the combined ovens was 6 kW.

I'd go with Kanthal A1 wire in your shoes, just because it's the way most folk do it and it is known to work well. Rod heaters might work, but I suspect you'd need elements with a low value of watts-per-square-inch to get the heat away into a chamber that is already at 1500 degF.

Stretch on the elements is not as clear-cut as all that. Generally at least a 2:1 stretch is required. If you are pinning the coils into the grooves with bent-wire U-shaped staples, you'll want to make sure there is enough stretch that the staple cannot short out a coil. It will not affect the oven performance to any noticeable extent if it does, but it tends to erode the element where it touches and will shorten the element life considerably. I aim for at least 3:1 stretch to overcome this and use staples bent from smaller wire than the coils themselves.
 
Skiddum said:
Ok so I'm building a small heat treating oven that's long out of k23 for brick. It'll be 50 inches long, buy 6 inches tall and 9 inches wide.. how much wattage would I need to power it. I'm trying to do it on a 120 if possible but can move to 220 just need to know what will and won't work. I'm using kenthal wire or a couple cartridge heaters cause there a little easier to to exactly what there ranges are and how much there pulling and resistance there is but I figured best to ask you guys cause you'd know far more than I do
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It's easy to calculate. Unfortunately it's in metric. P= 0,8-1,2 x surface of chamber [in cm2]. So for You it is 6 (15,24cm) x 9 [22,86 cm] x 50 [127 cm].
Front and back surface= 696,77 cm2
Both sides=3870,96 cm2
Top and bottom=5806,44 cm2
Overall surface= 10374,17 cm2

If we think of factor 1,0 [from limit 0,8-1,2] we got 10374,17W. Easy. :)

On 220V system You need line that will hold 48-50 Amp or two for 25A each.
 
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