Calculate how many Watts i need in an electric oven?

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samsagaz

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Oct 20, 2009
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Hi guys, i want to build an oven to thermal treatment.

I want to know how can i calculate how many watts i need to reach at least 1100Cº?

i found the wire diameter, wire mm2, and ohms per meter, but cant figure how can i calculate how many watts i need to reach at least 1100 degrees.

Thanks in advance
 
samsagaz said:
Hi guys, i want to build an oven to thermal treatment.

I want to know how can i calculate how many watts i need to reach at least 1100Cº?

i found the wire diameter, wire mm2, and ohms per meter, but cant figure how can i calculate how many watts i need to reach at least 1100 degrees.

Thanks in advance
Click to expand...

if you give me the size of you oven inside i can help you out with it. but its to late for me to just go through it all right now. but tomorrow i will post something a lot more helpfully if i have time.
 
My calculations were 5,700 W. At least for start up power.

Let's say your oven weighs 100 lbs. 100 lbs X 1,947 (number of ° of heat rise from ~65° F to 2012°F) (1,100C is 2,012F)

So 100 X 1,947 is 194,700 btus. 194,700 / 3,412 (btus per kWh) = 57kW, or 5,700 W

You could probably do it for less power but it would take longer. The idea with an oven is to generate tremendous heat immediately and cut it back as necessary.

You'll need the equivalent of 4 or 5 large range burners inside the oven to generate that heat.

The one variable I'm not sure of is how big or heavy the oven needs to be.
 
I have a 0.18 cubic foot chamber, with 4000W of power. It took about 12-15 minutes to reach 1100 °C, another 10 minutes to pass 1200 °C. Most ovens are bigger than mine, and would therefore need more power.

That said, most US households won't be able to output more than 4000W of power. Most commercial ovens are about 1600W and seem to do just fine, but I'm sure that they would take a long time to reach 1100 °C.

My advice is to use as much power as your power line can support. That way you can reach your temperature quicker.
 
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It's not necessarily a question of how much power you need until you figure out how well insulated (or not) your oven is. Obviously if you're limited to a certain size circuit you'll only be able to pull that much power off it.

Depending on size and insulation, you'd want anywhere from at least 1.8kW to upwards of 10kW.
 
65535 said:
It's not necessarily a question of how much power you need until you figure out how well insulated (or not) your oven is. Obviously if you're limited to a certain size circuit you'll only be able to pull that much power off it.

Depending on size and insulation, you'd want anywhere from at least 1.8kW to upwards of 10kW.
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By no insulation, you mean like heating elements hanging in mid-air? I think that would pose some safety hazards. If soft firebricks are used, it could be 1200C inside and cool to the touch outside, I think this is the standard insulating material.

BTW, you live in my neighborhood. UCI student? I have a knifemaking shop if you're ever interested in knife-related services locally/free.
 
cotdt said:
By no insulation, you mean like heating elements hanging in mid-air? I think that would pose some safety hazards. If soft firebricks are used, it could be 1200C inside and cool to the touch outside, I think this is the standard insulating material.

BTW, you live in my neighborhood. UCI student?
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IVC, living in Woodbridge.

I merely meant that depending on seals between bricks and overall construction some ovens leak more heat than others, the more heat leaked to more energy you need to sustain temperature.
 
65535 said:
I merely meant that depending on seals between bricks and overall construction some ovens leak more heat than others, the more heat leaked to more energy you need to sustain temperature.
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True, once I patch up some of the leaks in my oven, it should get hotter even faster. Problem is the high temperature cement develops cracks over time, but my oven can still reach 1200C no problem.
 
The original question is kind of like asking how much HP does a car need to hit 60 MPH.

In theory, on a perfectly insulated oven, you could eventually hit 1100C with just one watt. It would just take a long time. In reality, there are heat losses you have to overcome, and you want to hit temp in a reasonable amount of time.

The Evenheat knifemaker's HT ovens are between 3100-3600 watts. The Paragon oven is 3600 watts. Both of these ovens reach temp fairly slow, so I might use that power as a starting point.

My Lindberg Blue oven gets to temp quickly with a similar amount of power. I think the difference is insulation, not power. So I'd insulate it well. I'd also cover the heating elements on the inside - some of the ovens don't, but I think they should.
 
My homemade oven has a layer of soft brick set so the 2 1/2" thickness is toward the chamber, this is surrounded by a layer of kaowool that takes care of any leaks between the brick joints and allows the bricks to expand and contract. The bottom bricks set on the hard high temp insulation board instead of kaowool for stability. I used 309 stainless welding rods to pin all the bricks together. I have a chamber appox 4x4x22. I run 50 ft of 14 gauge Kanthol with the coils made by wrapping on a 1/2 rod. It right at 20 amps of 220v (4400 watts) and will hit 1500f in a little over 10 minutes. 1850f in a bit over 15 so I am sure I could do 2000 in under 20. I tried lighter wire (I think it was 18) and it took longer and the wire will not last as long. I changed the wire when it broke off one of the terminals. It takes more heavier wire to keep the amps in the same range but, in the long run it is worth it. I wish I knew a good way to coat or cover my elements to keep down oxygen exposure as I believe this is the enemy to coil life.
 
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Thanks guys, im making 2 ovens, the internal dimensions are

10*6*100 cm

and

10*6*30cm

Regards
 
I dont will use bricks to buils the oven, just will use 1" refractory ceramic fiber board + 2 layers of kaowool
 
ib2v4u said:
My homemade oven has a layer of soft brick set so the 2 1/2" thickness is toward the chamber, this is surrounded by a layer of kaowool that takes care of any leaks between the brick joints and allows the bricks to expand and contract. The bottom bricks set on the hard high temp insulation board instead of kaowool for stability. I used 309 stainless welding rods to pin all the bricks together. I have a chamber appox 4x4x22. I run 50 ft of 14 gauge Kanthol with the coils made by wrapping on a 1/2 rod. It right at 20 amps of 220v (4400 watts) and will hit 1500f in a little over 10 minutes. 1850f in a bit over 15 so I am sure I could do 2000 in under 20. I tried lighter wire (I think it was 18) and it took longer and the wire will not last as long. I changed the wire when it broke off one of the terminals. It takes more heavier wire to keep the amps in the same range but, in the long run it is worth it. I wish I knew a good way to coat or cover my elements to keep down oxygen exposure as I believe this is the enemy to coil life.
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There might be ceramic coatings for protecting the coils, but they would be horribly fragile. Using an Argon Purge and a well sealed unit will basically let your elements last forever. I believe they make ceramic sleeved elements that don't oxidize due to the ceramic shell.
 
cotdt said:
I have a 0.18 cubic foot chamber, with 4000W of power. It took about 12-15 minutes to reach 1100 °C, another 10 minutes to pass 1200 °C. Most ovens are bigger than mine, and would therefore need more power.

That said, most US households won't be able to output more than 4000W of power. Most commercial ovens are about 1600W and seem to do just fine, but I'm sure that they would take a long time to reach 1100 °C.

My advice is to use as much power as your power line can support. That way you can reach your temperature quicker.
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i think that mine will be something like 0.07 cubic foot. i think that 3500W will be OK, right?

here we use 220v so will be easy to reach the 4000w limit.
 
samsagaz said:
i think that mine will be something like 0.07 cubic foot. i think that 3500W will be OK, right?

here we use 220v so will be easy to reach the 4000w limit.
Click to expand...

I don't know if it's possible to make the oven that small, you don't want the knife to tip over and short the coils on each side of the oven. You also don't want the coils too close to prevent arcing.

Mine is 4"x4.5"x18" internal dimensions, top-loaded for the option of argon purge. You can try 4"x4.5"x9" but then you have to think of a way to get the right resistance Kanthal wire that is exactly 3.5' feet in length after stretching. With my 240V power supply, 16 gauge Kanthal coil stretched to 6' feet gives the perfect resistance to get 4000W. But 9" inch long oven, you want 3.5' feet. You would have to work that out.
 
is possible to make an argon purge at home? i never read about that stuff, where can i get mre info? looks interesting.
 
samsagaz said:
is possible to make an argon purge at home? i never read about that stuff, where can i get mre info? looks interesting.
Click to expand...

No reason why not, top loaders work a bit better because you don't have a door on the side for the Argon to "spill" out of as it pours almost like water at room temp since it is much denser than Nitrogen in air.

All you need is a well sealed oven a tank of Argon a regulator and a feed line going into your oven. You'll want some venting, but mostly sealed. Do NOT use any high pressures if you do.
 
nice, is possible to find the diameter of the coil that i need to make?

For example, i want the oven has 5000 Watts in 2 phases of 2500Watts each one. Now, then need something like 11A => i need like 20 Ohms.
Looking at the table of resistance, using

1.0 wire diameter need 8.5mts
1.5 wire diameter need 19mts
2.0 wire diameter need 35mts of wire,

now need to figure how many mt i will get after i create the coil.
 
samsagaz said:
nice, is possible to find the diameter of the coil that i need to make?

For example, i want the oven has 5000 Watts in 2 phases of 2500Watts each one. Now, then need something like 11A => i need like 20 Ohms.
Looking at the table of resistance, using

1.0 wire diameter need 8.5mts
1.5 wire diameter need 19mts
2.0 wire diameter need 35mts of wire,

now need to figure how many mt i will get after i create the coil.
Click to expand...

You also need to figure out what stretched coil length you need. Use 1/2" inch for the diameter of coil, and resistance tables for Kanthal A1 wire.
 
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