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Help needed in understanding heating coil math

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Hi all.

If this topic have already been covered then i will be most thankful for a link.


I want to build an electric furnace, Both for heat treatments and for pottery. 

I have a given dimensions and i need to figure out what size and resistance coil i need.

There are lots of calculators out there but they all "attack" the problem on a different angle then the one i want.

Basically my problem is this: I have a space that i need to heat (the inner space of the furnace) but i have no idea how long of a coil i need. More then that, i do not know how many watts i need to heat the space in a reasonable time. 

When i'm building a gas forge i know that in order to get good results i need X number of burners (of a certain type and characteristic) in order to heat a Y area. I have no idea how many watts i need to heat a certain area in a reasonable amount of time. 

I saw a youtube video of a guy called VegOilGuy who build a melting furnace of 1200 degree but it takes him 3 hours to achieve that. 




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19 minutes ago, ThomasPowers said:

Without knowing anything about how it's going to be lined you are basically asking:  "I have a bucket with a hole in it; how long will it take me to fill it?"

Ok, i get that.

After some calculations, it appears that i have a 210 liter furnace. 

or about 7.5 cubic feet. 

I will be using Kathal A1 wire. My power is 220V but i can go 3 phases if needed, i really prefer not to. 

What other info do you need? 

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As noted on this site http://www.joppaglass.com/elements/mainelpg.html you need additional information regarding temperature and insulation. I use his book which has a great calculator for power requirements as well as coil design. You can sometimes get away with single phase, but a kiln that size will need a large circuit breaker and feed wire to push the power required out to the elements. I don't know how things work in Israel, but demand charges may come into play as well as usage charges.

In any event I urge you to hookup with an electrician for the wiring, at least, and see if you can find an electrical engineer to help you with the design and controls. 

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Thank you.

I know all the additional info, i just did not think it was necessary. 

An electrician will look at it after i finish, especially if i will need to use 3 phase. However, i do have this furnace electric circuitry, it is just that the entire furnace got totaled on the move and i need to rebuild it. I can just copy but i want to understand and improve whenever i can.  

BTW, 200+ liters are calculated from the internal dimensions of the clear space. Now thinking of it, when i heat the furnace to X degree i also heat the isolation material. Meaning that the dimensions are way way bigger. No? 

It appears that 3 phase furnace is a must. xxxxxxxx

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  • 3 months later...

i hit 2300F without any problems using 18G kanthal a1 in my 220V furnace. I calculate on the short side for coil length and fine tune input voltage with a 10,000w voltage regulator. Voltage regulator makes the resistance calculation very forgiving and greatly improved pid controller temp variance. 

my build https://davidproberts.com/diy/2300f-heat-treat-oven/


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