Homemade Heat Treat Oven Element question

Fross

Fross

Joined
Jan 28, 2008
Messages
133
Hello guys,

I am looking for some advice from someone that has maybe built their own heat treat oven, or knows something about the electrical work involved.

I am currently in the shopping phase of making a heat treat oven from Rashid11's DIY video and google group page. I have decided to make the oven 26.5" x 4" x 4 1/2" inside dimensions instead of his 18" x 4" x 4".

I have found everything I need, k23 bricks from local supplier, K type shielded thermocouple, PID controller, misc wiring elements like ceramic tubes and such for passing element ends through oven wall and a DC input to 220v output 25 amp SSR.

Here is my dilemma, I have everything accounted for but the Kanthal A1 Heating element. I think I have figured out exactly what I need, but I honestly need someone to check my math and my reasoning as I am far from any kind of electrical engineer. Below are my oven specs and the electrical being dedicated to it.


26.5" x 4" x 4 1/2", running off of a 220v 20 amp dedicated circuit. Here is what I am coming up with as far as element needs if I push 17 amps through 17 ga kanthal A1(I have tried and tried to look up ampacity of this kanthal a1 and figure out what the max amp rating is on certain gauge wire but to no avail, Rashid seems to be using 18 gauge and pushing it to 15 amps so i figure 17 amps on 17 gauge should be fine, I WILL find out before making any type of purchase) if anyone knows for sure, please chime in.

OK so with 17 amps using kanthal a1.

220v/17 amps gives me 13 ohms. So to get 13 ohms out of kanthal a1 17 gauge wire rated at .427 ohms per ft. I would need 30.5 ft(366") of wire. If I coil this wire TIGHT with a ID of 5/8” or .625" and the wire itself is .045" diameter I would get a coil approx 26" long minus the 12" of lead I will have for connecting the coil. With this length of coil it will give me an almost perfect 2:1 ratio once stretched to the perimeter of my oven(2:1) I believe 2:1 is what is called for, please correct me if i am wrong the internal perimeter of my oven will be 61".

Here is how I am getting these calculations for length of wire and coil,

length of wire: ohms(13) * ohms per ft rating(.0427) = wire length(30.5')

Lenth of coil: Wire length in Inches(366") / Inside Diameter of coil(.625") * wire gauge(.045") = coil length (26)"

My question after all of this hoopla is, am I thinkin' right, and will this element with 220v - 17 amps get me to temp like I need(FAST) . I know it’s a lot and I appreciate all the help I can get. Thanks.
 
I used 40 ft of 18 gauge wound around a 1/4" mandrel. My chamber is roughly the same size but only about 16" long. It could probably work for a slightly longer oven, but I don't know about 26".
 
I have a similar setup, 240V at 16.7A. It reaches 1500F in about 4 minutes. Yours is longer and a little less total power, so probably 6 minutes.
 
cotdt said:
I have a similar setup, 240V at 16.7A. It reaches 1500F in about 4 minutes. Yours is longer and a little less total power, so probably 6 minutes.
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Are you using 17 or 18 gaage wire, and what is the length of your oven, if you dont mind me asking?
 
go to the paragon web site and look at the specs for the kmd 24. you should also look up the formulas for power amps and current. the basic ohms law is what you want. with the setup you have you are going to draw 17 amps and create more than 3700 watts. got to www.the12volt.com/ohm/page2.asp for an easy calculator. one more thing you are going to need at least 16 gauge wire and probably larger.
 
Bill Burke said:
go to the paragon web site and look at the specs for the kmd 24. you should also look up the formulas for power amps and current. the basic ohms law is what you want. with the setup you have you are going to draw 17 amps and create more than 3700 watts. got to www.the12volt.com/ohm/page2.asp for an easy calculator. one more thing you are going to need at least 16 gauge wire and probably larger.
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Ok, so If I use 15 gage wire I would need right at 48' making a 58" coil, I could loop the element like they do in the KMD24 and still get my 2:1 seperation and have a lot more coil to work with, would this work? I know I am pushing a lot of wattage per sq inch of this wire, but I dont know what its limits are, cant find that information, everyone else that has done it seems to be running about the same wattage.
 
frossbyte said:
Ok, so If I use 15 gage wire I would need right at 48' making a 58" coil, I could loop the element like they do in the KMD24 and still get my 2:1 seperation and have a lot more coil to work with, would this work? I know I am pushing a lot of wattage per sq inch of this wire, but I dont know what its limits are, cant find that information, everyone else that has done it seems to be running about the same wattage.
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If I were where you are at and trying to do this I think I would buy the coil for the kmd24 from paragon you can strech it to cover the extra length of your oven no problem as long as it has not been fired. this way you are not guessing at all.
 
I built an oven with 17A through 15g wire like you mentioned.

Its working great. I wrapped around a 3/8" rod and cut 1/2" slots.

You can get a 50' spool from DuraLite for $15.
 
patriqq said:
I built an oven with 17A through 15g wire like you mentioned.

Its working great. I wrapped around a 3/8" rod and cut 1/2" slots.

You can get a 50' spool from DuraLite for $15.
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Do you mind sharing what size oven you built? I am wanting to know the area in which you are heating. Also are you running 220/240v?
 
patriqq said:
Sure -

9" x 4.5" x 15"

You can see pics at:

http://picasaweb.google.com/patriqq/ShopBuiltOven#

Yes, I'm running 220/240 through 45-47 ft of 15g.
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Wow that is a nicely executed design, seems extremely functional. Since you are heating over 600 cubic inches of space there and I will only be heating 480 or so, this should work awesome and FAST. Im still thinking about whether or not I want a side open like yours or a top open, top open seems like it will get a good bit hot standing over it but seems it would be easier to access.

Did you just use a run of the mill PID controller like you would find on ebay with a 25 amp ssr? Last question, I swear. Its my day off and Im spending it researching, :D. Thanks again for the info.:cool:
 
No problem -

yes I use a cheapo SSR and PID from Aubers. A lot of us here have bought from Aubers with satisfaction.
 
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