Heat treat oven build

J

JustinWoody

Joined
Nov 10, 2017
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25
Building a heat treat oven. I am running 110/120v, (not sure which). I have the Auberins PID controller with ramp/soak, a 40a ssr with heat sink and k type thermocouple. Inside space of my oven is 4" tall, 5" wide and 18" deep. My element is 50' of 20g a1 kanthal wire coiled at about 5mm id.
I habe no idea what a sticky is, or how to find it so my question is, does anybody have a good wiring setup for what i have?
What may need to be changed to make this work better? I am sure bumping up to 220v will be one suggestion.
Auberins has not been very helpful. They did not send out a manual with the PID controller and the one i downloaded from them leaves a lot to the imagination.
Any help would be great!
 
I am also building an oven using auber electronics. All the pins on the pid and ssr are marked clearly, for the models i got anyway. I suggest google image searching some schematics and get the idea clear in your mind. Once you understand what each component does, it will be natural to wire it. I didnt even follow a schematic when i sat down and wired mine because i just thoroughly understood what everything did.

The general idea is the pid is on a 120v circuit, and the ssr+heating element is on a separate, parallel 120v circuit.

There is also a low voltage circuit between the pid and tc, and the pid and ssr. When the tc tells the pid the temp, and it is too low, the pid tells the ssr to activate. The ssr is just a switch, and if the pid is activating the ssr that switch closes and current can come from wall, through the ssr, and through the heating element.

There should be aswitch to turn on the pid circuit, and a switch to turn on the ssr+heating element circuit. I think this is bare minimum.

Optional items are a fuse (50milliamp for my setup) in the pid and ssr low voltage circuit so if one fried it doesnt fry the other. A fuse or breaker on the ssr+heating element circuit, if you want to limit the current to something smaller than your breaker for the outlet. And possibly indicator lights.

The thing about indicator lights is current has to flow through to light up, so if you put a light in series on the ssr+heating element circuit, it will only light up if the heating element is getting power, which only is meaningful if the light is on. If the light is off, it could be that the heating element is just not getting power because the ssr is not activated, but in a split second the pid can activate it and the heating element could come on while you are messing around in the oven. Or the light could be broken. Or the ac power to the ssr might be switched off. To get around this, you usually should run indicator lights in parallel circuits i think. For example, an indicator light would have a black wire branched out between the switch and ssr, and then a white wire coming back in between the wall and heating element, that way the light is always on if the hesting element has any chance at all of coming on.
 
Ok. Thank you gor this info! How do you figure oit what size fuses to put in the system? I have a 40a ssr running 50' of a1 wire coiled at 5mm inside diameter.
 
The amp rating of the ssr is just its rating, it can handle up to 40amp, although it should have much less current going through it. The heating coil is the only significant load in the ssr+heating element circuit, and so whatever amps your heating element says is about what it will be drawing out of the wall. Then i would get a fuse a few amps higher so it doesnt burn out with normal usage or if the current varies slightly.

Did you coil your own wire element? If you bought an element it should say what amps it pulls from a given voltage outlet.
 
As far as what gauge wire you should use to wire stuff, probably need to ask the other guys here. I was using too small wire initially and they set me straight. Apparently you need ti be fairly conservative on amp ratings for stuff and stay well under the limits because ovens run continuously for long periods.
 
Yes i coiled it myself. I coiled a 50' spool of 20g. The guage wire was a suggestion from another smith. He never did give me a length. Putting an ohm meter at each end of the wire it shows just over 50 ohms.
 
The formulas are
Volts = Amps × Ohms
Watts = Amps × Volts

So on a 120vac and 50 ohms that means the current is
120/50 = 2.4
On a 249vac it would be 4.8 amps.

That is awfully low. My element reads 11 ohms. If any coils are touching and creating a short, it would read lower, btw.

I looked at the ohms per feet for 20 gauga kanthal and your measurement seems reasonable.

If you cut the coil shorter it will have less resistance and will pull more current. So if you cut in half for instance it will be 25 ohms and the current is 4.8 amps from a 120volt supply. From a 240volt supply it would be 9.6 amp.

Figure out what watts you need and if you are going to use 120 or 240 volts, then determine the current you need, then you can find the resistance and cut the coil accordingly. Other posters here would be better to tell you what you need to be running.
 
Thank for that information! I just got the full diagram for wiring up this controller. If i can figure out how to post a picture i upload it so others can use it if necassary.
 
In determining what watts and current i need, is that what my outlet provides or the draw from my pid and ssr?
 
Just wanted to mention: When running full continuous wattage like that, 80% of your circuit's amperage is your max, not 100%.
Electrician told me that, what do I know.
 
So, yesterday i found a video that shows how to figure up the power needed to run an oven. After doing all the math, (which i am not done yet) i figured out that my oven will be really underpowered.
In order to run 120v on my oven, i will have to drop to about 13-14g wire. It is possible but does not seem very efficient.
So i am going to see about getting 220 ran into my garage so i have the power i need.
When i get it all figured out, i will try to post a condensed formula for everybody here.
 
I had 14 gauge wire in my oven and it held up fine, even with being re-positioned several times after it had been fired several times. I have gone to 16 gauge to up my watts, and it seems fine so far. I personally wouldn't go thicker than 14 gauge. DC knives has some great information and calculators for figuring out all aspects of this build, including wire size for given space/ watts needed, length of wire needed, and length of coiled and stretched elements.
 
Kevin McGovern said:
I had 14 gauge wire in my oven and it held up fine, even with being re-positioned several times after it had been fired several times. I have gone to 16 gauge to up my watts, and it seems fine so far. I personally wouldn't go thicker than 14 gauge. DC knives has some great information and calculators for figuring out all aspects of this build, including wire size for given space/ watts needed, length of wire needed, and length of coiled and stretched elements.
Click to expand...

Interesting! According to my figures i can run 35' of 14g wire and get right at 2k watts power. If i go any longer or any smaller, i loose power.
 
I ran the numbers through the calculator Dan Comeau has on his blog. I played with it to get to the wattage i wanted (4000) and to fill the existing grooves in my oven. My oven is 220v. I wound up using 2 elements each with 22' of 16AWG wire. you can drop the length of the wire somewhat to get more watts, but the result is early burnout of the coils, and if they aren't long enough to run the length of your oven 2x on both sides, you may have uneven heating. Basically, I used as much stretched element as i could fit, and adjusted the gauge to reach the watts I wanted. Make sense?
 
20 gauge is pretty light for a HT oven. I suspect it will have a much shorter life. 14 gauge is much better.

A stick is a thread or information "stuck" to the top of a page. If you look at the top of the Shop talk page, you will se four to six "stickys". Click any of them and you will get the thread full of information. Just follow the path from tere. There is info on forges, HT ovens, PIDs, etc.
Any new maker should read all the stickys ... even the ones that don't seem relevant to them. It will help them a lot in making knives, provide info you may want to come back to later on, and teach them a lot of basic metallurgy.
 
Kevin McGovern said:
I ran the numbers through the calculator Dan Comeau has on his blog. I played with it to get to the wattage i wanted (4000) and to fill the existing grooves in my oven. My oven is 220v. I wound up using 2 elements each with 22' of 16AWG wire. you can drop the length of the wire somewhat to get more watts, but the result is early burnout of the coils, and if they aren't long enough to run the length of your oven 2x on both sides, you may have uneven heating. Basically, I used as much stretched element as i could fit, and adjusted the gauge to reach the watts I wanted. Make sense?
Click to expand...

Yes it does. Most of the figures i have now are for 120v. I just started playing with the 220v last night. Then i started feeling sick again so i quit. Been down most of the day today so hopefully i will feel better tomorrow.
 
Stacy E. Apelt - Bladesmith said:
20 gauge is pretty light for a HT oven. I suspect it will have a much shorter life. 14 gauge is much better.

A stick is a thread or information "stuck" to the top of a page. If you look at the top of the Shop talk page, you will se four to six "stickys". Click any of them and you will get the thread full of information. Just follow the path from tere. There is info on forges, HT ovens, PIDs, etc.
Any new maker should read all the stickys ... even the ones that don't seem relevant to them. It will help them a lot in making knives, provide info you may want to come back to later on, and teach them a lot of basic metallurgy.
Click to expand...
Thanks for the info. I will see if i can find them and read them.
 
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