Wiring a Heat Treat Oven

silver_pilate

silver_pilate

Joined
Oct 30, 2002
Messages
3,974
Well, I finally couldn't live without the improved temp control of a heat treat oven and decided to build one using the design seen on the British blades website.

I have a programable PID temperature controller (thank you ebay), a solid state relay (thanks again, ebay), a 9" kiln-type ceramic insulated K thermocouple (ebay...seeing a pattern?), and I'm currently building the casing.

My question is this. The Kanthal elements I'm using will be wired in series to pull a total of 13amps at 240V/AC and deliver 3100 Watts. They will be powered off of the relay which will be controlled by the SSR outputs on the PID. Am I correct that dryer outlets are typically 240V 20amp outlets? So I should be fine powering the elements off my dryer outlet, right?

Also, the specs on the controller I'm using say it will take 85-260V/AC to power it. Would there be any benefit to running 120V to power the controller, or can I just run it straight off of the 240V I'll be using to power the elements (before the relay, of course)? It seems that since it's rated to take 240V, and the big juice pull wouldn't be going through the controller, it would be fine, but I wasn't sure if there were any longevity issues of 240V vs 120V.

Anyway, I appreciate any help I can get. I'm handy with most things, but I just need some reassurance/advice when it comes to electrical as I really want to be careful (obviously :D).

--nathan
 
You probably have more than 20 amps on your dryer outlet, but you should have a look in the breaker/fuse box before you do anything. That's the easiest way to know for sure. I don't think you'll have any problems running the controller on 220 if it's rated to 260. Just wire in some fuses when you build it, don't rely solely on whatever is in your fusebox, because you could set your relay on fire or burn out your elements long before you trip your house breaker/fuse.
 
Dope...noticed that dryer outlets are typically 220V, 30 amps.

Now, I guess my main problem is that I need to know how to wire it all together from a dryer cord. My outlet is the older 3 prong variety. Can anyone give me an idea/schematic as to how I will wire the controller (2 posts with polarity not mattering) and the SSRelay into the cord? If I can do this myself, I will, but I'm starting to think I should find an electrician to do this for me.

--nathan
 
Nathan

It sounds like your controller is currently wired to take a 110 V input. The manual for your controller should show how to wire it for 240 V. If you don't have a manual, you should be able to download one from the manufacturer's website.

The difficulty with wiring your controller for 240 V is that you usually only have one 240 V receptacle in your house. It may be nice to be able power up only the controller to program it then plug in the power for the heating elements afterwards. This means that you will need two plugs. Otherwise, you can wire both the controller and the heating coils to the same plug and put a switch in series with the heating coils.

Phil
 
OK, so here's the diagram for wiring the PID:

TET612-Pin.jpg


Obviously, 6/7 are for the SSR and 9/10 for the K-type TC. How do I wire power to the controller? Likely, I'll run the 220V to the SSR and tap a wire off of that to power the controller before the relay. I'll put a fuse in-line as well. The manual says the polarity of 1/2 doesn't matter.

Now, if I run a typical 3-prong 220V extension cord to the SSR, how do I set that up? Do I combine both live wires into the relay and run the ground/neutral to the controller? Do I ground/neutral to the case? How is the kanthal element wired into the SSR? I'm just having a hard time picturing it. Once I've got my head around it, it won't be a problem.

If someone with the know-how will point me in the right direction, I'd be greatly appreciated. If you could start with the 3-prong 220V extension cord and walk me through what to hook up where, I'd be in your debt.

Thanks!

--nathan
 
Here is as far as I have gotten:

Wiring.jpg


What do you think? Am I on the right track so far? I've read through multiple posts, but I am a very visual learner and have a hard time getting the big picture.

I guess the thing I'm not sure on is the power for the controller. I'm not sure what to attach at posts 1 and 2. And also, where do you attach the ground/neutral from the 220V source? Just trying to fit the last pieces in my mind.

--nathan
 
make sure to ground the oven. If it has exterior made out of sheet metal, ground that.
Wire up the 240V straight to the PID controller, it is fine. No longevity issue between
120v and 220v :) . This way you don't have to wire separate line to power up the PID.

However, with my, homemade oven, I have them separate - this way I first power up the PID, set the temp I want and _then_ power up the heating element by flipping the 240v breaker . Not sure if there's much benefit to this, but I kind of got used to it being like that :)
 
rashid,

So I will ground the frame of the oven to the ground from the 220V source.

As for the controller, for the number 1 and 2 posts (power source for controller): do I run two live wires to those from the 220 L1 and L2, or just one live wire and the ground from the 220V/oven?

That's really the last piece I'm not sure on.

Thanks for all ya'lls help!

--nathan
 
You can run both the hot legs for the 220 to the controller or a hot and a ground to the controller for 110 to the controller. I ran my 220 s 2 hots (actually 110 legs) to a 30 amp, 2 position switch. I broke off 1 leg on the input side and ran it over to the pid controls input and then connected the pids other input to the oven and the control box's ground. This gave me 110 to my pid input. I ran my 220 inputs ground leg to the ovens metal box via a lug in the metal mounted box I used for the controller and switch. I then ran one output of the 220 switch to the ssr and the other to the heater element, like your diagram. The other end of the element wen to the ssr, I also mounted a push button switch near the door and a arm on the door so that when the door is completely closed the switch is on. This switch is wired in line from one of the pids + line to the ssr. This is my interlock so that the coils are not hot when the door is open. This way when my unit is plugged in the pid can be viewed and set then when I want the oven to heat I flip on the switch and if the door is closed it heats up. You could place a small switch in the line from the large switch to the pid control input. This would allow you to completely power the unit down while having it plugged in. I could have also got the pids input off the output of the switch and powered everything down with that switch. But, with the door closed the unit would heat anytime the pid was on and viewable and below the set temp. I also use a 20 amp breaker and 20 amp 220v plug in I wired in my shop for my 220 volt air compressor. Hope this helps more than confuses. Jim
 
Yes, make sure that all the metal chassis parts are grounded. Run a 12 AWG wire from the door to the rest of the box so that you do not depend on the conductivity of the hinges. This is standard practice and is required by all the safety agencies that I have encountered (UL, CSA, CE).

Using a switch or breaker to cut off power to the heater coils is a good safety measure. It will prevent the heater coils from becoming energized if some fault occurs in your PID controller or in the SSR while the oven is plugged in. Jim's suggestions would make it safer and more convenient to use.

What is the make and model of your PID controller and SSR? It would be a lot easier for other people to help you if you provide this information since they are not all the same.

The first drawing that you have posted seems to imply that both pins 1 and 2 may be connected to hot(s). This would mean one would be connected to hot and the other to neutral with a 110 Vac input and both would be connected to the two hots with a 240 Vac input. You should confirm this by reading the manual.

Sometimes the ground connection is made using a stud (often tinted green) with a "ground" symbol near it. You have posted a picture of the terminal block for it so I am guessing that you have acess to a copy of the manual. The manual should have wiring diagrams showing how to connect up the power and the ground for the controller.

There are different SSR's with different input options avalilable. Hooking up the input to the SSR incorrectly may blow it up. If the output of the controller is not compatible with your SSR, either one may be damaged.

Phil
 
Yes may of these solid state devices will take a wide range of inputs, but go outside those ranges and kerpowee. For example your PID seems to take a wide range of inputs, but some may not take the same and would fry upon getting 220vac input.
 
The problem with having an inline switch that breaks the spiral circuit is that it has to establish/break fairly strong
current - 20A or so. So unless you use properly rated switch, it might burn out rather quickly.

A much better way is to instead use a NO (normally open) switch, that becomes closed
when the door is closed. And that switch, instead of breaking the spiral circuit, should instead
break the "SSR out" circuit (one leg will do, no need to do both) from the PID to the SSR. This
way you can use a tiny switch ($2 deal at nearby RatShack), as the current is literally ~10 000 times less :) .

Ground is of almost importance - 240V shocks pretty badly and you don't want to be buzzed while having a 2000F
oven right next to you . Do run a flex wire from the door to the rest of the oven.

The deadliest accidents happen when both hands are involved to where current can
establish a path between both of your arms. And such path will always go through
yer heart . When I worked on radars, I'd habitually use only one hand when there was
any danger of getting shocked, the other hand you keep in a pocket.



you can safely connect the 2 "hot" legs of 240V to #1 and #2 terminals.

the SSR output almost universally produces 5V DC output, while almost all SSRs
are rated to take in 3V-15V DC as control signal, so you should be fine


And some more on subject of safety.

In my case, when I am ready to take stuff out of the oven, I flip the breaker off before taking anything out.
It is quite possible that as you take your blades out, you might accidentally touch the spiral. And unless you
use the breaker to kill both legs of 240V circuit, that spiral WILL BE HOT (well, it will be hot all right as in glowing
white or yellow, but it will also have the 240V on it !). So, use insulated tongs, wear a glove. Dont lean against
or hold onto the oven with your other hand as you do that, unless u r 100% sure that there's no voltage on the
heating element.

For me, it is ez as I HT in the garage and my oven is 3 yards away from the breaker panel.
 
Thanks so much for all of your input. I'll make sure I have the box fully grounded and the door as well. I'll definately be sure to throw the breaker before opening the oven.

The frame is all but done and the bricks are mostly in. Just need to redo one brick to make the opening as flush as possible to seal better. It's been a fun and messy project that's cost me some sleep (hard for me to start and not finish a project). Just waiting on the rest of the parts and we'll see how she does.

Thanks again!

--nathan
 
Thanks again for all your help!

Here's the final diagram I am planning:

Oven.jpg



The big breaker switch will power on/off the entire oven/controller. The switch in line to the + on the SSR will allow me to switch the coils on/off by activating/deactivating the relay while still keeping power to the contoller. Any ideas as to what size fuse to place in line to the controller?

So, with the main power switch on, I can program the controller with the SSRrelay not powered, i.e. no power to the coils. When I want the oven to heat, flip the switch to activate the relay. When I go to remove the knife, flip the switch to deactivate the relay. When I'm done, throw the 20 amp switch to power down. Sound good?

Now just to wait for the final parts to get here!

--nathan
 
Nathan, you have a problem with your wiring diagram. Do NOT use your earth ground to ground the (-) power input of your controller. If you have 220 VAC coming into the breaker you have TWO hot lines of 110 VAC each, and your 20 amp breaker/switch has to be a 2 pole switch. You mentioned that your dryer plug is a 3 prong...that is the 2 hot legs with an earth ground. There is a very good reason that modern dryer (and all 220 vac) outlets have 4 poles and a separate common and ground leg...and it is specifically to prevent what you are doing.

The short fix to your last wiring diagram is to have a 2 pole switch (and 2 fuses) and run both legs to the power input, one to the (+) and one to the (-). Keep the ground as a safety ground and nothing more.

Keep the power cord at 10 AWG or larger too if you are plugging it into a 30 amp outlet. 8 AWG is ideal.

If you want to wire it like you have shown, go ahead and go 110VAC all the way. You diagram is a hybrid between the schemes and gives me the willies...basically if you have a bad ground you can get line voltage at the skin of your box. Not good!

I'm not confident about the SSR wiring either but your diagram lacks the detail I would need to figure it out. Remember, with 220 VAC you have 2 hot lines and you have to switch them both to keep things safe...otherwise you can have 110 VAC showing up in unexpected places on your (planned) "common/neutral" line even with the SSR off.

IMO you are much better served by sticking with a 110 VAC circuit and the simplicity it offers...the difference between 110 and 220 at the power levels you are running is negligible.
 
It was my understanding that the 220 was the way to go to power the oven for faster ramp times to temperature.

I am aware that the 220 has 2 lines of 110 and I have a 2 pole switch that I am planning to use for the power switch.

I guess the best way would be to go ahead and power the controller with 220V by using poth 110 lines instead of using the ground like you said. That's why I'm posting this stuff here, to keep myself alive :D. I also plan on having an electrician friend of mine look over the plans before I proceed.

I'll go ahead and keep the entire thing 220V to keep the ground as a true safety.

Oh, and BTW, the reason I haven't posted the specs on the controller is that I don't have many. I've got a very rudimentary manual to help me program, but this is a generic type controller, not a name brand. According to the details I have, the wiring to the controller is correct, and I know the controller is rated to take 110 or 220, AC or DC.

Thanks again for all your help, and thanks for keeping me out of the burn unit or the ground!

--nathan
 
Nathan

Make sure that the switch in between the controller output and the SSR is rated for 220V. This just to be safe since you don't have much information on your controller. It would not need a high current rating for this function.

CDH is correct that you should wire 240 V to the input of your controller. Otherwise you are using the ground as a return path for the current drawn by your controller.

Get a panel mount fuse holder for the controller power fuse. If the documentation does not give a current draw for 240 V, you have three options.

1) Call the people who sold the controller to you.

2) Measure the current using a clamp on meter around one of the wires going to the power input of your controller. Monitor the curent when you first apply power to the controller. Run it through various functions including turning on the SSR. Take the highest measurement and add about 25% to get the fuse rating. Use a slow-blow fuse that is equal to this value or the next larger rating.

3) You can experiment (carefully). Start with a 1 Amp slow-blow fuse. If it opens, install the next higher rating. I can see no reason for needing to go beyond a 2 or 3 Amp fuse for this type of equipment.

Good luck.

Phil
 
Would it be possible to run parallel coils off 110V current? The tutorial on BritishBlades didn't mention the voltages, and I know on Rashid's second design he mentioned 110 wasn't enough.
 
You could run 2 parallel 110 vac heater coils it would mean that you would need a 110 source rated for at least 35 amps. Probably have to go with a 40 amp breaker and about 6 gauge wire, Then find a 40 110 plug and I am not sure the make those. You could use a heavy amp rated plug for any voltage though. Not a good plan. By the way the controller uses such a tiny bit of power that using the ground as its neg is not a problem IMHO. You could uses a 4 wire setup. Yes but, it you open your breaker box and check the negative legs and earth ground are common. The 4th wire is to keep you from setting up an unbalanced draw. The controller just aint going to make that happen.
 
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