Trying to Put together plans for a 110V Home Made HT Oven

theWeatherman

theWeatherman

Well-Known Member
Hey guys,

I am having problems putting together plans for a 120V HT. I am going 120V because I do not have 220V and it will not happen. I was hoping someone had made a 120V Oven and not only had some plans but could talk me through it. Oh, and I have seen a couple sets of plans but they were for the 220V.

Thanks,

Brian
 
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Hi Brian,
how much amps can you pull from your system? I am from a 220V country so I do not know the exact specs for the US electrical system. I found a reference for the use of 110V and 26A max. Is this correct?
I am a metric guy so all my calculations are made metric.
As an example:
With 110V and 26A you can pull a max of V*A=110*26= 2860Watts. Its advisable to stay a little below this, you dont want to pop the fuse every time you turn on a light when the oven is running. So I would say you best stay between 2000-2500W for your oven.

This determines how big an oven you can build . If you look at the commercial ovens they use a power ensity of 0,8-1,1W/cm² chamber surface. So if you take your 2500W you can build an oven of 2200cm² total chamber surface which will give you a power density of 1,13W/cm². Its up to you how to design the chamber to suit your needs, squarish, rectangular etc.

As its used for blades you can reduce the diameter to make the oven longer. 10cmx10cmx50cm long or if you use 15x15cm diameter you can make it 29cm long. Depends on your needs.

After you have settled for the size you have to think of the element to use. The most importanf factor influencing the life of a heating element is its surface load. Kanthal recommends a surface load of up to 3,5W/cm² wire surface for spiral elements in grooves used in air. If a On/Off control is used (PID) it should be reduced a further 20%.

So not all wire sizes can be used, you have to balance between power, surface load and ultimately the stretched element has to have a size so it fits into the oven.

Best you tell me what size of oven you want to build then we can work out what size wire of what length we need. Maybe its possible to use a single element from thicker wire or you can use two elements of thinner wire connected in parallel.
 
Brian,
Is there some reason that 220V will not / can not happen? A 220VAC oven would be much more efficient in my opinion, as well as able to heat up much faster.

At any rate, what part of the plans are you hung up on? A 110VAC oven should be nearly identical to a 220VAC oven, if not a little more simple.
 
Andrew - I don't own the house or workshop that I live and work at, so I can't have 220V put in, owners saw no reason to and don't want to deal with it. So I am stuck with 110V until I either own my own house or get a different workshop. Both are not in the budget right now. As for being hung up, the problem that I have is not knowing if the chamber that I create will be small or big enough for the power allotments that I have. As well as what type of controls that I should use because there are a lot of different choices. I would like to just be able to set the oven to a temp, and soak the steel and then quench. It just gets confusing when there are so many different components that are available and I would like to do it simple and least expensive.

rolynd - I actually don't know the Amps that I have in my system yet, I need to go find out. As for a size I was thinking 16.5cm wide x 11.5cm tall x 45.75 cm deep (inner chamber); calculates to about 6.5" wide x 4.5" tall x 18" long (inner chamber)

Thanks for your help guys.
 
http://www.auberins.com/index.php?m...s_id=3&zenid=596672a29c8d9e0d34c6f6f7a3af52fd

IIRC, this is what I'm using on my oven. You can download the instructions and see the schematic for hookup. You'll need little more than an appropriately rated SSR (size based on amps you'll be pulling, which is based on Voltage and Wattage rating of your element), a couple of switches (power for the PID and I recommend power for the element as well, so that you can turn it off briefly while the door is open), a fuse for your PID and probably for your element, and then of course your Thermocouple.

Don't forget a heat sink for the SSR too, as they tend to get too hot and self destruct otherwise. If using a metal case to house your controls, this will probably be enough... just make sure to apply a moderate amount of heat sinking compound before you mount it.

Now, I just did a quick google search for kanthal element and this is what I found from budgetcastingsupply.com. It should work for your oven:

#7101: 120 Vac Kanthal Heating Element - 2300 °F Max

#7101 SPECIFICATIONS:

Material: Kanthal A1 Wire
Maximum Temperature: 2300°F
Power: 120 Vac, 13 Amps, 1550 Watts
Wire Size: .056", (15 AWG)
Unstretched Length: 34"
Minimum Operational (Stretched) Length: 60"
Maximum Stretched Lenght: 140"
Coil Outer Diameter: .285"
Pig Tail Length: 9"


That means at full draw you'll be pulling roughly 13 amps, so you probably want at least a 15 amp SSR. 20 to 25 amp would be even better and likely run a little cooler/last longer.

Tying this into a circuit with a 15 to 20 amp breaker should be fine, as long as your not trying to run grinders or other high draw equipement while your heat treating.

The biggest draw back (in my opinion) to using 110VAC as opposed to 240VAC is that your oven may take a little longer to heat up, but once it does, it should hold the temperature fairly well. A couple of things factor into your oven's efficiency is how well you insulate/seal the oven, what type of bricks you use, how big your cavity is, and whether you have any major leaks at the door or where your elements and TC are running into the oven.

A couple of ways to mitigate this are as follows:
1.Use refractory mortar to seal any joints between the bricks.
2. Use appropriately rated fire bricks (grade 23). You may think that grade 26 is better since it has a higher heat tolerance (2600F vs 2300F) but they actually don't insulate as well.
3. Use a door seal. You can use ceramic fiber rope similar to what they use on fireplaces, or a pice of kaowool (ceramic fiber insulation) between your door and the cavity.
4. You may think about coating the inside of your oven with ITC100 or something similar, as this holds/reflects heat a little more efficiently than just the brick alone.
5. When running your element, don't be afraid to made a few rows. My oven has 4 rows on each side, and 2 in the back (top and bottom) where the element enters from the back.

Side View inside oven:
______________________________
______________________________|
|_____________________________ Front
______________________________|

Something like the above diagram if that makes sense.

Ok... I think I've droned on long enough. Any questions?
 
The budgetcasting element is fine if you dont want to make your own but I think it will be struggling to heat an oven of your intended size up to temp.

The simplest control setup consists of a PID an SSR and a Thermocouple but I would advise to use a relais and a door switch in conjunction with the rest for safety reasons. You dont want to touch the live elements accidentally and pulling the plug everytime before opening the door is possible but a hassle.

If you want more power you can use 2 of the aforementioned budgetcasting elements and run them from two different wall outlets/circuits (each with its own breaker) at the same time. The Pid is usually able to control 2 SSR connected to it in parallel simultanously. This circumvents your 240V problem.

The circuit would look something like this: I would work the same for 120V, the (x) means not connected and the switch would be the door switch. Green is grounds. yellow is neutral and blue is live.
 
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rolynd said:
The budgetcasting element is fine if you dont want to make your own but I think it will be struggling to heat an oven of your intended size up to temp.

The simplest control setup consists of a PID an SSR and a Thermocouple but I would advise to use a relais and a door switch in conjunction with the rest for safety reasons. You dont want to touch the live elements accidentally and pulling the plug everytime before opening the door is possible but a hassle.

If you want more power you can use 2 of the aforementioned budgetcasting elements and run them from two different wall outlets/circuits (each with its own breaker) at the same time. The Pid is usually able to control 2 SSR connected to it in parallel simultanously. This circumvents your 240V problem.

The circuit would look something like this: I would work the same for 120V, the (x) means not connected and the switch would be the door switch. Green is grounds. yellow is neutral and blue is live.

pid-wiring1.jpg
Click to expand...

Couple of things:
I doubt he'll have enough room to run TWO elements, but even if he did, I doubt he'd have two outlets, from two seperate circuits from two seperate poles within close enough proximity to eachother to do what your suggesting.

Not only that, but I think it violates an electrical code or two to have two seperate circuits actively feeding one piece of equipment, even if it is "two separate" elements.
Then again, whether it technically does or doesn't, it's really not a safe practice to get into. There's a reason 220V outlets are run from a single breaker and a single conductor to a single box. Trying to "circumvent" electrical standards, codes, and ultimately common sense is what gets people hurt (or worse).

Not trying to sound like a jerk here, but I don't think that would be a very wise move.
 
Well, as said I am not from the US and I dont know how the electrical system/safety codes there exactly works. If the whole house is only able to use 26A max its definitely a bad idea.

Over here the wife is cooking in the kitchen while the daughter uses the 2500W hairdrier in the bathroom and I run the HT oven in the basement Workshop, all at the same time with no problem, so it would be possible to run a line from another part of the house to the workshop and use more power there. All the different rooms are on different breakers and can be run at 16A max.

But I dont want to encourage bad practice and remove the diagram.
My best advice would then be you ask an certified electrician or pull the plug and by a commercial product.
 
IMHO find out the size of your largest breaker and work backward. I take it you do not have an electric range or electric clothes dryer? these are usually 230vac 30 amps. if you dont have a electric range or clothes dryer outlet, you are probably stuck with 120vac 20amp as your largest circuit. keeping safety in mind, i would go no bigger than 13 amps continous duty. your choices are a small furnace that will reach temperature quickly but will limit you on blade size or something bigger where you set the temperature then go cut the grass while it struggles to reach hardening temperature. budget casting and joppa glassworks (http://www.joppaglass.com/) should have all the stuff you need. joppa says email them your plans and they will review them and make recommendations.
i would check ebay and craigslist for a 120vac glass kiln. if money is an issue, go manual and spend the extra cash on good fire brick, mortar and ceramic fiber.
hope this helps.
scott
 
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It doesn't really matter very much whether you are on on 120V or 220V. The important thing is the power you can get into the oven: Volts times Amps.

I am in the UK, where we have 230V domestic supplies, but the standard outlet is only rated for 13A: 2990W

120V, 20A would give you 2400W, so 80% of what I can get. A 120V, 25A supply would match the power I can get.

I have built 5 HT ovens/furnaces so far, 4 of them 230V, 13A, and I'd expect a 20A, 120V unit to get the job done with a reasonable sized chamber.

Most of mine have had chambers 18" deep, 6" high and 7" wide. I use two 120V, 13A elements, connected in series for the 230V supply. On a 120V, 20A supply, I'd use 2 elements rated at 10A, 120V connected in parallel. I'd still have one element per side.

There are a couple of things you can do to minimize the power requirement.

First is materials selection: Use JM23 Insulating Fire Bricks made by Morgan Thermal Ceramics. They are only made in the USA and Italy, so they are expensive here in Britain, but they have less thermal mass and are better insulators than any other IFB I've been able to find. They are what I use.

Second is careful fitting of the bricks. Again the JM23s are pretty helpful here as they seem to be more dimensionally consistent than the cheaper IFBs I've tried. I have faffed about trying to fit the bricks together with fire cement, but they just suck all the water out of the jointing compound if you try to keep the joint line thin, so it won't squidge properly. I now just paint on the cement from the outside and stipple it into any gaps, if I really feel it needs it afterwards.

To cap it all, the JM23s are the easiest to work. They will cut with a tenon saw and file with a piece of allthread (it's how I cut the element grooves in my first 2 ovens. After that, I used a router)

In case this is coming across as a selling job for the JM23s, I actually prefer the cheapies for gas forges and would use them even if they were the same price as JM23s, but for electric HT ovens, the JM23s are a no-brainer.

I'm pretty sure a decent door seal also helps. I've seen lots of write-ups with ceramic fiber rope seals, but I just use 1" ceramic fiber blanket and give it some compression. It seems to work.

Something that is worth bearing in mind is that almost all modern controllers will run on 100-264VAC and 50 Hz or 60 Hz supplies so they can be sold in a world market. This means that you can build a control box that will work on 120v now, and can use it on 220V as and when it becomes available.
If you use an SSR, this is driven by the controller output.

I don't trust SSRs to provide safety isolation, so I tend to use a contactor as well. Contactors need the correct coil to suit the voltage, so bear this in mind if you use one.

It's worth checking out Andy Gascoigne's HT furnace .pdf at http://knifemaking.webs.com/heattreatmentfurnace.htm

It's still good on the physical build, though things have moved on a bit in terms of controllers since then.
 
theWeatherman said:
I am not sure yet. Depends on what you really want and your time. I'm starting to lean towards just buying an even heat 120V
Click to expand...

yeah, cause i just picked up an old 120v ceramic kiln for free (my coworker was throwing it out). i rebuilt the control box and put a new cord on it, now its good as new...sure it looks like it was built in 1902 but hey, who cares! its an old Ace Ceramic Kiln thats rated at 1650*

i have seen many used ones available for a couple hundred bucks...just my .02, for whatever thats worth :)
 
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