Designing a HT oven

rashid11 said:
Deker -

it will be slow @ that dimension, unless you go 30A @ 240V .
Click to expand...

Can you help me understand what evenheat is doing then? They list their 22.5" deep unit at:

KF 22.5, 240V, 15A, 3600W

The interior of that oven is 6.5x10x22.5. I've never used the 22.5, but Butch has an 18 (KF 18, 240V, 13A, 3120W) and it hardly seems slow to me.

rashid11 said:
The calculation is very ez: the length of wire (L) in feet, per-foot-resistance (R) in Ohm, desired Amps (A) and voltage (V) are related like this:

A = V/ (R*L) . Solving for L: L = V/(A*R) . To get 20A out of 220V with
.5 Ohm/F wire, L = 220/(20*.5) = 22 feet of wire.

I wind my own spirals out of wire I got from resistancewire.com. It is very
ez to do if you have a lathe.

Kanthal A1 spiral will last you forever, as long as you stretch the spiral so that coils don't touch e.o. The spiral should be stretched evenly and tucked
into the groves w/o stress . After first firing, the spiral will become very brittle and you won't be able to adjust it (bend, strech, compress etc)
Click to expand...

Excellent, that's the math I needed Rashid, thanks!

-d
 
well, at the very least get the SSR that is rated to 30A. This way,
you can always make it fast later, by reducing the length/resistance.

May be I am just spoiled by my oven :) , it is really fast. Problem
is: real slow ovens keep the metal exposed to HT temp for too long.
Some steels don't mind, some won't like additional 20 min @ all.
 
rashid11 said:
well, at the very least get the SSR that is rated to 30A. This way,
you can always make it fast later, by reducing the length/resistance.
Click to expand...

Yup.

rashid11 said:
May be I am just spoiled by my oven :) , it is really fast. Problem
is: real slow ovens keep the metal exposed to HT temp for too long.
Some steels don't mind, some won't like additional 20 min @ all.
Click to expand...

Do you start your HT in a cold oven? I always figured on pre-heating the oven and putting blades in once it was up to temp. Sure there's rebound time from opening the door, but that shouldn't be too bad.
 
Deker,
As long as you go with 240v and 30A-40A, you should have no problem reaching the temps you require at a reasonable rate. The key is to, as you said use 2 elements. You can dump a lot of heat into that space with the right resistance.

Kerry,
Your right it is some work, but with a good oven costing in the 800$-1000$ range, the time invested was well worth it….to me anyway.
Scrap sheet metal and angle iron for shell…..0$
Controller, and SSR off of EBay…….85$
K-Thermocouple from Omega……..35$
Firebricks and Inswool……100$
A-1 Kanthal elements from Duralite……65$
Misc. screws, wire, Marinite connecting board, 220 plug and 2 ceramic rods…75$
Total….360$
The cost of not having to shipping out my blades……not even going to say it!
Brent
 
Thats's quite a savings and well worth building your own. Thanks Brent :)
 
How did I miss this. Guess it is what happens when you get into diferent stuff. I been thinking about one of these for a while but don't do the electronics thing. I got a few other projects in the works but this is on the list for the near future.
Lots of info here.....Keep it up guys.

Larry
 
Nowicki said:
How did I miss this. Guess it is what happens when you get into diferent stuff. I been thinking about one of these for a while but don't do the electronics thing. I got a few other projects in the works but this is on the list for the near future.
Lots of info here.....Keep it up guys.
Click to expand...

If it goes well, I can hekp you with the 'lectrical bits.

-d
 
Folx,

I had an electrical diagram of sorts, for the oven, in one of my prev posts.
That and complete description of how the whole thing works.

Play it safe and make sure to ground the exterior of the oven.
 
After I get one of these things built I'll probably do the Plate Quench thing. I know there has been stuff posted and I plan to do some.
 
rashid11 said:
Deker -

it will be slow @ that dimension, unless you go 30A @ 240V .

The calculation is very ez: the length of wire (L) in feet, per-foot-resistance (R) in Ohm, desired Amps (A) and voltage (V) are related like this:

A = V/ (R*L) . Solving for L: L = V/(A*R) . To get 20A out of 220V with
.5 Ohm/F wire, L = 220/(20*.5) = 22 feet of wire.

I wind my own spirals out of wire I got from resistancewire.com. It is very
ez to do if you have a lathe.

Kanthal A1 spiral will last you forever, as long as you stretch the spiral so that coils don't touch e.o. The spiral should be stretched evenly and tucked
into the groves w/o stress . After first firing, the spiral will become very brittle and you won't be able to adjust it (bend, strech, compress etc)
Click to expand...

I am in the process of building a 4.5"X5.5"X24" interior HT oven.

According to the formula above, you get higher Amps by using shorter wire. This does not make sense to me. Can someone explain???

For example using the formula above yields the following results when trying to achieve a 30 Amp oven vs. a 20 Amp oven:

Wire 16 AWG KA1 with a rating of .3376 Ohms per ft
230 V power source

Solving for L: L = V/(A*R)

V = 230
A = 20
R = .3376

First 20 Amps -- 230/(20*.3376) = 34.06 ft wire
Using A x V = 4660 Watts

V = 230
A = 30
R = .3376

Next 30 Amps -- 230/(30*.3376) = 22.71 ft wire
Using A x V = 6900 Watts

Looking at http://www.budgetcastingsupply.com/Heating_Elements_Controllers.html under #7101 Kanthal Heating Element - it references hooking two elements togehter in series, effectively doubling the length of the wire while maintaining the exact same Amps (13) but doubling the Watts from 1550 to 3100. Looking at this it seems to show that wire length has nothing to do with Amps used

What am I missing in the formula above. I need to calculate how much wire to use to heat my desired chamber size. Any insight here would be great. Thx.
 
With this type of oven design - long'n'narrow, you will have difficulties
with having more than one spiral groove around the perimeter.

Now, your 16 gage wire will be dying way too soon if you let 20A current
rip through it - it has to do with surface area of the wire, that's what actually
let's the heat out into the oven. What I recommend is to go with say 14 Ohm
resistance, for slightly smaller current (230/14 = 16.4A vs 20A) & power rating - but the spiral will last much, much longer.

So to get to 14 Ohm resistance, you will need a spiral that is 14/.3376 = N feet long. Make the groove at least 5/8 wide and equally deep, angled slightly so that wire will "drop" into it. Wind the wire on a 1/2 OD round and this way it will fit like a glove into the groove.

About parallel connection of 2 or more spirals: we are always limited by wire's ability to effectively emit heat, while having decent longevity.

So with 20A current and 16 gage wire, you will have a mighty fast oven, but it won't leave long, before the spiral fails. So what is one to do ? Imagine you drop the current to 15A - now the spiral will last a few hundred firings, but it will be slower to come up to temp ... Hmmm ... what if we add another spiral, rated for same current - 15A, in parallel to the 1st one ? Bingo ! We have doubled number of "lanes" current can take - so twice the current, 30A, can flow now, yet ea lane only carries 1/2 of it: 15A

Now, we have double the power output - to 30A, yet ea spiral still carries only 15A - and thusly the thing is uber fast and lasts forever !

Problem comes from having to find space inside of one's oven to have these 2
grooves cut. And of course, you need to have 30A available - both the breaker rated to that amperage and also the wires from the breaker to the oven. Would be an extremely bad idea, for example, to swap laundry room's breaker for 30A one, while keeping the 20F of 20A rated wires and then fire your oven like that. It will create a very significant fire hazard - don't do it.

The safest way is to install a dedicated 30A break into the main panel, install 30A rated receptacle with a short run of 30A rated wire, the power cord of the oven will also need to be rated to 30A and then you're golden.

Again, don't forget to ground the exterior of the oven !
 
I've known a tradesman get around that problem by whipping up a little fused box with one socket hooked to two plugs on heavy duty extransion cords. Check the fusebox of the house and pull the fuse on a power socket loop, and find which sockets arent working, plug the fuse back in and pull another one out and find which sets of power sockets use that fuse. run the extension cords in to those separatly fused sockets and hey presto, a 35A machine can run off two 20A domestic 240V circuits instead of needing a dedicated line. or effectively 17.5A on each line.

Cheaper for him to use the customers power than haul around a generator.
 
rashid11 said:
With this type of oven design - long'n'narrow, you will have difficulties
with having more than one spiral groove around the perimeter.

Now, your 16 gage wire will be dying way too soon if you let 20A current
rip through it - it has to do with surface area of the wire, that's what actually
let's the heat out into the oven. What I recommend is to go with say 14 Ohm
resistance, for slightly smaller current (230/14 = 16.4A vs 20A) & power rating - but the spiral will last much, much longer.

So to get to 14 Ohm resistance, you will need a spiral that is 14/.3376 = N feet long. Make the groove at least 5/8 wide and equally deep, angled slightly so that wire will "drop" into it. Wind the wire on a 1/2 OD round and this way it will fit like a glove into the groove.

About parallel connection of 2 or more spirals: we are always limited by wire's ability to effectively emit heat, while having decent longevity.

So with 20A current and 16 gage wire, you will have a mighty fast oven, but it won't leave long, before the spiral fails. So what is one to do ? Imagine you drop the current to 15A - now the spiral will last a few hundred firings, but it will be slower to come up to temp ... Hmmm ... what if we add another spiral, rated for same current - 15A, in parallel to the 1st one ? Bingo ! We have doubled number of "lanes" current can take - so twice the current, 30A, can flow now, yet ea lane only carries 1/2 of it: 15A

Now, we have double the power output - to 30A, yet ea spiral still carries only 15A - and thusly the thing is uber fast and lasts forever !

Problem comes from having to find space inside of one's oven to have these 2
grooves cut. And of course, you need to have 30A available - both the breaker rated to that amperage and also the wires from the breaker to the oven. Would be an extremely bad idea, for example, to swap laundry room's breaker for 30A one, while keeping the 20F of 20A rated wires and then fire your oven like that. It will create a very significant fire hazard - don't do it.

The safest way is to install a dedicated 30A break into the main panel, install 30A rated receptacle with a short run of 30A rated wire, the power cord of the oven will also need to be rated to 30A and then you're golden.

Again, don't forget to ground the exterior of the oven !
Click to expand...

Rashid, this really helps. No problem with the breaker. I have a dedicated 230V/50 Amp circuit for my welder that I'll be using when heat treating. So it seems the key item here is to hook the elements up in parallel rather than in series... I'll also have to get a SSR that is rated for 30A. I've seen lots of SSR's rated at 40A but none lately at 30A. Is it a probem to get a SSR that is rated at a higher amperage than what I will be using. Sorry for the very basic electrical questions but this area (amps/ohms) is an area that i've never really had down... Just want to make sure I get this right.

I'm also getting a controller from Auber Instruments. http://auberins.com/index.php?main_...s_id=5&zenid=25a46c6f7d530647385b779f160f6c67 with ramp/soak abilities. Have you heard any good/bad things about this controller? I really appreciate all your feedback. :)
 
I built the oven by Andy Gasciogne Very good plans. My chamber is 5.5x 4.5 high by 18 inches long.Inside
I used the 2.5 bricks but would go to 3 inch next time. You can touch the outside of the oven at 1500 degrees until it has sat about 30 min then it is to hot to handle.
I had an Auber control with out ramping and made for a relay but switched to an ssr switch as it switches on and off quite a bit. I can change to a ramp type for $85.00 if I decide I need it.
My oven will reach 1500 degrees in under 10 minutes.
My old oven took 1.5 hours to hit that temp.
Hope this helps
TJ
 
It is prudent to get an SSR that is rated higher than what you intend to use it for. And SSR rated for more than N amps, will happily work @ N amps and below.
If course, don't overspend getting 100A SSR for 20A oven.

As far as controllers go - I got me the $30 "generic PID controller" from Ebay. It doesn't have ramps, but I always watch the process and manually time it, as I heat treat, so it is not a problem for me all. And that's what I recommend - start nice and easy, for less $$$, and upgrade later, when do feel you have a legitimate need for an advanced controller.

Me also thinks the advanced ones are more for potters - when you fire clay, it is a multi-hour process, with lots of ramp-ups/downs, and this is where ability to ramp up/down helps.
 
rashid11 said:
Make the groove at least 5/8 wide and equally deep, angled slightly so that wire will "drop" into it. Wind the wire on a 1/2 OD round and this way it will fit like a glove into the groove. !
Click to expand...

Is there a disadvantage to using a 1/2 inch grove and winding the wire on 3/8 OD round? This will produce the perfect element length for the chamber size while maintaining a 3:1 spacing stretch on the element. If it is better to go with a wind on the 1/2 OD round then I'll have to stretch the wire to a 4:1 spacing to reach around the chamber. Thx :D
 
rashid11 said:
I had an electrical diagram of sorts, for the oven, in one of my prev posts.
That and complete description of how the whole thing works.
Click to expand...

rashid11,

I have been searching and searching for it and I can not find it. Would you please re-post it?
 
Kiwi303 said:
I've known a tradesman get around that problem by whipping up a little fused box with one socket hooked to two plugs on heavy duty extransion cords. Check the fusebox of the house and pull the fuse on a power socket loop, and find which sockets arent working, plug the fuse back in and pull another one out and find which sets of power sockets use that fuse. run the extension cords in to those separatly fused sockets and hey presto, a 35A machine can run off two 20A domestic 240V circuits instead of needing a dedicated line. or effectively 17.5A on each line.

Cheaper for him to use the customers power than haul around a generator.
Click to expand...

... So long as he is aware that once plug 1 is plugged in, exposed plug 2 will be live, unless he has built a safeguard around it! I thought about this for my welder once but abandoned the idea for that reason.:)
 
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