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- Feb 17, 2007
- Messages
- 3,375
Having spent hours on the phone with several people making Heat Treat Ovens or Modifying Kilns I thought I would post some basic things you must understand to be successful. Please don't think any of this is real criticism of those who have made the leap. Just trying to help those on the verge of starting.
The larger the volume inside the oven the more wattage you will need. Don't try to decrease the volume by adding stuff to the inside of the oven. This will only increase the amount of stuff the oven needs to heat up. (Thermal mass). Soft fire bricks are great insulators, but adding a good layer of Kaowool between the bricks and the oven case will make the oven lose less heat and become more efficient. It also gives the bricks some expansion room.
Leaky ovens are poor ovens. Make the door close up as tight as possible. Plug anything like extra thermocouple holes with Kaowool. Where your element ends exit use Kaowool to fill any gaps not only does it insulate heat it will not conduct electricity.
SSRs. I recommend 2 for 220v 0vens one on each of the hots and have a switch on the door that breaks the signal line from the PID to the SSRs. A simple push button swithc correctly mounted works. The voltage and amperage from the PID is low so it does't have to be an expensive complicated switch. GET THE NEXT SIZE BIGGER SSR THAN YOU THINK YOU NEED. Not much more and money well spend.
There is an excellent drawing of how to correctly wire a 220 oven posted here.
http://www.bladeforums.com/forums/s...eat-Treat-Oven-Wiring-Schematic-Future-Sticky
The heat led is unnecessary as the PID has one already. The rest of it is perfect. USE IT
You are far better off in my opinion having your element connections outside of the ovens heat chamber. The heat and pressure of the connection is hard on something that gets around 2400f
NOW THE ELEMENTS
YOU MUST UNDERSTAND THIS
P (watts) = voltage X amperage.
Amperage is voltage divided by resistance (measured in ohms)
Having a 220 element doesn't mean much unless you understand what kind of 220 element. If you have a 220 element with 100 ohms it would use 2.2 amps of 220v and put out 484 watts and wouldn't make toast. If you have a 220 element that has 5 ohms it would use 44 amps of 220 and make 9,680 watts. Both are 220 elements. Which one you buy or have makes a lot of difference.
5 ohms- 44 amps -9680 watts
8 ohms -27.5 amps-6050 watts
10 ohms-22 amps -4800 watts
11ohms-20 amps-4400watts
15 ohms-14.666amps- 3226 watts
Series and parallel are also important fundamentals you must understand when working with more than 2 elements.
SERIES means in line or one end of each element is connected to the other and power goes from one power line through one element then to the other element, through it, then to the other power line.
PARALLEL means the elements are connected together at both ends. Power goes into both from the same power line and leaves both at the the same place at the other power line.
example 2 8 ohm elements connected in series would measure 16 ohms (8 through the 1st then 8 through the second)(twice the length) use less than 14 amps and make around 3000watts.
2 8 ohm elements connected in parallel would measure 4 ohms (goes through 2 paths and is twice as easy) use 55 amps and make 12,000 watts.
Same 2 elements way different results
YOU NEED ELEMENTS THAT MATCH THE WATTAGE YOU WANT TO ACHIEVE. There is actually no such thing as a 220 element in my opinion.
VOLTAGE WILL NOT BURN UP A ELEMENT.
TOO MUCH AMPERAGE WILL BURN UP AN ELEMENT
I could put 100,000,000,000,000,000,000 volts across an element and not burn it up as long as I keep the amperage below what that gauge of element can handle.
What you are buying when you buy a 110 element is an element with enough resistance to keep its amperage down to a level that it will not burn up. Same thing with a 220 element.
The gauge of the wire is related to its diameter. The larger the diameter (and thus the smaller the gauge number) the more amps it will handle before burning up and incidentally the longer it will last at a certain amperage. 14 gauge Kanthol A1 will survive 20 amps much longer than 16 gauge.
The larger the diameter (smaller gauge number) the less RESISTANCE THE WIRE HAS PER FOOT. (OHMS) Just like water and a pipe the bigger the wire the easier electricity flows through it.
Where it takes 50 ft 14 gauge of Kanthol A1 to make 10 ohms it only takes about 30 ft of 16 gauge (.0510 diameter). The will both take the same amperage and produce the same wattage. The 14 gauge will last longer.
Now lets say you went on Ebay and bought a 25' long piece of 16 gauge Kanthal A1 that is advertised as a 110 element with 8 ohms of resistance. You are stuck at 110 because at 220 it will use 27.5 amps and burn up pretty fast. If you place 2 of these in series you have 16 ohms and at 220v less than 14 amps and about 3000 watts. Incidentally 2 of these in series using 220 would mean that 110v drops across each element. You can't put them in parallel because then each would use 27.5 amp for a total of 55 amps and if the elements don't burn up before your shop you have some heavy duty wiring. Adding a 3rd wire in series would make things worse. Then you would have 24 ohms less than 10 amps and 2200 watts, more isn't always better! 3 in parallel would make the ohms drop to 2.6667 and amperage jump to over 80 amps.
IF YOU WANT an oversized oven or a quick oven you need to think about your elements and get the ones you need.
You also need to think about placement. They need to make the oven head evenly. Hard to put elements in the door, so get them as close as safely possible and then keep any run across the back wall straight (no coils) that way the back wall isn't making a bunch of heat while the front wall (door) makes none. The smaller the oven chamber the more likely to keep oven heat even. Also the longer you take to get to final heat the more likely to be even. That doesn't mean you need to make a slow oven. Mine is fast, but I take it to near my desired temp then hold it for a bit until everything has a chance to get that temp then climb the last 50-100 degrees to my desired temp. This keeps everything even, and gets rid of any overshoot problems.
Think about where you want the thermocouple. I like near the center and the tip down a bit past center height wise. That is where my blades are going to be. If I was going to make a long oven for something like swords, I think stick my pids thermocouple 1/3 the way back from the door and add another thermocouple and PID just to read the temp about 1/4 of the way from the rear. You could also set it up with 2 elements and 2 pids and thermocouples and have a pid run the element in the front and another run the element in the rear. With the correct wiring you could use 2 15 amp elements at 220v for a 30 amp oven with 6600 watts and have a very uniform heat the whole length of the oven. But, even on a 40 inch long oven if you kept the height and width to say 5x5 and used a single 20 amp element (50' of 14 gauge) for 4400watts it would be fairly fast and even if you laided out the coils evenly.
I will try to help those who seek it but, please learn the basics of electricity before you jump into such a project. It really isn't that complicated. But, it can be dangerous, frustrating and rewarding.
The larger the volume inside the oven the more wattage you will need. Don't try to decrease the volume by adding stuff to the inside of the oven. This will only increase the amount of stuff the oven needs to heat up. (Thermal mass). Soft fire bricks are great insulators, but adding a good layer of Kaowool between the bricks and the oven case will make the oven lose less heat and become more efficient. It also gives the bricks some expansion room.
Leaky ovens are poor ovens. Make the door close up as tight as possible. Plug anything like extra thermocouple holes with Kaowool. Where your element ends exit use Kaowool to fill any gaps not only does it insulate heat it will not conduct electricity.
SSRs. I recommend 2 for 220v 0vens one on each of the hots and have a switch on the door that breaks the signal line from the PID to the SSRs. A simple push button swithc correctly mounted works. The voltage and amperage from the PID is low so it does't have to be an expensive complicated switch. GET THE NEXT SIZE BIGGER SSR THAN YOU THINK YOU NEED. Not much more and money well spend.
There is an excellent drawing of how to correctly wire a 220 oven posted here.
http://www.bladeforums.com/forums/s...eat-Treat-Oven-Wiring-Schematic-Future-Sticky
The heat led is unnecessary as the PID has one already. The rest of it is perfect. USE IT
You are far better off in my opinion having your element connections outside of the ovens heat chamber. The heat and pressure of the connection is hard on something that gets around 2400f
NOW THE ELEMENTS
YOU MUST UNDERSTAND THIS
P (watts) = voltage X amperage.
Amperage is voltage divided by resistance (measured in ohms)
Having a 220 element doesn't mean much unless you understand what kind of 220 element. If you have a 220 element with 100 ohms it would use 2.2 amps of 220v and put out 484 watts and wouldn't make toast. If you have a 220 element that has 5 ohms it would use 44 amps of 220 and make 9,680 watts. Both are 220 elements. Which one you buy or have makes a lot of difference.
5 ohms- 44 amps -9680 watts
8 ohms -27.5 amps-6050 watts
10 ohms-22 amps -4800 watts
11ohms-20 amps-4400watts
15 ohms-14.666amps- 3226 watts
Series and parallel are also important fundamentals you must understand when working with more than 2 elements.
SERIES means in line or one end of each element is connected to the other and power goes from one power line through one element then to the other element, through it, then to the other power line.
PARALLEL means the elements are connected together at both ends. Power goes into both from the same power line and leaves both at the the same place at the other power line.
example 2 8 ohm elements connected in series would measure 16 ohms (8 through the 1st then 8 through the second)(twice the length) use less than 14 amps and make around 3000watts.
2 8 ohm elements connected in parallel would measure 4 ohms (goes through 2 paths and is twice as easy) use 55 amps and make 12,000 watts.
Same 2 elements way different results
YOU NEED ELEMENTS THAT MATCH THE WATTAGE YOU WANT TO ACHIEVE. There is actually no such thing as a 220 element in my opinion.
VOLTAGE WILL NOT BURN UP A ELEMENT.
TOO MUCH AMPERAGE WILL BURN UP AN ELEMENT
I could put 100,000,000,000,000,000,000 volts across an element and not burn it up as long as I keep the amperage below what that gauge of element can handle.
What you are buying when you buy a 110 element is an element with enough resistance to keep its amperage down to a level that it will not burn up. Same thing with a 220 element.
The gauge of the wire is related to its diameter. The larger the diameter (and thus the smaller the gauge number) the more amps it will handle before burning up and incidentally the longer it will last at a certain amperage. 14 gauge Kanthol A1 will survive 20 amps much longer than 16 gauge.
The larger the diameter (smaller gauge number) the less RESISTANCE THE WIRE HAS PER FOOT. (OHMS) Just like water and a pipe the bigger the wire the easier electricity flows through it.
Where it takes 50 ft 14 gauge of Kanthol A1 to make 10 ohms it only takes about 30 ft of 16 gauge (.0510 diameter). The will both take the same amperage and produce the same wattage. The 14 gauge will last longer.
Now lets say you went on Ebay and bought a 25' long piece of 16 gauge Kanthal A1 that is advertised as a 110 element with 8 ohms of resistance. You are stuck at 110 because at 220 it will use 27.5 amps and burn up pretty fast. If you place 2 of these in series you have 16 ohms and at 220v less than 14 amps and about 3000 watts. Incidentally 2 of these in series using 220 would mean that 110v drops across each element. You can't put them in parallel because then each would use 27.5 amp for a total of 55 amps and if the elements don't burn up before your shop you have some heavy duty wiring. Adding a 3rd wire in series would make things worse. Then you would have 24 ohms less than 10 amps and 2200 watts, more isn't always better! 3 in parallel would make the ohms drop to 2.6667 and amperage jump to over 80 amps.
IF YOU WANT an oversized oven or a quick oven you need to think about your elements and get the ones you need.
You also need to think about placement. They need to make the oven head evenly. Hard to put elements in the door, so get them as close as safely possible and then keep any run across the back wall straight (no coils) that way the back wall isn't making a bunch of heat while the front wall (door) makes none. The smaller the oven chamber the more likely to keep oven heat even. Also the longer you take to get to final heat the more likely to be even. That doesn't mean you need to make a slow oven. Mine is fast, but I take it to near my desired temp then hold it for a bit until everything has a chance to get that temp then climb the last 50-100 degrees to my desired temp. This keeps everything even, and gets rid of any overshoot problems.
Think about where you want the thermocouple. I like near the center and the tip down a bit past center height wise. That is where my blades are going to be. If I was going to make a long oven for something like swords, I think stick my pids thermocouple 1/3 the way back from the door and add another thermocouple and PID just to read the temp about 1/4 of the way from the rear. You could also set it up with 2 elements and 2 pids and thermocouples and have a pid run the element in the front and another run the element in the rear. With the correct wiring you could use 2 15 amp elements at 220v for a 30 amp oven with 6600 watts and have a very uniform heat the whole length of the oven. But, even on a 40 inch long oven if you kept the height and width to say 5x5 and used a single 20 amp element (50' of 14 gauge) for 4400watts it would be fairly fast and even if you laided out the coils evenly.
I will try to help those who seek it but, please learn the basics of electricity before you jump into such a project. It really isn't that complicated. But, it can be dangerous, frustrating and rewarding.
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