Cold you are waisting you time trying to measure the element resistance as has been said. Personally I'd chop a lump of each coil as Jason said and see if you get a raise in temp., If you are concerned about the current draw a cheap clamp meter will give you more of an insight into what is going. I'd be very surprised if you are hitting the limit of the control gear and likely the coils are too long.
Ok that might be a good idea then, just trial and error it haha. I attempted to measure volts and current using the intact element and an AA battery. Not sure if that is helpful in any way, but a fresh AA battery putting out 1.56v and 16.7 milliamps across the terminals when connected to the element had: 1.38v and 11.5 mili amps which I think means the wire is 120 ohms of resistance. Is that a number/method that makes sense? I realize this is DC and I'll be using AC to power it but I figure it should be able to tell us something? or maybe I'm just way off base here... There's always the chop the element shorter method but I am actually fairly curious now what the actual original element needs to be.
Nope, as Kelly said it is cold. The only way you'll know what your elements are drawing is to measure the current. As I said, if I didn't have a meter I would take a chance at it and shorten the coils. If you really want to get clever then shut everything in the house off and use the electric meter to record KWh over about 1/2 hour but they can be plus/minus 2%
So let me sum up what I think I understand here and what I'm considering. 1) The 16 gauge kanthal A1 wire I bought and made new elements from is thinner than the original elements which are about 14 gauge in diameter and look longer overall. This means the original elements probably aren't kanthal wire, maybe nichrome? 2) If I want kanthal wire elements I need to make the next set of elements shorter, or thinner. Basically reduce the amount of kanthal wire inside the kiln so that the ohms are lower. 3) If I buy thinner wire then I will be able to make longer elements and still be able to reduce the total resistance. 4) I'm thinking of buying 17 or 18 gauge kanthal wire and then cutting enough footage to make up 9 Ohms of resistance per coil instead of the 10 that I originally had cut with the elements I first made. That's about a 10% drop in resistance. 5) Does that mean with a 10% drop in resistance I get a 10% boost in heat output? So I'll go from 2088 to plus or minus (2088 +208.8 = 2296.8 F) ? Or does this make no sense 6) Will any of this be likely to damage the electronics inside the kiln if I try it? Alternatively, 7) I buy an amp clamp, plug the one element in and wire it up so that I guess its on its own without the new kanthal element in series, measure the amps going through that then figure out the resistance and I'll then know what to make the new elements to match. 8) or do I wire it up in series with one of the newly made kanthal elements and measure just the original amperage draw? 9) How to measure the amperage and figure out the ohms of the original intact one remaining element is confusing and I am unclear on exactly how to do it.
Can you rewire and run one coil at a time? looks like i missed a couple of posts. I'm knee deep in lathe dro today.
No it doesn't necessarily mean the originals were not Kanthal. When you switched from 14ga to 16ga this required a shorter 16ga coil because 16ga is higher resistance than 14ga per foot, thus you need a shorter length of 16ga for the same resistance and same material. For a given gauge wire, Kanthal is about 75% of the resistance of NiCr 80/20......so a Kanthal coil of the same gauge and resistance will always be longer than a NiCr. Reducing the amount of wire (shortening) will reduce the resistance and increase the current and power. Reducing diameter will reduce the coil length needed for a given resistance and power. Thinner wire will produce shorter elements at the same resistance. Smaller gauge is more fragile. You should use the largest gauge that practically fits your grooves with some trade off for wire formability. A 10% drop in resistance will produce a 10% increase in power, producing more heat, and will likely increase the temp, but it wont necessarily create a proportional (10%) increase in temperature. You're really not certain where you're at now with respect to current. Alternatively, Ding Ding! If you plug in only one element it will draw twice the current and this likely will cause some damage. If you are lucky, it will also trip your 120vac circuit breaker in your house because the single 5 ohm coil will draw 24amps at 120vac. If you are unlucky and the circuit breaker doesn't protect you, it may damage the insulation on the conductor in your wall and/or start a fire. You don't need to measure the resistance in your old coil because you already know your oven is rated for 12 amps from the name plate and you have determined the you need 10 ohms total to do that. I would design for 10 ohms hot which for Kanthal A1 would be about 9.5 Ohm. -You designed for 10 ohms cold. This alone will get you 5% more power/heat. You can shorten your coil 5% but if you don't really know where you're at now you're just guessing. Do as you wish. Best, Kelly
Ahhh ok that straightens a lot of things up. So, 1) I had that backwards: Larger diameter wire means more wire needed for the same resistance because the resistance is lower per foot in a large diameter wire. I found this chart that shows that: 2) So if I shoot for 9.5 ohms of resistance total and I use say 15 gauge wire that means I need 37.1 feet of wire total for 2 elements (each element would now be 18.55 feet long) (because 9.5 ohms/0.256 ohms/foot = 15 feet), or if I made it out of 14 gauge then I'd need 46.8 feet (23.4 each coil). This makes much more sense and I think is more inline with what the original element was: longer and thicker. I'll get a lot of wire so I can make multiple sets of elements if needed. 3) I'll order an amp clamp on amazon, probably the one Jason showed me. Do I need a multi meter as well or does it double up as one too? 4) Do you think that perhaps the density of the coils makes a difference in the total temperature? If I had a straight piece of wire with the same ohms/power draw as a coiled thick piece of wire element I'd guess that the thicker coiled element would put out a lot more heat for the same power stats since the coils heat up the coil next to them and retain more heat. I don't know for sure if that works in practice but I'm wondering if that may be another reason my elements aren't heating up the kiln to where I want it? I think that's what this is saying - a) puts out more heat for a lower watt/cm compared with the more linear C and D configuration? From http://www.kilnparts.com/kanthal-a1-element-120-volts-12-amps-1440-watts.html Thanks a ton this is making more sense.
15 Gauge might be a happy medium. What are your groove dimensions? My elements are 14 gauge and I wind them to 1/2" OD. In the theory the surface area of the heating element doesn't change the heat put into the furnace. It's pure resistive heating. In practice a high area coil may cause faster heating but within the coil differences we are talking, it's probably insignificant. The wall and coil surface loading are factors in the charts below are to prevent the localized over heating of the metal element which affects life, not putting heat into the furnace. When you have a coiled element in a groove the local temp is higher than the furnace temp. That's why the Kanthal is derated for coils in grooves. The charts are saying you can apply more power in a smaller area with different heating element styles. Styles that hang in free air can be loaded the highest. Styles that are surrounded or more surrounded/contained, the least. Best, Kelly
The link you PMed me to buy thicker large quantities of wire: https://www.euclids.com/index.php?cat_id=159 I used my digital calipers and measured the wire in multiple locations. The diameter of the wire is 0.056 to 0.058" judging by the chart here: https://www.euclids.com/index.php?view_cart=1&new_item=WK15X&cat=159&qty=1&x=101&y=14 that means it looks closest to the 15 gauge wire. 14 gauge wire has a diameter of 0.063" so that is quite a bit bigger than what I've got. If I use their kanthal wire and use 9.5 ohms as the new goal then the total length of each element I need is (9.5/0.213 ohms/foot = 17.67 feet per element. ) If I use 10 ohms then it would be 18.6 feet per element. Does that sound about right? The groove dimensions are 1/2" wide grooves in the brick. I'll be wrapping the wire around a 1/4" rod which should make a coiled element close to the 0.38" diameter original outer diameter of the original element. ---------------- And since it took me a year and a half to track down the right bit, here it is for posterity the carbide cutting I used: Yonico 14173q 3/4-Inch Diameter Flush Trim Template Router Bit 1/4-Inch Shank KATUR Top Bearing Flush Trim Pattern Router Bit, Hinge Mortising Router Bit, Template Router Bit Set, 1/4 Inch Shank with Alloy Blade Carbon Steel (1/4" Shank,1/2" Tooth width,38mm Tooth depth)
Here's the link to Euclids resistance chart for various gauge Kanthal A1 and NiCr.-Pretty handy for comparison and those who think in imperial units. I use Euclids but most larger pottery and kiln shops sell resistance wire. I just use these guys because the prices are competitive, their specs are accurate and you can just buy it by the pound. Kanthal A1 vs NiCr 80/20 Resistance Yes, for 15 Ga Kanthal A1 at .2687 ohm/ft, but like I said in the previous post, I'd design for 10 ohms hot resistance which will be ~95-96% of that length. That would be a pretty tight diameter for 14ga and produce a quite stiff coil. For 15ga, a little better. Are the old coils .38" diameter? You should use the largest diameter coil that fits your groove well but you also want it to only have to be stretched 3x-5x of the close wound length. A bigger diameter coil will result in a shorter over all length for a given resistance. Coupled with the 3x-5x stretch rule, this helps manage the localized temperature increase caused by the coil being surrounded on three sides by the coil shelf. Details, but they are the manufacture's design guidelines. Your coil shelves are a good design with the step. I'd make sure the coils can seat and nest down in the bottom those grooves. Stretching them slightly over length helps keep them in place because they tend to grow when heated and then shrink when they cool and work their way out of the grooves into your furnace which is a PITA. Honestly Zap, there isn't that much magic in it. If you are already willing to buy new resistive wire, why not just measure voltage and current of what you presently have and if indicates a lower power level, just do what you described, trim what you have and restretch to fit. If it breaks, so what. You are already willing to replace it. You're temperature is going to be a strong function of the power input not these differences in coil design. It just doesn't make any sense to me to just start randomly changing things without verifying where your at first. You may find you have lower resistance or even voltage than what you think you have. On voltage, I think it's unlikely that it strays much from 120vac but I have seen figures that approach 110Vac. That alone would drop your power 8%, the hot resistance another 4-5% and suddenly you're down 13% from where you thought you were. Best, Kelly
The amp clamp came. When the kiln was cold I measured the amps coming on the live wire coming from the wall to the kiln and found that the entire kiln draws 11.86 amps. The voltage coming out the plug is 122.8V which means I have 10.35413 ohms resistance. So slightly more than I had wanted. I wonder if this resistance includes all the control circuitry since it isn't a direct measure of what is going into the coils, but rather the voltage going to the entire kiln. Do I need to measure the amps and voltage from the wire feeding the element itself or is what I have done above the same thing?
It is quite a neat device. Definitely better build quality compared with the $5 horrible freight crap I normally use. I'll have to hook this thing up to my pyrometer when I do my next melt. It even has a little LED backlight for night use. Although why someone would be measuring electricity in the dark and needs a built in device is something to think about... The amperage draw seems to be around 11.56-11.79 amps (seems to go up the hotter the elements as well?) depending on where I measure the amps over which coil. And voltage 118.3 across both coils. According to the resistance equation that makes both coils about 10.2 Ohms combined. I measured the resistance as well to see how close we got and found each element is 5.3 ohms individually.When measured with both elements in series it gives me 10.3 ohms across both (I thought they just added?). I think that is within the error range of the meter which is rated at +/- 1.2 % for resistance. So the coils together are very close to what I wanted them to be but still not putting out the heat I need, so I think that must mean we need to go shorter like we said before and try to shoot for 9.5 Ohms with the new 15 gauge wire. That way when hot around 2000F the resistance will go up and be around 10 Ohms. The kiln supply company who is shipping me the new element is delayed due to limited # of people working for corona virus, so who knows when it will be delivered.
Hmmm, current should be the highest cold and then decrease as the coil heats up because the resistance in the coil increases with increasing temp. This measured cold, correct. Would be worth getting a reading and at 2000F. My furnace starts at 8.4kw cold, and settles in at 8.0kw hot. This method will pick up the resistance of any other components too but this should be small. Does it have a mechanical or solid state relay that turns the coils on and off? Older units had mechanical relays and you can usually here them click. The contacts on mechanical relays can degrade and create some resistance but I suspect in the range of the variation you are already measuring, else they'd heat up. The lugs where you connect resistance wire to the conductor can also foul, but sounds like you've had those apart if you replaced the coils. If you are in the vicinity of 10.2 ohms cold, reducing the resistance by a half an ohm or so should get you in that 10 ohm hot range. How far you'd want to go beyond that really depends on the rest electrical components and also the household circuit you are operating with. Is it a 20amp breaker? or 15amp? Best, Kelly
It's on it's own devoted 20 amp breaker at the end of a 25 foot extension cord with 12/3 cable. It has a mechanical clicking relay. I'm looking forward to the new wire and supplies. I'll also see if I can measure the values again at 2000f later on.
I wound the new elements from the 15 gauge wire at 18 feet 1 inch long.The coiled length needed to fit the inside of the kiln is 39 inches plus two roughly 2.25" tails on the ends to poke through the walls and connect (43.5 total length each coil) While I was stretching the finished coil longer on the steel rod it slipped off the top groove that was holding the too and the bottom part of the fucking coil sprung into my thigh and went maybe an inch or so deep. Hurts like all hell. Lucky me.
Good thing you weren't an airplane crew chief. Getting stabbed with safety wire happens almost daily! Are you up to date on your tetnus shot? Booster ever 10yrs I do believe.
Yep got my last one 4 years ago. The criteria is more complicated. If it's a dirty wound or you haven't had several tetanus shots then you need it within 5 years. If you've had many shots and it's a clean wound then 10 is ok.
Ouch!! but could have been worse. Like a free piercing through your man hood or a needle in the eye....
