So to understand these elements better, and to check my math, I bought some very light weight wire (32ga) and decided to run some experiments. Based on my original math, I was originally looking at heat loadings between 1W/cm² and 5W/cm² which should have been 380mA to 800mA. But with a piece of wire on the power supply, it didn't give me any appreciable glow. Luckily this power supply goes up to 11. So here you see it at more than 22W/cm² and we're barely at 1400°F. Cranking it up to three amps (60W/cm²), and we finally passed its working temperature and it started to sag: Tried a slightly larger piece, and played with making a coil around a screwdriver shaft: similar sag at around three amps, and probably 2500°F. Caused a failure at 4amps, so I went back and clipped on the the remaining bits and tried to get some better pictures. This is at 1200mA, barely glowing (maybe 1100-1200°F ): At 2000mA, we seem to be around 1600°F: And back to 3A, cause its like an old lightbulb element at this point, and gives off a nice glow: 50W in that little piece. While the manufacture specs the resistance of A-1 at 1.45 Ω mm²/m, all of the actual wire resistances come in a little lower, and I had to adjust my number to 1.39 to match the actual published numbers. Also, I'm guessing that when you fire up an electric kiln or furnace, the wires don't immediately light up like the elements in a toaster oven or heat gun. I did get some heat off the early wire tests, just guess you have to build them into an insulated structure and wait for the heat to build up before you see the glow. If I had jumped right in and built something bigger, the first time I turned it on, I probably would have thought it was broken.
love seeing these kinds of tests nothing ever behaves quite like you expect it to. Open-air elements are such a heat sink that it always feels like you're dumping in way more power than you should need just to get anything useful. If you ever want to go way off the deep end, try messing around with carbon arc rods. Not the usual metal-wire elements, but the carbon electrodes they used in old-school projectors and welding gouging rods. They dont sag, dont really oxidize if you choke the airflow a bit, and they get stupidly hot at way lower power densities than Kanthal. The resistance curve is totally different, though, so it’s not a drop-in replacement youd need to tweak voltage and current to make it work. I always wanted to see if you could get one running in a sealed chamber with a bit of controlled atmosphere to keep it from burning itself outta.
I see 1.45 Ω mm²/m as a number published by/for Kanthal resistance, but that's just a nominal number. All the Kanthal brand FeCrAl I've bought comes with the resistance stated on the package. I haven't figured the variation in those dimensional units but my purchases have varied a couple percent. Your packaging doesn't appear to be Kanthal. Is it? Or is it just FeCrAl? If you're trying to measure the resistance with a multimeter, it can be difficult to do with precision because the resistance in cheap probes and gator clips, and also the wire is oxidized. Once fired, the oxide layer is thicker and higher resistance, and that protective oxide layer is why it can live at temp. It also becomes so brittle you can't reliably restretch it without breakage If you are trying to infer the resistance to this precision from the indicated current on PS, that's an exercise in futility. The current will vary by length of the element and that can't be very closely controlled as a % of full length with the alligator clips on that short sample. Also, the resistance of KA1 increases with element temperature up to 5-6% within it's operating range. Trying to estimate the actual operating temp of that element with that precision is also futile. It really depends on what you're trying to do. If it's just a science experiment, then all the above applies. If it's just sizing for a power target and electrical components, why do you need to be within a couple percent when resistance varies 2x-3x that much with temp? Mine don't change color like a light switch but are red within a couple minutes and then orange pretty quickly thereafter as the coil shelf temp surrounding them increases and stops sinking heat from them. At steady state, the element temp in a coil captured on three sides in a shelf will be several hundred degrees F higher than the furnace temp. That's why that style of element is the most derated for all the service parameters. There are several versions of the Kanthal Mini Handbook. I attached my favorite below. That sure hasn't been my experience. I use them for thermocouple sheaths in my resistive electric furnace. I only dip with them to limit their exposure because continuous exposure in air at 1800F will reduce a 5/8"D rod to half its diameter in about 3hrs, while the portion immersed in aluminum remained unaffected. When just in dip duty, they last 100-200 dips.....if I don't accidently break it first. Best, Kelly
