Electrical Update March 23, 2006

Yesterday when I was taking the picture of the element in the groove I noticed that Euclid included a tag that I can attach to the kiln. The tag includes a custom serial number that I can use to reference the elements should I ever need replacements. Very cool.

Also on the tag is the resistance of each element, 12.2 ohms. This struck me as strange because I could have sworn that I had asked for 12.8. So, I checked, and I was right, my original design (9000 watts) inferred 12.8 ohm elements, when four circuits were wired with eight elements and series pairs.

Immediately I worried that this meant my kiln would be underpowered. Less resistance means less power required to push the electrons right? But, I know that I don't know that much about electricity. I hope I wrote my little kiln design program correctly. It's pretty simple, it's just programmed with the arithmetic relationship between power, current and voltage.

Here's the original design again:

~/pwork/src/kilndesign$ kilndesign -t circle -C 9 -R 11.5 -w 9000 -c 4 -e 8
  cubic feet : 5.41
  cubic inch : 9348.20
  wattage       : 9000.0
  amperage      : 37.5 (0.62)
  courses       : 9.0
  height        : 22.5
  kW / c.f.     : 1.7


  4 circuits
  8 elements


  wattage:
  per circuit: 2250.0
  per element: 1125.0


  amperage:
  per circuit: 9.4
  per element: 4.688


  element gauge 15


  resistance:
  total:       102.40
  per circuit: 25.60
  per element: 12.80


  wirelength: 47.8 feet per element
  watts/foot: 23.55
  watts/in^2: 11.0

The program isn't capable of figuring things out given a resistance for each element, so I played around a bit and got to this point:

~/pwork/src/kilndesign$ kilndesign -t circle -C 9 -R 11.5 -w 9445 -c 4 -e 8
  cubic feet : 5.41
  cubic inch : 9348.20
  wattage       : 9445.0
  amperage      : 39.4 (0.66)
  courses       : 9.0
  height        : 22.5
  kW / c.f.     : 1.7


  4 circuits
  8 elements


  wattage:
  per circuit: 2361.2
  per element: 1180.6


  amperage:
  per circuit: 9.8
  per element: 4.919


  element gauge 15


  resistance:
  total:       97.58
  per circuit: 24.39
  per element: 12.20


  wirelength: 45.5 feet per element
  watts/foot: 25.94
  watts/in^2: 12.1

So, the implication here is that my kiln will be slightly higher in power than originally intended. Not necessarily a bad thing. However, take note of the watts per square inch, it's gone up by almost 10%. This figure is referred to as the watt loading of the elements. It's an important factor in element longevity. The higher the watt loading the shorter the life of the elements.

I sent an email to my contact at Euclid asking about this, so I'll find out shortly if I'm right. I'm not concerned though. As Tim Allen says .... more power isn't really bad, and truthfully, I was worried that 9000 watts was a bit on the short side. I'm guessing that Euclid did this because it seems to be what they put in the same sized kiln. They have a 23 inch diameter, 22.5 inch high kiln that they say draws 40 amps. So, I'm guessing they just wound me the same elements. They knew I had 60 amps, so it's all fine.

Update: I heard back from Euclid, and I am wrong. Surprise, surprise. They design their elements considering the resistance at temperature. Resistance goes down when the wire gets hot. Elements designed from the point of view of hot resistance such that the kiln requires 9000 watts means 12.8 ohm elements when cold. But I still think that 9445 watts will be going into my kiln when it's at top temperature.