Element Design --- The Three Bears (Part 1)

Here is a photo of my 3 electric kilns. They are all built by L and L and I have found the company wonderful to deal with, and open to learning the special needs of crystalline potters. 

I must confess that the kilns have names and they are Papa Bear, Mama Bear, and Baby Bear. It's kind of embarrassing to admit, but it does make identifying them much easier so the large one is Papa Bear, and so forth. Each kiln is 18 inches high and their diameters are 29, 24, and 18 inches respectively. The cubic footage of each of them is 6.7, 4.8,  and 2.7, also respectively.

So the first question we have to ask is, "How much power do we need to fire these kilns?" There is a wonderful book by Robert Fournier called "Electric Kiln Construction for Potters" and it is full of information like this. Actually he gives 2 different tables, "Power/Volume Relationship in British Commercial Kilns," and " Power/Volume Relationship in American Commercial Kilns." The British table suggests more kW (Kilowatts) than the American table, and since we want our elements to last, I decided to use the British Table. The British table allots each kiln almost half again as much power, and since I want to power my kilns so that the elements do not have to work so hard,  using the British table seems like the correct choice. 

Papa Bear, which is 6.7 cubic feet will require about 16kW, Mama Bear at 4.8 cubic feet will need 13kW, and Baby Bear, at 2.7 cubic feet gets 9kW. 

So now we need to know 2 simple formulas. 

The first is Watts = Volts x Amps or W = V x I where I is the current in Amperes, V is the voltage and W is the power to the kiln. 

The second is V = I x R where R is the resistance in Ohms. 

For my kilns the voltage is 240 so this will remain constant throughout the calculations. 

OK. 

Papa Bear needs 16kW of power at 240 volts so 16,000/240 = 66.67 amps. We may not be able to supply that much because of the wire leading from the breaker to the kiln. But we will be able to improve on the 38 amps that the kiln was originally designed for, and which proved to be inadequate. 

Mama Bear needs  13kW of power at 240 volts so 13,000/240 = 54.16 amps.

Baby Bear needs 9 kW of power at 240 volts so 9000/240 = 37.5 amps.

Tonight I lead the chanting in our Temple and I have to sign off for the moment. 

But below is a photo of the inside of Baby Bear, and the double sets of elements. For some reason the hairpin turns offend my sense of craftsmanship --- I suppose it is the fact that the hairpin was not planned, someone just took the element and stretched it  ---- and I am going to try to eliminate the hairpins.