Firing Schedule - Fine tuning your electric kiln controller

[Brent Farler]

 I am working with an Orten controller on my electric kiln.  In spite of low use (<30 firings) my thermocouple doesn't appear to read very accurately.  The automatic cone fire programs consistently overfire.  

I am trying to get the adjustments just right to get the combination of a good soak, slow cool and actually hitting cone 6.  

My teacher really recommends I soak for 30 minutes and cool at 90 degrees and hour.  If I set my controller to fire cone 6 with these parameters it will flatten a 7 cone flat as a pancake not to mention flattening all of my colors along with it.

I fiddled with a few firings and found a cone 4, slow ramp, with 30 minute soak, Thermocouple offset of -10 degrees and 90 degree cool down would put a cone 5 over and leave my cone 6 at about 2:30.  Colors looked pretty good but my teacher is telling me the clay body feels underfired (using a cone 6 stoneware).  I would like to hit the cone 6 on the nose but not sure which factor to tweak.  My controller manual isn't much help since it pretty much only gives the conversion chart for what looks like a no soak firing and my temp is unreliable.

Thoughts?

[Neil Estrick]

If a manufacturer says the kiln will go to cone 10, it will. If it didn't they'd catch *$#@! from their customers. How quickly it will do it is another story. And if type K thermos didn't work fine for most people, they wouldn't use them, either. They'd catch &%*#@! from their customers if nothing ever came out right due to faulty temperature readings.

Kiln manufacturers have a lot of different financial and performance related variables to deal with in designing their kilns, all related to keeping their customers happy on a dozen different levels. The modern electric kiln is a marvel of compromise. Yes, pretty much any complaint you ever hear about a kiln can be fixed by spending more money, but not every kiln can be a $20,000 front loader with Wi-Fi and an ice maker. So we get what we pay for, which is an appliance that can pay for itself in a very short time, and will outlast any refrigerator of the same price.

The L&L element holders make element changes almost twice as fast. I can do all 9 elements in my 20 cu/ft DaVinci in less time than the 6 elements in a Skutt 1027 or 1227. And no other kiln bricks will last longer.

[Robert Coyle]

Jeff Poulter said:

Hi Robert,

    Which Skutt is it?  My little KM-818 will go to ^10.  It doesn't like it, but it does it better since I had Euclids make up some beefier elements.  If you beef them up too much, you may have to redo your breaker & wiring and the relays may not like it. Heavier gauge elements last longer, but cost more, cause you're using more wire in each element(weight wise).  I am always looking through the local on-line ads & I am amazed at what some of the older model kilns have in them.  I would swear I have seen beefier elements in some of the old toaster ovens!  The Skutt PK kilns are all beefed up as that is what the P stands for, Production.  I am somewhat partial to L&L as they say the Hard Ceramic Element holders radiate the heat better into the kiln & cook the element less.  All I know is that they make it a breeze to change elements with no messy brick damage & using binding posts instead of crimping is an added bonus!  jhp

Its a 1027-24. Interesting thing is it only is rared for 48 amps... only 10 amps more than my old cone 6 Cress that was not nearly the capacity.

Since I am never going to fire at cone 10, this is no problem. Just seems people who want to fire at 10 might be stuck with a pretty slow ramp.

[Jeff Poulter]

My L&L e18t only pulls 35 amps to produce 8400 watts, but it is only 18"wide & 27" tall.  I think your Skutt should pull the 48 amps & over 11,000 watts.  I know the wider & taller you go, it really increases the demand for power.  Are the elements "stock" elements from Skutt or from somewhere else?  Have you measured the resistance on each element?  It should be able to hit ^10 fairly easily.  Maybe the elements were for a 208v model or something like that.  That would make it pretty hard to get to ^10.  Skutt can tell you what the resistance should be.  It will change as the element ages, but should be in the ballpark.  jhp

[Robert Coyle]

Jeff...It's marked as a 240 volt kiln. It was purchased locally and 240 Volt is all they carry. I measured the resistance early on and it seemed reasonable for 48 amps. As I said, it works fine for cone 6, so I won't be changing out elements or anything.

[Neil Estrick]

48 amps is the magic number for kiln manufacturers. It allows them to put a 50 amp plug on the kiln. Anything larger has to be hard wired. Being able to plug it in makes it easy for home use- hard wiring scares people who aren't familiar with it.

[Norm Stuart]

If hard wiring is dissuasive, that's often accompanied by the use of three phase AC, where you have to pay the electric company to install a three phase transformer on their pole, unless you happen to be in an industrial district where they're already in use.

Paying the licensed electrician $320 to change out our 30 amp outlet for a 50 amp outlet, and adding a ground-fault interrupter on our 110 volt lines for pottery wheels and accessories was shock enough for the people paying the bill.

[Neil Estrick]

If I remember right, around here they won't give you 3 phase in a residential building.

[Robert Coyle]

I try to avoid electricians...maybe at the risk of my life...but I know enough to change out a breaker and wire in an outlet for 240. I put together my own kiln controller that controlled the ramp with a PC  through a 50 amp solid state relay. Had it all wired up connected a 5 volt battery across the input of the relay and FLASH! BOOM! threw the 50 amp breaker in the studio and also the 100 amp in the main box. Did I wire it wrong? Well no, I got cheap and bought an old used female connector from Habitat for Humanity. 50 amp cable is like re-bar and when I shoved the connecter hard to get it to seat in the box, the cable busted the plastic and made contact with the case.

So I made sure that everything was tight and tried it again. On came the kiln pilot light. It worked.

Not sure what the moral of the story is?

[Norm Stuart]

Our studio is in a retail area and I think the veterinary hospital next door switched over to 3 phase when they had their emergency generator installed.

We really didn't have a choice of not using a licensed electrician, and he had to make the final connections live without turning-off the power to the building because we couldn't have the adjoining business shut down. He took a short nap in his truck after getting a jolt tightening the connections.

I worked for PG&E during the summer while I went to college. Many who worked there envied the salary earned by utility company linemen, and PG&E would pay for the required education, but there weren't that many people signing up.  One mistake and you're dead.