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clay lover

Elec. Kiln Advice, Please

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clay lover    133

The last 2 firing, my Skutt 1027 has been producing witness cones that are increasingly more different in temp readings. Just unloaded the third firing since I ve noticed this, It is WAY off. Thermocouple cone read perfect 6, tip just down, the bottom was a slightly bent ^5. That's almost 2 cones difference. I use 1/2 shelves with spaces between and have been doing fine temp wise until recently. I have a 25 minute soak at peak and no down draft vent of any kind. I have been firing for 2 years with no more than 1/2 cone difference throughout. Similar loading and size of work, same schedule

Does this mean the elements are wearing out? After I emptied it, I set it to ramp up at top speed, and watched until it reached 500*. Peeked in, the top 2 rings and the bottom 2 rings were glowing but the middle 8 rings had not kicked on yet. I checked the output 3 firings ago and the elements were firing as they should, but it's much more off now than then.

Any advice? This is the one and only elec kiln I have had, it's the original elements, and unfortunately, I did not keep a record of how many firings I have done . 60? bisque, 40 glaze? is a guess only.

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Your uneven firing can be caused by a failed power relay, about $60, or one or more failed heating elements a set costs us about $200.  By the time you notice a difference in witness cones, or your electronic controller errs out, you've lost more than one heating element.

 

I'm a big fan of the "paper test" where you place paper strips under each element to find strips of paper which don't char within the first few minutes after firing the kiln on a fast speed. It's often more accurate than watching for glowing wires but provides somewhat less information than ohmmeters. A monthly paper test will tell you about failed elements long before witness cones do.

 

If all of the heating elements controlled by one relay are not heating, then the relay needs to be replaced. If the failed elements are not all of the elements controlled by a relay, the failure is merely those heating elements.

 

After running an 18 month experiment at our studio replacing coils and relays one at a time, we've resumed replacing all wires and relays at the same time, about once a year for our heavy use.

 

We discovered with our particular kiln that after one element fails, it's not too many more firings until almost all of them fail. Additionally we learned that the specs on the relays are designed to last longer than the heating elements, but not much longer. Know that relays can occasionally fail in an on position.

 

For us it's economical to replace the heating elements and relays about once a year rather than deal with frequent firing failures. An exception would be a single element which we know has failed prematurely because of mechanical damage, or damage from splattered glaze.

If its a potter brumfield relay (the black ones in most skutt & L&L top loaders--not a mercury relay), even from skutt or l&l theyre ~30.00 a piece, order them from allied electronics or comparable and theyre under 15.00 a piece.

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neilestrick    1,381

If a relay or element were out, the kiln would not have reached temperature, and you would have received Error 1. A kiln cannot reach cone 6 with a relay out, because 1/3 of the kiln would not be getting heat. Even with one element out, it most likely won't reach cone 6. Check your elements for wear. If you have a multi-meter, test the element resistance and compare it to the factory original. Visually, if the element coils are starting to lay down and pile up on each other, or the elements are looking pretty crispy, it's time to change them.

 

HERE is one place you can get the relays for your Skutt. Or HERE

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clay lover    133

Neil, the elements don't look laid and over aren't hanging out. They look just like they did when it was new.

I was looking for a reason that the bottom cones didn't reach more than ^4, with the cones at the thermocouple at a solid ^6. Everything else about the kiln was the same. I never use less that 5" posts on the bottom shelf The schedule was the same. What else can be going on?

I emptied the kiln, set the ramp to 999* per hour and watched it until it hit 500*. I lifted the lid and peeked in. The top 2 rings of elements were red, the bottom 2 rings were red. The center 8 rings were dark. I let it run up to 800* and that did not change. Since the Skutt is supposed to have hotter elements on the top 1/3 and bottom 1/3 of the 3 sections, I was puzzled as to why I did not see 4 rings red top and bottom.

How many ^04 bisque and ^6 glaze firing should I get from a set of elements?

I appreciate all educated advice, I'm in the dark with this.

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neilestrick    1,381

Neil, the elements don't look laid and over aren't hanging out. They look just like they did when it was new.

I was looking for a reason that the bottom cones didn't reach more than ^4, with the cones at the thermocouple at a solid ^6. Everything else about the kiln was the same. I never use less that 5" posts on the bottom shelf The schedule was the same. What else can be going on?

I emptied the kiln, set the ramp to 999* per hour and watched it until it hit 500*. I lifted the lid and peeked in. The top 2 rings of elements were red, the bottom 2 rings were red. The center 8 rings were dark. I let it run up to 800* and that did not change. Since the Skutt is supposed to have hotter elements on the top 1/3 and bottom 1/3 of the 3 sections, I was puzzled as to why I did not see 4 rings red top and bottom.

How many ^04 bisque and ^6 glaze firing should I get from a set of elements?

I appreciate all educated advice, I'm in the dark with this.

 

Claylover, only the very top and very bottom elements run hot. Each elements loops twice, so you'll see two rows glowing on top and two on bottom before the others. It can take up to several hundred degrees before the middle elements start glowing, often 700 or 800 degrees. If they all glow eventually, but it's firing unevenly, then you likely have worn elements, or possibly a sticky relay. If the relay sticks off near the end of a firing, it could cause the unevenness problem and still reach temperature. Sticky relays are very difficult to diagnose without a meter.

 

Norm, I agree that all kilns are different. I was giving advice based on my experience with that particular model of kiln. Plus, firing bisque with a relay out is very different than firing to cone 6 with a relay out. And 27" tall kilns, like claylover's 1027 Skutt, will typically fail to reach cone 6 with just one element out. Smaller kilns like your E23 often have more power per cubic foot and can get away with more element issues before real problems arise. But I respectfully have a hard time believing it will get to cone 6 with 3 elements out. That's only a 4 element kiln, right?

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neilestrick    1,381

Norm- you have a very unique kiln there. Typically a kiln that size is fed by 4 elements. With 6, it is much more powerful, and can therefore handle running with a couple of elements out. So that's an unusual situation that won't apply to most other kilns, definitely not a Skutt 1027.

 

As for those relays, the two you say originally came with your kiln, PRD7AYO-240, and PRD7AGO-240,  should not be interchangeable with the T92P7D22-12, since the first two have an 240V AC coil, and the T92 is a 12V DC coil. The first two would not run off the Bartlett controller since it has a 12VDC output. That said, there is a 240VAC version of the T92 available. I've seen that used on the Olympic glass kilns that have a separate element in the lid that can be controlled manually. I suppose it's also possible they are using an arrangement like in the L&L DaVinci models where the T92 12VDC is used as a link between the Bartlett controller and the 240VAC relay. Functionally, both types are the same, however the closed case of the T92 makes it less susceptible to corrosion and dust.

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neilestrick    1,381

PRD7AYO-240 and PRD7AGO-240:

PRD- Open relay

7- DPST-NO (dual pole single throw, normally open contact)

A- 50/60hz AC coil input

Y or G- Refers to the type of contact material (silver, silver cad, etc)

0- Terminal type (in this case screws)

240- coil voltage

The only difference these two relays is the type of material used in the contact itself, so the Y model is 25 amps, the G model is 30 amps.

 

T92P7D22-12:

T92- Relay  model T92

P- Dust protected case (also available as 'S', wash tight tape sealed)

7- Contact arrangement (DPST, NO)

D- Coil Input (DC in this case)

2- Mounting type (Panel, in this case)

2- Contact material

12- Coil voltage

 

The difference between the PRD and the T92 relays is the case itself (T92 is closed, PRD are open), the terminal types (PRD are screws, T92 are slip on), and the coil voltage. But again, the Bartlett V6CF controller only has 12VDC outputs, so cannot run the PRD relays if they have 240VAC coils like in the part numbers you've listed above. Have you followed the link I put in for the PRD relays? Do yours look like that?

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neilestrick    1,381

Those look like T92 relays to me. And according to the E23 wiring diagram, that's what they are. The PRD relays are used in the FX series kilns with the thumb wheel controls, where everything runs at 240VAC. So that all makes sense. Have you pulled out one of those black relays to verify the part number?

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neilestrick    1,381

 

Having just reassembled our kiln, I discover PRD7AGO-240 power-relays Cress sells us are currently:

 

TE CONNECTIVITY / POTTER & BRUMFIELD  T92S7D22-12  POWER RELAY, DPST-NO, 12VDC, 30A, FLANGE

 

Which are available for a mere $12.20 each. Made by Tyco everyone's favorite Chinese out-sourcer.

 

http://www.newark.com/te-connectivity-potter-brumfield/t92s7d22-12/power-relay-dpst-no-12vdc-30a/dp/17M3099

 

So we won't be buying anymore from Cress at $48.

 

Those look like T92 relays to me. And according to the E23 wiring diagram, that's what they are. The PRD relays are used in the FX series kilns with the thumb wheel controls, where everything runs at 240VAC. So that all makes sense. Have you pulled out one of those black relays to verify the part number?

 

 

I'm thinking I'd be calling Cress and asking for some refunds if they were selling you the cheaper relays under the more expensive relays part numbers.

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JBaymore    1,432

 

Having just reassembled our kiln, I discover PRD7AGO-240 power-relays Cress sells us are currently:

 

TE CONNECTIVITY / POTTER & BRUMFIELD  T92S7D22-12  POWER RELAY, DPST-NO, 12VDC, 30A, FLANGE

 

Which are available for a mere $12.20 each. Made by Tyco everyone's favorite Chinese out-sourcer.

 

http://www.newark.com/te-connectivity-potter-brumfield/t92s7d22-12/power-relay-dpst-no-12vdc-30a/dp/17M3099

 

So we won't be buying anymore from Cress at $48.

 

Those look like T92 relays to me. And according to the E23 wiring diagram, that's what they are. The PRD relays are used in the FX series kilns with the thumb wheel controls, where everything runs at 240VAC. So that all makes sense. Have you pulled out one of those black relays to verify the part number?

 

 

Nice % markup. ;)

 

best,

 

................john

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