Thermocouple replacement for old Evenheat kiln

[kylies.clay]

Howdy y'all! Last time I posted I had an old Paragon that was pretty rough; I never got it to work and recently bought a newer kiln from a family friend. I got an Evenheat kiln with a DTC 100C controller, bricks all in perfect shape and hardly ever fired. My first bisque fire went as well as anyone could hope for and when I attempted my first ^6 glaze fire, that's when stuff went tricky. I noticed toward the end of the firing that the controller was reporting the temperature erratically -- jumping hundreds of degrees each click, displaying a range from 1700F to 2000F. I turned the kiln off and it had wayyy overfired. The ^5, ^6, and ^7 cones I'd put in were a puddle on the kiln shelf and all my wares were bloated and ugly.

Today I opened up the controller, tested the resistance on all the elements (just in case), checked all the wiring, and did a "paperclip test" on the thermocouple terminals which reported back room temperature. A Paragon branded troubleshooting guide for this controller says this indicates I need a new thermocouple.

What brand thermocouple do I need? Since this kiln/controller is no longer made I'm not sure what replacement I need. Will any Evenheat Type K thermocouple work? Thanks!

[Bill Kielb]

Type K are typical, post a picture of your thermocouple and the information on your equipment tag of the kiln. (Model, voltage, cone, etc…) to be sure. Thermocouples act like a battery and output a very tiny voltage proportional to their temperature so while it does happen, jumping from one reading to another may indicate a loose connection, contact with the metal shell of the kiln as things expand, etc…. The more pictures here (off the thermocouple and connections) the more informed the answers will be.

[neilestrick]

Post a pic. It's easiest to get the same size/shape thermocouple that you already have. Most likely it's a type K, but they come in lots of different shapes and sizes. If the temp is flickering like that, I'm more inclined to blame a connection somewhere along the thermocouple system, rather than the age of the thermocouple itself. Check every connection, especially where the wires connect to the mounting block. 

[kylies.clay]

Okay y’all good calls. I just got home and took the controller cover off to check out the thermocouple. The other day when I was checking things out I did do a quick test fire after up to ^06. There was no jumping around. I’m considering trying a ^6 test fire maybe tomorrow so that I can monitor it and see if it starts jumping around and if it does, where in temperature. 
 

There were also no loose connections anywhere on the relays, thermocouple, or controller board. The wire from the thermocouple mounting block does go up to the controller through an open space that’s bordered by a metal sheet (the yellow wire is the thermocouple wire) so I wonder if that may be the issue, but that’s also the heat protection so I’m not sure. 

[Bill Kielb]

Nice picture(s). 8 gauge type K I believe. If you buy it 6” long then trim leads from the back to match the existing size. The good news is that the weld at the tip appears to be failing which definitely could cause erratic operation.

Usually it corrodes away and is very visible see below. Yours looks like the weld is defective. To make a thermocouple the two dissimilar wires need to be reliably connected to each other. Your weld looks cold and twisted so may be  intermittent. Still check all connections visibly and with a screw driver - the yellow thermocouple wire. Make sure the bare wire is actually under the screw and it is reasonably tightened

FYI - After many firings, when we see the wear bellow we just replace them beforehand knowing they only have a few firings left on them.

Picture of a new thermocouple below for reference

 

 

Edited February 10, 2023 by Bill Kielb

[neilestrick]

I don't think that tip looks bad at all, but it's possible that the weld has split, which would cause erratic readings. Be sure to check that one of the TC wires hasn't broken under the screw in the porcelain block. Also check for any splits in the wire where it goes around the metal shield.

The Evenheat thermocouples are narrower than the typical 8ga ones used by L&L, Skutt, and others. Buy it directly from Evenheat to make sure it fits.

[Jeff Longtin]

I've been looking at lots of thermocouples this week. We have 18 kilns and I thought the prev kiln person was checking thermo's but it appears he was not. The Skutt's are easy enough to see the L&L Davinci's are less so. (Enclosed ceramic tube.) So I spent some time pulling out tubes and inspecting things. 

While your photos are good its hard to tell the true state of your thermo. Bill's pictures show the extreme end of thermo wear. The kiln manufacturers suggest replacing thermo's after 60 firings. In our case thats about 3 months. (At the pottery shop new kilns become "glaze kilns" and are fired, every day, to glaze temps.) We only honor the 3 month rule when the kiln is firing slowly or giving odd readings. Otherwise 4-5 months isn't bad. When the thermo has reached the stage pictured it's definitely time to replace.

Another example of an old thermo is a bloated end. Rather than seeing two rods welded at the end it appears to be two bloated wires side by side. (With a bloated/bulbous tip.) This was the case this week. I saw lots of bloated tips. While the thermo works the kilns are taking longer than expected and some of them are seeing greater-than-normal temperature variations.

Additionally, Bill's other picture shows a thermo as they typically are set. Straight, with a ceramic block that holds the wires and the thermo together. I've not seen a thermo bent, as yours are. When you replace it you might consider replacing your block as well. I'm not a kiln expert but maintaining straightness might not be a bad thing?

 

 

[neilestrick]

1 hour ago, Jeff Longtin said:

Additionally, Bill's other picture shows a thermo as they typically are set. Straight, with a ceramic block that holds the wires and the thermo together. I've not seen a thermo bent, as yours are. When you replace it you might consider replacing your block as well. I'm not a kiln expert but maintaining straightness might not be a bad thing?

The bent TC is standard on a lot (all?) Evenheat kilns. They way they mount them is very solid, and the bend doesn't affect the performance.

@Bill Kielb I found one here in my shop and it's not 8 gauge. It measures out to be 14 gauge, which is why it can be bent like that. Beads only measure about 1/4" across and the protection tube is much smaller than what you'd find in an L&L or ConeArt.

[Bill Kielb]

13 minutes ago, neilestrick said:

found one here in my shop and it's not 8 gauge. It measures out to be 14 gauge

Good catch! I thought his looked like 8 in the picture. Unfortunately 14 gauge has a lower lifespan, but if that is what fits. I have bent #8’s - no issue, just need a decent tool. I want to say the only #14’s I have found in a kiln was in someone’s alpine inside the protection tubes, twisted tip as well. Not good for longevity! Might have been a Geil that was reworked. For cone ten I would definitely try and use 8 gauge and if a complicated bend is needed a propane torch and decent needle nose pliers certainly make it easy to shape the 8 gauge wire neatly any way you might need.

Looks like a standard protection tube with a spacer installed- just rechecking the picture.

Edited February 11, 2023 by Bill Kielb

[kylies.clay]

2 hours ago, Jeff Longtin said:

The kiln manufacturers suggest replacing thermo's after 60 firings.

…

Another example of an old thermo is a bloated end. Rather than seeing two rods welded at the end it appears to be two bloated wires side by side. (With a bloated/bulbous tip.)

Yes it’s definitely not as bad as Bill’s pictures that’s for sure! It has a protective ceramic tube inside the kiln and when I pulled it out I did remember thinking the weld looked a little funny. This wasn’t based off of thermocouple knowledge, but just a bit of regular welding I’ve done in the past (basically all bad welds… ha). I didn’t take any of the tube sections off to check past the tip, but I figure a thermocouple is only $45 and this kiln is likely older than me and I’m not sure how many times it’s been fired so I may as well go ahead and replace it. 

It’s definitely 14gauge and I found a 5” one on evenheat’s website that seems to be about the same, but the block is different. All the ones that are sold now have the oval base like in Bill’s picture, but mine has a square block. I’ll attach a picture of how it’s mounted to the kiln. I’m thinking I may just have to remove the thermocouple from the new block and rewire it to mine? 
 

Y’all have been awful helpful and I thank you! I’m about to do a big project that would be too big for the studio I go to so this kiln is going to be getting a good workout once it’s fixed up. 

[kylies.clay]

Oh I also meant to add the kiln itself is only rated up to ^8 and at this point I only ever do ^6 firings so the 14gauge will definitely be sufficient! 

[neilestrick]

See if they sell the thermocouple without the block. It'll be cheaper.

[kylies.clay]

Okay y’all so I need your direction on which thermocouple to buy. It seems there is not a 5” long 14gauge thermocouple without the block that you can buy. I found one 14ga at Bailey ceramic that’s 7” long, according to @Bill Kielb I should be able to trim it to the length I need, correct? Then bend the leads and put them in the block. 
 

I would buy straight from evenheat, but there only options for 14gauge are too short (4” tip to end of block) and the 5” tip to block one is 8 gauge, which would be too large. They also don’t sell them without a block. 
 

Sorry if these are silly questions, this is my first time around! But I’ll know forevermore after this. Also I took the thermocouple back out and checked it again more thouroughly - the weld on the tip is definitely bloated. It’s worse on the side you can’t see in the picture.

 

This is the generic 14ga one from bailey and then these are all of evenheat’s options.

[Bill Kielb]

Yep, you can trim them from the back with wire cutters. If it makes you feel better a thermocouple is made of one type of wire welded to another type at the tip. What makes it work is the connection of the dissimilar metals at the tip, so length is absolutely meaningless other than to fit the machine. For this reason I will often keep 12” around and just trim as needed.

Edited February 13, 2023 by Bill Kielb

[kylies.clay]

Thank you everyone for all of your help! I wound up finding one from Euclid and a few other things that Bailey didn’t have. It was 14gauge, 6”, no block, and only $18! I wouldn’t have known what to find or look for if it weren’t for y’all. You’ve made a little potter like me super happy! As soon as I get the thermocouple and replace it I’ll be on my way to making tiles. 

[kylies.clay]

Okay hey guys. The thermocouple did not fix my issue. I took a video to include of what the kiln is doing. It seems really odd. The first time I ever did a ^6 firing And it did this, everything overfired - cones totally melted. This time the cone 6 cone wasn’t even bent. I’ll include a picture of it later once it’s cool enough
 

Here you are, it only starts up high around 1900°, but I did not catch it right when it started.

[neilestrick]

1 hour ago, kylies.clay said:

Okay hey guys. The thermocouple did not fix my issue. I took a video to include of what the kiln is doing. It seems really odd. The first time I ever did a ^6 firing And it did this, everything overfired - cones totally melted. This time the cone 6 cone wasn’t even bent. I’ll include a picture of it later once it’s cool enough
 

Here you are, it only starts up high around 1900°, but I did not catch it right when it started.

Assuming all of your thermocouple connections are tight (check the entire length of the wire for loos connections or breaks in the wire casing) I'd say it's probably time to replace the controller. That is a first generation digital controller that's like 30 years old. The only other thing you may want to try is adding a ground wire that goes from the center tap tab on the controller directly to a grounding screw. It's possible you're getting electrical interference and a direct ground can get rid of it. I've only ever seen that on 2 kilns before, though, so it's more likely a bad controller.

[kylies.clay]

Okay… the thermocouple wire is definitely connected correctly, tight connections, and the casing is intact along the whole length. One manual for the controller said it could be a ground interference and to rearrange, but the wires been moved around like 10 times from me opening and closing it so I don’t see how it could be that. I’ll try a grounding wire and see if that helps at all. 
I was really hoping I wouldn’t need a new controller. But I guess if that’s what it needs it’s what it will get. Could it not be an issue with relays at all? Just hoping for a cheaper solution than a controller. I felt it was odd how they kept clicking but no buzzing like at lower temperature. 

[High Bridge Pottery]

I find elements only hum or buzz at lower temperatures anyway so I wouldn't worry about that.

 

I know in my D.I.Y controller when it gets up to higher temperatures it starts reporting a lot of 'shorts to ground' because of the plasma generated in the kiln at higher temperatures. At least that is what I read.

[Bill Kielb]

5 hours ago, kylies.clay said:

was really hoping I wouldn’t need a new controller. But I guess if that’s what it needs it’s what it will get. Could it not be an issue with relays at all? Just hoping for a cheaper solution than a controller. I felt it was odd how they kept clicking but no buzzing like at lower temperature. 

The cooler observation MIGHT be relay arcing and electrical noise generated by the relays. Watched your video makes this a real possibility. Need to ponder a bit to see if there is something relatively goof proof and easy to suggest. One thing for sure - Making sure the kiln ground is actually connected from the kiln to a good earth ground is something to check and grounding the center tap of that transformer can be be very helpful with noise generated.

If you have a shielded thermocouple wire, make sure the shield is ONLY grounded at one end ( preferably the circuit board end) Sounds silly but both ends would be a no go for sure.

Edited February 21, 2023 by Bill Kielb

[kylies.clay]

I’ll be honest, I’m not sure how I would check the ground. I know the panel to the kiln has good ground. Also when you’re talking about the transformer, do you mean the 240 to 24 transformer? 
 

I’m in Georgia so I was about to go head to Olympic and pick up a V6-DF as I’m only 40 minutes away. Should I hold off? 
 

i don’t believe it’s shielded. It seemed like just regular old two stranded wire. 

Edited February 21, 2023 by kylies.clay

[Bill Kielb]

31 minutes ago, kylies.clay said:

I’m in Georgia so I was about to go head to Olympic and pick up a V6-DF as I’m only 40 minutes away. Should I hold off? 

I am a big fan of the V6cf so even if you have relay noise, newer controllers are built to suppress it. If you can find a good deal on a v6cf I really like the controller and it has performed for many many years.. to check you r service ground takes a bit of investigation on the actual wire run. It should terminate at a ground rod outside your service entrance and be tight and well connected. Good to always check, it is a safety component of your service. Typical method below, there are several common methods.

Edited February 21, 2023 by Bill Kielb

[Bill Kielb]

37 minutes ago, kylies.clay said:

do you mean the 240 to 24 transformer?

Yes, the center tap of the 24 v side. Definitely NOT the 240 v side

[High Bridge Pottery]

56 minutes ago, Bill Kielb said:

Need to ponder a bit to see if there is something relatively goof proof and easy to suggest.

You can twist the wires, that means the noise on each line cancel each other out. Used to do it with phone lines. If it was noise wouldn't it be happening throughout the firing?

[Bill Kielb]

Just now, High Bridge Pottery said:

You can twist the wires, that means the noise on each line cancel each other out. Used to do it with phone lines. If it was noise wouldn't it be happening throughout the firing?

Since they are sheathed, not really twistable but that definitely is a technique. Since a relay can wear to the point of generating obnoxious arc noise (No good way I can think of capturing without an oscilloscope or digitally some way) just pondering if there is an easy one stop sort of sure fire way to minimize for future likely occurrences.