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Chilly

Time for a New Thermocouple?

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My kiln is on wheels, and lives under the bench in the greenhouse, and is rolled out to the middle for firing.

After the last time I fired I got an error, telling me there was something wrong with the thermocouple.  As I nudged the kiln, something must have moved inside and the error went away.  Firing was fine, according to witness cones.

Opened up the "wiring box" today, to find the thermocouple wires were no longer connected to the connector box, and on removing the rod part from the ceramic sheath, it is broken in two, although the wire looks intact.

Why do I wait till closing time on a Friday before investigating?  Why indeed.

Looking at the kiln manufacturers website this tiny piece of wire and connector box is going to cost just short of £100.  What!  Is it gold-plated or something?

Have sent e-mails off to a few other kiln suppliers/repairers to see if  can find it cheaper.  Remember I'm in the UK if you've got any suggestions.

Thermocouple.jpg.a0a00e64a78a6ea9f8bb4277e81297eb.jpg

 

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The thermocouple is simply too dissimilar wires welded together at their tip. The ceramic insulation only keeps these wires from touching  and separated from each other . The Crack in the ceramic sheath normally would not affect the operation. This thermocouple appears to be still connected to its ceramic holder so I am not sure I fully understand what the issue is here.

if the thermocouple was broken your kiln likely would have an error and most likely would not have fired to the programmed temperature. Again, a mystery so perhaps You could provide more info.

i added some pictures for clarity after a simple google search to illustrate that these often come beaded so the length can be customized by removing the beads and cutting to length. Again, only the very tip makes this function as a thermocouple.

9337D652-5D62-440E-AB12-E42D7758D428.jpeg

8EA21C3A-5FC1-4673-A63F-5FDBBD38D7AA.jpeg

Edited by Bill Kielb

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5 hours ago, Bill Kielb said:

The thermocouple is simply too dissimilar wires welded together at their tip. The ceramic insulation only keeps these wires from touching  and separated from each other . The Crack in the ceramic sheath normally would not affect the operation. This thermocouple appears to be still connected to its ceramic holder so I am not sure I fully understand what the issue is here.

if the thermocouple was broken your kiln likely would have an error and most likely would not have fired to the programmed temperature. Again, a mystery so perhaps You could provide more info.

i added some pictures for clarity after a simple google search to illustrate that these often come beaded so the length can be customized by removing the beads and cutting to length. Again, only the very tip makes this function as a thermocouple.

 

 

The connector block is singed, the screws will not undo to enable re-connection of the wire from the controller.

5 hours ago, Mark C. said:

Is this an s thermocouple ? or a K type

its different than most on this side of the pond as the sheath is a solid one piece not a bunch of small pieces of insulators .

It's an R type.  

 

The replacements come complete with the bracket to attach to the wiring box, and the ceramic sheath.

Z-Bracket-Head-Thermocouple-Front-View.jpg

 

Just seems like a lot of ££ for such a small item.  

 

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These two pictures are very different. R type is good but one is fully shielded and the other open ended and of course very different lengths.

r type thermocouples are platinum based and usually utilize a full protection tube. I am sorry, if you  can  post a picture of the broken one, tip, middle and connector I might be able to understand and provide more insight. Right now I am still wondering why the original is considered bad yet the kiln had no error and fired properly.

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2 hours ago, Bill Kielb said:

These two pictures are very different. R type is good but one is fully shielded and the other open ended and of course very different lengths.

 

My photo shows the "inside" bit. 

2 hours ago, Bill Kielb said:

 

r type thermocouples are platinum based and usually utilize a full protection tube.

The ceramic sheath is still attached to the kiln.

2 hours ago, Bill Kielb said:

if you  can  post a picture of the broken one, tip, middle and connector I might be able to understand and provide more insight. 

Will do

2 hours ago, Bill Kielb said:

Right now I am still wondering why the original is considered bad yet the kiln had no error and fired properly.

The end of the wire from the controller to the connector box shown here  was fried.  The four screws are burnt and will not undo.Thermocouple.jpg.a0a00e64a78a6ea9f8bb427

The kiln fired OK, then when I moved it to put it back under the bench, it showed the error.

 

At the very least I need to replace the connector box.

 

Thanks for you help @Bill Kielb.  My other half is a mechanical engineer, with a knowledge of "heat and electrics",  but not of kilns as such !

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Ahh yes, I would probably drill out the original screws, tap for slightly larger new ones and put it back in service or keep it entirely as a spare if you already have the new one ordered. Not an easy project though.

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By the time you figure out how to repair the old one to make it useable, you'll probably wish you had just spend the money on the new one. Get the new one, and then work on the old one when you have some free time. If you can make it work again, great, you've got a backup. If not, you've got the new one already.

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That connection ceramic box with screws is pretty standard. I have a box of them as they come with a new thermocouple. I use the old ones and just remove the new one and toss it in my thermocouple spare box-I like to stock at least 3-4 as spares.Since yours are cooked I would sumize they (screws) where a tad loose as that builds up heat and can cook them

Edited by Mark C.

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16 minutes ago, Mark C. said:

That connection ceramic box with screws is pretty standard. I have a box of them as they come with a new thermocouple. I use the old ones and just remove the new one and toss it in my thermocouple spare box-I like to stock at least 3-4 as spares.Since yours are cooked I would sumize they (screws) where a tad loose as that builds up heat and can cook them

Thermocouples are 40 microvolts per degree C hard to believe they would char or burn because they are loose. Can you tell what they are made of. I ask because there are situations where stainless steel connections simply seize as they are tightened. These connections always require some anti seize and have surprised many an owner and many industrial designers as well.

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I think you are right Bill about the heat as the mil amps are so small-My new guess is moisture-on steel screws over time. Mine are all away from the sidewall of my kilns so steam/mositure is a non factor . I have never had a stuck or rusted screw and all my kilns are outside in a covered area in a rainy climate.A few drops of anti seize would work wonders on  the new one.I'm pretty sure they are not stainless connections but steel.

They could get hot close to kiln if mounted against sidewall but moisture may be more a factor ?Just spitballing about this as I have never experienced it myself in 45 years  firing kilns-mostly to cone 11.

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Not gold plated but titanium!

The broken ceramic wont make a difference unless the wires touch.

Keep as spare if you buy a  new one.

Did you put your kiln on wheels Chilly?

Most not robust enough to wheel around....

I fired for ages with similsr damage after friend unloaded her pots fro.  my kiln shattering sheath and cracking ceramic as yours is. The sheath alone Aussie price $80 at the time....forget that till richer...another reason not to fire or allow folk near your kiln

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10 hours ago, Babs said:

Not gold plated but titanium! - lol, price makes it feel like it

The broken ceramic wont make a difference unless the wires touch.  OK

Keep as spare if you buy a  new one. ;)

Did you put your kiln on wheels Chilly? - No, it was on casters as original supply

Most not robust enough to wheel around....Only gets moved a metre, back and forth from under the bench.

I fired for ages with similsr damage after friend unloaded her pots fro.  my kiln shattering sheath and cracking ceramic as yours is. The sheath alone Aussie price $80 at the time....forget that till richer...another reason not to fire or allow folk near your kiln  I have to replace, at the very least, the connector block as the extension wire to the controller had fried and the connector box screws are fried and won't undo :-(  Found a source for £60 which isn't so bad.

 

Thank you all for your assistance.

One supplier is insisting I should remove the ceramic sheath from the kiln and replace it.    Doesn't say why, and as it is firmly attached I really don't want to rip it out and break something else, so have found a supplier that will just sell the bits I need.

Edited by Chilly

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On 1/15/2019 at 7:20 PM, Babs said:

Think it really may be titanium. Thought I read it somewhere once upon a time 

 

One wire is Platinum/13 % Rhodium the other is  platinum

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I've replaced the thermocouple and all seems OK.

Except.  If I wiggle the bundle of cables that go from the kiln to the controller, the temp readout goes up and up and up.  When I stop wiggling, it goes down, down, down, back to ambient.

Surprisingly, I've never done this before, so I don't know if it's normal for my kiln or not.  (I do know if I move the cables on the kiln at the centre nothing changes.)

I've put a continuity tester from the thermocouple plug in the controller and that seems OK.

I'm now guessing there must be a tiny break in the thermocouple extension cable that is causing this weirdness.  Oh, and this happened at "closing time on a Friday night" - what the $%^&.

Any other suggestions.

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Definitely a loose connection or intermittent open in the wiring. I would check all Connections both ends as soon as practical and locate the intermittent connection.

running it with an intermittent fault and hoping  seems risky to me.

Edited by Bill Kielb

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Thanks @Bill Kielb  Connections are fine, going to order new thermocouple extension right now!  

Not going to run it till it's fixed.  My next fire is a first-time glass tack firing, so need it working at it's best.  Glass stuck to glass, no clay involved !!!

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On 1/20/2019 at 1:57 AM, Babs said:

Glass on glass...gutsy. mat need to fire down to avoid cracking unless kiln is a slow cooler.....

Oh yes, firing down is a must, luckily controller is 9 segments and 9 programs.  I've been doing fused, stained and copper-foiled glass at a studio for a while.  This will be my first glass firing in my kiln.

Edited by Chilly
Missed a word

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