New Relays Failed in a New Way

[Hyn Patty]

So, while swapping out the elements on my 20 year old Skutt, when I went to test fire it afterwards the kiln firing schedule starts, the relays click, but there's no heat.  In fact there is no power at all getting to the elements. After a few minutes into the firing schedule the relays stop clicking and the kiln just sits there displaying the same temperature it started with.  No error code.

I sent photos to Ryan at Kruger Pottery of various things to make sure I had done my re-wiring precisely and he says it's fine.  But he did notice (as I had) that both of my recently replaced relays had bent connection pins in one corner.  I replaced those about three months ago but clearly they have already failed in a new, strange way.    I'm attaching a photo to show how the two lower left connections sank into the relay body and went crooked instead of staying straight like the other connection pins.

I contacted the company that sold me the relays and we chatted about whether or not they'd had any similar failures like this, especially in that batch.  But they said no.  My old relays failed in the usual manner by burning out internally and the clear plastic went black.  But never seen this kind of failure before.  They are kindly sending me a replacement pair of relays but I'd love to know what might cause it and certainly do not wish to keep repeating it.

After chatting we decided that my 20 year old kiln's Signal Transformer might be failing.  There is no discoloration on it, and it tested fine using a multimeter for continuity, but I went ahead and ordered a replacement transformer since it's only about $15 anyway.  I double checked my Olympic Doll E and it uses the same kind so I went ahead and ordered a second one for that kiln too, since I fire it a great deal more often than I use my big Skutt.  My replacement parts are long overdue so I'm trying to get a leg up and make sure both kilns, and especially my heavily used Olympic, are kept in tip top shape.

Anyway, if you have had this kind of failure on relays before, or if your signal transformer in your kiln controller has gone bad, I am just fishing to see if you had similar experiences.  The more I know the better!  Thank you for your input.

 

Edited November 17, 2023 by Hyn Patty
typo

[Dick White]

I'll let the professional electricians (you know who you are...) have the last word, but I have heard that these "ice cube" relays used in many Skutt kilns are subject to more heat stress than the brown ones used in most other kiln brands because these are crammed into too small of a space. Poor design of the control column. But what else can one do about it now?

[Bill Kielb]

While not the expert I’ll offer this thought and suggestion: Both relays appear to have failed due to overheating resulting in the plastic melting enough so the quick connection tipped to one side. The corresponding moveable contact in the relay on the right appears to show signs of overheating as well.

So why so much heat? Electrical load or inability to cool itself with the updraft in the kiln. It failed quickly so, electrically overloaded or just a defective relay that can not tolerate the load …. Or ….. new relays use a thinner moveable contact? First step tell us the model so we can look at the wiring diagram which should allow us to see how closely the relay is to or above the rated load and rated operating temperature. From they’re easy enough to measure the element resistance right at the relay contacts to verify the elements are as expected with respect to loading. Maybe the last piece in the puzzle would be this relay in spec is rated by horsepower. Converting to amps gets the contacts down to prox. 12 amps. Elements (resistance loads) cause significant heating in the controls and wiring, so it will be interesting just to see just how many amps the elements are and if the newest forms of this relay handle less than previous for a resistive load. Table below

Just adding relay specs below - all appear spot on except for the meaning of 2hp @ …… rating.

 

Edited November 18, 2023 by Bill Kielb

[neilestrick]

The clear relays run hot because the box that they're in is shallow. You'll notice on the top that there are 5 louvers. They switched to the black relays at some point, presumably because they were cheaper, and found that they burned out really fast, so they made the box deeper (6 louvers) to provide more air flow, and it made more room for the wire terminals so they didn't have to use right angle terminals with those relays. They recommend still using the clear relays in the 5 louver boxes. The clear ones are rated for high heat areas, and in general they do pretty well.

@Hyn Patty You need a new wiring harness. You've still got the original 20 year old wires connected to the relays, and they are most likely what is causing them to overheat. I see this all the time in Skutt kilns, and new wires solve the problem. Transformers rarely fail, and I don't see how it could cause the relay to fail, but as long as you have one coming, go ahead and replace it and all the wiring in the box at the same time.

[Bill Kielb]

3 hours ago, neilestrick said:

You've still got the original 20 year old wires connected to the relays

Wires Might be a solution, but the connections and wire we can see  look pristine and the copper in the relay overheated, but no signs whatsoever on the wire or connections. Bad wires / connections ought to raise the resistance of the circuit and lower the load on the relay unless they are shorted somewhat. Still - could be downstream of this picture and new wires never a bad idea but I would definitely measure the resistance from the relay terminals just to understand at what load this relay was running at.

Only parallel I have experienced - carbon tracking or something slightly conductive acting as a slight short to ground around element connections etc… If the wires are replaced, also strongly suggest cleaning any coating off the porcelain element bushings and such. A resistance measurement at the relay terminals likely can confirm this.

[Hyn Patty]

I can certainly replace wiring and I'm about to that with my Olympic already.  The wiring in that one is looking pretty shabby but the wiring in my Skutt still looks clean and new.  Testing the wiring in the Skutt with a multimeter also shows very little resistance in the wiring - and we checked every wire in there.  Not sure I can replace these with another style of relay or not.  My first thought was that this pair was faulty since my last pair of relays, which were the exact same kind, lasted 20 years without issue.  Still reading all other comments...

[neilestrick]

You can't replace the relays with anything different. There are other types that will fit, but the ones you have are made for high heat locations. They're the best you can do. And for the most part they will work fine. The only other option is to get a new control box and move everything over to it and use the black relays. I don't think that's necessary, though.

I've seen relays fail prematurely on Skutt kilns dozens of times, and the solution, per Skutt, is to change the wiring harness.

[Bill Kielb]

@Hyn Patty Just curious, can you measure the resistance (unpowered kiln) across the two wires that go directly to the elements and post? Just curious how much load is on these relays and what their current specified rating implies.  Also curious what the element insulators look like, basically if they are clean. A picture would be great.

 

Edited November 18, 2023 by Bill Kielb

[Hyn Patty]

While looking into replacing the wiring - I have also learned that the Skutt kilns were originally set up with 14 gauge wiring to and from the relays.  But more recently they have swapped to 12 gauge in order to keep the relays (both black and clears) cooler and lasting longer.  So I think that will be helpful, whether I order ready made wiring kits or just get spools of wire and make my own, that I be sure it's the heavier gauge and not the more common & thinner 14 g.  Useful info and practice for any appliance rewiring, kilns or otherwise.

Can anyone here tell me what kind of wire the thinner red wiring is?  Probably they can tell me if I take a sample to my local hardware store.

Edited November 19, 2023 by Hyn Patty

[PeterH]

1 hour ago, Hyn Patty said:

While looking into replacing the wiring - I have also learned that the Skutt kilns were originally set up with 14 gauge wiring to and from the relays.  But more recently they have swapped to 12 gauge in order to keep the relays (both black and clears) cooler and lasting longer.  So I think that will be helpful, whether I order ready made wiring kits or just get spools of wire and make my own, that I be sure it's the heavier gauge and not the more common & thinner 14 g.  Useful info and practice for any appliance rewiring, kilns or otherwise.

Can anyone here tell me what kind of wire the thinner red wiring is?  Probably they can tell me if I take a sample to my local hardware store.

I wonder what is the relative contributions of the resistance of the wires and that of the various connections (crimped? push-fit? compression? soldered?).

[Bill Kielb]

my thoughts
Renewing the wiring harness is a great idea. Making your own great too, but high quality crimp and crimp work is key. If you make your own, please buy a decent locking crimper and good quality welded seam crimps, else the premade harnesses likely a best choice. When I rewire, I use #12 and #10 MG (mica glass) rated wire good to 450c all in an overkill fashion so I can identify with make it better.

Low voltage harness
The current low voltage harness likely is ok and should currently experience less than 1/2 amp of load …….. but 18 gauge stranded is plenty sufficient. You should be able to read the side of the existing wire harness to determine what gauge and what temperature it is rated at. Again the crimp work is the important part with respect to longevity and kiln manufactures rarely seem to use high temp insulation on these.

Again I strongly suggest Measuring the resistance at these element circuits ….. at the relay, would definitely be helpful, possibly for knowledge useful by others but now will also give you a real idea of how much over designed you would want to pursue by knowing your current amperage and looking in an open air amoacity of wire table. Lots of tables here is one https://up.codes/s/ampacities-of-single-insulated-conductors-in-free-air

Since you are exploring rewiring general insulation and it’s typical ratings in order of temperature tolerance:

• Mg (Mica Glass) - 450c
• Teflon products - 200c - 250c (fep, etfe, pef,    And others with f in them)
• Silicone Products 150c-200c  (srg, srk, smrl - silicone motor lead developed for small motors vibration and temperature)

All the above though generally is a decent reason to just buy a premade harness that fits perfectly though. Most wiring begins to fail at their connections which overheat, anneal the copper and continue to overheat more as the conductivity decreases. The physics says this will decrease the electric load on the relays, but a harness that overheats also adds heat to an already confined space. The latter being bad for the relays as well so replacing a harness not a bad thing, replacing with a better harness, even better, but does take some diligent work, good crimps and good crimpers to achieve this.

Airflow and cooling helps everything regardless of gauge and insulation, so making sure there are no obstructions or the kiln is not enclosed in an overheated area with no way to get relatively cool air is a no cost best practice for all the electrical components inside. The control box depends heavily on stack effect which means relatively cool room air can freely flow from bottom to top and out of the louvers.

Edited November 19, 2023 by Bill Kielb

[neilestrick]

Did you install new feeder wires when you replaced the elements? I've only ever seen feeder wires cause trouble with the relays if they fry really hard at the terminal strip, and that manages to work its way back to the relay. It's very rare, though. Mostly they will be an issue at the element connection. 99% of the time, the problem is with the wires connected directly to the relays.

Just buy the Skutt wiring harness and install it with new relays and carry on.

Make sure your slip-on terminals are snug. They should take a bit of force to slide on. If they're loose, slightly crimp them with pliers.

[Hyn Patty]

For now I just bought the Skutt wiring harness so I can get my kiln back up and running.  I haven't entirely dismissed getting wire to rebuild the wiring harness in my other kiln since it isn't available as a ready made set.   This isn't rocket science guys and I have done some wiring before.  As for the rest, I do know about crimping properly. Yep, slip on terminals were all removed, cleaned, and retightened.   My son apprenticed as an electrician for quite a while and has all the right tools so that's not an issue, and he's my go to with most questions electrical.  Handy that!  But he's not worked on kilns before so his help is limited.   I do think my multimeter however needs to be replaced (it's old and not giving as accurate readings as I'd like) so further testing of resistance for my personal notes has to wait until I can get another one.

I DO appreciate all the feedback.  Thank you!  I'm a huge fan of learning new things and doing research.  I'm also a big fan of not letting something stop me if say  a ready made wiring harness kit simply isn't available.   It is for my Skutt so I decided to just order that one but apparently what I need to replace on my Olympic is a bit more complex.  Olympic can only help me with some of it and I'm not ready to replace my entire Bartlett controller just yet.  So we'll see.  I'll give it further thought.

I have not yet replaced the Radix  200C wiring from the elements to the controller.  That is indeed some of the wiring I'll probably do myself later since it's even more super simple than the wiring inside of the controller.  The resistance on that wiring seemed very low and I'll recheck it when I have a new multimeter but I think it's still good enough to keep using it for a while yet.

[Hyn Patty]

Hahaha!  I just got off the phone with Olympic and they do not make wiring harnesses - they just sell the wire for me to build my own!  So, looks like I'll order a spool of Radix 200C like I was planning to do anyway.  They also told me the rest of my Bartlett controller wiring can be replaced by the foot at Home Depot and they do that all the time themselves for repairs sent in to them.  So I'll finish up the Skutt first when the replacement relays and wiring arrives, and then I'll tackle the Olympic after.  I should have my new multimeter by then anyway so I can recheck everything.

I figured if I can  help my husband rebuild an entire wiring harness for the Jeep last year, I think I can probably tackle a kiln...  We also did the same for our double ovens and dishwasher recently.  It's not like we can get techs to come out to this wilderness area hours from any city.

Edited November 21, 2023 by Hyn Patty

[Bill Kielb]

11 hours ago, Hyn Patty said:

So, looks like I'll order a spool of Radix 200C like I was planning to do anyway.

Just some things you might want to double check-
Not familiar with Radix brand. You might want to double check the olympic which very well might have been wired with MG (mica glass 450c). For connection to elements some of the silicon HT wire will char and burn to ash well above 200c. Also might double check the voltage rating (basically insulation thickness) and get 600v rather than 300v. For longevity sake.

Edited November 22, 2023 by Bill Kielb

[Hyn Patty]

Skutt rewiring was delayed a bit due to deadlines to finish other work, holiday decorating, packages to ship, and so much more.  BUT I finally finished up all of the rewiring yesterday, with new elements, new relays, new transmitter, everything except the motherboard changed out for new in the controller.  Test fired last night to cone 04 to oxidize the new elements and it performed beautifully!   I'll work on gutting and rewiring my Olympic sometime after the holidays. 

Thanks everyone.  Good to have my larger kiln back online!

Edited December 18, 2023 by Hyn Patty

[Bill Kielb]

On 12/18/2023 at 2:54 PM, Hyn Patty said:

Test fired last night to cone 04 to oxidize the new elements and it performed beautifully! 

Any definitive evidence what caused the early relay failure?

[neilestrick]

12 minutes ago, Bill Kielb said:

Any definitive evidence what caused the early relay failure?

It was the old wiring. I've literally seen it dozens of times. Even Skutt recommends replacing the harness if relays are burning out prematurely.

[Bill Kielb]

29 minutes ago, neilestrick said:

t was the old wiring. I've literally seen it dozens of times. Even Skutt recommends replacing the harness if relays are burning out prematurely.

Not doubting that especially if the old connections are failing and heating things or the wire is heating the cabinet because its resistance is rising. Gaining. more resistance will not burnout relays it actually decreases the current through the contacts. Just trying to understand how to test for this.

[PeterH]

5 hours ago, Bill Kielb said:

Not doubting that especially if the old connections are failing and heating things or the wire is heating the cabinet because its resistance is rising. Gaining. more resistance will not burnout relays it actually decreases the current through the contacts. Just trying to understand how to test for this.

I had a vague memory of  possibly related postings using IR thermometers and/or IR cameras. Having been impressed by images such as this one showing an overheated relay lead.

Turns out it was from one of your postings, What's your current position on these techniques?

PS I also have a vague feeling that some mobiles were sufficiently sensitive to IR to give useful images.

[neilestrick]

Hot spots at the elements connections don't cause the relays to fail, they just cause that connection to fail. There's no safe way to get access to a Skutt relay while it's under load, due to the way the box is constructed. You just track the number of firings you have on a set of relays, and if they're burning out under 150 firings then you replace the wiring harness and it's good to go.

[Bill Kielb]

7 hours ago, PeterH said:

Turns out it was from one of your postings, What's your current position on these techniques?

They work well. I have just a bit of over 40 years experience with lots of machinery, big small, inductive, resistive likely miles and miles of high, medium and low voltage wiring. I never teach or allow replacement of unit assemblies  without testing to confirm why it is failing.

Just trying to understand in this situation how to diagnose and I think the answer is there is none, the wiring wears out - just install new if your relays aren’t lasting.  

The IR stuff is supposed to help be somewhat predictive and fairly non invasive in lieu of measurements with a meter. Regular measurement techniques work on other stuff for these (kilns) - I don’t know there is a clear answer. Lots and lots of very old wiring, kilns and machinery, that are still working as designed. 

My guess, it is a real thing with some Skutt equipment and maybe just adds enough heat to the cabinet to cause issues. In other words the wire is known to wear out.

If they simply wear out, the IR solution likely would be the same as for motors. Measurement of temperature above ambient or the trend of measurements above ambient over time could provide reasonable confidence in prediction.

Interesting to note in the picture above, the loose connection is adding heat to the wiring, noticeable on both sides of the relay. The fix here is new connector or tighten the connection -all the heat goes away. This is a very common failure. Her picture shows melting within the relay but very good looking connections, not even discolored, pointing to a relay contact issue or overloaded contacts for reasons unknown.

Edited December 20, 2023 by Bill Kielb

[neilestrick]

2 hours ago, Bill Kielb said:

My guess, it is a real thing with some Skutt equipment and maybe just adds enough heat to the cabinet to cause issues. In other words the wire is known to wear out.

It's not just a Skutt thing. Kiln power wires wear out and must be replaced at some point.

[Bill Kielb]

2 hours ago, neilestrick said:

It's not just a Skutt thing. Kiln power wires wear out and must be replaced at some point.

I believe you, just have never seen it without physical or measurable damage. Just wondering how to test for the wear.