Relay Switches on Kilns

[DirtRoads]

How often do these usually need replacing?

My Paragon bisque kiln will go through 2 relay switches a year.

L&L kilns .. maybe 1 a year.

This electrical engineer that works & designs power welding machines (really expensive & high tech ones) suggested getting a 50 amp  relay instead of a 30 amp one.     Not rushing out to do it but ... would this help?  He said this one company had some heat problems and they went from a 50 to 70 amp and it cleared up the problems.

 

[neilestrick]

The difference in life you're seeing there between the two brands is most likely due to how well the relay is insulated from the heat of the kiln. How often they need replacing depends on that, how often you fire, your firing schedule, and the condition of the wires connected to the relays. If everything stays cool, the relays last longer. I've got a set of relays on my smaller kiln that has over 400 firings. That kiln fires fast, and the amount of waste heat coming off it isn't as high as a big kiln.

There's something to be said for oversized relays, but the relays in kilns are already oversized for the amperage they are carrying, so I don't think going even larger will make that much of a difference. In your L&L kilns, each section draws about 21 amp, so the relays are plenty big at 30 amps. IMO, the heat that kilns them is more from the heat of the kiln and the wires that feed them than from the heat that builds up from the amperage draw. I regularly see relays die due to the condition of the wires rather than the age of the relay. If you consistently see relays dying early, change out the wires or go up one wire size.

[Bill Kielb]

Neil is correct in that heat wrecks things. Your friend is correct in that bigger contacts will take more abuse as well as more heat. All relays come with a defined number of probable cycles until failure. The point being, they are electromechanical and will fail.

When AC current travels along a conductor it travels along the outside surface (skin effect)  as opposed to DC which relies on the area of the conductor. So bigger relay = bigger contacts (more surface area) = (generally) longer lasting contacts at a given load and greater cooling capacity.

An interesting point about heating conductors is that when heat is added the conductor resistance actually increases a bit which then generates a bit more heat. The action of heating a wire makes the wire ever so slightly less conductive from a valence electron point of view. Additionally when junctions are heated usually corrosion is promoted which adds further to the ever so slight increase in resistance. Yikes!

Not to be such a downer but your friend is likely correct in that higher rated relays probably would last longer but Neil is correct in saying maintenance is probably more productive. Most kiln are designed with fairly light weight connections and marginally rated relays; however for their use, they are fairly dependable, economical, and easy to replace.

I just finished repairing one of our kilns which had a thermal runaway issue which actually began in a pre-molded power plug. My current thinking, for those that are capable, non contact thermometers could provide an easy way for folks to do predictive maintenance and replace parts in advance of failing or set up with their tech to replace prior to failure. This is probably more productive than changing crimp on spades for bolted connections and redesigning airflow and insulating better from heat radiated from the kiln shell …… I could go on and on

It has some interesting observations and images of overheated relays and connections you might appreciate.

woops, been a while, second video has better relay pictures

 

[DirtRoads]

Nice video.  Makes sense to replace the wires.    A small cost for the added benefits.  I'm thinking I will get an electrician to replace all of mine.   I've got 1177 firings on my first L&L and 500 on the 2nd one.   I've replaced wires once on first L&L and replaced a the wires to elements last week.   But putting lower gauge wires and better connections would seem to solve a lot of problems.   I am going to put a better relay on my Paragon bisque kiln.   This is my 3rd Paragon ... when they start giving too much trouble I just buy another one.  Sometimes I notice a correlation between a burnt out element and replacing a relay on that kiln.

[Bill Kielb]

7 minutes ago, DirtRoads said:

Nice video.  Makes sense to replace the wires.    A small cost for the added benefits.  I'm thinking I will get an electrician to replace all of mine.   I've got 1177 firings on my first L&L and 500 on the 2nd one.   I've replaced wires once on first L&L and replaced a the wires to elements last week.   But putting lower gauge wires and better connections would seem to solve a lot of problems.   I am going to put a better relay on my Paragon bisque kiln.   This is my 3rd Paragon ... when they start giving too much trouble I just buy another one.  Sometimes I notice a correlation between a burnt out element and replacing a relay on that kiln.

Thanks! These require pretty high temperature rated  wire/ insulation. (450c or more) which is pricey. I would suggest new crimp connectors to the relays . The wire can usually be cut back and a new connector installed. Generally the spade connectors become the weak link as  most kiln manufactures use 30 amp wire for 20 amp loads  and  20 amp wire for most all other significant loads.  

Those connections just never stay tight though.

just a thought

[neilestrick]

If the terminal connectors are loose you can crimp them down with needle nose pliers to tighten them up. Often they're a little loose from the factory, but once you crimp them down they tend to stay if you get them tight from the start. There's no need to go with 450 C wire.  200C will run you about 40 cents per foot and will work just fine. That said, buying a wiring harness form the kiln manufacturer is pretty cheap, and a lot faster than cutting your own.

[Bill Kielb]

9 minutes ago, neilestrick said:

If the terminal connectors are loose you can crimp them down with needle nose pliers to tighten them up. Often they're a little loose from the factory, but once you crimp them down they tend to stay if you get them tight from the start. There's no need to go with 450 C wire.  200C will run you about 40 cents per foot and will work just fine. That said, buying a wiring harness form the kiln manufacturer is pretty cheap, and a lot faster than cutting your own.

I could be wrong but TGGT is rated at 250C and I think for stove service and the like. TGGT is obvious in that it has an inner Teflon sheath whereas MG is rated at 450C and the wire actually containeds nickel to be more temperature tolerant. I believe MG has been the wire I have replaced in the past as a match within the kiln but your pricing seems correct for MG. Not sure, I will have a peek tomorrow but 200 C seems a bit  low. Definitely would not want him  or his electrician rewiring  with THHN by mistake.

[neilestrick]

57 minutes ago, Bill Kielb said:

I could be wrong but TGGT is rated at 250C and I think for stove service and the like. TGGT is obvious in that it has an inner Teflon sheath whereas MG is rated at 450C and the wire actually containeds nickel to be more temperature tolerant. I believe MG has been the wire I have replaced in the past as a match within the kiln but your pricing seems correct for MG. Not sure, I will have a peek tomorrow but 200 C seems a bit  low. Definitely would not want him  or his electrician rewiring  with THHN by mistake.

I've got Skutt wires here in my parts bins that are labeled 200C. I use 150C or 200C, depending on what's available at a decent price and have never had a problem with either. Especially for harness wires for the relays, they're behind the baffle wall and somewhat insulated from the direct heat coming off the kiln. The controller ambient operating max temp is 71C, so it's not getting super hot in there. The power cord is only 105C, and all the disconnect terminals are only rated for 105C as well. For feeder wires it wouldn't hurt to go above a 200C rating, but I think it's probably a waste of money considering all the other parts in the system are rated lower.

[Bill Kielb]

On 12/6/2018 at 8:38 PM, neilestrick said:

I've got Skutt wires here in my parts bins that are labeled 200C. I use 150C or 200C, depending on what's available at a decent price and have never had a problem with either. Especially for harness wires for the relays, they're behind the baffle wall and somewhat insulated from the direct heat coming off the kiln. The controller ambient operating max temp is 71C, so it's not getting super hot in there. The power cord is only 105C, and all the disconnect terminals are only rated for 105C as well. For feeder wires it wouldn't hurt to go above a 200C rating, but I think it's probably a waste of money considering all the other parts in the system are rated lower.

Maybe, as I said, will check tomorrow. 105Cfor power cord is decent but different animal since it’s open air cooled.  Might just be the cone arts that use the MG wire. Will look tomorrow regardless.

Alrighty the definitive word is in, or maybe not, maybe just A definitive word. Picture number one is an L&L which looks like MG (Mica Glass 450 degrees) but if you search L&L they advocate 150C for everything front and back plane of their baffle. Very baffling actually! The Cone Arts look like MG and to go a step further I was rebuilding an old Paragon at the time which was a huge wiring mess so:

I ordered MG for all.  50' of #12 and 25' of #10. All for about 100 bucks (Much  more than .40 / foot), figuring that in the case of the Cone Art and Paragon they certainly needed it due to their method for bringing the element wiring into the control box ( I had a Cress with the same method actually as well) and these areas are routinely 400 degrees or more locally.

My Final take - I like my decision as the MG will work (and is superior) in all cases  and …. I likely wont run out of it soon for any minor repairs. None of the wiring appears to be SRML 150C or motor lead stuff so L&L's web site is a bit of a mystery. 150C or approximately 300 F  ambient is certainly the normal temperature near the element connections so what gives using wire rated to just that temperature?

Wire insulation temperatures are designed to handle a short circuit for a given time at a specific amount of rated current. (A lot to say in one sentence) So, a 150C conductor that operates in a 150C environment might be de-rated from its normal 20 amp max to something lessor or something to that effect.  Basically, allowable current (Amps) is de-rated to a particular insulation temperature.

UL, CSA  and others: When the appliance is approved the design needs to prove out to be in accordance with the various standards so lets assume L&L got their design approved at those ratings 150C. Well it must work, simple as that. Nothing says it complies with the strictest standards so 150C must be fine.

My advice - for 100.00 I believe I will maintain at least five kilns for the next five years as needed and not have to worry when I need to replace an element jumper that is just too short or the end has burned off. I am not a design at the margins guy, but it looks like instead of the $100.00 bucks I spent on MG one could use 150C Motor lead stuff which is way cheaper. Maybe 25.00 bucks

Or - there is a typo in the L&L stuff

Either way, none of it is marked in the five kilns I opened today and the Paragon is gone so have at it with whatever specification applies. For me I think I will stick with the 450C stuff and actually have been looking at the next model Potter & Brumfield relays rated higher in current than what come with many kilns.  I also would be open to trying a bolt up connection relay instead of the spades but that is another story. Direct pricing of the higher rated relays still keeps them in the 10.00 - 15.00 range which is ok with me for some reason I cannot explain. It just seems an acceptable amount.

That's my findings - have at it!

Oh one other project that is on the board is to devise an economical way for folks to monitor and diagnose their kilns. It may never get attention but the idea would be to provide a simple digital interface allowing them to diagnose their kilns easily. Maybe a good 2019 project, then again my head is starting to hurt.

Come to think of it, are all these UL listed? UL Approved, CSA approved, Yikes, hurts too much to think about.