Firing Un-Attended & Failure of Relays

Marty Daily @ CDV · Post by **Marty Daily @ CDV** » Wed Jun 11, 2003 1:40 pm

Hi All,

I guess that there are 2 different topics to be discussed.

First Problem = Controller Failure:

The concern appears to be the failure of a controller during firing of a kiln unattended (gone to work - running errands) or maybe be sleeping while it fires during the night. It is a BAD idea to leave any kiln unattended when firing.

Paragon & Skutt DO NOT have off switches on their kilns for the controller. So when the kiln is pluged the controller is powered whether or not it is firing. There are know cases where kilns have started firing during an electrical storm (California) when it was just sitting there and not being used, a fire was close to hapening because the owners of the kiln were also using the kiln as a table and had paper and othere stuff on top of the kiln. I have suggested to both Paragon and Skutt to put off/on switches on their glass kilns. They both prefer that the artist either unplug or turn off the circuit breaker when the kiln is not in use thus killing ALL power to the kiln.

Note: The Bartlett Controllers have the most redundant safety features to prevent this from happening. I think that Orton has added features, they did not have them originally. The CIC controller is the one with the most problems that I know of.

Here are 4 options for the above problem:

First you turn off the circuit breaker when the kiln is not being used.

Second you unplug the kiln when not in use.

I am told by my electrician that turning circuit breakers on/off and pluging/unplugging 240 volt outlets will shorten their life, however they are relatively cheap and easy to replace.

Third, you install a knife off/on switch between outlet and the circuit breaker. This is not real expensive to install.

Forth, there is a remote knife switch box available. It works by plugging the remote knife switch box into the wall outlet and then plug the kiln into the remote knife switch box.

Jen-Ken has an off/on switch on thier kiln which kills power to the controller so the controller cannot start the kiln by accident.

THE BEST WAY AND LEAST EXPENSIVE WAY TO AVOID THIS PROBLEM IS DO NOT FIRE THE KILN UNATTENDED!!!!!

Second Problem = Relay Failure:

Most of the kiln companies bring the electric into the kiln and split it off to the relays and the controller. The relays are always hot (electrified) and if they should decide to fail they usually fail in the on position. This failure must occure when the controller tells the relay to turn off. However, I have replaced more relays that failed in the off postion than the on position. In this case the relay failed when the controller told it to turn on.

Also, when dealing with the larger 240 volt kilns which have multiple elements the kiln companies have multiple relays, so if one relay fails it only affects the element it controlls while the other relays contol the other elements. Thus the controller still has some control of the heating of the kiln because it will tell the other relays to turn off when the heat gets too high. A single element in a 3 or 4 element kiln would probably only be able to reach about 500 degrees F by itself. The single element kiln would experience China Syndrom. A 2 element kiln would depened if the failed relay is the lid element or the side element. The lid element produces more heat than the side element the kiln may or may not super heat depends on how much it relies on both elements.

This method of wiring a kiln is the standard of the industry. One also has to look at it from a statistical point of view - even if we do not want to - that is that there are tens of thousands of kilns in use and the occurance of one failing and failing in the on position is rare - until it is your kiln.

I have been working with Jen-Ken at locating a high amperage (this is the problem) off/on swithch to be put in line with the relays. This has become a problem due to need of the high amperage, the high temperature environment, size, price, and long term relialbility but we will find one I am sure.

Jen-Ken does have pilot lights on most of thier kilns and have now made it standard on all kilns with relays that the pilot light is on when ever the relay is on. Thus if a pilot light is on and does not go off you can quickly tell that the relay has failed in the on position. If the pilot light does not come on then the relay has failed in the off position.

A solution would be to put dual realays on the kiln. This will increase the cost of the kiln. The control boxes would have to be made larger and or a second control box would have to be added for the additional relays and appropriate cooling for the components (the present control boxes are full with the transformer, relays, digital controller and other stuff).

Another solution is to put a kiln sitter on the kiln. This uses cones and a cone can be placed in it that would prevent the kiln from overfiring and running away because it could be set up to kill all power coming to the kiln.
This could be added at a cost of about $250.00

AGAIN, THE BEST AND LEAST EXPENSIVE METHOD TO CONTROL THIS POSSIBLE PROBLEM IS NOT TO LEAVE YOUR KILN UNATTENDED WHILE FIRING.

I cannot easily proof read this comment because it is small on my screen and I do not know how to print it to proof it. I apoligize if there are errors or if I have forgotten to address something. Email me with your specific questions or comments and I will be glad to address them.

Also I am a slave to spell checker, I am not sure it works with here.

Thanks for reading this posting!

Marty Daily
Centre DeVerre

Phil Hoppes · Post by **Phil Hoppes** » Wed Jun 11, 2003 1:57 pm

Marty,

I just made a post on the other thread but I'll repeat some of it here. I could not agree with you more that the safest procedure is to not leave your kiln when you fire. That being said, kilns today are built with microcontrollers for a reason, so you can attend to other things while your kiln is firing. In a very real sense the design of these kilns promotes users to leave them somewhat unattended. For this reason I think that it is irresponsible that the manufactureres don't at least offer some type of overtemp kill capability.

I was just on KilnSitters web site and can buy a type P KilnSitter for around $80. Drill a hole on the side of my kiln and a few wires and you have a very cheap overtemp kill switch. If this is my retail price unbundled, I have to believe any of the manufactures could offer this to me as a $50 option. For a $500 and up kiln I would consider this cheap insurance. My point is they don't even offer this as an option. I commented on a little more sophisticated solution on the other post but my point really is that this type of back up is not that expensive to implement. That you have replaced more relays failing in the off position is good news but the consequences of a failure in the on positon is REALLY BAD. (I don't even want to go there on your comment of people using their kiln for a table..........how's that again, 'What are the two most common things in the universe? Hydrogen and stupidity)

You make lots of good points and advice for people to be aware of in using their kilns. I just wish that the manufacturers would at least offer people the option of getting a little more protection.

Phil

Stuart Clayman · Post by **Stuart Clayman** » Wed Jun 11, 2003 2:05 pm

Marty,
Thanks for the info. Recently I was working with top element kiln and a firing that normally took 4 to 5 hrs took 10 hrs. Once it cooled down I turned the kiln back on and opened the door to find one side of the elements were not working. I initial thought was that it was a break in the element but in fact it was one of the 2 relay were bad.

Stuart

Amy Schleif-Mohr · Post by **Amy Schleif-Mohr** » Wed Jun 11, 2003 2:43 pm

Marty,

I believe I understand what you have said, but wanted to make one point and see if there is a solution.

I can say with quite a bit of certianty that 99% of my firings are 17hrs long or more. I agree with you about the safest way of monitoring your kiln is to always be there. But what do you do when you have firings that are so long and you need to sleep? I can't afford to pay anyone to sit there and watch my kilns while I sleep. So, it's a practicality thing.

Your insight is always welcome and I would love to hear what you have to say.

Amy

Bob · Post by **Bob** » Wed Jun 11, 2003 3:28 pm

[ But what do you do when you have firings that are so long and you need to sleep? I can't afford to pay anyone to sit there and watch my kilns while I sleep. So, it's a practicality thing.

Your insight is always welcome and I would love to hear what you have to say.

Amy

Hi Amy,

I believe sleep is considered "optional". When I had a manual fired kiln there used to be an saying in the house... "Not tonight dear, I'm annealing".

I set an alarm and get up midway through the night to check the kiln. It might only be unattended for 2 to 3 hours that way. Not an ideal solution but it does lessen the risk.

Cheers,

Bob

Amy Schleif-Mohr · Post by **Amy Schleif-Mohr** » Wed Jun 11, 2003 3:53 pm

That's very funny Bob!

I do something similar to what you do. When I am up in the middle of the night I listen for the click of the relays and sometimes I go down to check them.

Amy

Marty Daily @ CDV · Post by **Marty Daily @ CDV** » Wed Jun 11, 2003 4:08 pm

Hi Again,

Ok, here is the real skinny.

The pure facts of the matter is that:

If a kiln is installed properly you do not have to be present.

Why? Well here are the reasons.

1. A kiln cannot catch fire, it is brick or fiberboard. The outside of kilns with stainless steel and painted control boxes cannot catch fire. On some kilns, mostly front load models, the outside cabinet is painted and the paint could possibly catch fire. But remember it is only the paint buring and the burn will be very limited due to the small amount of paint present. Also the outside temperature of a runaway kiln may never reach a temp high enough to ignite the paint anyway.
2. If the kiln controller or relays fail on all the kiln can do is heat until the elements burn out - about 2500 deg F.
3. The PROPER kiln instalation includes that the kiln be on a metal kiln stand to allow air circulation below the kiln. The kiln is installed on a concrete floor. The kiln is installed so that the sides and top of the kiln are at least 18 inches from any noncombustible wall surface or at least 3 feet from any combustible wall surfaces.

Installed as above there is nothing to burn, thus no fire potential.

You can also install a smoke detector above a kiln if you want but remember you have to have something smoldering (making smoke) for the detector to work.

There are actual fire detectors which monitor changes in temperature that you can install above a kiln which would alert you should the kiln runaway and generate enough heat.

First, I do not know for a fact, i repeat fact, know of a relay which has failed in the on position. I have replaced 100's of relays in the past 8 years and guess what it was because they failed and would not come on. The customer would call and say their kiln would not heat and it turned out to be the relay that had failed not the element. I have heard of relays failing in the on position but i have never seen it nor talked to the person who it actually happened to - always get the info from someone who hear about it. The manufacturers state that relays fail in the on position most of the time but I think it depends on what causes the relay failure.

Second, several of the kiln compaines produce kilns which are UL approved as such to offer special modifications or options for these kiln is very costly and the price of the kiln price will increase $100's of dollars. Even though you may be able to purchase an item and add it to your kiln your self inexpensively the kiln companies cannot. They have to purchase the item, pay labor to install it assume all the liability and responsibliity for warranty and remain in business - this costs many times more than what you can do it for yourself. Example: You may be able to put in your own sink in the basement for $200 however if you have a plumber do it you will pay upwards of $600. This example can be taken to another level: Why should you expect someone to pay $35.00 for your fused glass pendent when they can make it themselves for $2.00. In the business world there, unfortunatley, is nothing that can be done inexpensively.

Companies who produce a line of kiln which are not UL approved can make all kinds of custom modification with out any problem. The customer justs has to be willing to pay for those add ons.

Kiln companies all try to make safe kilns. They do not build redundancy into the kilns for the past 100 years there has not been a problem. Your your refridgerator does not have redundcy with 2 compressors should one fail and stop cooling, your automobile does not have redundancy in starters or any other main components, your computer does not have redundancy by doing dual writing to 2 main disc. So why should a kiln company have to build in redundancy standard.

Now optional redundancy is a whole new issue. Custom built redundancy is availble from Jen-Ken no problem, Paragon to some extent, and Skutt to a much lesser extent, but be prepaired to pay for it. Another reason that addons are so expensive is that a kiln has to be pulled of the normal assemly line and go to a seperate person for the custom addons this becomes time consuming and drives up the cost.

Using common sense safety and a good installation one should not have to have a custom kiln in order to fire it unattended nor worry about relay failure.

I am trying to explain this in a maner which brings out some common sense in why kilns do not normally have all these fancy things. In relaity the number of kiln failures are rare as a percentage of kilns which are in operation. Example, Ken-Ken has a customer who has 30 digital controlled kilns which are fired 6 days a week 2 shifts a day and they have never had a runaway kiln. Each kiln has 3 relays they go though about 100 replacement relays a year but they all fail in the off position from hundreds of thousands cycles of operation for the past 7 years.

I hope that this gives some added insite into the questions an concerns. As a final note I would like to point out that this exact topic comes up on the warm glass board about every 4 - 6 months.

Oh, by the way I just learned that the Bartlett controller, for about 2 years, has software protection so if the software decides to go bannas the controller has overriding firmware which shuts the controller off.

Marty Daily
Centre DeVerre

Amy Schleif-Mohr · Post by **Amy Schleif-Mohr** » Wed Jun 11, 2003 4:48 pm

Thanks Marty!

Good to know about the software thing.

Amy

Phil Hoppes · Post by **Phil Hoppes** » Wed Jun 11, 2003 4:51 pm

Marty,

That was a very good explination. I agree with most of your points and while you may have not seen runaway kilns, I have more than a little concern with the 24" Paragon I have as it is the same model that Brock and Avery were using at Vitrium last fall and they had two of them go and melt down their entire loads. To your point, to my knowledge, there were no fires started, just a real mess in the bottom of the kilns.

On the price of add-ons, I've worked in electronics, semiconductors in particular, and I know that what I described is just not that expensive to do. It's not a cost to the manufactures if it is an option. They have plenty of options right now. My Paragon normally comes with a brick top. I opted for the fiber top. It was an option, I paid more for it and I'm sure it added a few points of nice margin to Paragon's bottom line. That's what I'm talking about. They don't even offer it. To your point, maybe they don't see it as necessary, or possibly there is a greater liability at stake that in offering it they are admitting that a meltdown could occour and from the litegious nature of our society these days that would be a bad thing to do. Now that I think about it, I would guess that this more than anything is probably the reason why they don't offer it.

Phil

Tony Smith · Post by **Tony Smith** » Wed Jun 11, 2003 8:26 pm

Marty,

You made a comment that caught my attention:

First, I do not know for a fact, i repeat fact, know of a relay which has failed in the on position. I have replaced 100's of relays in the past 8 years and guess what it was because they failed and would not come on. The customer would call and say their kiln would not heat and it turned out to be the relay that had failed not the element. I have heard of relays failing in the on position but i have never seen it nor talked to the person who it actually happened to - always get the info from someone who hear about it. The manufacturers state that relays fail in the on position most of the time but I think it depends on what causes the relay failure.

From what you have said, the chance of a kiln getting stuck in the full-on condition with an ordinary electro-mechanical relay is slim... very slim.

Second is that the new Bartlett controllers have software that will prevent the controller from running amok.

Third is that only kilns without power switches might turn themselves on if there is a power glitch

Finally, if you maintain a non-combustible environment around your kiln, the chances of a fire are remote even in the event of a runaway condition.

Thanks again for contributing your experience to this thread.

Tony

Bert Weiss · Post by **Bert Weiss** » Wed Jun 11, 2003 8:39 pm

Marty

Thank you for your second post. my control equipment is industrial in design as opposed to the consumer products that are more commonly used. I trust my equipment and usually leave it unattended in an a garage not attached to my house.

I have been known to do the 2 AM check that the kiln made temp drill, though.

I once did have one of 3 zones run away, but other than the glass being overfired, no other damage was done. I use SCR electornic switches. We have had several reports about runaway SSR's. An SSR is a simpler, cheaper version of an SCR. Electronic switches heat up and if they are mounted on a kiln, they often have problems. Mounted properly they can last a long time. I have had 3 or 4 relay breakages since 1982. They can be repaired. I don't remember ever having a relay failure in the middle of a firing. My issues mainly come when the kiln is working to make high temp. I used to have problems with the copper to nichrome connection. These problems seem to be solved now using special hitemp wire as an interface.

I am sorry to report that somebody I know who runs a Skutt pottery kiln had a runaway with a kiln sitter set up. For unknown reasons it didn't trip. Consequently I wouldn't recommend relying on one of those.

As usual COMMON SENSE RULES. Set it up right and sleep well. The more expensive is your control equipment, the more reliable it should be, I hope. (Brock's controller is the most expensive but only he knows just how reliable it really is)

Jack Bowman · Post by **Jack Bowman** » Wed Jun 11, 2003 9:19 pm

Marty,

Nice post, thank you.

The controller I am building now will be around a Cal9500P process controller with redundant overtemp protection provided by a CAL9900 temp controller. In the power circuit is a Furnas 75Amp definite purpose contactor. This contactor can be activated by the 9500P alarm as well as the 9900 which will be set to shut down at 1850F. The contactor can also be opened by the lid switch and the on/off switch I will put on the panel. I paid around $60 dollars for the Furnas contactor.

I wanted to get UL approval and market my controllers but the cost was prohibitive. I feel the redundant OT features I put on my controllers make them safer than a UL approval on a controller without any redundant OT features. Politics.

Jack

Ron Bell · Post by **Ron Bell** » Wed Jun 11, 2003 11:04 pm

Most all controllers have a programmable alarm setting (I have a Bartlett). The alarms are generally Sonalert type alarms that are powered by a logic level pulse. If this same signal were to be used to shut off the controller, the problem would be solved (with operator control of the shutdown temperature). This is a trivial change for the controller folks, it just takes enough people clammering for it!

Lynne Chappell · Post by **Lynne Chappell** » Thu Jun 12, 2003 1:06 am

Ron Bell wrote:Most all controllers have a programmable alarm setting (I have a Bartlett). The alarms are generally Sonalert type alarms that are powered by a logic level pulse. If this same signal were to be used to shut off the controller, the problem would be solved (with operator control of the shutdown temperature). This is a trivial change for the controller folks, it just takes enough people clammering for it!

The problem though Ron, is that it isn't the controller that's causing the problem, it's the contact switch. So the controller can tell it to shut off, but the contact switch doesn't obey.

David Williams · Post by **David Williams** » Thu Jun 12, 2003 1:33 am

Lynne Chappell wrote:
Ron Bell wrote:Most all controllers have a programmable alarm setting (I have a Bartlett). The alarms are generally Sonalert type alarms that are powered by a logic level pulse. If this same signal were to be used to shut off the controller, the problem would be solved (with operator control of the shutdown temperature). This is a trivial change for the controller folks, it just takes enough people clammering for it!
The problem though Ron, is that it isn't the controller that's causing the problem, it's the contact switch. So the controller can tell it to shut off, but the contact switch doesn't obey.

True; though the alarm feature of a primary controller can be used to operate a seperate second relay in an overtemp circuit. To make it perfectly fail safe you'd want an overtemp circuit with its own controller and thermocouple. Given the inexpensive bare bones controllers these days you could get the whole set up, controller relay and thermocouple for around 200$. The thing is though I've really reconsidered the need for this as people have pointed out above. If you keep non flammable environment you should be fine. The biggest thing is the glass will drill though the soft brick and may reach the ground.

I don't see how you can run a glass business or be a working artist without leaving your equipment unattended.

Paul Tarlow · Post by **Paul Tarlow** » Thu Jun 12, 2003 8:04 am

An even cheaper solution for firing while you sleep that has been posted before (and the one that I use) is to buy a used baby monitor (< $10 on Ebay) and set the controller alarm for 50 degrees over your top temp.

Don Burt · Post by **Don Burt** » Thu Jun 12, 2003 8:20 am

David Williams wrote: clip
To make it perfectly fail safe you'd want an overtemp circuit with its own controller and thermocouple. Given the inexpensive bare bones controllers these days you could get the whole set up, controller relay and thermocouple for around 200$. The thing is though I've really reconsidered the need for this as people have pointed out above. If you keep non flammable environment you should be fine. The biggest thing is the glass will drill though the soft brick and may reach the ground.

I don't see how you can run a glass business or be a working artist without leaving your equipment unattended.

If you were a rich and famous artist you could buy a more elaborate process control paging unit like the one at the link below. You could program it to page everyone on the board when your controllers signaled an alarm. Once.

http://www.tricountycom.com/wireless.ht ... x%20VS1100

Barbara Cashman · Post by **Barbara Cashman** » Thu Jun 12, 2003 6:15 pm

Excellent post, Marty. The one thing I might add is that I understand a kiln has a temperature limit. The kiln may keep firing, but it shouldn't exceed the temperature limit for its elements. Correct? I woke up at 4am realizing I had left the manual enameling kiln on. In pajamas, I drove to the shop to find the kiln over 2000F and glass melted all over the inside of the kiln. However, there wasn't anything around the kiln to catch fire, so I turned it off and went home. Ceramic kilns go to about 2200-2400F, I think, and glass kilns to 1600-1800F. Right? Anyway, there shouldn't be a panic that the thing will reach 4000 deg and melt. You'll just get an incredible power bill. - Barbara

rosanna gusler · Post by **rosanna gusler** » Thu Jun 12, 2003 10:38 pm

hi barbara, i understand the 'limit' to be the temp that you must not exceed so as not to damage the kiln. the kiln elements are capable of reaching much higher temps. i think that given enough time ungoverned on high, any kiln can do a three mile island. i think that, i do not know that for sure. rosanna

Brad Walker · Post by **Brad Walker** » Fri Jun 13, 2003 12:02 am

rosanna gusler wrote:hi barbara, i understand the 'limit' to be the temp that you must not exceed so as not to damage the kiln. the kiln elements are capable of reaching much higher temps. i think that given enough time ungoverned on high, any kiln can do a three mile island. i think that, i do not know that for sure. rosanna

Standard kiln elements burn out at around 2500F. Most kilns can withstand this temperature, at least for a short while. (Standard bricks and fiber tend to be rated around 2300F, but they can withstand higher temps for brief periods.)

By the way, Three Mile Island reached a temperature of 4300 F, so the elements would burn out long before the kiln did a Three Mile Island. That's not to suggest that a kiln's a great place to store your excess uranium, of course.