electric kiln going berserk

Leslie Ihde · Post by **Leslie Ihde** » Sat Aug 09, 2003 7:41 am

Hello and help!

I've been firing my evenheat kiln almost daily for at least a year and is has behaved wonderfully. It has a rampmaster computerized controller. Last night, it was going through it's cycle and on the way down, and I went to bed. Perhaps some of you will stay up all night, but I don't usually since it is a cycle I've done so often.

Well skip to the chase: this morning I looked at it expecting it to read 150 degrees or so and it was 1770! It has never been programed so high. I immediately pushed the button on the rampmaster to go off, and took a shower. Then, after my shower, I saw it was still rising in temperature!! I ran down to the basement and turned the power off to the kiln.

Please don't scold me about not watching better-it's worked perfectly so often it's hard to stay up all night just to watch it. But I learned my lesson.

Question-is my computer fryed? I've peeked inside and the glass ran quite a bit, but I haven't seen my kiln floor yet. We have had alot of rain and thunder lately, but no thunder or lightening last night that I heard. It did rain though.

Thanks in advance for any thoughts. I hope to see you at the warm glass weekend

Leslie Ihde
Turning Point Studio
Vestal, NY

Tony Smith · Post by **Tony Smith** » Sat Aug 09, 2003 7:58 am

Was it the Rampmaster 2 or the older rampmaster?

I had an older Rampmaster do that to me in June after a power glitch... no lightning, the power just went out for a few seconds. I had to shut off the circuit breaker for a minute, then switch it back on, then I heard the rhythmic clicking of relays again. It was fine after that.

Rob Bartlett at Bartlett Instruments may be able to help (or at least explain). They make the Rampmaster 2's and made the original Rampmasters. Call him at (319)372-8366

Tony

Catharine Newell · Post by **Catharine Newell** » Sat Aug 09, 2003 9:08 am

I don't have your equipment, but I'm thinking relays... I've recently had problems with mechanical relays and have had to throw the circuit breaker each time to cut power to the elements; however this problem did not ultimately affect my controller. These mechanical relays have since been replaced with mercury...

Something to check into,
Catharine

Tony Smith · Post by **Tony Smith** » Sat Aug 09, 2003 9:30 am

Catharine,

Did you happen to save the failed relays??? It would be helpful to know what the manufacturer and model number were. A recent conversation with Marty at Centre DeVerre indicated that of the hundreds of relays that he has replaced in kilns, a very small percentage, if any, of the mechanical relays had failed in the on position.

If you still have them, I would like to disassemble them to document the failure.

Tony

Catharine Newell · Post by **Catharine Newell** » Sat Aug 09, 2003 9:51 am

Tony Smith wrote:Catharine,

Did you happen to save the failed relays??? It would be helpful to know what the manufacturer and model number were. A recent conversation with Marty at Centre DeVerre indicated that of the hundreds of relays that he has replaced in kilns, a very small percentage, if any, of the mechanical relays had failed in the on position.

If you still have them, I would like to disassemble them to document the failure.

Tony

I do have the failed relays... and upon examination of them, it was extremely obvious that they were stuck in the on position - visible to the eye when we opened them up. These were Omrons G7L-2A-TUBJ-CB, which replaced the initial bad relays installed in my kiln. There is no doubt that they were the cause of the continuing power to the elements. I went through 4 of them (same problem each time - only affecting the lid elements)) before John Hohenshelt was able to replace/rewire with the mercury relays. Go figure.

Catharine

Tony Smith · Post by **Tony Smith** » Sat Aug 09, 2003 10:11 am

Those particular relays have an electrical life expectancy of 100,000 cycles at 25 Amps. If you assume the relays click every 10 seconds when the kiln is on, that's a million seconds of operation or 277 hours of operation. That's really not a lot of time. And since relays are rated for average life, that means that 50% will fail in less than 100,000 cycles.

It would be interesting to know when the last time you changed the relays was... I would guess that they lasted between 50 and 100 firings.

Tony

Catharine Newell · Post by **Catharine Newell** » Sat Aug 09, 2003 10:21 am

Tony Smith wrote:Those particular relays have an electrical life expectancy of 100,000 cycles at 25 Amps. If you assume the relays click every 10 seconds when the kiln is on, that's a million seconds of operation or 277 hours of operation. That's really not a lot of time. And since relays are rated for average life, that means that 50% will fail in less than 100,000 cycles.

It would be interesting to know when the last time you changed the relays was... I would guess that they lasted between 50 and 100 firings.

Tony

Two of them did... The last one failed after a week and a half, and the one before failed at about a month and a half. I fire constantly, but really can't manage 50 firings in that time! The major problem had to do with the amt of current for their rating - a wiring problem.

Catharine

Paul Tarlow · Post by **Paul Tarlow** » Sat Aug 09, 2003 10:22 am

These threads always give me heartburn. I never leave the house with the kiln running -- but most of my firings are at night while I sleep. It was 110F in Austin yesterday and my studio is in my garage -- daytime its just too hot to run the kiln.

I have a Bartlett 12 key. Just how hard is it to replace the mechanical relays with mercury? What's the life expectancy for mercury relays and is it true that they only fail in the off position?

- Paul

Tony Smith · Post by **Tony Smith** » Sat Aug 09, 2003 10:54 am

The mercury relays have a much longer lifespan since there are no contacts to wear. Their life is rated in the millions of cycles. The downside is that they require a specific mounting orientation and they take up more space than a mechanical relay. They also don't like to be overheated and can create an environmental hazard if they overheat and explode.

I think a major point to be made here is that mechanical relays should not be used at their rated current or above. The life of a mechanical relay increases inversely with current (more or less). If you have a relay rated at 30 Amps for 100,000 cycles, by decreasing the current to 15 Amps, you'll increase the life to 200,000 cycles. Mechanically, these relays have a lifetime around 5,000,000 cycles, so the electrical contacts are where the failure will occur.

But to answer your question Paul, you would probably have to modify your controller box to provide space for mercury relays.

Tony

Paul Tarlow · Post by **Paul Tarlow** » Sat Aug 09, 2003 11:09 am

So the controller says its rated for 55 amps. The electrician said that for something that is continuous use you want to build some buffer when you size the circuit breaker -- so the circuit breaker is 70 amps. Does that mean that I'm more likely to fail sooner?

Knows-enough-about-electicity-to-be-dangerous-boy

Tony Smith · Post by **Tony Smith** » Sat Aug 09, 2003 11:53 am

Paul Tarlow wrote:So the controller says its rated for 55 amps. The electrician said that for something that is continuous use you want to build some buffer when you size the circuit breaker -- so the circuit breaker is 70 amps. Does that mean that I'm more likely to fail sooner?

Knows-enough-about-electicity-to-be-dangerous-boy

What that means is that you probably have two thirty amp mechanical relays in your controller box to handle the 55 Amp current. I would open the box and get the manufacturer and model numbers off the relays, then look up the spec sheet online to see what the rated lifetime of the relay is. From there, you can estimate the lifetime in hours (or #of firings) and make a plan as to when you should change your relays for preventative maintenance.
.
The fact that you have a 70 Amp breaker in the distribution panel means that the breaker will only trip if there is a real electrical short, but it will help you through brown-outs. I would have put in a 60 Amp breaker, but that's me.

Tony

Bert Weiss · Post by **Bert Weiss** » Sat Aug 09, 2003 12:51 pm

I use SCR relays. They are electronic and are on or off 120 times a second. They cost a lot more and are a lot more reliable. I have been running one since 1982 with no problems. Some others have experienced problems. In 13 years, I had one stick closed. Since my kiln has 3 zones, one runaway will mess up the kiln load, but nothing more. I am using 3 out of 4 right now that I bought used several years ago and have had no problems at all.

I always start the program and leave. I check to see that I have made temp and leave again. The major problems that I encounter are from corroding connections and I fixed that problem with the addition of some hitemp wire. Since then everything works consistently.

There has been a lot of talk about SCR's over on Craftweb and the experts there agree that they are worth the money.

KILN-TEC · Post by **KILN-TEC** » Sat Aug 09, 2003 1:13 pm

Hi:
Omron relays are rated at 25amps. I like using Potter-Brumfeld because they are rated at 30amps. Gives you a little bit extra head room. Switching to mercury relays ( must be mounted upright +/- 15degrees), is common, however, unless the mercury has 12volt coils you still need a switching relay (omron or P-B) in the circuit.
I have seen a few people use mercury's with 12volt coils, but inductance could play a factor. You have to watch that your cicuit board can handle the load of the coil on the mercury relay. If you do not have a switching relay in the circuit , check that your controller temp. does not jump around when the controller is cycling.
As an aside: I totally agree that Bartlett Instrument Co. (Iowa) are the best people in the business. I have been dealing with them since 1994, and love their products.
Rich KILN-TEC

Leslie Ihde · Post by **Leslie Ihde** » Sat Aug 09, 2003 1:56 pm

Hi Tony,

I think my evenheat is a rampmaster #1 since it doesn't say "2" , but says perfect fire. It's still too hot to really explore the damage, but I'll at least have some brick and kiln furniture to clean up. Thanks for the phone number, and thanks also to everyone who has replied. I'm quite upset about this, but I guess I'll figure it out bit by bit.

Leslie

Tony Smith wrote:Was it the Rampmaster 2 or the older rampmaster?

I had an older Rampmaster do that to me in June after a power glitch... no lightning, the power just went out for a few seconds. I had to shut off the circuit breaker for a minute, then switch it back on, then I heard the rhythmic clicking of relays again. It was fine after that.

Rob Bartlett at Bartlett Instruments may be able to help (or at least explain). They make the Rampmaster 2's and made the original Rampmasters. Call him at (319)372-8366

Tony

Tony Serviente · Post by **Tony Serviente** » Sat Aug 09, 2003 2:37 pm

I fire my kilns unattended about 95% of the time, and have used mechanical relays(contactors) from the start, about twelve years ago. In that time I have had numerous relay failures, but never have had them stick closed. The problems I see are : 1-deterioration of the contacts, which once begun causes a negative cycle of heating and oxidation. 2-Buzzing, the coils get loose and make a really loud noise, but still function. 3-Very rarely the control coil opens or gets too weak to pull the switches closed. I can still have overfires for other reasons, like failed thermocouples, operator error, elements opening, etc. What I did to limit the damage is to put all of my control circuitry on a household timer. You can buy one at Radio Shack for less than twenty dollars, and program it to only allow power to your relay control circuit for a certain time period, in my case 10PM to 6AM. This means that if I have an always on situation it can only cook till 6, then the power goes off. This has saved my butt a few times. It also insures I can only fire when power is cheap, a very important factor in NY state, where electricity is the most expensive in the country. Wiring the timer up can either be easy or difficult, depending on how the contactors are controlled, but with very basic electrical knowledge, or the help of an electrician, it is less than an afternoons work, and can limit a catastrophes scope.

Leslie Ihde · Post by **Leslie Ihde** » Sat Aug 09, 2003 4:13 pm

Tony S.,
I see you are a neighber, in Ithaca. That sounds like a good idea- to have the timer as a safety. I will ask my electrician to do it as soon as I figure out whats wrong.
Leslie

Tony Smith · Post by **Tony Smith** » Sat Aug 09, 2003 5:45 pm

Tony Serviente wrote: What I did to limit the damage is to put all of my control circuitry on a household timer. You can buy one at Radio Shack for less than twenty dollars, and program it to only allow power to your relay control circuit for a certain time period, in my case 10PM to 6AM.

Unfortunately, if only the control circuitry is on the timer and the relay siezes in the on position, turning off the control circuitry will not shut off the power. On the other hand, if you had the timer contolling a single mercury contactor, you would have a very reliable, low-cycle, safety circuit.

Tony

Leslie Ihde · Post by **Leslie Ihde** » Sat Aug 09, 2003 7:22 pm

This is all quite beyond me- relays, mercury, circuts. However, I really appreciate all the remarks because I will get help figuring it out and use these suggestions as a starting place. Thanks again,

Leslie

Tony Serviente · Post by **Tony Serviente** » Mon Aug 11, 2003 9:37 am

Unfortunately, if only the control circuitry is on the timer and the relay siezes in the on position, turning off the control circuitry will not shut off the power.

Tony is right, but this scenario has never happened with my mechanical contactors. The biggest failure issue I have is associated with open elements, which can lead to severe overfires. Any control circuit disabling scheme will not address high temperature issues within the window of the kilns normal firing cycle. Only way to limit overfires within this window is with something like a kiln sitter, or a thermocouple and controller dedicated to monitoring for a high temperature, and if that is acheived disabling supply power to the contactor, not the control circuit. Another possible solution is a thermal fuse. I consulted with a metallurgist years ago and he presented me with a list of alloys that would have a melting point at what I determined to be in the overfire zone, say 1650 F. My idea was to put either bars or wires of this alloy in the firing chamber, and have its continuity as part of the control circuit. Too hot, metal melts, and the contactor turns off. I did not pursue this for a few reasons, one of which was addressed by Tony. I built my system to address the most likely failure, which it does, but it certainly does not protect against every possibility.[/quote]

Tony Serviente · Post by **Tony Serviente** » Mon Aug 11, 2003 9:37 am

Unfortunately, if only the control circuitry is on the timer and the relay siezes in the on position, turning off the control circuitry will not shut off the power.

Tony is right, but this scenario has never happened with my mechanical contactors. The biggest failure issue I have is associated with open elements, which can lead to severe overfires. Any control circuit disabling scheme will not address high temperature issues within the window of the kilns normal firing cycle. Only way to limit overfires within this window is with something like a kiln sitter, or a thermocouple and controller dedicated to monitoring for a high temperature, and if that is acheived disabling supply power to the contactor, not the control circuit. Another possible solution is a thermal fuse. I consulted with a metallurgist years ago and he presented me with a list of alloys that would have a melting point at what I determined to be in the overfire zone, say 1650 F. My idea was to put either bars or wires of this alloy in the firing chamber, and have its continuity as part of the control circuit. Too hot, metal melts, and the contactor turns off. I did not pursue this for a few reasons, one of which was addressed by Tony. I built my system to address the most likely failure, which it does, but it certainly does not protect against every possibility.[/quote]