Kiln Relays - WarmGlass.com

Kiln Relays

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aliceRI
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Kiln Relays

Postby aliceRI » Sun Jul 06, 2014 2:11 pm

How many of you out there change your kiln relays on a regular basis? And if you do, how often do you change them? I have had two minor melt-downs with no real big damage but don't want to keep taking such big chances with such pricey equipment. I was thinking about changing them annually along with my smoke alarm batteries and passwords. Any thoughts?

charlie
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Re: Kiln Relays

Postby charlie » Sun Jul 06, 2014 2:46 pm

it really depends upon your usage. perhaps you want to put an hour meter on it, and change it every 5000 hours or so. someone who fires once/week wears them out quicker than one who fires 2x/day.

Brad Walker
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Re: Kiln Relays

Postby Brad Walker » Sun Jul 06, 2014 3:13 pm

charlie wrote:someone who fires once/week wears them out quicker than one who fires 2x/day.


You mean the opposite, right?

Valerie Adams
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Re: Kiln Relays

Postby Valerie Adams » Sun Jul 06, 2014 3:59 pm

I've had two meltdowns, one which was nasty enough that I had to rebuild my kiln (which I did myself!), so I started changing them annually.

But that started to seem like overkill, so now I'm doing it every two years. I buy relays from Online Components.

Morganica
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Re: Kiln Relays

Postby Morganica » Sun Jul 06, 2014 4:16 pm

As Charlie said, it depends on your usage and also on the type of relay. In my GM1414, the mechanical relays that came with the kiln lasted for almost 7 years, then died in the middle of a big project. Swapped them out...and the new ones died before the year was out. Was annoyed because my firing rates had stayed constant--the kiln was more or less busy all the time.

A little investigation with Skutt, though, came up with a probable answer: About a year before the first relays died, I'd moved from mostly fusing to almost entirely casting in that kiln, with typically 5-10 day firing schedules. The relays were doing a lot more cycles, and the moisture from drying-out molds didn't help. We swapped over to a hybrid mercury relay, and I haven't had a problem since (it's been 5 years).
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charlie
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Re: Kiln Relays

Postby charlie » Sun Jul 06, 2014 4:19 pm

[quote="Brad Walker"][quote="charlie"]someone who fires once/week wears them out quicker than one who fires 2x/day.[/quote]

You mean the opposite, right?[/quote]

doh! dog darn it!

suds
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Re: Kiln Relays

Postby suds » Sun Jul 06, 2014 4:35 pm

Relay life span is usually rated by the number of "operations" (on-off cycles) they can withstand before failure.
The T92 series relays that came as standard equipment in my Paragon kiln are rated at 200,000 operations.
The number of operations is usually a typical life span not a guaranteed one. Some relays may not make it to 200K, others may live well beyond 200K. It may be a good idea to replace them at 100,000 operations to be on the safe side.

I don't have any idea how many times the relays turn on & off during a "typical" firing but it must be several hundred times. Maybe I'll count some day.
If you assume a 200K lifespan and 500 on-off cycles per kiln firing that works out to 400 firings before the average relay should crap out. A little over a year if you fire every day.

That doesn't answer your question about how often to change your relays, but if you knew how many times you kiln cycled on-off during a typical firing and look up the specifications for the relays you could come up with a "reasonable" estimate.

I am curious how often folks actually change their relays in the real world and whether they have a regular schedule or wait for failure before changing.
Steve

Bert Weiss
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Re: Kiln Relays

Postby Bert Weiss » Sun Jul 06, 2014 4:44 pm

The average mechanical relay is good for 100,000 clicks. Note: average means some more, some less.

I have one solid state SCR relay that has been in service for over 30 years. It is on or off 120 times a second. 3 others are about 16 years old, but I bought them all used. These relays can only be mounted in a not hot place, which is to say, not on the side of a hot kiln.
Bert

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David Jenkins
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Re: Kiln Relays

Postby David Jenkins » Sun Jul 06, 2014 5:10 pm

A cycle every 6 seconds would be 10/duty minute, 600/duty hour. My costs per firing are about $1.80, and it's a 7200W kiln. I pay about 10 cents per KWH, so I use about 18 KWH. so that's about .5 duty hours for the complete firing cycle. Hence maybe 300 cycles?

Have no idea if that math holds up - I'm sure somebody who really knows will chime in.
Dave Jenkins
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aliceRI
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Re: Kiln Relays

Postby aliceRI » Sun Jul 06, 2014 8:05 pm

Well I have to say I'm a bit POed anyway. My Olympic GF8 is 14 months old and already I had to replace a broken top element (which they sent me free of charge) and now an error message. Although I haven't been able to call yet (will be calling tomorrow AM), the error E--2, is either a stuck relay or a controller problem. There are no clicks and the kiln stays on while plugged in so I'm assuming relay but not sure. (would love expert advice). I use the kiln approximately once a week with a schedule of 12-14 hours on average. Not close to relay life.

Tom Fuhrman
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Re: Kiln Relays

Postby Tom Fuhrman » Sun Jul 06, 2014 8:33 pm

Try to always have your controller several feet from your kiln and use SCR electronic relays with large heat sinks and possibly a ccooling fan. I went thru several SCR's till I put a small repurposed computer on the unit to cool the SCR. I been using the same SCR now for over 10 years with no problem. I also use some mechanical relays on other units and they need to be replaced about every year.

Bert Weiss
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Re: Kiln Relays

Postby Bert Weiss » Sun Jul 06, 2014 9:41 pm

Tom Fuhrman wrote:Try to always have your controller several feet from your kiln and use SCR electronic relays with large heat sinks and possibly a ccooling fan. I went thru several SCR's till I put a small repurposed computer on the unit to cool the SCR. I been using the same SCR now for over 10 years with no problem. I also use some mechanical relays on other units and they need to be replaced about every year.

For those not in the relay know, the relays Tom and I are referring to are specific types of electronic relays. There are different styles within the SCR genre. These relays have heat sensitive electronics. I place mine on a board on the wall and then travel the power wires and thermocouple wires over to the kiln. My big kiln runs on 3 zones, each with their own thermocouple and relay. To control these relays, you need a controller with a specific type of output, called 4-20milliamp output. The controllers most glass artists use have a 12v dc output. This tells a relay to be on or off in several second cycles. A mechanical relay makes a click each time it opens or closes.

There are simple SSR relays that do exactly what the mechanical relays do, only electronically. These work fine with the exact same controllers used for mechanical relays. They are however also heat sensitive. I have used these relays on 3 zone systems with Bartlett RTC 1000 controllers. I bet they have lasted a long time.

On my personal kilns, I use SCR's. The one I got 30 years ago, cost $500 at the time, and I got if from my dad. The rest of the SCR's I have in use now, are Watlow Dinamite SCR's that are rated for up to 75 amps with a fan blowing on them. I run them at 40 - 60 amps with no fan. I bought mine used, 16 or 17 years ago. I think I paid about $35 each. These show up on Ebay from time to time. You have to totally understand the codes on them or you will get the wrong ones. I have done that. If anybody wants some that run on single phase 480v, message me lol... You do need a controller with the proper output. Digitry can accommodate this on special order. Watlow, Eurotherm etc sell controllers for this type of relay.
Bert



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Rick Wilton
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Re: Kiln Relays

Postby Rick Wilton » Sun Jul 06, 2014 10:29 pm

I have three SSR's running my large kiln, the relays are close to ten years old, I have a smaller kiln with two relays that is 6-7 years. These both are fired almost daily and I have never replaced any of the relays.

I also have a smaller kiln with mechanical relays that is hardly ever used and the relays are a pain the butt, they breakdown way too easily.

SSR relays cost around $20 - $30.00 comparable or less than mechanical and will last virtually forever to the average fuser.

The issue is heat however you can't mount them on the side of a kiln.
Rick Wilton

Geo
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Re: Kiln Relays

Postby Geo » Mon Jul 07, 2014 12:55 pm

Cynthia, did you install the mercury relay yourself? I usually have a kiln repair guy from a local ceramic shop change my relays for me. I have a Paragon GL24. Last time he was here I asked him about installing a mercury relay, he said he's never installed one before. I think I need to switch over. I also use my kiln for casting and pate de verre and am getting very tired of changing the relays.

Bert Weiss
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Re: Kiln Relays

Postby Bert Weiss » Mon Jul 07, 2014 3:07 pm

In industry mercury relays are not used. The reason for this, is if one should happen to break, and OSHA gets wind of that, the company will be required to remove and replace the floor, including a concrete floor. In private studios, they are used, and I've never heard of one breaking. They do however have a shorter average life than solid state relays installed with proper cooling available.

I once installed a mercury relay sideways, and lo and behold, it didn't work. They require gravity to move the mercury.
Bert



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suds
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Re: Kiln Relays

Postby suds » Mon Jul 07, 2014 10:53 pm

David Jenkins wrote:A cycle every 6 seconds would be 10/duty minute, 600/duty hour. My costs per firing are about $1.80, and it's a 7200W kiln. I pay about 10 cents per KWH, so I use about 18 KWH. so that's about .5 duty hours for the complete firing cycle. Hence maybe 300 cycles?

Have no idea if that math holds up - I'm sure somebody who really knows will chime in.


I had to think about that one for a while but I don't believe that the number of relay cycles can be estimated just from the run time and the power use info, even assuming that the total cycle time is constant at 6 seconds.The on/off duty cycle varies all over the place and there's probably quite a bit of time "coasting down" from max temp to annealing temp when the relay is simply off for a long period of time. I played a few different scenarios on the calculator and just couldn't make it happen. Not that my math skills are that great.

No worries though, If I can't calculate it then I'll just count it. :D

Being the electronics geek that I am I poked through one of my boxes of discarded projects and found an old circuit board that I hacked together for some other weird experiment. It contains a small micro-controller hooked up to an LCD.

I connected one of the processors input pins to the kiln relay coil circuit and wrote a few lines of code politely asking the processor to count the pulses on that pin and display a running total on the display.

I'll probably run a load of glass on wednesday and report back on thursday with the specifics of my firing cycle and a count of how many times the relays turned on & off.
I have to know. Sometimes curiosity does stupid things to me. sigh...


Here's "The Hardware" all hooked up and ready to go. The red & green wires on the right connect to a small battery pack and the blue cat5 connects to the kiln. Today's cycle count = 0.
Image

Stay tuned for more...
Steve

Bert Weiss
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Re: Kiln Relays

Postby Bert Weiss » Mon Jul 07, 2014 11:14 pm

I believe you will find the click count changing relative to firing schedule and kiln load. More glass requires more kwh to heat up. That could result in fewer clicks with more on time. But then again, if you leave your counter in place, and note when it hits 100,000 you would have a clue how long it takes.
Bert



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suds
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Re: Kiln Relays

Postby suds » Mon Jul 07, 2014 11:45 pm

Bert Weiss wrote:I believe you will find the click count changing relative to firing schedule and kiln load. More glass requires more kwh to heat up. That could result in fewer clicks with more on time. But then again, if you leave your counter in place, and note when it hits 100,000 you would have a clue how long it takes.


Oh yes, it will certainly change with varying glass loads & firing schedules. And the numbers will only be relevant to my kiln and controller and no one elses. And I already converted my kiln to SSR's so I dunno why I even care anyway. #-o

But curiosity can be a cruel bitch, and I had the electronics hardware already laying around just begging for a job to do, and I already wanted to open up the controller box and add a connection to the relay circuit to turn on my ventilation fan when the kiln starts, and.. well... I'll let y'all know how many licks it takes to get to the center of a Tootsie Pop just as soon as I know. :)
Steve

Bert Weiss
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Re: Kiln Relays

Postby Bert Weiss » Tue Jul 08, 2014 11:35 am

suds wrote:
Bert Weiss wrote:I believe you will find the click count changing relative to firing schedule and kiln load. More glass requires more kwh to heat up. That could result in fewer clicks with more on time. But then again, if you leave your counter in place, and note when it hits 100,000 you would have a clue how long it takes.


Oh yes, it will certainly change with varying glass loads & firing schedules. And the numbers will only be relevant to my kiln and controller and no one elses. And I already converted my kiln to SSR's so I dunno why I even care anyway. #-o

But curiosity can be a cruel bitch, and I had the electronics hardware already laying around just begging for a job to do, and I already wanted to open up the controller box and add a connection to the relay circuit to turn on my ventilation fan when the kiln starts, and.. well... I'll let y'all know how many licks it takes to get to the center of a Tootsie Pop just as soon as I know. :)

The Average tootsie pop takes 200 licks and 15 bites...
Bert



Bert Weiss Art Glass*

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David Jenkins
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Re: Kiln Relays

Postby David Jenkins » Wed Jul 09, 2014 4:02 pm

And I in no way was trying to imply that I had any kind of an idea how to compute an accurate count - I was just trying to come up with some ROM.

On my controller, it sounds like the relay makes, and then drops out after about 1-2 seconds. If the schedule is on the way up, with any kind of medium rate, sounds like it updates every 5 seconds or so and then calls for a relay cycle. Must confess: I got bored with the whole exercise after about 30 seconds. But I'll be very interested to see what an actual count turns out to be.
Dave Jenkins
Glass at Harbor Gates
Cypress, TX


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