Kiln Relays

[suds]

Todays firing is complete.

Survey says....



2384 on-off cycles!
Wow.

The kiln is a small "dual purpose" kiln...Paragon Janus 1613 with Sentry 2.0 controller.

I cast a few knick-knacks in small open faced molds Total load was less than 600 grams of glass plus the molds.

I used this schedule (degrees F):

500 > 1230 > 20 min
600 > 1480 > 10 min
AFAP > 900 > 90 min
100 > 700 > off

Elapsed time = 6 hours 35 minutes
Total relay cycles = 2384
Total number of firings required to reach 100,000 relay cycles = aprox 42 (the T92 series relays that came with my Paragon are rated at 200,000 cycles)

This was a short & simple firing. It's easy to imagine that large thick glass that needs long slow ramp times and very long annealing time could eat up a set of standard mechanical relays *very* quickly.
I'll probably plug the counting device in once in a while when I do different firing schedules just to see what kind of numbers I get, but I'm already glad that I converted to SSR's. The constant click-clack of the standard relays was driving me crazy anyway.

It was an interesting and somewhat enlightening experiment. It's amazing how quickly those "clicks" add up!

[Buttercup]

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

An 'industrial electrician' installed the mercury relays sideways after a renovation. We didn't notice and the kiln didn't shut off, melting a shelf full of glass which stuck to the shelf, ruining that too. (The same company connected the dishwasher to 240v frying that, too.) Pay attention to the arrows on the mercury relays which show which way is UP!

[lbailey]

I've been following this thread with interest and am puzzled (again, it happens a lot).

If a relay is rated for 200K cycles and that equates to less than 100 relatively short, 6 hr firings I assume that many of us run these mechanical relays waaaaay past their rated life. Is this rating artificially low due to legal or warranty issues or are we living very dangerously by not either upgrading to better relays or frequently replacing the mechanical ones?

I am pretty new to this, have two kilns and am over 100 firings in one or both of them......

[David Jenkins]

@Suds: Any way to modify your baby-sitter to measure and accumulate the time the relay is energized? It'd be fun to know the distribution of on-times, wouldn't it?

[Kate Saunders]

I had a Skutt bathtub kiln and was replacing relays at least annually until I started using a small fan to keep the relay switches cool(er). After that, I didn't change a relay until I sold the kiln a few years later. The kiln was on every day and the folks at Skutt told me it was a "hobby" kiln, not designed for that kind of heavy use. Not what I was told when I bought it!

[Tony Smith]

I've been following this thread with interest and am puzzled (again, it happens a lot).

If a relay is rated for 200K cycles and that equates to less than 100 relatively short, 6 hr firings I assume that many of us run these mechanical relays waaaaay past their rated life. Is this rating artificially low due to legal or warranty issues or are we living very dangerously by not either upgrading to better relays or frequently replacing the mechanical ones?

I am pretty new to this, have two kilns and am over 100 firings in one or both of them......

Relay life curves (very hard to find these days) plot the average number of cycles before failure against current at a specific operating temperature. A mechanical relay that is rated for 30 amps and is actually switching 30 amps will have a very short life compared to a relay that is rated for 30 amps and switches only 10 amps. At some low current and room temperature, the contact life approaches the expected life of the electromagnetic solenoid, which is around 1 million cycles.

Bottom line is if you want longer relay life, install a larger relay than you need, then keep it cool.

Tony

[Bert Weiss]

Relay life curves (very hard to find these days) plot the average number of cycles before failure against current at a specific operating temperature. A mechanical relay that is rated for 30 amps and is actually switching 30 amps will have a very short life compared to a relay that is rated for 30 amps and switches only 10 amps. At some low current and room temperature, the contact life approaches the expected life of the electromagnetic solenoid, which is around 1 million cycles.

Bottom line is if you want longer relay life, install a larger relay than you need, then keep it cool.

Tony

Tony hit the nail on the head here. Most often, relays fail closed. If the springs manage to leave the contacts in a position where they can arc, it welds the contacts together, leaving the power permanently on.

[suds]

Relay life curves (very hard to find these days) plot the average number of cycles before failure against current at a specific operating temperature. A mechanical relay that is rated for 30 amps and is actually switching 30 amps will have a very short life compared to a relay that is rated for 30 amps and switches only 10 amps. At some low current and room temperature, the contact life approaches the expected life of the electromagnetic solenoid, which is around 1 million cycles.

Bottom line is if you want longer relay life, install a larger relay than you need, then keep it cool.

Tony

^This is correct. Running relays at less than rated current gives longer contact life.

[lbailey]

Relay life curves (very hard to find these days) plot the average number of cycles before failure against current at a specific operating temperature. A mechanical relay that is rated for 30 amps and is actually switching 30 amps will have a very short life compared to a relay that is rated for 30 amps and switches only 10 amps. At some low current and room temperature, the contact life approaches the expected life of the electromagnetic solenoid, which is around 1 million cycles.

Bottom line is if you want longer relay life, install a larger relay than you need, then keep it cool.

Tony

Thanks Tony, Bert, this make sense. I don't really have a good location to pull high current wiring for an SSR to a wall or other remote location where cooling can be managed away from the kiln. What's my next best option? I hear about mercury relays, or would it be smarter to just upgrade the current relays with ones rate for higher amps than the kilns pull?

Sorry if this has been covered before but a short list of options, relative cost, expected life, pros/cons would be awesome....or a link to where this has been summarized before?

[Bert Weiss]

Relay life curves (very hard to find these days) plot the average number of cycles before failure against current at a specific operating temperature. A mechanical relay that is rated for 30 amps and is actually switching 30 amps will have a very short life compared to a relay that is rated for 30 amps and switches only 10 amps. At some low current and room temperature, the contact life approaches the expected life of the electromagnetic solenoid, which is around 1 million cycles.

Bottom line is if you want longer relay life, install a larger relay than you need, then keep it cool.

Tony

Thanks Tony, Bert, this make sense. I don't really have a good location to pull high current wiring for an SSR to a wall or other remote location where cooling can be managed away from the kiln. What's my next best option? I hear about mercury relays, or would it be smarter to just upgrade the current relays with ones rate for higher amps than the kilns pull?

Sorry if this has been covered before but a short list of options, relative cost, expected life, pros/cons would be awesome....or a link to where this has been summarized before?

I imagine your challenge is to fit relays in to a small enclosed box on the side of a hot kiln. Understand the parameters, do the best you can. Either figure out how to cool them off, increase their size, or replace them regularly. Another solution I have heard suggested is to add another relay in series with the ones that are there. Chances are, only one will fail at a time. But again, you need space to do that.

[Tony Smith]

Thanks Tony, Bert, this make sense. I don't really have a good location to pull high current wiring for an SSR to a wall or other remote location where cooling can be managed away from the kiln. What's my next best option? I hear about mercury relays, or would it be smarter to just upgrade the current relays with ones rate for higher amps than the kilns pull?

Sorry if this has been covered before but a short list of options, relative cost, expected life, pros/cons would be awesome....or a link to where this has been summarized before?

You've already heard that a typical firing is about 2400 cycles. That says 40-50 firings will get you to 100,000 cycles which is the average number of cycles before failure at their rated current. My old 27" Evenheat drew 27 Amps, but the load was split between two relays. The kiln was used moderately, maybe 50 firings per year, for four years before the top relay failed. The bottom relay failed four months later. If you keep a kiln log (I never got into the habit), you should count how many firings you had before your relay failed. If not, then estimate the number of firings. Knock off 25% as a safety factor, and plan on replacing your relays as a precaution after that number of cycles. From Allied Electronics, Tyco T92P7D22-12 relays are about $13 each and they're pretty easy to replace.
http://www.alliedelec.com/search/result ... 92p7d22+12
For me, if I had kept up firing at the same pace, I would have replaced my relays every three years as preventative maintenance. It's how they would do it in industry and it's a cheap solution if you do it in advance.

Tony

[charlie]

i use a small desk fan pointed up at the bottom of the controller box. it's on the floor, so is next to the concrete which is cooler than the air temp usually. it've only had to replace my relays once in 15 years, about 4 years after i got the kiln (probably because i bought a box of them to keep spares on hand after the 1st meltdown).

[lbailey]

You've already heard that a typical firing is about 2400 cycles. That says 40-50 firings will get you to 100,000 cycles which is the average number of cycles before failure at their rated current. My old 27" Evenheat drew 27 Amps, but the load was split between two relays. The kiln was used moderately, maybe 50 firings per year, for four years before the top relay failed. The bottom relay failed four months later. If you keep a kiln log (I never got into the habit), you should count how many firings you had before your relay failed. If not, then estimate the number of firings. Knock off 25% as a safety factor, and plan on replacing your relays as a precaution after that number of cycles. From Allied Electronics, Tyco T92P7D22-12 relays are about $13 each and they're pretty easy to replace.
http://www.alliedelec.com/search/result ... 92p7d22+12
For me, if I had kept up firing at the same pace, I would have replaced my relays every three years as preventative maintenance. It's how they would do it in industry and it's a cheap solution if you do it in advance.

Tony

Got it, makes sense. I have a little Olympic SQ146GFE which is 115VAC, rated at 16A. Bought it new and certainly over 75-80 firings. So may need to replace those relays.

The other kiln is an Olympic GF314ETLC which I bought "reconditioned". It had definitely been used but was in great shape, looked almost new. I've fired it at least 50-60 times but I don't have a firing count before it came to me. I doubt the Olympic folks replace relays in their refurbs but will double check with them Monday. In any case I plan to replace those relays ASAP.

Both kilns have the Bartlett RTC 1000 controller, both appear to be 700 series. Couple of quick questions, and BTW, thanks for all the helpful info:

- The Bartlett specifications indicate that there are 3 relays in these controllers, "top, middle and bottom". I assume this means sets of heating elements and there are 3 sets in each kiln? I suspect this means that the duty cyle of all 3 is the same as it is for one since they control separate elements? BTW, seem logical for the larger kiln to have 3 separate elements, but for the small 14" kiln, I'd think 2, top and bottom?

- When replacing relays in these kilns I assume I'll need to do them in sets, replacing all 3 at once. Where would I find specifications to purchase the correct relays? I guess I could crack open the controller and jot down the specs written on a relay, or simply call Oplympic? For the mechanical relays are there brands/types you prefer over the OEM?

- Tony, you didn't mention mercury relays so I assume they are not worth the trouble or money? I know that some kiln manufacturers offer them as an option. I don't really care about the clicking sounds from the mechanical relays but wondered if mercury relays last longer and are less prone to failure (ruining whatever project is in the kiln and damaging the kiln)?

- Finally, I've always been nervous about the risk of fire. The kilns are in an attached garage which is now a dedicated glass shop. It is heated and cooled and I have both kilns located at least 2-3 feet away from walls, work tables or anything else. Nothing flammable under or around them, just some kiln furniture underneath.The ceiling is 8 ft high, finished sheet rock. If either kin has a relay failure/sticks closed and the kiln "runs away" what is the realistic risk of fire? I intend to regularly change relays or do whatever is needed to avoid relay failure but would like to know what happens in a relay failure or what other scenarios frequently cause glass studio fires.......

Thanks for your collective patience with all the questions, this is an outstanding forum that has made a huge difference for me and so many others.

[suds]

- When replacing relays in these kilns I assume I'll need to do them in sets, replacing all 3 at once. Where would I find specifications to purchase the correct relays? I guess I could crack open the controller and jot down the specs written on a relay, or simply call Oplympic? For the mechanical relays are there brands/types you prefer over the OEM?

If you write down the numbers on the relay, or better yet take a photo of the side of the relay with all the numbers on it I'm sure someone here can help you choose an appropriate replacement.
Yes, I'd do all 3 at once. Might as well while you've got the controller opened up.

[Tony Smith]

Got it, makes sense. I have a little Olympic SQ146GFE which is 115VAC, rated at 16A. Bought it new and certainly over 75-80 firings. So may need to replace those relays.

The other kiln is an Olympic GF314ETLC which I bought "reconditioned". It had definitely been used but was in great shape, looked almost new. I've fired it at least 50-60 times but I don't have a firing count before it came to me. I doubt the Olympic folks replace relays in their refurbs but will double check with them Monday. In any case I plan to replace those relays ASAP.

Both kilns have the Bartlett RTC 1000 controller, both appear to be 700 series. Couple of quick questions, and BTW, thanks for all the helpful info:

- The Bartlett specifications indicate that there are 3 relays in these controllers, "top, middle and bottom". I assume this means sets of heating elements and there are 3 sets in each kiln? I suspect this means that the duty cyle of all 3 is the same as it is for one since they control separate elements? BTW, seem logical for the larger kiln to have 3 separate elements, but for the small 14" kiln, I'd think 2, top and bottom?

- When replacing relays in these kilns I assume I'll need to do them in sets, replacing all 3 at once. Where would I find specifications to purchase the correct relays? I guess I could crack open the controller and jot down the specs written on a relay, or simply call Oplympic? For the mechanical relays are there brands/types you prefer over the OEM?

- Tony, you didn't mention mercury relays so I assume they are not worth the trouble or money? I know that some kiln manufacturers offer them as an option. I don't really care about the clicking sounds from the mechanical relays but wondered if mercury relays last longer and are less prone to failure (ruining whatever project is in the kiln and damaging the kiln)?

- Finally, I've always been nervous about the risk of fire. The kilns are in an attached garage which is now a dedicated glass shop. It is heated and cooled and I have both kilns located at least 2-3 feet away from walls, work tables or anything else. Nothing flammable under or around them, just some kiln furniture underneath.The ceiling is 8 ft high, finished sheet rock. If either kin has a relay failure/sticks closed and the kiln "runs away" what is the realistic risk of fire? I intend to regularly change relays or do whatever is needed to avoid relay failure but would like to know what happens in a relay failure or what other scenarios frequently cause glass studio fires.......

Thanks for your collective patience with all the questions, this is an outstanding forum that has made a huge difference for me and so many others.

Evenheat uses the relays that I mentioned and they are available from Allied Electronics... The link is in my post above. They're much less expensive from a distributor than from the manufacturer. Potter & Brumfield and Tyco Electronics both come to mind as manufacturers of this relay. I would replace the set. As I explained above, my second relay failed a few months after the first. Open up your controller box and copy the numbers off of the side. If they're less than 30 amps, try to get the same model with higher current capacity. If you go to Allied Electronics, you can just enter the model number in their search function.

I've never considered mercury relays. I think the EPA should ban them. There's way too much mercury already poisoning our waterways, so it's a personal decision. I might go to solid state relays (SSRs) one of these days. It's a relatively easy changeover and they're not very expensive.

I've seen a lot of relays fail, and a lot of meltdowns, but I've never seen one result in a fire. Keep in mind that if a single relay fails on in a kiln that has three relays, the kiln won't get hotter than normal because it takes all three sets of elements to get the kiln to its max temperature... a single element full-on probably won't get the kiln above 1000 F. I added switches to my 27" kiln that allowed me to turn off the top and side elements and found this out by accidentally turning off the top element during a firing.

It sounds like you have plenty of free air around your kilns, and a non-flammable floor, so I think the chance of a total, three relay failure resulting in fire is near zero. You have a greater chance of causing a meltdown by mis-programming your controller... Usually by getting out of sequence and entering 9999 as the process temperature rather than the ramp rate... so don't do that.

I hope this helps.

Tony

[Bert Weiss]

The RTC 1000 is capable of controlling 3 zones if there are 3 thermocouples and 3 relays. When it does this, they all follow the same firing schedule, but do so independently. So, the upper zones are likely to have fewer on cycles than the lower zones.

I have used this setup for a large bell kiln. A bell kiln is a large rectangle. If you cut it in to 3 zones by drawing lines across the short side, you will see that these zones have different parameters. The 2 outer zones, have 3 cold sides and 1 hotside. The central zone, has 2 colds sides and 2 hot sides. Consequently, the center zone wants to be hotter than the outer zones. It requires shorter on cycles to maintain the same temperature. So, when all three zones are under control, they can be maintained at the same temperature at the thermocouples. By the time the power gets shut off during the cool down, the center zone will get hotter than the outer zones.

[Peg W]

I just joined this group after spending time as a visitor. I saved myself a lot of money because I bought $13 relays and fixed my kilns myself.

[tbach]

I have had a Skutt 1014 for about 3 years. In the first 2 years I replaced both relays 5 times ... yeah ... pretty excessive. It was to the point where I was afraid to fire anything that I wouldn't want to lose. To add insult to injury, when I called about the first relay replacement, only 4 months after purchasing the kiln, I was not informed that relays were included in the kiln's warranty ... so I paid for all of those 5 sets of relays. Eventually I talked to Perry at Skutt. When I explained what had been going on, they agreed to switch out the standard relays for a solid state relay system with a huge heat sink for a very reasonable cost since I had already paid for so many sets of relays.

No problems since then ... and the incessant "click" is gone - just one click at the beginning of each firing ... after that, apparently the solid state system takes over. I now fire with wild abandon.

[Tony Smith]

That's great to hear. I've said it before, but I think solid state relays are the way to go.

Tony

[Bert Weiss]

That's great to hear. I've said it before, but I think solid state relays are the way to go.

Tony

It is best to mount solid state relays on the wall, not on the side of a hot kiln. You can create a box with the controller, an outlet socket, and the relays. You will need to get long enough thermocouple wires to extend over to the kiln from the controller.