Bill Kielb

Nice!!!!

@jbruce just my opinion, still a nice project, alpha stage as you say and has brought forward many suggestions. In the end these are all opinions and one can argue often informed by different life experiences and backgrounds. Folks offering advice based upon their experience is always valuable in my opinion and can help shed new light on a particular issue or simply be dismissed as being incorrect which usually can be disproven or tested to invalidity. I am not a big fan of adding exculpatory clauses to everything that I may say or others may say to protect an opinion. I have struggled with this in teaching at the college level in that it tends to stifle creativity, critical thought and the energy to take on new things. I think sharing your experience and getting quality feedback or opinions from a diverse group has value. Asking moderators to be accountable to correct incorrrect opinions is impossible. Knowingly providing misinformation is key here. to me you are on a good path and now hopefully will put more energy and research into taking the project to beta stage and folks can continue to provide conscientious criticism or suggestions. My opinion, project is fine, moderators fine, everyone with a concerned opinion fine. Just my thoughts though

Nice holder! Just catching up on custom orders for mugs and underglazed stuff. Also working through fixing an existing Bristol glaze for the studio . Arrrrgh dislike these glaze recipes but almost done, I think. After spraying countless ornaments and now these little mugs, cups, treasure boxes I think I need a throwing break from this stuff! Took a picture of myself spraying and I do not appear to be excited. LOL

I agree, my present thought for adding to an existing kiln is to mount a flat parallel exchanger on the outside of an existing kiln control box. Cut completely through the box behind the exchanger and direct mount the SSR to it. Exchanger on the outside, SSRs on the inside but still directly connected to the heatsink. Heatsink vertical for best performance out where the ambient temperature is relatively cool. just an idea so far though with a little research. Have not done any calcs yet or tests. Heat sinks are pretty economical actually. As a one time cost this may be a way to go in retrofit.

Most of the curves I have viewed show 1.8C/W cooling works fine. Ambient air at 80-90 degrees means a 4” X 4” X 1-1/2” parallel fin exchanger is likely fine. Powered cooling is a solution to shrink the form factor but also relies on another mechanical device. Doing it with convection if reasonable is probably most dependable.

Most of these issues go away when this moves from alpha to beta. conductors will likely change when you make this into a fixture wire project as long as you are dead set on the temporary extension cord approach. Grommets will likely not be needed again as this gets packaged for permanence not as a development project. The heatsink design is a bit more difficult but I have a retrofit that I am going to try that solves this for me. It entails using production linear heatsink material (very inexpensive) designed at about 1.8C/W or you simply would make the final version bigger and stick this on the inside, vertical with ventilation holes which would reduce its effectiveness. Fast acting fuse to protect your SSR, single SSR is fine, solid safety relay protection is all that is necessary. Most kilns use double pole relays for a reason. Whether the double pole relay would be sufficient as a disconnect is the overriding question here or is a definite purpose contactor necessary. i think a lot of this goes away as you look to incorporate the design into something permanent. Now that you are thinking of these things it’s half the battle. I expect to try and do a retrofit SSR on an existing kiln within a month or so. I will post some of the choices we make and why and see if I can make it easy and safe. Not sure how this will go though so we are moving slow and gathering data and requirements. its still a wonderful project

Good thread, good info, still a nice project but there are many things in the world more complicated than googling and reading tables and trying your best to understand the basis. As a last note, SSR’s fail quickly under short circuit. Much quicker than a circuit breaker will trip and often quicker than a standard fuse will protect. The manufactures provide the appropriate amps squared seconds rating to protect their device. I should have been more clear, the fuse is intended to protect the SSR and all manufactures provide data and the appropriate fuse to use so your SSR will have a long useful life. I definitely did not intend the SSR protection to fall into the machine protection required line of thinking. They are different and I should have been clearer.

As I said this is still a nice project and it is not worth the time to talk about why extension cords are not used as a single conductor or whether a fuse is way faster than your breaker and highly suggested by SSR folks or why mounting the heat sink outside was necessary when designed for direct mount with a saddle for the SSR and thermal calculations that clearly show this in not desireable, or why we didn’t criticize the raw hole drilled for the wires without grommet or any number of things in a beta stage project. That anyone would seek to defend these issues without saying simply it’s not a finished project is a bit troubling in my view. again it’s a nice project and if you produce it for others you need to step up your game a whole bunch, none of that will fly as code or be approved for many reasons, none of which entail reading a chart and not understanding the application of or the proper way to derate things. I am not here to argue the obvious, it is not code or UL or CSA or FM, and won’t be in its present form. So last thing to say It’s in a great stage and has performed well. Hats off to your hard work and wonderful success, I believe it’s important to encourage, but the reality of needing to now make it industry standard and as safe as practical is your next step in your own development. just my opinion so take it for what it’s worth but I have a lifetime of working through these types of issues.

Yes, it is common for higher amperage services where 4” pipe is the raceway limitation so Parallel feeders is the only practical way to do this economically using multiple network sets to get to the desired service amperage and often a secondary set (s) as backup for critical loads / structures. an extension cord used in this way is not good practice, nor generally code compliant in any way.

Single SSR and the power disabled by relay is the norm. Actually it’s common to see the existing relays stay in place and feed the SSR. The relays are driven by a safety output so once the program is run they are latched closed for the entire firing and the SSR’s are switched on and off by the controller. Often the existing relays are safety looped through a lid switch as well. the end result: lid closed + no controller errors + program start pulls in all the regular relays which then provide power to the elements and SSR’s. As long as no errors and the lid is closed these relays stay closed and the computer controller is free to cycle the SSRs to heat the kiln. SSRs often fail shorted as much as open so it is absolutely necessary to have another way to disconnect them from the load. A new device design often has a main contactor that disconnects all power incorporated into its safety loop design. SSRs are heat and overload sensitive so it is absolutely necessary to heatsink them to 2C/W or less and install fast blow fuse protection properly sized to the SSR. interesting tidbits on SSRs, they are starting to make them with current sensors built in. The relevance? An SSR controlled kiln with these could also display the amperage of each element as it is operating. Really cool diagnostic tool!

Parallel feeder idea, not skookum or good practice.

This needs to be cleaned up a bunch. Running the cord as parallel feeder will get you a derated 60 amps or 45 amps for 12 and 14 gauge cord respectively. The SSR needs fuse protection , the SSR heat sink is inverted and mounted externally. It is ok as a prototype, but needs a bunch before this could be offered to the general public. i suggest you get data and perfect the beta project then redesign with an eye towards electrical safety and device longevity. still a nice project.

Are ýour elements always hot? One leg connected?

Engineering alert! Just a crazy add here and this has happened to several folks drilling holes in flat clock faces. Our best theory thusfar: It turns out clay acts like many materials with stress developing as result of the drilled hole. I had a friend that made clock faces, very flat and often thin for their overall size. On several occasions the faces split completely in half during the glaze firing (Like 1/2" apart as the stress ejected each half). This can be common and present itself in flat faced items and likely presents itself similar to the stress and strain we find on other drilled materials. Our solution was to thicken the slab in the area of the bored hole one to two diameters larger than the hole …….. (reinforce with a washer over it, how original we are!)) The hard lesson: always chamfer and smooth any hole cut in the clay so as not to provide an easy path for the material to begin cracking. The forces around it will be real and will appear, so always do your best. Kind of like concrete shrinkage cracks developing at an inside corner. Kind of geeky but good clay construction practice likely will help avoid disappointment later. Nice to see everyone has a favorite way to chamfer these.

The normal way this is accounted for is to establish 108 degree per hour in approximately the last 250 degrees of firing. I think I mentioned this but if you look at the Bartlett schedules you will see they have perfected firing speeds along with final firing temperatures with a final rate of 120 degrees per hour in the last 250 degrees of firing. heatwork is difficult to calculate and thermocouple offsets to tabled cone values are often the solution based on witness cone tests and can be taylored to each cone. Rarely does one offset serve all cones exactly. just my experience though.

Looks good, did you install firing cones so we will know the effective heat work throughout the kiln?

Fantastic! Can’t wait to see the firing. in the next few weeks we are going to design and install a retrofit SSR to one of our existing kilns. We will publish complete with thermal analysis and proper overcurrent protection for the SSR in the hopes that there will be folks who wish to convert and possibly use the raspberry pi as well. cool stuff!

I personally see an interesting similarity yet contrast in the top one and bottom right. They have matching glazes yet different offsetting contrast and the diversity in the texture yet similar textural design would make me want to display them together.

Don’t forget switching at zero crossing, meaning his relays always wait till zero volts and fire. Elements are never subjected to startup at 170 v peak or worst case 340 v. Peak for two phase operation. As well as smoother temperature control allows the overall duty cycle of the element to match the load more practically.

Really nice project and thanks for sharing. If you ever need the PLC code created for the monitor we created ( simple ladder logic for Click PLC stuff) just drop me a message. You are welcome to it.

Nice on both fronts! I was an electrician at age 20 (some time ago) and would offer to help but the distance from Wa to IL is rather significant. I will have to cheer you on from a distance. With respect to the Rpi I was going to drop you a note that said funny, now you have some programming to perfect along with your wares. Sounds like a fun project, hope you can keep us apprised.

Old general filter was to add a small rc filter network to both legs of the thermocouple. They needed to be identical to offset the error and also needed decent capacitors. I was hoping shielded thermocouple would solve your noise issue. Hard to tell from the data you have what magnitude the noise is but likely microvolt average on a .6 to 52 millivolt signal.. Does the thermocouple board auto detect shorted and open circuit thermocouple failures? I only ask because in PLC land temperature transmitters do this for us so we need not have to worry. all still looks great BTW, under three hundred with a decent web server interface! Cool!

Looks pretty nice! I am still curious how hot the SSR gets since we have been debating on retrofitting a kiln or two with ssr replacements downstream of the existing relays. The relays would only serve as an enable during operation or a positive means of disconnect under alarm. My limited research has always indicated the use of a fairly significant heat sink install. Your SSR I believe is rated at about 12000 watts controlling approximately 10000 watts of load so not grossly over sized. At this point it looks like you could fire and be successful with about 6000 watts of power - interesting! snce this is zero crossing it should be kinder to the elements since no 177v peak starts, ever! two thoughts: do you currently have shielded cable for the thermocouple leads? did you install fuse protection for the SSR occasionally in some kilns it is possible to have an element short depending upon how much they have been allowed to crawl out and where they touch.