MarkTilles

Yes, about the extra connection that could cause reading inaccuracies, I thought about that briefly, I’ve been slowly learning about those things. I just ordered a 25 m spool of compensation cable to connect my thermocouple to my PID controller. I will do some experimentation and see how it looks. About my SSRs in particular, they are surely over rated for my needs, as I’m only pulling about 10 A on each of the 3 phases. It’s great to have experienced resources like you online here! Thank you for being involved and helping out all of us.

Thanks Bill, great ideas and information. Regarding the fan for my three phase power supply, I have already have a k-type thermocouple and PID attached to the heat sink to monitor its temperature, and then I will see whether I really even need it. I have a speed controller on the fan so I can simply turn it up to the point that keeps things at a comfortable temperature, I heard a heat sink attached to SSRs shouldn’t exceed 50°C? ... and as far as protection for the solid-state relays, I’m not planning any, if any should fail I have spares. They are cheap. The heating coils shouldn’t suddenly short out and caused an overload on any of these relays. If they are going to fail they are going to fail :-)

Great idea! Double pole - double throw?

Cool, I’m still waiting for my MAX31856 thermocouple interface card! I ordered it from a company in Holland, it was shipped and made it to the local post office, but I never got a notification so it went back to the seller. They wrote me after six weeks that it came back to them. So they have shipped it again… argh! Otherwise I have my raspberry pi zero w all set up and ready to go. I have set up a three-phase 240 V solid-state relay bank with a big aluminum tube heat sink and cooling fan. I built it as a modular extension cord so I can plug it together with either of my two 3-phase kilns, since I can only run one at a time. All I need to do is swap over the thermocouple connections between the kilns and I can use the one raspberry controller for either. Then I bought some of the proper type of compensating cable for my secondary S-type thermocouples I will be using with a separate REX-type PID controller for overheating protection (that’s what will handle the original main 3-phase magnetic relay into each kiln). This controller will also give me a secondary parallel view of the temperature in the kiln. Looks like you also use solid-state relays what I can see in your picture. Here is my three phase solid-state relay extension cord which uses 40 amp SSRs from China, but since my circuits are only 16 amp max I’m not worried about them not containing true 40a triacs inside them (as I have read on the Internet that they are often under overrated). Yes it will be inside a metal chassis, and yes I have a ground fault interrupter on all circuits in the garage

(Don't know why but I think my first reply disappeared, so ...) Yes, Jason Bruce and I have been corresponding. I am still waiting for my 31856 card to show up in the mail, and once it does I will wire it up and my Python programmer buddy will help me with the code installation and setup. My lasty programming experience was PERL about 15 years ago LOL. I would be interested to hear more about your own enhancements, I want and need an extra relay trigger for overheating protection to shut down the source to the main heating circuit (can use the original relays in the kilns themselves) if any of my solid state relays should get stuck in the ON state. // Mark

Yes, @jbruce (and clearly others) did put together a fantastic system, and the possibility for any heating curve desired - well, that’s what I am looking for. My current controller on my big oven, well I have to go in at least twice an hour to adjust the effect just to make sure it’s not going to fast or too slow. I back up my raspberry pi boot partition regularly to my laptop, as I don’t want to take a chance of losing my small tweaks in the pi’s OS if the card should get fried or corrupted. I used to work in the computer service industry, and watched customer after customer lose critical data because they didn’t “back up” in a reliable regular fashion. Once you again gain access to your memory card I would love to give it a try - just as it is. What’s important to me is that it works. Anything will work better than what I have right now :-)

Thank you Newps! I know nothing about python coding, as I haven’t touched a computer in 10 years, so I will need to wait until you’ve moved and unpacked. I’m sure Bruce will look forward to looking through your code as well! My Adafruit card should arrive any day now from Holland, but I’m still waiting for my solid-state relays and heat sinks, so I’m not ready to roll just yet anyway. Looking forward to hearing back from you! Best regards from the country of Sweden, Mark

Understood, but I already have two extras of them and my two ovens also came with them. So for consistency ...

@jbruceIs there any chance you could offer assistance to configure your kiln controller with the max 31856 breakout board instead of the 31855? I really want to use an S-type thermocouple instead of K. Thanks in advance, Mark (in Sweden)