jbruce

I got tired with going down to the basement to make sure my kiln was working properly and running on schedule so I started (forked) a project to control my KS-1018 using a raspberry pi. With this I can:
monitor my kiln from anywhere using any device that has a web browser (phone/tablet/computer) easily create new schedules, edit existing schedules, including infinite ramps & soaks accurate PID control get schedule cost estimates and actuals If anyone is interested, here is the github link... https://github.com/jbruce12000/kiln-controller
The cost for everything I bought was under $200.00, but my time investment has been high.  Again, this is for geeks that were born with a soldering iron in one hand.

Hi @MikP. I'm the author of this software. If you're still having trouble, lmk and I'll do what I can to help. It's best to open an issue on github at https://github.com/jbruce12000/kiln-controller/issues
From what I've read, it looks like the elements need replacing. We can help with PID tuning after you get the heating problem sorted.
For everyone else, this software acts like an on-off switch until it gets N degrees away from the set point, so in this case, since it is way under the set point, the controller is telling the elements to heat at 100% continuously. Once it is within the window, it uses a PID to control temps.

I got tired with going down to the basement to make sure my kiln was working properly and running on schedule so I started (forked) a project to control my KS-1018 using a raspberry pi. With this I can:
monitor my kiln from anywhere using any device that has a web browser (phone/tablet/computer) easily create new schedules, edit existing schedules, including infinite ramps & soaks accurate PID control get schedule cost estimates and actuals If anyone is interested, here is the github link... https://github.com/jbruce12000/kiln-controller
The cost for everything I bought was under $200.00, but my time investment has been high.  Again, this is for geeks that were born with a soldering iron in one hand.

I think a cooled solid state relay will have long life.  Wear and tear on SSRs is mainly from heating (expansion) / cooling (contraction) of the components in the package.
The increasing amplitude of the waveform as your kiln gets hotter is due to cooling because of the 60s cycle time.  A faster cycle time would be harder on your mechanical relays, but would yield more accurate ramps / soaks.
 
WARNING !!! WARNING !!! WARNING !!! WARNING !!! WARNING !!! WARNING !!! WARNING !!!
running a kiln in an enclosed space is extremely dangerous.  some fumes are noxious. please dont. running a kiln within 8 feet of anything flammable is extremely dangerous.  please dont. WARNING !!! WARNING !!! WARNING !!! WARNING !!! WARNING !!! WARNING !!! WARNING !!!
 
This is the pot calling the kettle black (because I made some mistakes too), but the best thing you could do if you choose to run this in its current location & state is to automate a call to 911 when it starts. :-)

@High Bridge Pottery With a cycle time of 2s my controller switches on about 11,000 times in a 13 hour firing.  I'm not sure what "a lot" means to you.  I'm not worried about the number of switching cycles - as long as I keep my SSR cool - it will have a long life.
If you're switching using a mechanical relay or contactor, I would set the cycle time to at least 10s.  I'm not sure about 60s... I'd have to test that.  By experience, my kiln drops a F degree per second when not being heated at 2000 degrees or more.  Setting a cycle time of 60s means the temp swing could be 30-40 degrees or more.  I want to be more precise than this.  I think a 3  degree swing is acceptable.

@High Bridge Pottery Are you deciding if you should turn the relay off or on every 2 seconds?
Yes.  This is a configurable parameter. The code originally made this decision every .5s and that duty cycle was too high for kilns.  I have heard some folks going as high as 10s.  Since it is configurable, you decide the value that works best for your kiln.
How did you come up with the PID values to use?
I read many articles discussing PID tuning.  Some were complex algorithms, some simple.  I tried to find the simplest method that could be done in a few hours.  The process I used is described here... https://github.com/jbruce12000/kiln-controller/blob/master/docs/pid_tuning.md
The tuning it provided the first time around is good for my use.  If you find a simpler, better tact, post a PR and I'll check it out.
Part of our duties...
@Min
@neilestrick @Bill Kielb
If you, Neil, or Bill feel like this has become too big a risk to remain on the site, I totally understand. The last thing I want is for anyone to violate local code or endanger themselves.  I am committed to improving my implementation, but it will take time.  I have a full time job and this is a side project / experiment for me.
I cannot stress enough the value I have found in this forum.  I thought I was pretty good at what I was doing.  Turns out, I made lots of mistakes.  If I made these mistakes, others will too.  I think if folks had a resource where they could learn these things, it could prevent folks going down the same road I have.
Not sure what else to say on this topic.  Assumptions can be dangerous.  Reflect carefully on risks others point out.  Strive to become better.

I test fired my kiln with the new controller to 1000F last night.  It included some fast ramps of 1200F/hour to 800F and from there 600F/hour to 1000F plus a soak of a few minutes.  This was just to work out any glitches before I do a bisque fire.  The software is configured to run every 2s and I grabbed some stats from that...

average error in degrees F 0.7665486726 solid state relay cycles 977 schedule length in hours 1.00 elements on (s) 1934.91 element percent on 53.75 element watts 9640 cost per kwh 0.126 schedule total cost $0.65 I'll pack the kiln today and bisque fire tomorrow.  I'll post details after that.

@liambesaw Here is the pic I promised.

Input is a nema male plug with three conductors (2 hot, 1 neutral).  I used an old extension cord for this to make sure it could handle the current.  Turns out it could handle about 4 times the 40A current max, so lots of safety margin there (and free wire). One hot leg is switched by the SSR, everything else runs straight to the output on the right hand side where the female nema plug is mounted.  The RPI is in a plastic case and is covered by a breadboard with all the spaghetti wiring.  You can see the max31855 in there. The thermocouple is the red/yellow wire.  The rpi connects to the control side of the ssr.  There is also power for the rpi (that black cable coming out the square hole in the front).
That big square hole is from a previous incarnation of the controller that used a PID controller purchased from a company.
Note the BIG heatsink with thermal paste and the BIG aluminum box.  If you want your SSR to survive, keep it cool.  There will be times where the SSR is on 100% of the time and that will generate significant heat.
 

The cone 6 glaze firing went pretty well.  You can see in the image that my kiln sitter tripped just before reaching 2232.  It had a cone 7 kiln sitter cone in it.  I think I had a kiln shelf too close to it. No worries, I just by-passed the sitter with slow-flip and used the api to start the cooling phase. You can see I skipped the initial drying phase of this schedule. There is more error this time than previous runs because I included the initial warm up, the part of the schedule where my kiln could not keep up, and the kiln-sitter flip. It was usually within a degree F though.  There were points in the schedule where the elements were on 100% of the time.

schedule name cone-6-long-glaze schedule date 1/5/2019 average error in degrees F 3.25 solid state relay cycles 11934 schedule length in hours 11:25:12 elements on (s) 6:34:00 element percent on 57.50 element watts 9640 cost per kwh 0.126 schedule total cost $7.98

Happy Holidays Potters!
I did another bisque fire today and got very consistent results when compared to the last bisque firing.  I started this firing at 2AM using the new API and it ended just before 3pm.  I also used a new API feature that allows me to start a kiln run anywhere in a schedule.  With this run, I skipped the first two hours because I knew my pots were bone dry.  I added this feature for power outages, but it is handy for this too.

schedule name cone-05-long-bisque schedule date 12/28/2018 average error in degrees F 0.78 solid state relay cycles 11086 schedule length in hours 15.17 elements on (s) 21955.36 element percent on 47.78 element watts 9640 cost per kwh 0.126 schedule total cost $7.41 The capacitors I added did not improve thermocouple noise or thermocouple errors. I discovered that thermocouple noise is caused by me when I connect a device via wifi.  It is either causing noise from the wifi transmission being picked up by the thermocouple cable... or it could be power supply noise.  I'm not sure, but it does not affect firing at all, so I'm going to ignore it until it becomes a problem. 

Next is a cone 6 glaze firing.  I'll post results for that.
 

Please understand that this is just an interesting project / experiment. Please note that I have no intentions of creating a product.  Please understand that this hardware is not finished and is in an alpha state.  I do not want defend improper practices and I am here to learn from others and improve.
I love that I have found a passionate, intelligent, experienced group of people in this forum.  If I had a forum with information like this when I started the project, it would have changed the course of the project.  So now, I'm left to make things right with folks so they don't follow the wrong path.  Please help me do that.
1. Conductors on the input side need to be to code (could I use a replacement 50A dryer cable for this?)
2. Grommets for any conductor that goes into the bud box
3. connect the heatsink directly to the SSR (can I then mount the heatsink to the bud box?)
4. use an Ultra Fast Acting fuse at the rated amperage of the circuit to protect each of the SSRs - 50A
5. use an SSR on each leg, instead of just one
6. use mechanical safety relay to disable all SSRs in the event there is an SSR failure/short.  I'm not at all sure how to implement this.  Can someone post a link to a schematic?
 
Did I leave anything out?

Yep. It's a small kiln, so I just have one set of witness cones.  In this case, 5,6,7 on the center shelf.  In past firings, I've watched these to determine when to shut down (or move on to the next part of the schedule). This time I did not get the chance because the kiln sitter flipped before I thought it would.  Next time.
 

I test fired my kiln with the new controller to 1000F last night.  It included some fast ramps of 1200F/hour to 800F and from there 600F/hour to 1000F plus a soak of a few minutes.  This was just to work out any glitches before I do a bisque fire.  The software is configured to run every 2s and I grabbed some stats from that...

average error in degrees F 0.7665486726 solid state relay cycles 977 schedule length in hours 1.00 elements on (s) 1934.91 element percent on 53.75 element watts 9640 cost per kwh 0.126 schedule total cost $0.65 I'll pack the kiln today and bisque fire tomorrow.  I'll post details after that.

I got tired with going down to the basement to make sure my kiln was working properly and running on schedule so I started (forked) a project to control my KS-1018 using a raspberry pi. With this I can:
monitor my kiln from anywhere using any device that has a web browser (phone/tablet/computer) easily create new schedules, edit existing schedules, including infinite ramps & soaks accurate PID control get schedule cost estimates and actuals If anyone is interested, here is the github link... https://github.com/jbruce12000/kiln-controller
The cost for everything I bought was under $200.00, but my time investment has been high.  Again, this is for geeks that were born with a soldering iron in one hand.

Hi Bill,
Cool project! and great to meet you.  That looks like a lot of work too!  So, you're regulating a gas kiln!  What kind of regulator/actuator do you use to control the gas pressure?
My kiln is an old Skutt kiln sitter so it is electric. I hope to have the kiln firing in the next two weeks.  We'll see how busy things get with the holidays coming up.
 
Thanks for the suggestion on Bartlett schedules. I'll check them out. I've found a couple schedules and they all advocate a slow approach to the final temperature.  I plan to soak for as long as it takes for the witness cone to reach 90.
 
Everything in the project is released under the gnu gpl license, so liability will not be an issue for me (as far as others using the code or ideas in github).  If I was to implement this for say... a school... especially if I charged for my work, I could be held liable... but this is my personal kiln.

Thanks with regards to safety.  I'll continue to use both the kiln sitter (with one cone above intended firing temp), and safety timer so that I don't burn down the house.  When solid state relays fail, they usually fail with a short circuit... so the kiln get's full power.  The safety I have in place today is...

1. warning if temp is N degrees outside of schedule
2. software shutdown if max temp limit is reached
3. kiln sitter
4. kiln timer
and of course walking down to the basement to check near end of schedule
 
 

I got tired with going down to the basement to make sure my kiln was working properly and running on schedule so I started (forked) a project to control my KS-1018 using a raspberry pi. With this I can:
monitor my kiln from anywhere using any device that has a web browser (phone/tablet/computer) easily create new schedules, edit existing schedules, including infinite ramps & soaks accurate PID control get schedule cost estimates and actuals If anyone is interested, here is the github link... https://github.com/jbruce12000/kiln-controller
The cost for everything I bought was under $200.00, but my time investment has been high.  Again, this is for geeks that were born with a soldering iron in one hand.

I got tired with going down to the basement to make sure my kiln was working properly and running on schedule so I started (forked) a project to control my KS-1018 using a raspberry pi. With this I can:
monitor my kiln from anywhere using any device that has a web browser (phone/tablet/computer) easily create new schedules, edit existing schedules, including infinite ramps & soaks accurate PID control get schedule cost estimates and actuals If anyone is interested, here is the github link... https://github.com/jbruce12000/kiln-controller
The cost for everything I bought was under $200.00, but my time investment has been high.  Again, this is for geeks that were born with a soldering iron in one hand.