jbruce12000
Question about possibility of controlling two SSR units from the same GPIO
I will be controlling an ancient smaller L&L kiln from the 60s ( 1960s ) as a test kiln. It runs on 240V/single phase - three wires ( two hot and neutral ). This little Oldy but Goldy fires a hot cone 9 in ten hours drawing 25 amps. The rudimentary controls are three knobs for bottom, middle and top heating elements. The original idea was to replace those knobs with a 3 Phase SSR and be done with it. Keeping the SSR cool in that location turned to be nearly impossible and I am not keen on extending wires etc.
The cool idea is using two SSRs on the main cable and mounting the project box with proper cooling fan on the wall. Can I run two Bc547 transistors from the same GPIO to power the two separate SSR?
I understand there are logic level converters that could be used for this case but I can't figure out how to use the reliably.
A simple solution would be to use just one SSR. Cooling with 25 amps flowing thru the SSR is no problem . The power lost in the SSR is only about 25 to 30 watts. A small fan will do that. Can you explain why you want multiple SSRs?
On Sun, Jun 22, 2025, 8:42 AM TinMaan @.***> wrote:
TinMaan created an issue (jbruce12000/kiln-controller#219) https://github.com/jbruce12000/kiln-controller/issues/219
I will be controlling an ancient smaller L&L kiln from the 60s ( 1960s ) as a test kiln. It runs on 240V/single phase - three wires ( two hot and neutral ). This little Oldy but Goldy fires a hot cone 9 in ten hours drawing 25 amps. The rudimentary controls are three knobs for bottom, middle and top heating elements. The original idea was to replace those knobs with a 3 Phase SSR and be done with it. Keeping the SSR cool in that location turned to be nearly impossible and I am not keen on extending wires etc.
The cool idea is using two SSRs on the main cable and mounting the project box with proper cooling fan on the wall. Can I run two Bc547 transistors from the same GPIO to power the two separate SSR?
I understand there are logic level converters that could be used for this case but I can't figure out how to use the reliably.
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A simple solution would be to use just one SSR. Cooling with 25 amps flowing thru the SSR is no problem . The power lost in the SSR is only about 25 to 30 watts. A small fan will do that. Can you explain why you want multiple SSRs? …
I assumed I need two SSRs as there are two hot lines powering the kiln. I have read a few heated discussions on the internet on the subject to no end. Some people strongly advise to cut both hot lines with SSR on each hot leg and some people ( including pro electricians ) claiming it's un-necessary or over protectionist using two SSRs and one will do the job.
Honestly I don't know and I would prefer simple workflows as I am only a simple man. So, I am open to suggestions.
Is the usual mode to have all on at the end? If so then running all together with the pi controller would be fine. The pi will pulse the power so that the kiln will heat up along a path you can decide on. Eveness of heating in kilns can be a problem and that may be why 3 elements. The pi control.only can handle 1 element so joing all 3 together will work but the temperatures in the kiln will not be even. The ultimate system for you could go to have 3 controllers and 3 pi systems. It is also to use one pi with a sequential switching using three thermocouples but I don't think you want that complex a system. I would start with all three connected together and one SSR and using the pi control see how it works. You should start with a bisque firing and put cones on each shelf so you can see how even the heat was. I am an engineer and ceramicist so.please ask questions off this site . Send to me at @.*** Ron.
Anger is usually regrettable, kindness rarely.
On Sun, Jun 22, 2025, 10:19 AM TinMaan @.***> wrote:
TinMaan left a comment (jbruce12000/kiln-controller#219) https://github.com/jbruce12000/kiln-controller/issues/219#issuecomment-2994332094
A simple solution would be to use just one SSR. Cooling with 25 amps flowing thru the SSR is no problem . The power lost in the SSR is only about 25 to 30 watts. A small fan will do that. Can you explain why you want multiple SSRs? … <#m_8950350120334014699_>
I assumed I need two SSRs as there are two hot lines powering the kiln. I have read a few heated discussions on the internet on the subject to no end. Some people strongly advise to cut both hot lines with SSR on each hot leg and some people ( including pro electricians ) claiming it's un-necessary or over protectionist using two SSRs and one will do the job.
Honestly I don't know and I would prefer simple workflows as I am only a simple man. So, I am open to suggestions.
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Thank you for the thorough reply. I see your point about the heat uniformity. That said, considering the size of the kiln ( 18"x18"x18" fire chamber ) and triple walled insulation this kiln never needed three heating zones controls. I have tested the differences. In a cone 6 firing the bottom is about half bend while the middle is perfect and the top fully bent. So, the usual half cone difference. I am going to keep the controller knobs for a while. I'll set them on highest setting ( high ) just in case. The added benefit would be an arguable " fine tuning " option of zones with trial n' error. As you mentioned the simplest solution for this test kiln would be controlling it with one Pi board and one SSR. Currently it is connected to the mains through a three prong 250V - 50A NEMA 6-50. I used a shortened cut portion of an RV cable ( 40 amps ). I could make an incision through the tough cover(s) of the cable and place the SSR on one of hot legs of it ( ceramic terminal ). The SSR and the Pi board will be inside a reclaimed DATA server with a perfectly functioning PSU ( 3.3V, 5.1V and 12V regulated ). There are an array of ultra quiet fans in there also. So, I have all the flavours of the power and cooling on the wall near the kiln. I understand I need to make accommodations for the Wifi signal out of that metal box.
Thank you for checking the idea. As we do in ceramics works : " more testing :-) "
If you do not switch both hot wires, the elements stay energized and touching them will shock you. You can get a 3 phase SSR and use 2 sets of contacts. If you decided to only switch one side, I would not load/unload without disconnecting power.
I use 3 - 2 wire 35amp relays, one for each element (16 amp elements), then 3 sets of 10 awg wire to the kiln. If I switched with one big relay, the wire would be 6 awg, and a 60 amp relay/ssr is more expensive. I took apart some cheap 40amp SSRs, They had 15amp components.
I use a dip chip, unl2003a, 8 channels, to switch 12v with gpio pins. I have a channel per relay and I use a few more channels for fans. The MAX31856 and MAX31855 have an internal thermocouple that I use to monitor controller temp, compare it to room temp and switch cooling fans in the control box. I keep meaning to control the fans with pid and pwm. Right now just off/on.
3 gpio pins, one for each relay allows individual control and it is modular. I have a second kiln that has only 2 (16 amp) elements and I can switch the controller to either kiln with 30 amp twist lock connectors.
On Sun, Jun 22, 2025 at 12:19 PM TinMaan @.***> wrote:
TinMaan left a comment (jbruce12000/kiln-controller#219) https://github.com/jbruce12000/kiln-controller/issues/219#issuecomment-2994332094
A simple solution would be to use just one SSR. Cooling with 25 amps flowing thru the SSR is no problem . The power lost in the SSR is only about 25 to 30 watts. A small fan will do that. Can you explain why you want multiple SSRs? … <#m_-7331725841750155419_>
I assumed I need two SSRs as there are two hot lines powering the kiln. I have read a few heated discussions on the internet on the subject to no end. Some people strongly advise to cut both hot lines with SSR on each hot leg and some people ( including pro electricians ) claiming it's un-necessary or over protectionist using two SSRs and one will do the job.
Honestly I don't know and I would prefer simple workflows as I am only a simple man. So, I am open to suggestions.
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-- Blake C. Lewis
If you do not switch both hot wires, the elements stay energized and touching them will shock you. ... … Yes, I perfectly understand that vital point. As a general practice of years, I never load or unload electric kilns powered. Also nobody else is allowed ( ... er crazy enough ) to enter my kiln room. Even then I have a sign stating that the main panel must be off before loading or unloading any of the kilns. That rule includes the newer kilns with modern Bartlett controllers
Thank you for this important reminder.
I see no reason to switch both sides of a 240 system. Yes it's true if you touch ground and the non switched line you'll get 120 volts pass through you. However why would you risk that. Have a full breaker and disconnect everything when loading etc. Just switch one a side it's much easier. BTW. as an EE I wouldn't trust the SSR to provide " touch free" isolation. They have leakage current that might be felt. REMEMBER KISS...
On Sun, Jun 22, 2025, 12:41 PM TinMaan @.***> wrote:
TinMaan left a comment (jbruce12000/kiln-controller#219) https://github.com/jbruce12000/kiln-controller/issues/219#issuecomment-2994402190
If you do not switch both hot wires, the elements stay energized and touching them will shock you. ... … <#m_-3846946711555606433_> Yes, I perfectly understand that vital point. As a general practice of years, I never load or unload electric kilns powered. Also nobody else is allowed ( ... er crazy enough ) to enter my kiln room. Even then I have a sign stating that the main panel must be off before loading or unloading any of the kilns. That rule includes the newer kilns with modern Bartlett controllers Thank you for this important reminder.
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I see no reason to switch both sides of a 240 system. Yes it's true if you touch ground and the non switched line you'll get 120 volts pass through you. However why would you risk that. Have a full breaker and disconnect everything when loading etc. Just switch one a side it's much easier. BTW. as an EE I wouldn't trust the SSR to provide " touch free" isolation. They have leakage current that might be felt. REMEMBER KISS... …
Here is an update. The electrician finally dropped in. After a bit of pondering on my old hand drawn schematics that originally was done and issued by L&L ( of the bygone era ) and then a bit of organizing a jungle of wires creeping everywhere inside the " OEM control box ", he said : " We have two options. A- getting rid of the control knobs and ganging the hot wires into two and then controlling one of the two with the one SSR discussed here. ... or ... B- using two separate SSRs on existing mains before entering the kiln ( on the wall ) and with that we can keep the control knobs for fine tuning zone control."
What would you do?
Here is a copy of the old schematics wiring of the little kiln:
H1500 L&L DynaKiln wiring diagram - A-103X.pdf
I have 24 volt 3 phase contactors unused and good for at least 25A you can have for shipping cost . You could use them for safety or whatever. I would have one SSR controlled by the pi kiln controller. And if the existing switches are functional leave them in the system. The SSR will switch the 240 incoming to whatever setup you have with existing switches . It doesn't care! Then you can have best of both worlds. The local switches will allow for balancing the temps and the pi will try and keep the temp profile you've programmed. You will.need to.set up the PID logic so they.match your kiln. Don't worry if the pi doesn't track at start up. It should follow within a degree after about 300F.
This is the simplest solution i think. Don't try multiple SSRs it's not necessary. I would have a main breaker near by or easily accessible. It seems that a 50 amp.breaker would be fine if not a bit overkill.
Ronald.
Anger is usually regrettable, kindness rarely.
On Sun, Jun 29, 2025, 10:16 AM TinMaan @.***> wrote:
TinMaan left a comment (jbruce12000/kiln-controller#219) https://github.com/jbruce12000/kiln-controller/issues/219#issuecomment-3016878287
I see no reason to switch both sides of a 240 system. Yes it's true if you touch ground and the non switched line you'll get 120 volts pass through you. However why would you risk that. Have a full breaker and disconnect everything when loading etc. Just switch one a side it's much easier. BTW. as an EE I wouldn't trust the SSR to provide " touch free" isolation. They have leakage current that might be felt. REMEMBER KISS... … <#m_-8423411331909300681_>
Here is an update. The electrician finally dropped in. After a bit of pondering on my old hand drawn schematics that oroginally was done and issued by L&L ( of the bygone era ) and then a bit of organizing a jungle of wires creeping everywhere indie the " OEM control box ", he said : " We have two options. A- getting rid of the control knobs and ganging the hot wires into two and then controlling one of the two with the one SSR discussed here. ... or ... B- using two separate SSRs on existing mains before entering the kiln ( on the wall ) and with that we can keeping the control knobs for fine tuning zone control." What would you do?
Here is a copy of the old schematics wiring of the little kiln:
H1500 L&L DynaKiln wiring diagram - A-103X.pdf https://github.com/user-attachments/files/20968996/H1500.L.L.DynaKiln.wiring.diagram.-.A-103X.pdf
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I have 24 volt 3 phase contactors unused and good for at least 25A you can have for shipping cost . You could use them for safety or whatever. I would have one SSR controlled by the pi kiln controller. And if the existing switches are functional leave them in the system. The SSR will switch the 240 incoming to whatever setup you have with existing switches . It doesn't care! Then you can have best of both worlds. The local switches will allow for balancing the temps and the pi will try and keep the temp profile you've programmed. You will.need to.set up the PID logic so they.match your kiln. Don't worry if the pi doesn't track at start up. It should follow within a degree after about 300F.
This is the simplest solution i think. Don't try multiple SSRs it's not necessary. I would have a main breaker near by or easily accessible. It seems that a 50 amp.breaker would be fine if not a bit overkill.
Ronald.
Anger is usually regrettable, kindness rarely. …
I also prefer to keep things as simple as possible. I assumed I was able to place the single SSR on one of " hot " legs of 240V power cable ( three wires 50 amp ). They had wired the top zone of this little kiln to one hot wire ( L2 ) and the middle+bottom of the kiln is wired to the other hot wire ( L1 ). With this configuration, I am not sure how to control all the power to all the zones with only one SSR. Could you take a look at the attached wiring diagram of the kiln and suggest how to proceed with the idea of controlling the kiln with only one SSR please?
H1500 L&L DynaKiln wiring diagram-worked - A-103X copy.pdf
I'd like to help but I don't know what the switches do. I can guess but that's all. WITH NO POWER CONNECTED you could take a VOM and find out what the switches do. To do this make a table. Position 1 : A connects to what B connects to what Same for all three positions. It seems that the original system ran I'm some positions with elements on 120 volts and the max went to 240. I wish I was close by as the challenge is not hard but trying to.help.remotely is very difficult. The simplest solution would be to use all elements together going to.one SSR powered by 240. No.connection the neutral. This would be like a domestic 240 oven. This won't help to balance the temperatures . Another suggest is use the pi only for monitoring and control kiln manually. It works well for that. Sorry not to.be more help. Ronald.
On Sun, Jun 29, 2025, 6:14 PM TinMaan @.***> wrote:
TinMaan left a comment (jbruce12000/kiln-controller#219) https://github.com/jbruce12000/kiln-controller/issues/219#issuecomment-3017417789
I have 24 volt 3 phase contactors unused and good for at least 25A you can have for shipping cost . You could use them for safety or whatever. I would have one SSR controlled by the pi kiln controller. And if the existing switches are functional leave them in the system. The SSR will switch the 240 incoming to whatever setup you have with existing switches . It doesn't care! Then you can have best of both worlds. The local switches will allow for balancing the temps and the pi will try and keep the temp profile you've programmed. You will.need to.set up the PID logic so they.match your kiln. Don't worry if the pi doesn't track at start up. It should follow within a degree after about 300F.
This is the simplest solution i think. Don't try multiple SSRs it's not necessary. I would have a main breaker near by or easily accessible. It seems that a 50 amp.breaker would be fine if not a bit overkill.
Ronald.
Anger is usually regrettable, kindness rarely. … <#m_23973019758288496_>
I also prefer to keep things as simple as possible. I assumed I was able to place the single SSR on one of " hot " legs of 240V power cable ( three wires 50 amp ). They had wired the top zone of this little kiln to one hot wire ( L2 ) and the middle+bottom of the kiln is wired to the other hot wire ( L1 ). With this configuration, I am not sure how to control all the power to all the zones with only one SSR. Could you take a look at the attached wiring diagram of the kiln and suggest how to proceed with the idea of controlling the kiln with only one SSR please?
H1500 L&L DynaKiln wiring diagram-worked - A-103X copy.pdf https://github.com/user-attachments/files/20971097/H1500.L.L.DynaKiln.wiring.diagram-worked.-.A-103X.copy.pdf
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I'd like to help but I don't know what the switches do. I can guess but that's all. WITH NO POWER CONNECTED you could take a VOM and find out what the switches do. To do this make a table. Position 1 : A connects to what B connects to what Same for all three positions. It seems that the original system ran I'm some positions with elements on 120 volts and the max went to 240. I wish I was close by as the challenge is not hard but trying to.help.remotely is very difficult. The simplest solution would be to use all elements together going to.one SSR powered by 240. No.connection the neutral. This would be like a domestic 240 oven. This won't help to balance the temperatures . Another suggest is use the pi only for monitoring and control kiln manually. It works well for that. Sorry not to.be more help. Ronald. …
Thank you for taking the time to reply. In fact your suggestion for ignoring the switches and " binding " all the heating elements to be powered as an electric oven is similar to what the electrician is calling the plan B. This kiln is small enough to fire uniform enough that way. I have contacted L&L tech also. Occasionally they help with user friendly cases of maintenance ( of their own machines ). They might have a suggestions.
Last idea when you have all the elements connected as one you or the electrician can determine the current load. Then choosing a single SSR will be better. The reason for using a SSR is that the pi system switches often and a contactor would be worn out quickly. SSRs dont worry about that. Best and let us know how it worked out. One of the best things about the pi control is that you can monitor the kiln from your phone . I often start late in the day and check from my bed during the night. ronald.
On Sun, Jun 29, 2025 at 8:47 PM TinMaan @.***> wrote:
TinMaan left a comment (jbruce12000/kiln-controller#219) https://github.com/jbruce12000/kiln-controller/issues/219#issuecomment-3017678550
I'd like to help but I don't know what the switches do. I can guess but that's all. WITH NO POWER CONNECTED you could take a VOM and find out what the switches do. To do this make a table. Position 1 : A connects to what B connects to what Same for all three positions. It seems that the original system ran I'm some positions with elements on 120 volts and the max went to 240. I wish I was close by as the challenge is not hard but trying to.help.remotely is very difficult. The simplest solution would be to use all elements together going to.one SSR powered by 240. No.connection the neutral. This would be like a domestic 240 oven. This won't help to balance the temperatures . Another suggest is use the pi only for monitoring and control kiln manually. It works well for that. Sorry not to.be more help. Ronald. … <#m_-8472039619795077475_>
Thank you for taking the time to reply. In fact your suggestion for ignoring the switches and " binding " all the heating elements to be powered as an electric oven is similar to what the electrician is calling the plan B. This kiln is small enough to fire uniform enough that way. I have contacted L&L tech also. Occasionally they help with user friendly cases of maintenance ( of their own machines ). They might have a suggestions.
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-- Anger is usually regrettable, kindness rarely.
The schematic shows that each element is 120V. It is a bit weird, it is not a balanced load, L1 has 2x the load as L2. Each knob/switch gets a Neutral and a Hot, either L1 or L2. Top switch, L2 and N (120V), and the bottom 2 switches, L1 and N (120V). No elements have both L1 and L2 (240V).
The way to rewire and run it on 240v is to run each pair of elements in series as defined below. This will create 120V drop per element, which is what the switched high setting would have been. Get rid of the switches. I have found that one of the issues with old kilns is all the electrical contacts are a bit corroded, and the resistance adds up and people think it is an element problem. Have your electrical buddy turn the kiln on high and measure the voltage of each of the 6 elements. I am pretty sure it will be 120V. If you want to control zones, 3 thermocouples and 3 SSR/relays, and do it in software.
If 120V/element, then this will work: L1---element1----element2----L2 L1---element3----element4----L2 L1---element5----element6----L2
If you choose to do this, use this math: (the kilns rated Watts)/240 = Amps. Then (Amps x 1.25) is the minimum breaker size and is what the wire should be sized for. 25amps * 1.25 = 31.25amp, you can fudge it a bit and use 30 amp breaker and #10 awg wires, or if running over 20' then #8 awg wire on a 40amp breaker. 45amps * 1.25 = 52.25, so a 60 amp breaker, #6 awg and if you are running wire over 20' use #4 awg I say calculate the amps, because if it is running 120v elements and you convert to 240v, the amps may be different, but the Watts will be the same.
I am pretty sure the knobs work the way they did on my Skutts: My skutts use 240V per element.
All of these are 120V Low: 1 element of each pair is on (L2---element1 ---N) (L1---element3 ---N) (L1---element5 ---N) Med: all elements are on, but run in series of 2, each element drops 60V (L2---element1---element2---N) (L1---element3---element4---N) (L1---element5---element6---N) High: all 6 element are on in parallel (L2---element1---N) (L2---element2---N) (L1---element3---N) (L1---element4---N) (L1---element5---N) (L1---element6---N)
At 240V: you would wire it like the med setting: each element drops 120V. (L1---element1---element2---L2) (L1---element3---element4---L2) (L1---element5---element6---L2) And it would output like the high 120v setting.
I would switch it with a SSRs. These 2 SSR configurations will switch both L1 and L2 at the same time: Double Pole, Double Throw (DPDT), which has both NO and NC, but you only use the NO contacts (Normally Open); Double Pole, Single Throw, which I have only seen Normally Open (NO). I used 3 relays (about $20 each), one for each pair of elements. I use relays, but my switching frequency is once every 30 seconds. At high switching rates SSRs will be a better choice. I mount everything in an external box about 1 meter away from the kiln. Put heatsinks on SSRs and move some air over them. If you use 1 SSR, use one that is rated at about 1.5x the Amps of the kiln calculated above.
Use high temp appliance wire, glass fibre insulated, also appliance crimp terminals. They are plated steel and take some muscle to crimp. The crimper is different than the one used for normal terminal crimps. Amazon has both.
The schematic shows that each element is 120V. It is a bit weird, it is not a balanced load, L1 has 2x the load as L2. Each knob/switch gets a Neutral and a Hot, either L1 or L2. Top switch, L2 and N (120V), and the bottom 2 switches, L1 and N (120V). No elements have both L1 and L2 (240V).
The way to rewire and run it on 240v is to run each pair of elements in series as defined below. This will create 120V drop per element, which is what the switched high setting would have been. Get rid of the switches. I have found that one of the issues with old kilns is all the electrical contacts are a bit corroded, and the resistance adds up and people think it is an element problem. Have your electrical buddy turn the kiln on high and measure the voltage of each of the 6 elements. I am pretty sure it will be 120V. If you want to control zones, 3 thermocouples and 3 SSR/relays, and do it in software.
If 120V/element, then this will work: L1---element1----element2----L2 L1---element3----element4----L2 L1---element5----element6----L2
If you choose to do this, use this math: (the kilns rated Watts)/240 = Amps. Then (Amps x 1.25) is the minimum breaker size and is what the wire should be sized for. 25amps * 1.25 = 31.25amp, you can fudge it a bit and use 30 amp breaker and #10 awg wires, or if running over 20' then #8 awg wire on a 40amp breaker. 45amps * 1.25 = 52.25, so a 60 amp breaker, #6 awg and if you are running wire over 20' use #4 awg I say calculate the amps, because if it is running 120v elements and you convert to 240v, the amps may be different, but the Watts will be the same.
I am pretty sure the knobs work the way they did on my Skutts: My skutts use 240V per element.
All of these are 120V Low: 1 element of each pair is on (L2---element1 ---N) (L1---element3 ---N) (L1---element5 ---N) Med: all elements are on, but run in series of 2, each element drops 60V (L2---element1---element2---N) (L1---element3---element4---N) (L1---element5---element6---N) High: all 6 element are on in parallel (L2---element1---N) (L2---element2---N) (L1---element3---N) (L1---element4---N) (L1---element5---N) (L1---element6---N)
At 240V: you would wire it like the med setting: each element drops 120V. (L1---element1---element2---L2) (L1---element3---element4---L2) (L1---element5---element6---L2) And it would output like the high 120v setting.
I would switch it with a SSRs. These 2 SSR configurations will switch both L1 and L2 at the same time: Double Pole, Double Throw (DPDT), which has both NO and NC, but you only use the NO contacts (Normally Open); Double Pole, Single Throw, which I have only seen Normally Open (NO). I used 3 relays (about $20 each), one for each pair of elements. I use relays, but my switching frequency is once every 30 seconds. At high switching rates SSRs will be a better choice. I mount everything in an external box about 1 meter away from the kiln. Put heatsinks on SSRs and move some air over them. If you use 1 SSR, use one that is rated at about 1.5x the Amps of the kiln calculated above.
Use high temp appliance wire, glass fibre insulated, also appliance crimp terminals. They are plated steel and take some muscle to crimp. The crimper is different than the one used for normal terminal crimps. Amazon has both.
Thank you for this thorough and complete " How to ". I learned a lot. Yes you are correct about those switching knobs. One of them has lost one step and another one intermittently disconnects. The electrician said, he might be able to replace them with new ones. Good point about the heating elements being 120V. With that, they have to be powered separately on each hot leg ( two of the in parallel ) I found a similar case in archives of Ceramic Daily. Somebody had tried to convert his older SKUTT kiln ( with kiln sitter and switching kmobs ) to run on cheap PID controllers - SSR combined. Other members cautioned about the usual concerns about the use of SSRs and the need for additional safety contactor etc. But generally they agreed with the concept of wiring and idea. Here is the OP wiring diagram:
I think the simple run all levels at 240 with one SSR and use the pi controller is the easiest. It's simple cheap and reliable. Other ideas are great but this is an old kiln and KISS really applies unless you have time and money..if you have the later buy a new kiln. The old ones are not efficient as insulation is far better now so operational cost will be lower.
On Sun, Jun 29, 2025, 9:57 PM TinMaan @.***> wrote:
TinMaan left a comment (jbruce12000/kiln-controller#219) https://github.com/jbruce12000/kiln-controller/issues/219#issuecomment-3017800498
The schematic shows that each element is 120V. It is a bit weird, it is not a balanced load, L1 has 2x the load as L2. Each knob/switch gets a Neutral and a Hot, either L1 or L2. Top switch, L2 and N (120V), and the bottom 2 switches, L1 and N (120V). No elements have both L1 and L2 (240V).
The way to rewire and run it on 240v is to run each pair of elements in series as defined below. This will create 120V drop per element, which is what the switched high setting would have been. Get rid of the switches. I have found that one of the issues with old kilns is all the electrical contacts are a bit corroded, and the resistance adds up and people think it is an element problem. Have your electrical buddy turn the kiln on high and measure the voltage of each of the 6 elements. I am pretty sure it will be 120V. If you want to control zones, 3 thermocouples and 3 SSR/relays, and do it in software.
If 120V/element, then this will work: L1---element1----element2----L2 L1---element3----element4----L2 L1---element5----element6----L2
If you choose to do this, use this math: (the kilns rated Watts)/240 = Amps. Then (Amps x 1.25) is the minimum breaker size and is what the wire should be sized for. 25amps * 1.25 = 31.25amp, you can fudge it a bit and use 30 amp breaker and #10 https://github.com/jbruce12000/kiln-controller/issues/10 awg wires, or if running over 20' then #8 https://github.com/jbruce12000/kiln-controller/issues/8 awg wire on a 40amp breaker. 45amps * 1.25 = 52.25, so a 60 amp breaker, #6 https://github.com/jbruce12000/kiln-controller/issues/6 awg and if you are running wire over 20' use #4 https://github.com/jbruce12000/kiln-controller/issues/4 awg I say calculate the amps, because if it is running 120v elements and you convert to 240v, the amps may be different, but the Watts will be the same.
I am pretty sure the knobs work the way they did on my Skutts: My skutts use 240V per element.
All of these are 120V Low: 1 element of each pair is on (L2---element1 ---N) (L1---element3 ---N) (L1---element5 ---N) Med: all elements are on, but run in series of 2, each element drops 60V (L2---element1---element2---N) (L1---element3---element4---N) (L1---element5---element6---N) High: all 6 element are on in parallel (L2---element1---N) (L2---element2---N) (L1---element3---N) (L1---element4---N) (L1---element5---N) (L1---element6---N)
At 240V: you would wire it like the med setting: each element drops 120V. (L1---element1---element2---L2) (L1---element3---element4---L2) (L1---element5---element6---L2) And it would output like the high 120v setting.
I would switch it with a SSRs. These 2 SSR configurations will switch both L1 and L2 at the same time: Double Pole, Double Throw (DPDT), which has both NO and NC, but you only use the NO contacts (Normally Open); Double Pole, Single Throw, which I have only seen Normally Open (NO). I used 3 relays (about $20 each), one for each pair of elements. I use relays, but my switching frequency is once every 30 seconds. At high switching rates SSRs will be a better choice. I mount everything in an external box about 1 meter away from the kiln. Put heatsinks on SSRs and move some air over them. If you use 1 SSR, use one that is rated at about 1.5x the Amps of the kiln calculated above.
Use high temp appliance wire, glass fibre insulated, also appliance crimp terminals. They are plated steel and take some muscle to crimp. The crimper is different than the one used for normal terminal crimps. Amazon has both.
Thank you for this thorough and complete " How to ". I learned a lot. Yes you are correct about those switching knobs. One of them has lost one step and another one intermittently disconnects. The electrician said, he might be able to replace them with new ones. Good point about the heating elements being 120V. With that, they have to be powered separately on each hot leg ( two of the in parallel ) I found a similar case in archives of Ceramic Daily. Somebody had tried to convert his older SKUTT kiln ( with kiln sitter and switching kmobs ) to run on cheap PID controllers - SSR combined. Other members cautioned about the usual concerns about the use of SSRs and the need for additional safety contactor etc. But generally they agreed with the concept of wiring and idea. Here is the OP wiring diagram:
Kiln Controller - DIY.pdf https://github.com/user-attachments/files/20972850/Kiln.Controller.-.DIY.pdf
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I think the simple run all levels at 240 with one SSR and use the pi controller is the easiest. It's simple cheap and reliable. Other ideas are great but this is an old kiln and KISS really applies unless you have time and money..if you have the later buy a new kiln. The old ones are not efficient as insulation is far better now so operational cost will be lower. …
Yes, that's how I intended to do this. But the in person inspection of the kiln by an electrician and understanding the wiring is forcing me to take the alternative rout:
- The top zone of the kiln is wired to one hot leg of 240V and the middle combined with bottom zone is wired to the other hot leg.
- The heating elements are all 120V individually.
- In order to fire and control all the heating elements with one SSR I will have to change over the heating elements to 240V type. At this point it seams a lot more convenient to control each 120V leg of the three-wire 240V separately and keep the switching knobs in place for the fine tuning the zones with trial and error. I also assume two separate sets of controllers will have a better chance to fine tune the PID and keep the heating more uniformly and that is just the bonus point. Unless I am missing something as usual.
You just connect the 120 elements in series 2 together make a 240 volt.one You will then have 3 240 volt elements Top middle and bottom. You then connect these 3 in parallel making ONE 240 element equivalent. This will.have 2 ends one will.go to one of the 240 lines the other to the SSR and then to the other 240 v. Leg. Got it?
On Mon, Jun 30, 2025, 1:49 PM TinMaan @.***> wrote:
TinMaan left a comment (jbruce12000/kiln-controller#219) https://github.com/jbruce12000/kiln-controller/issues/219#issuecomment-3020650685
I think the simple run all levels at 240 with one SSR and use the pi controller is the easiest. It's simple cheap and reliable. Other ideas are great but this is an old kiln and KISS really applies unless you have time and money..if you have the later buy a new kiln. The old ones are not efficient as insulation is far better now so operational cost will be lower. … <#m_7680685199186093139_>
Yes, that's how I intended to do this. But the in person inspection of the kiln by an electrician and understanding the wiring is forcing me to take the alternative rout:
- The top zone of the kiln is wired to one hot leg of 240V and the middle combined with bottom zone is wired to the other hot leg.
- The heating elements are all 120V individually.
- In order to fire and control all the heating elements with one SSR I will have to change over the heating elements to 240V type. At this point it seams a lot more convenient to control each 120V leg of the three-wire 240V separately and keep the switching knobs in place for the fine tuning the zones with trial and error. I also assume two separate sets of controllers will have a better chance to fine tune the PID and keep the heating more uniformly and that is just the bonus point. Unless I am missing something as usual.
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You just connect the 120 elements in series 2 together make a 240 volt.one You will then have 3 240 volt elements Top middle and bottom. You then connect these 3 in parallel making ONE 240 element equivalent. This will.have 2 ends one will.go to one of the 240 lines the other to the SSR and then to the other 240 v. Leg. Got it? …
Yes, yes it sounds quite simple to do. I will sketch a simple diagram for sanity check with you before getting it done. BTW, in this configuration what will happen to the neutral wire of 240V cable ( three wire 240V )?
No connection to neutral.unless you want a 120 supply for pi controller set up.
On Mon, Jun 30, 2025, 2:15 PM TinMaan @.***> wrote:
TinMaan left a comment (jbruce12000/kiln-controller#219) https://github.com/jbruce12000/kiln-controller/issues/219#issuecomment-3020773611
You just connect the 120 elements in series 2 together make a 240 volt.one You will then have 3 240 volt elements Top middle and bottom. You then connect these 3 in parallel making ONE 240 element equivalent. This will.have 2 ends one will.go to one of the 240 lines the other to the SSR and then to the other 240 v. Leg. Got it? … <#m_-6475798148111481329_>
Yes, yes it sounds quite simple to do. I will sketch a simple diagram for sanity check with you before getting it done. BTW, in this configuration what will happen to the neutral wire of 240V cable ( three wire 240V )?
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No connection to neutral.unless you want a 120 supply for pi controller set up. …
here is the simplistic schematics digram for creating the three sets of 240v elements in parallel I am going to make. Is this correct?
Looks good to me. If you wanted to add 3 switches you could turn on or off the 3 coils . You might need to do this to keep temperatures even. Use the k type thermocouple. The pi works fine with that. You'll need the little board that has the chip that reads the thermocouple and sends it to the pi. I like the Adafruit one. If you haven't set up a kiln the instructions on the site are very good. Ronald
Anger is usually regrettable, kindness rarely.
On Mon, Jun 30, 2025, 4:19 PM TinMaan @.***> wrote:
TinMaan left a comment (jbruce12000/kiln-controller#219) https://github.com/jbruce12000/kiln-controller/issues/219#issuecomment-3021130120
No connection to neutral.unless you want a 120 supply for pi controller set up. … <#m_6922550330858412810_>
here is the simplistic schematics digram for creating the three sets of 240v elements in parallel:
H1500.L.L.DynaKiln.wiring.diagram-mod.240v.Elements.jpg (view on web) https://github.com/user-attachments/assets/f8c5f97f-a8eb-47ff-8ae6-905747f9760b
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Looks good to me. If you wanted to add 3 switches you could turn on or off the 3 coils . You might need to do this to keep temperatures even. Use the k type thermocouple. The pi works fine with that. You'll need the little board that has the chip that reads the thermocouple and sends it to the pi. I like the Adafruit one. If you haven't set up a kiln the instructions on the site are very good. Ronald
Anger is usually regrettable, kindness rarely. …
I understand the theory of schematics. Each pair of originally 120V heating elements wired in series to function as one 240V heating element. What I don't understand is how the same 120V coil can physically withstand 240V?
Yes, I have the better quality K type thermocouples and the Adafruit brand Max31855 board. I have been experimenting with a test set up ( hot lamp and low heat cheap thermocouples etc. ). Also I've been thinking about setting up toggle switches for each set of elements. Next is fitting everything in the project box(s) and configuring the kiln. As usual I will call the electrician to check everything before firing.
A third wire for a case ground is needed. If the controller is using 120v for a pi power supply, then you need a 4th wire for neutral, or a second circuit providing 120v.
On Mon, Jun 30, 2025 at 6:19 PM TinMaan @.***> wrote:
TinMaan left a comment (jbruce12000/kiln-controller#219) https://github.com/jbruce12000/kiln-controller/issues/219#issuecomment-3021130120
No connection to neutral.unless you want a 120 supply for pi controller set up. … <#m_-405882763906408979_>
here is the simplistic schematics digram for creating the three sets of 240v elements in parallel:
H1500.L.L.DynaKiln.wiring.diagram-mod.240v.Elements.jpg (view on web) https://github.com/user-attachments/assets/f8c5f97f-a8eb-47ff-8ae6-905747f9760b
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-- Blake C. Lewis
Otherwise the schematic looks correct
On Mon, Jun 30, 2025 at 10:18 PM Blake Lewis @.***> wrote:
A third wire for a case ground is needed. If the controller is using 120v for a pi power supply, then you need a 4th wire for neutral, or a second circuit providing 120v.
On Mon, Jun 30, 2025 at 6:19 PM TinMaan @.***> wrote:
TinMaan left a comment (jbruce12000/kiln-controller#219) https://github.com/jbruce12000/kiln-controller/issues/219#issuecomment-3021130120
No connection to neutral.unless you want a 120 supply for pi controller set up. … <#m_-7101325894593173109_m_-405882763906408979_>
here is the simplistic schematics digram for creating the three sets of 240v elements in parallel:
H1500.L.L.DynaKiln.wiring.diagram-mod.240v.Elements.jpg (view on web) https://github.com/user-attachments/assets/f8c5f97f-a8eb-47ff-8ae6-905747f9760b
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-- Blake C. Lewis
-- Blake C. Lewis
A third wire for a case ground is needed. If the controller is using 120v for a pi power supply, then you need a 4th wire for neutral, or a second circuit providing 120v. …
The control box(s) will be powered with 120v wall plug-in ( through a small UPS ) as we get brownouts and short ( merely seconds ) blackouts in our region. I have been thinking about grounding the kiln wiring. Can I use the neutral wire of my three-wire 240 cable for grounding the kiln?
Otherwise the schematic looks correct …
It's great to know. I really couldn't imagined this project would be this involved. Honestly, I think a Bartlett V6 at about $200 gets the job done. Buy, hey - I learned a lot and that makes the whole troubles worthwhile. Thank you for all the help.
In electronics they call it voltage drop. With 2 elements (the elements match) in series, each will drop half the voltage. For 240V, if you measure across one of the elements, the voltage would measure 120V.
The way it was wired, on either medium or low (can't remember which), 2 elements are run in series. With the 120V setup, measure across 1 of the elements, and it will be 60V.
On Mon, Jun 30, 2025 at 10:13 PM TinMaan @.***> wrote:
TinMaan left a comment (jbruce12000/kiln-controller#219) https://github.com/jbruce12000/kiln-controller/issues/219#issuecomment-3021592213
Looks good to me. If you wanted to add 3 switches you could turn on or off the 3 coils . You might need to do this to keep temperatures even. Use the k type thermocouple. The pi works fine with that. You'll need the little board that has the chip that reads the thermocouple and sends it to the pi. I like the Adafruit one. If you haven't set up a kiln the instructions on the site are very good. Ronald
Anger is usually regrettable, kindness rarely. … <#m_7212971468493681476_>
I understand the theory of schematics. Each pair of originally 120V heating elements wired in series to function as one 240V heating element. What I don't understand is how the same 120V coil can physically withstand 240V?
Yes, I have the better quality K type thermocouples and the Adafruit brand Max31855 board. I have been experimenting with a test set up ( hot lamp and low heat cheap thermocouples etc. ). Also I've been thinking about setting up toggle switches for each set of elements. Next is fitting everything in the project box(s) and configuring the kiln. As usual I will call the electrician to check everything before firing.
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-- Blake C. Lewis
When two 120 volt coils are in series to make a 240 volt one each of the coil gets 120 volts . The connection between the two needs to be very solid. I don't know what wires some out of the kiln but making good connections with hot ( temperature) wires is not trivial. It's best if connections are made where it's cooler.. Ronald.
On Mon, Jun 30, 2025, 8:29 PM TinMaan @.***> wrote:
TinMaan left a comment (jbruce12000/kiln-controller#219) https://github.com/jbruce12000/kiln-controller/issues/219#issuecomment-3021615647
A third wire for a case ground is needed. If the controller is using 120v for a pi power supply, then you need a 4th wire for neutral, or a second circuit providing 120v. … <#m_-2679994029260490230_>
The control box(s) will be powered with 120v wall plug-in ( through a small UPS ) as we get brownouts and short ( merely seconds ) blackouts in our region. I have been thinking about grounding the kiln wiring. Can I use the neutral wire of my three-wire 240 cable for grounding the kiln?
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You can use the neutral wire as most ovens do that. It's better to use a ground wire that doesn't get used to carry any power. I have done it both ways and although I am an EE I'm not an electrician who has to live with building codes!
On Mon, Jun 30, 2025, 8:38 PM ron doctors @.***> wrote:
When two 120 volt coils are in series to make a 240 volt one each of the coil gets 120 volts . The connection between the two needs to be very solid. I don't know what wires some out of the kiln but making good connections with hot ( temperature) wires is not trivial. It's best if connections are made where it's cooler.. Ronald.
On Mon, Jun 30, 2025, 8:29 PM TinMaan @.***> wrote:
TinMaan left a comment (jbruce12000/kiln-controller#219) https://github.com/jbruce12000/kiln-controller/issues/219#issuecomment-3021615647
A third wire for a case ground is needed. If the controller is using 120v for a pi power supply, then you need a 4th wire for neutral, or a second circuit providing 120v. … <#m_1125471559917791791_m_-2679994029260490230_>
The control box(s) will be powered with 120v wall plug-in ( through a small UPS ) as we get brownouts and short ( merely seconds ) blackouts in our region. I have been thinking about grounding the kiln wiring. Can I use the neutral wire of my three-wire 240 cable for grounding the kiln?
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