Duet wiring recommendations



  • Hi all,

    First apologies for the long post.

    Got my Duet Ethernet board and Tevo Tornado a few days ago. Right now printing using Tevo controller. 3D printers take a long time to print and I live in a 1-bedroom apartment which I love. Also my building is a few decades old and the regulations here for existing electrical work is questionable at best. I don't want to put my faith on what protection the Tevo printer provides but feel free if all this is overkill and not required. I intend to rewire the printer to make it as safe as possible.

    I plan to house my Duet board in an all metal mini-ITX case.The printer frame will be housed inside an enclosure made with High Strength PVC sheets.(https://www.tapplastics.com/product/plastics/plastic_sheets_rolls/pvc_sheets/531 https://www.tapplastics.com/uploads/pdf/PVC_Ultra_White_Properties.pdf). These sheets have UL-94 V0 flammability rating, which is the highest rating possible. Optionally I will also add one of these (https://www.amazon.com/Fireball-Automatic-Fire-Extinguisher-HY-0500/dp/B0748MPFCS). Filament spool will be inside the enclosure and the mini-ITX case will be outside the enclosure on the table.

    I have attached a copy of the circuit I have envisioned.
    https://ibb.co/gVPL2x
    Other safety additions :

    1. Currently my printer is on top of a stainless steel table. The steel table will be covered with a polycarbonate sheet to provide insulation. If some cheaper option is available please suggest. With my 3d printer the circuit starts with a 15 amp C13 cable which will be connected to a C14 plug(Top-left on the diagram). This plug has a 5Amp 250V glass fuse. Is 5Amp glass fuse sufficient(I am in US 110V)? I can easily get glass fuses of 10-15-20 Amps.
    2. My apartment only has MCB and no AFCI/GFCI breaker. I am currently using my Tevo with a GFCI adapter because of the 110V heat bed and unprotected table. In my circuit the C14 terminals will be connected to a 20Amp AFCI/GFCI breaker (https://www.amazon.com/gp/product/B00LN74OO2. Using 20Amp because currently 15Amp is more expensive on Amazon.
    3. Then I will have an ESP32 external board to protect against thermal runaway, smoke, fire, duet malfunctioning, etc. At first I will only have a thermal sensor connected to the heat bed with a thermally conductive silicone. This silicone is graded up to 200 degree celcius https://www.amazon.com/gp/product/B072MSXHJD. This ESP32 will control the 40A master SSR. All printer components(24V PSUcomponents and 110V hot end) will be powered by this SSR. So if bed temperature rises above 120 Celsius ESP32 will shut everything down and send a notification to me. I will have a 5V 100 watt PSU to power Duet, ESP32 and front panel usb ports and this PSU will not be powered by the ssr. My main question here is that I have read that the thermally conductive silicone is also electrically conductive. Is this true? If yes what should I use to attach sensors reliably(not tape)?
    4. The output of the 1st SSR is connected to the 24V stock PSU and to the 2nd SSR. This SSR is triggered by the heat bed terminals of Duet. Output of this SSR is connected to the 110V probably 750 Watt heat bed. Would connecting multiple SSR in series be an issue? If SSR gets fused at ON position will AFCI trip? Should I use 1 SSR and 1 mechanical relay to spread my bets?
    5. 24V PSU output will be connected to the Vin and Gnd of Duet. This 24V will also be connected to a buck converter which will convert the voltage to 12V. I will use the 12V to power ALWAYS ON PC fans(I have Noctua Silent fans lying around). Are their any side effects of connecting a buck converter to PSU? I have not checked the power rating of stock PSU but if power seems insufficient I will upgrade.
    6. Since the tevo frame is not grounded, I will connect a wire to the frame + table + case and ground it.
    7. I want to use the ATX button on the case as POWER ON and 1-click emergency stop. I was thinking that I will connect it to the ESP32 and use the SSR connected to it to turn on/off the printer components. Of course the duet will be powered by the independent 5V psu so will always be available.
    8. I will be using 12 gauge(Tinned Copper Stranding: #680/0.08mm) wire for heat bed, 110V/24V wiring. 18 gauge for everything else.
    9. I have considered thermal fuses but am not clear about how to mount them(See point above electrically conductive silicone). Based on above protections is a thermal fuse required?
      Thanks for reading through all this and your feedback is highly appreciated.


  • @eorl_young:

    1. I will be using 12 gauge(Tinned Copper Stranding: #680/0.08mm) wire for heat bed, 110V/24V wiring. 18 gauge for everything else.

    do NOT use tinned copper stranding, the solder will melt and cause problems!!!
    Use ferrules instead!



  • eorl_young, your list of precautions sounds very thorough.

    To expand on what whosrdaddy said:

    Generally, any wire that is "clamped" in a screw fitting should NOT be soldered. No matter how much or how little the electrical current, the mechanical pressure alone will cause the solder to very slowly flow. This will loosen the pressure over time, causing more resistance, causing more heat, causing a degenerating circle.

    As mentioned, ALWAYS use a crimp on connector, sometimes called a "ferrule" or a "bootlace" connector. If you can't do that, then bare wire is clamped in the screw is still better than solder.



  • @eorl_young:

    With my 3d printer the circuit starts with a 15 amp C13 cable which will be connected to a C14 plug(Top-left on the diagram). This plug has a 5Amp 250V glass fuse. Is 5Amp glass fuse sufficient(I am in US 110V)? I can easily get glass fuses of 10-15-20 Amps.

    Depends on the wattage of the heat bed, more than anything else. The controller/motors will only draw a fraction of an amp on the 110V side. Below you said 750W 110V that's about 6 or 7 amps. So, yes, I'd go 10 Amp slo-blow

    My main question here is that I have read that the thermally conductive silicone is also electrically conductive. Is this true? If yes what should I use to attach sensors reliably(not tape)?

    Some are conductive, some are not. This should be specified in the data sheet for the individual thermal adhesive/paste.

    1. The output of the 1st SSR is connected to the 24V stock PSU and to the 2nd SSR. This SSR is triggered by the heat bed terminals of Duet. Output of this SSR is connected to the 110V probably 750 Watt heat bed. Would connecting multiple SSR in series be an issue? If SSR gets fused at ON position will AFCI trip? Should I use 1 SSR and 1 mechanical relay to spread my bets?

    Personally, I would use an SSR to PWM the Heat Bed itself (i.e. the 'second' SSR) and use a mechanical relay as the safety device (the 'first' one).

    1. 24V PSU output will be connected to the Vin and Gnd of Duet. This 24V will also be connected to a buck converter which will convert the voltage to 12V. I will use the 12V to power ALWAYS ON PC fans(I have Noctua Silent fans lying around). Are their any side effects of connecting a buck converter to PSU? I have not checked the power rating of stock PSU but if power seems insufficient I will upgrade.

    No issues that I see

    1. Since the tevo frame is not grounded, I will connect a wire to the frame + table + case and ground it.

    YES. And check if the frame is actually conductive across the various mechanical assemblies, and use short jumper wires where it is not.

    1. I have considered thermal fuses but am not clear about how to mount them(See point above electrically conductive silicone). Based on above protections is a thermal fuse required?

    Me, personally, I'd ditch most of what you are doing as overly complex (no offense) and just go with a single thermal fuse on the bed, and another in the enclosure, series wired to the first entry point of mains power. Given what you are doing, yes, I'd use a thermal fuse as the ultimate safety net.

    Other changes: I'd consider making the 5V supply subject to the first SSR (which I suggested above be a relay). Meaning, if the ESP32 decides to cut power, it should cut ALL power. The fire could be in the 5V areas… I've seen it happen. This does mean you need a way to power up, perhaps a momentary contact mechanical switch that bypasses the first SSR/Relay to get things going, or similar. Short version: If you are going to the depth of your original design, go all the way.

    Along those same lines, if you want an E-Stop, wire one of these into the 5V line leading to the first SSR/Relay. Again, go all the way.



  • Those kinds of estops are $5 to $10 on ebay.



  • @whosrdaddy:

    @eorl_young:

    1. I will be using 12 gauge(Tinned Copper Stranding: #680/0.08mm) wire for heat bed, 110V/24V wiring. 18 gauge for everything else.

    do NOT use tinned copper stranding, the solder will melt and cause problems!!!
    Use ferrules instead!

    @Danal:

    eorl_young, your list of precautions sounds very thorough.

    To expand on what whosrdaddy said:

    Generally, any wire that is "clamped" in a screw fitting should NOT be soldered. No matter how much or how little the electrical current, the mechanical pressure alone will cause the solder to very slowly flow. This will loosen the pressure over time, causing more resistance, causing more heat, causing a degenerating circle.

    As mentioned, ALWAYS use a crimp on connector, sometimes called a "ferrule" or a "bootlace" connector. If you can't do that, then bare wire is clamped in the screw is still better than solder.

    Thanks, whosrdaddy and Danal. I will not be using solder anywhere. Only ferrule connectors, heat shrink crimp connectors(ring, hook, butt), lever nuts(connect multiple wires) and jst. Does you point against tinned copper still stand? What type of stranding should I use then?



  • Hi eolr_young, I must say I am wrong, I incorrectly thought that tinned copper is the same as soldered copper.
    So it should be fine (when used in combination with ferrule)



  • Danal based on you responses:

    1. Replace glass fuse to 10A

    Personally, I would use an SSR to PWM the Heat Bed itself (i.e. the 'second' SSR) and use a mechanical relay as the safety device (the 'first' one).

    I don't understand this point as the heat bed is AC. How will I use PWM with AC current and does this require addition of a 3rd SSR???

    Me, personally, I'd ditch most of what you are doing as overly complex (no offense) and just go with a single thermal fuse on the bed, and another in the enclosure, series wired to the first entry point of mains power. Given what you are doing, yes, I'd use a thermal fuse as the ultimate safety net.

    No offense taken. This is overly complex and along with safety implications I also want to do this to see what I am capable of designing. I am in software and believe in writing defensive code and that has probably flown into my hardware design. But your point is well taken. Thermal fuses should be in my protection scheme as they are reliable and easily solve many of the problems I am solving using SSR's.
    So I should mount the thermal fuse in series with the heatbed and then attach the fuse to the bed using proper epoxy.
    As a side question how do you connect the thermal fuse to 12 AWG wire. Butt connectors I have are 10-12 AWG both sides and if the fuse is not 12AWG the butt connector will not work. Also butt connectors will probably melt when heated.

    Other changes: I'd consider making the 5V supply subject to the first SSR (which I suggested above be a relay). Meaning, if the ESP32 decides to cut power, it should cut ALL power. The fire could be in the 5V areas… I've seen it happen. This does mean you need a way to power up, perhaps a momentary contact mechanical switch that bypasses the first SSR/Relay to get things going, or similar. Short version: If you are going to the depth of your original design, go all the way.

    What is I just replace 5V PSU with a USB jack charger 5V 2A connected to a USB hub. The hub will power the ESP32. Then I can connect the ATX on/off switch for my case to the ESP32 and use it as a switch to turn on/off the 24V PSU.

    Will also incorporate the E-Stop switch in the design. And for relay I have an optocoupler isolated electromagnetic relay rated at 250VAC 30A which should fit nicely.


 

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