Large Silicone Heat bed 500mm x 500mm power supply and wiring?



  • This is my first project with the Duet Wifi so I am very new here. I'm looking to use the Duet wifi with this KEENOVO 500mm x 500mm 1600w 120v silicone heated bed.

    What kind of power supply would be needed to make this work and how could that be wired to the Duet wifi? From the setup wiki, it is not apparent how you would supply a heated bed at this wattage. Also, I have not picked out the stepper motors or anything so I'm pretty flexible on that.

    I appreciate the advice in advance!



  • You would need to use an AC solid state relay to switch mains voltage.

    Check this out: https://duet3d.dozuki.com/Wiki/Choosing_a_bed_heater


  • administrators

    @SensibleDesign a 120v heater is going to be powered from mains (A/C) power.

    This is accomplished through the use of a DC-AC relay, which is sort of like a fancy type of switch. There are two types of relays mechanical where there is literally a physical switch, and solid state where the switching happens using a circuit.

    Essentially what happens is when a relay has power across one side of it, it actives the switch which allows power to flow through the other side of it. You would then use this to turn on and off the mains circuit and power the bed.

    More information here: Duet Documentation: Choosing a Bed Heater

    There are many places you can buy these relays online (eBay, Amazon, Alibaba, etc...).

    A word of caution, mains voltage is no joke and relays - in particular solid state relays - can fail "closed" meaning that it could fail in such a way that it would leave your bed heater on. A 1600w bed heater is going to be capable of achieving some remarkable temperatures left unchecked. Further complicating this situation is that the way we use our printers they have the ability to turn the relay on and off very frequently and this can increase the likelihood of failure. I would be wary of super cheap relays as they tend to be knockoffs and have been known to fail more often. I personally spent about $30 on mine and got a premium brand because the last thing I wanted was a melted relay causing a fire. Not trying to scare you off, I use a mains heater and I love it, but do not skimp on safety when it comes to 3D printing especially if you are powering anything with mains voltage.

    -M2

    ----edit to provide some additional links --
    Duet Documentation: Choosing Stepper Motors
    Duet Documentation: Choosing A Power Supply
    Amazon: Opto 22 120v 25A DC-AC relay



  • @msquared

    Thank you so much for the quick reply guys. It is clear I need to use a relay and that I don't want to be a cheap about it! @MSquared what premium relay would you recommend in this situation?

    I would like the option of leaving my printer monitored without worrying about it failing and leaving the heat bed on. A good relay will be a big part of this it seems. I also see in the docs that you could install a thermal cutout to disconnect the heater at a certain temp. Do you recommend this too? Or is this unnecessary with a good relay?


  • administrators

    @sensibledesign said in Large Silicone Heat bed 500mm x 500mm power supply and wiring?:

    @msquared

    Thank you so much for the quick reply guys. It is clear I need to use a relay and that I don't want to be a cheap about it! @MSquared what premium relay would you recommend in this situation?

    I would like the option of leaving my printer monitored without worrying about it failing and leaving the heat bed on. A good relay will be a big part of this it seems. I also see in the docs that you could install a thermal cutout to disconnect the heater at a certain temp. Do you recommend this too? Or is this unnecessary with a good relay?

    I updated my post with a link to the relay I use. It's possibly overkill on a Duet because the Duet is designed to make lesser relays usable, but I already had it and would probably go that route again just for peace of mind.

    Full disclosure I do not have a thermal cutoff switch, but I plan on installing one soon. One can never be too safe. I would tell you "I have never had an issue" because I have not, but that is the weakest argument ever when it comes to keeping things safe.

    -M



  • @msquared

    Thanks for the relay link. Is there any documentation on wiring a bed with a relay to the duet?

    My next question is about the power supply for the heated bed. What kind of power supply will I need to supply the necessary power for this bed? Will i need something that can get 1600w? I assume that's what we connect the power supply to the relay and back to the board? Then do we need a separate power supply for the duet board and motors themselves? Still trying to figure this out. Sorry for my ignorance. Thanks!



  • With an AC heat bed you only need a PSU large enough for your DC components. The bed heater draws its power directly from the wall socket. The Duet simply tells the relay to turn the power on and off as needed.

    For example, I have a Meanwell 200 watt DC PSU powering my printer, and a 600 watt silicone heater on the bed controlled through a Fotek SSR. There is a thermal cut out fuse inline with the bed power cable attached to the bottom of the bed.

    Fotek SSR: https://www.amazon.com/Fotek-SSR-40DA-Solid-state-relay/dp/B01I5HRTEO
    Thermal Cut out: http://www.be-electronics.com/product_p/ecg8149.htm

    At this point you should be doing a lot of reading. The links already provided will be a good start.

    http://www.sublimelayers.com/2016/03/how-to-choose-ssr-to-drive-your-heated.html


  • administrators

    @SensibleDesign You are very welcome. Here is a VERY poorly drawn diagram of the way my heated bed is connected.

    0_1523264316873_Heated Bed Diagram.png

    This circuit is pretty basic, but due to the elements involved (mains power, heaters, etc...), I would be 1000% sure you know exactly what you are doing before attempting to recreate anything like this. Before you attempt to build anything like this be certain you understand all of the pieces involved as you are quite literally playing with fire 🙂

    To that end, I am happy to continue to share my knowledge, experience, and resources; and as @Phaedrux mentioned there is a lot of good information out there you should probably seek out as well!

    -M2



  • If you are using mains earth (ground) your printer and fuse the feed to the heated bed. If there is any failure in the heater that increases its draw, or a wiring short to ground failure it is more likely to blow the fuse. Fuse level should be no more than 80% of the rated current of the cabling. Cabling should be sized so the expected draw is within the rated limit of the cable and it does not introduce a significant voltage drop.

    In addition the Duet can be set up to kill the power to heaters using the PSU_ON pin on one of the headers. I'm not using mains voltage but I have set the system up using the PSU_ON to open/close a breaker that interrupts the mains side of the PSUs used for the heaters and steppers on the system, but not the fans or duet power supply.



  • @Phaedrux Thank you for the links, I'm definietely going to install a thermal cut out after all this discussion. Will read up more as well on heated beds and SSR

    @MSquared Thanks for the drawing! I really appreciate it. I'm a very visual person so this is great for my understanding. I will make sure I'm 100% confident in my circuit before doing. Will read up more as well. Might reach out in the future with questions!



  • I found this site very helpful when I was designing my own bed. I followed his principles if not the exact implementation.

    https://drmrehorst.blogspot.ca/2017/07/ultra-megamax-dominator-3d-printer-bed.html



  • @phaedrux Thank you sir. Any more articles on wiring other components would be helpful if you know of any. Stepper motors, extruder, etc. This is very good one though that will help me with my bed design


 

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