Control dual heaters of the same heatbed.



  • Is it possible to have dual heaters at the same heat bed?

    I am wondering if it is possible to have a "hybrid" AC+DC heatbed. With a high power AC to speed up heating time up to a specified temperature and a lower power DC element for keeping the temperature.



  • Physical possible - Yes.

    Possible from the way that Duet/RepRap has inputs / outputs for control of a heater - Not directly... it may be possible to do it externally. For example, I can imagine the following:

    • Wiring a low voltage bed heater to the Duet, just like normal, except maybe a bit lower wattage. This is the "maintenance" heater.

    • Wiring the low-voltage side of an SSR (Solid State Relay) to the heater output on the Duet. The high voltage side of this SSR would control the AC (mains) heater. This is the "boost" heater, for quick heat up.

    • Wiring a thermal sensor of some kind, either physical or electronic, that goes "open" at about 45C, in series with the low voltage side of the SSR.

    This would cause the AC (mains) heater to run when the bed is commanded to heat AND the bed temp is below 45C.

    Don't know if that would affect PID tuning any. Probably be OK in actual operation, given that the initial heating phase is just "ON". Probably would mess up auto-tune, given that it times things. So you'd probably want to leave PID at default, and/or set it by hand.



  • Having said all of that, it would seem to be needlessly complicated and to no real advantage.

    You'd still have all the setup to make the AC (mains) heater work and be safe... and add on top of that additional stuff for the low voltage heater... all to accomplish what exactly??

    AC heaters work just great via PWM to maintain the bed.



  • Why not just use the AC heat without the DC part? The AC bed is low wattage (current draw) and works very well.

    Just curious is all.



  • @danal said in Control dual heaters of the same heatbed.:

    all to accomplish what exactly??

    I am planning to use a DC UPS for my printer - that excludes the use of an AC heated bed as if the power fails it will cause a thermal runway due to the bed cooling down. But I would like to have the benefits of a quick heating up heated bed 😄



  • Another situation would be a huge area printer with a segmented heated bed - where I can head only 1/4 of it, for example, when using "area 1" and the firmware would know that - that I have four heaters at the same printer and a series of possible combinations of them (1/4, 1/2, full bed)


  • administrators

    @brunofporto said in Control dual heaters of the same heatbed.:

    @danal said in Control dual heaters of the same heatbed.:

    all to accomplish what exactly??

    I am planning to use a DC UPS for my printer - that excludes the use of an AC heated bed as if the power fails it will cause a thermal runway due to the bed cooling down. But I would like to have the benefits of a quick heating up heated bed 😄

    To get the advantage of faster heat up times, I would suggest having the AC and DC heaters producing about the same power, assuming you run them both during heat-up.

    The sole advantage would be that you could get the fast heatup time using a smaller DC PSU and UPS, because they would only need to provide half the maximum total bed heating power. Is that really an advantage? If you want to go on printing for some time using UPS power alone, you will need a beefy UPS anyway, because a smaller UPS will generally have a smaller battery.



  • @brunofporto said in Control dual heaters of the same heatbed.:

    @danal said in Control dual heaters of the same heatbed.:

    all to accomplish what exactly??

    I am planning to use a DC UPS for my printer - that excludes the use of an AC heated bed as if the power fails it will cause a thermal runway due to the bed cooling down. But I would like to have the benefits of a quick heating up heated bed 😄

    Of course, this also depends on how long an outage you plan to cover. I use a small UPS with my big printers that have AC beds. During brief outages, up to several minutes, the bed temp doesn't change that much. Given that the print is unlikely to "let go" until the bed temp changes by -15C or more, the "no heat during outage" could probably cover up to 10 or 15 minutes.

    Longer outages? Very, very, rare where I live. I'll put up with those.

    In fact, that's been the pattern at my house. Power out is either a few seconds, or many, many, many, hours (beyond any reasonable UPS).

    .

    Of course, that's my use case. Your situation may be different.



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  • @brunofporto said in Control dual heaters of the same heatbed.:

    Another situation would be a huge area printer with a segmented heated bed - where I can head only 1/4 of it, for example, when using "area 1" and the firmware would know that - that I have four heaters at the same printer and a series of possible combinations of them (1/4, 1/2, full bed)

    I'm actually building a printer now that will have a zoned heatbed and while I'm building it initially with Arduino/Marlin electronics, I was thinking of switching to Duet3D as an upgrade. I was going to work on the Marlin code to do this in software and expand G-code to support it. Has there been any work on this for RepRap? I could also write similar code once I switched over.



  • @kerseyfabrications A simple macro could change the configurations between areas. But I am not sure how it will control multiple all heaters as one.


  • administrators

    @kerseyfabrications said in Control dual heaters of the same heatbed.:

    @brunofporto said in Control dual heaters of the same heatbed.:

    Another situation would be a huge area printer with a segmented heated bed - where I can head only 1/4 of it, for example, when using "area 1" and the firmware would know that - that I have four heaters at the same printer and a series of possible combinations of them (1/4, 1/2, full bed)

    I'm actually building a printer now that will have a zoned heatbed and while I'm building it initially with Arduino/Marlin electronics, I was thinking of switching to Duet3D as an upgrade. I was going to work on the Marlin code to do this in software and expand G-code to support it. Has there been any work on this for RepRap? I could also write similar code once I switched over.

    RepRapFirmware on the Duet WiFi/Ethernet already supports up to 4 bed heaters, see https://duet3d.dozuki.com/Wiki/GCode#Section_M140_Set_Bed_Temperature_Fast.



  • @dc42 That's great! Thanks for the reply! Is this reflected on a display somehow? Meaning can I see the temperatures of all four heaters? Also, do you know any printer using this today?


  • administrators

    PanelDue only supports displaying one bed temperature. I think Duet Web Control will display all of them, but I haven't confirmed that. I'm fairly sure someone is already using multiple bed heaters because I implemented it in response to a particular request.



  • @dc42 said in Control dual heaters of the same heatbed.:

    .............. I'm fairly sure someone is already using multiple bed heaters because I implemented it in response to a particular request.

    That would be @justine-haupt in this thread https://forum.duet3d.com/topic/3516/using-multiple-bed-heaters. She's using 4 bed heaters with a Duet.

    Edit. BTW, I found that by just searching this forum for "multipe bed heaters". It seems the form search funtion works really well.



  • @deckingman My apologies for wasting your time.

    @dc42 Thank you for the support. I'm seriously considering ordering one of these now once I've finished figuring out what all I need.



  • @kerseyfabrications
    Oh, I didn't mean that in a derogatory or critical fashion. If you think that is the case, then I apologise in turn. It was meant as a "for future reference" comment.
    If we all used the search function more (myself included) then we might get the information we need faster than starting a new thread and awaiting a response.
    HTH



  • @deckingman No problem. It's so difficult to tell online sometimes, especially the way some people are in forums. I didn't mean to jump to conclusions.



  • @kerseyfabrications said in Control dual heaters of the same heatbed.:

    @deckingman No problem. It's so difficult to tell online sometimes, especially the way some people are in forums. I didn't mean to jump to conclusions.

    No worries. As you say, without the benefit of facial expressions, it's sometimes difficult to understand the meaning behind a comment.



  • @deckingman said in Control dual heaters of the same heatbed.:

    It seems the form search funtion works really well.

    It is really dumb and obvious when I use the right set of words to search something I was struggling to find information about 😄


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