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Under Bed Insulation -> Faster bed heating and better temperature control

Discussion in 'Mods and Upgrades' started by Ziggy, Dec 22, 2014.

  1. Ziggy

    Ziggy Moderator
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    I finally got around to adding under bed insulation to my Robo. I’ve also added a purpose built Solid State Relay to avoid over heating of the RAMPS polyfuse and the mosfet. In my case the bed is the kickstarter 3mm thick borosilicate.

    Before the under bed insulation and SSR were added the heated bed was taking more than 10 minutes to get to 115C and struggling to hold temperature. To verify this @Galaxius has done a test on a unmodded Robo which shows it took 14 minutes to reach 115C and needed full power to hold temperature.

    temp graph 1 - 14min to 115c from 29c ambient .png

    The next screenshot shows that after the mod the bed temp profile from ambient (23c) to 115c is 6 minutes. Power to hold the bed at 115c is reduced to approximately 60 - 65%. TBH I was surprised by the dramatic improvement.

    bedtemp006.jpg

    The insulation material I used is a type of reflective foil used widely in the building industry (in Australia anyway). Brand names in Australia are Sisalation, HardieWrap and WallWrap.

    IMG_0471.JPG IMG_0470.JPG

    The foil is thin (less than 1 mm) but very tough and is attached underneath the bed foil side up using kapton tape. The reflective surface improves thermal performance without the need for any kind of bulk insulation (eg such as cork) which would interfere with the Y belt. The foil also has a high fire rating (ie low flamability)

    To get this better performance I also had to recalibrate the Marlin heated bed PID values in configuration.h. With the old PID values for the bed, the firmware paused the faster temperature rise way too early.

    To update the bed PID, make sure #define PIDTEMPBED is uncommented in configuration.h and use gcode M303 to run bed PID tuning and display the new heated bed PID values Kp, Ki and Kd. Update these values

    #define DEFAULT_bedKp ?
    #define DEFAULT_bedKi ?
    #define DEFAULT_bedKd ?

    in configuration.h, recompile and reflash the firmware.

    I’m very interested to hear any feedback from anyone using similar foil insulation.
     
    #1 Ziggy, Dec 22, 2014
    Last edited by a moderator: Dec 22, 2014
    jim3Dbot, Paul Yeh, Galaxius and 2 others like this.
  2. John Durr

    John Durr Member

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    Hi

    have you posted where you purchased your ssr and any installation pictures?

    I saw your posts on the fake ones from ebay.
     
  3. Tony Janus

    Tony Janus Member

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    Is the SSR necessary? Also, I had a similar idea and picked up some DEI 2" Exhaust Wrap based on a lava rock formulation (http://www.amazon.com/gp/product/B0039Z1UHA/ref=oh_aui_detailpage_o09_s00?ie=UTF8&psc=1 it says titanium, but that's the color of the wrap, not the material). It's heavy, but I'll be upgrading the y-axis stepper with a planetary geared stepper motor to compensate for the extra inertia. Plan on using 3M Hi-Strength 90 Spray Adhesive to attach it.

    Should this not work, I was also considering 1 or 2 layers of ceramic fiber insulation. I've used some that's found on amazon.com (http://www.amazon.com/gp/product/B00I5093KU/ref=oh_aui_detailpage_o05_s00?ie=UTF8&psc=1) on my hotend and plan on wrapping that in a thin layer of aluminum to keep the fibers clean.

    I'll be performing this upgrade after doing the 330mm y-axis upgrade (this thing has a 2nd version that requires longer rods & belt: http://www.thingiverse.com/thing:439036/#comments)

    Any opinions on either of these 2 methods?
     
  4. Ziggy

    Ziggy Moderator
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    SSR is my own design. It is opto isolated, has very low on resistance and just gets warm under the full load of the heated bed.

    An SSR is not absolutely necessary, but it means the polyfuse on the RAMPS is no longer a problem with over heating and the RAMPS mosfet does not get hot. Overall, having the SSR saves a few watts (which are better used heating the bed) and avoids any bed cut outs due to overheating of the polyfuse.

    IMG_0492_mod.png

    I am getting some professional PCBs made for the SSR design as they are useful in many projects.

    Re the insulation material:

    First requirement is the insulation needs to be thin (ideally < 1 mm). Reason is there is very little clearance under the bed and above the Y axis pulley, idlers and belt. The sisalation (brand name) I am using is very thin 0.11 mm (and consequently very light). I think similar material in the US is called ActicFoil.

    Second I am convinced reflective insulation (radiant barrier) gives a better result than thermal resistance, conductive type insulation (eg fibreglass, cork, exhaust wrap etc) in this particular under bed application. This demo


    shows the incident radiant heat is being reflected back by the radiant barrier - which is exactly what we want under the heated bed.
     
    #4 Ziggy, Dec 28, 2014
    Last edited by a moderator: Dec 28, 2014
  5. Tony Janus

    Tony Janus Member

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  6. Ziggy

    Ziggy Moderator
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    I think the problem with the roll of foil (radiant barrier) tape is the tape would stick to the bed foil side out. You actually need to have the reflective surface facing the under side of the bed.

    One possible solution is shiny aluminum foil lightly glued onto thick paper (like some drawing paper or cardboard). Place this foil side facing the underside of the bed and use kapton tape around the edges to secure it to the bed. You actually want some air gap between the bed and the reflective foil surface so the radiant barrier works properly. I haven't tested this, but the principle is exactly the same as the "sisalation" I used or ActicFoil.
     
    #6 Ziggy, Dec 28, 2014
    Last edited by a moderator: Dec 28, 2014
  7. Tony Janus

    Tony Janus Member

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  8. Ziggy

    Ziggy Moderator
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  9. Galaxius

    Galaxius Well-Known Member

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    I'm using 2 layers of aluminium foil and a layer of baking paper held on with kapton tape successfully. Though the kapton tape doesn't really sick to the baking paper, hence the grid of tape to help hold it up. I'm using this until I can get a hold of some sisalation, but I'm in no rush to change since it works well.
    It's important to run the kapton tape all the way around the edge of the foil to keep the heat in. Covering a larger area than just the heater means the heat can spread through the glass a little further, I think :)
    [​IMG][​IMG][​IMG]
     
  10. Steven Stowell

    Steven Stowell New Member

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    Galaxius

    May I ask if you have the part numbers for the SSR you built and the schematic. I would like get some parts on order and build one for a fellow printer and my self as well.

    Thanks in advance
    Steve
     
  11. Robert Choban

    Robert Choban Active Member

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    What does SSR mean
     
  12. Mike Kelly

    Mike Kelly Volunteer

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    Solid State Relay
     
  13. Ziggy

    Ziggy Moderator
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    @Steven Stowell

    SSR circuit is as in the eagle schematic attached.

    Mosfet is type IRL1404 http://www.irf.com/product-info/datasheets/data/irl1404.pdf
    Similar type is ok but make sure the on resistance is at least as low as the IRL1404

    Opto Coupler is 4N25 http://www.vishay.com/docs/83725/4n25.pdf but any similar type eg TIL111 would be ok.

    SSR_Circuit.png

    I had some SSR printed circuit boards made by OSH PARK (What a fantastic service that guy offers!!) - I am testing these to make sure they can handle the bed current.
     
    #13 Ziggy, Feb 4, 2015
    Last edited by a moderator: Feb 4, 2015
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  14. Steven Stowell

    Steven Stowell New Member

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    Thanks. I can make the board mymyself. I have the opto just need the mosfett.
    Thanks again.
     
  15. Robb

    Robb Member

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    I plan on adding this insulation this weekend. Can someone recommend a good 4 pin connector for the heated bed and therm? I'm worried about getting something that can withstand the heat.
     
  16. Galaxius

    Galaxius Well-Known Member

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  17. Robb

    Robb Member

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    I like it! Easy and cheep insulation.
     

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