Stock configuration

  • Previous bed heating was Kapton (polyamide) style. 
  • Heating element was bonded to borosilicate glass bed with double sided adhesive tape. 
  • The the bottom of the element was insulated with a sheet of cork. The cork was sagging into the Y axis belt drive mechanism. 
  • Heating element cabling is repurposed ribbon cable with tripled up parallel conductors on each of the power lines to handle the necessary current (increase ampacity).
  • Heating element resistance is 1.2 Ohms.  V/R = I (12V/1.2R = 10A)  ~120Watts
  • Heating element power is switched by two parallel MOSFETs on the RAMPS PCBA. (these get very hot and fail commonly, not being used IAW manufacturer documentation)
  • Heated bed MOSFETs are not actively cooled or sinked into any thermal mass. 

Post Modification

  • New bed heating element is silicone. 
    • Signswise 200x200mm 12V 220W Silicone Rubber Heating Heater for 3D Printer Heated Beds 
      Signswise 
      Link: http://a.co/d/bCBSjx8
  • Silicone heating element will be bonded to borosilicate glass bed with double sided thermal adhesive sheets.
    • Gizmo Dorks 3M 468MP Adhesive Transfer Tape Sheets 8" x 8" (5-Pack) 
      Gizmo Dorks 
      Link: http://a.co/d/hMhrvf2
  • The Silicone heater will not be installed with an insulator. Low risk of sagging
  • Heating element cabling is QTY. 2 14AWG red silicone insulated wires. (very flexible)
  • Heating element resistance is 0.6 Ohms V/R = I (12V/0.6R = 20A)  ~240Watts
  • DC Solid state relay (SSR) has a switching capacity of 25A, significant passively cooled heat sink. (Fan can be added if install in a location without airflow)
    • Ogrmar Solid State Relay SSR-25 DD DC-DC 25A 3-32VDC/5-200V DC SSR-25DD with Heat Sink 
      by Ogrmar 
      Link: http://a.co/d/i5SM7Dq
  • DC solid state relay will receive its "ON" commands from the heated bed FET outputs of the RAMPs boards. (Previously attached directly to the heated bed power leads.)

WARNING: Be sure to purchase a DC rated SSR which are less common than their AC cousins. AC SSR's latch closed when used with DC power. (They tend to close and stay closed regardless of command signal) Your heated bed will turn on and dead short to the power supply.  This could cause serious damage or fire if not de-energized quickly.

Other suitable high current MOSFET based switching modules.

ANYCUBIC 3D Printer Heating Controller MKS MOSFET for Heatbed Extruder MOS Module 
ANYCUBIC 
Link: http://a.co/d/1y3vxQn

BIQU Heat Bed Power Module Expansion Hot Bed MOS Tube for 3D Printer 
BIQU 
Link: http://a.co/d/gV1afo0

ReliaBot Hot Bed Power Expansion Board Heating Controller MOSFET High Current Load Module Over 30A 12V or 24V for 3D Printer 
ReliaBot 
Link: http://a.co/d/1SxmKC1

Post Upgrade Power Assessment

It's always a good idea to reassess the power requirements of your printer after performing a major upgrade.  My primary motivation for this  assessment is to understand the impact of installing the new 240W build plate heater. 

The ROBO 3D R1 stock power supply is capable of delivering 12VDC 30A (360W). With that said, the power supply is of suspect quality and a as a Manufacturing Engineer, I consider it prudent to derate lightweight power supplies without a brand name on them. 

For my assessment, I will consider the power supply capable of delivering 300W which could pose a problem if my build plate heater now consumes 240, leaving 60W for everything else. 

Power Roll-up

394W total in worst case scenario conditions. This puts me well over the 300W derating threshold and 34W over the stock power supply's advertized 360W rating....

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