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Installing a MK3 heated bed

Why install a heated bed?

The glass plate covered with a Buildtak does its job. Usually the objects stick well and are reasonably easy to remove, at least as far as PLA is involved.
With ABS you often will experience warping(ABS doesn't like it cold), objects not sticking enough or on the contrary sticking too much (if you increase the flow or narrow the space between the bed and the nose) and removing the object can be an almost impossible mission resulting in a rapidly damaged Builtak (which replacement is not cheap).

With a heated bed, you can get ABS sticking better and it's a one time and for all investment.

Which heated bed install?

Two models are an easy replacement for the Glass/Buildtak pair.
Both are available on the ReprapMe website
MK2 is a PCB only heated bed.
;Mk2.jpg
Main specs are :
Dimensions 214 x 214mm
12V/10A, 120W
Mounting holes 4x ø3mm. 5mm from edge in each corner.
Resistance ~1.2ohm


MK3 is an Alu heated bed with 3mm Aluminum core and Dual power.
Mk3.jpg
Main specs are :
Dimensions 214 x 214mm
3mm aluminum build plate. Print directly on the heatbed, no need for glass plate.
Dual power supply. Operate at 12 Volt or 24 Volt.
Resistance at 12 Volt is between 1.0 and 1.25 Ohm (115~144 Watt). At 24 Volt between 4.0 and 5.0 Ohm (144 ~115 Watt)


What do you need to install a Heated bed?

Heatbed.jpg

  1. Power Supply
    The stock power supply of the Vertex is not powerful enough to power the heated bed.
    You have 2 options :
    1. Add a 2nd Power supply
      • 24V-150W for the MK3.
      • 12V-150W or 15V-200W for the MK2.
    2. Replace the stock power supply with a more powerful one :
      • 15V-350W for both MK2 and 3.

    SNTMW150.jpgSNT HRP 300 XX.jpg

  2. Heated Bed
    Mk2.jpg or Mk3.jpg

  3. 100K Thermistor
    Ntc100k-1206 sp.jpg

  4. Thermal Insulator
    Insulator.jpg

  5. Glass plate
    Not necessary for the MK3 but required for the MK2
    You can use the one provided with the Vertex.

  6. Power expander
    The on board MOS-fet can't take the current needed for the heated bed so you need to insert a dedicated circuit that can.
    Two options :
    1. Buy a ready made one :&
      PW expander.jpg
    2. Build one yourself :
  7. Connectors and wires
    • one 2 pins and one 4 pins Molex connector to plug on the controller board.
    • 2 x 0.5 or 0.75 mm wires for the heated bed. Smaller wires for the +15/24V and the thermistor.
  8. Soldering iron and solder


Below you can find the schematics and implantation to build a power expander yourself :
Mosfet b.png

Pcb-layout.png

Components list :

1x IRLU8743PbF MosFet
1x SFH610A-1 Optocoupler
1x 1N4148 Diode
1x 1.2K Resistor
1x 2.2K Resistor
1x 2.7K Resistor
2x 2-pole Terminal block
1x 4-pole Terminal block
1x Strip Grid PCB


Connecting things together

Heatbedconnect.jpg


Modifying the G-code

Before you can get your bed heating, you still have to make some modifications to the Cura settings.
  • First you have to define a bed temperature for each of your filament settings :

Curabedpla.jpgCurabedabs.jpg

  • Then you need to modify the Start and End G-codes :
Start G-code
G28 ; Home extruder
G1 Z5 F{Z_TRAVEL_SPEED}
G1 Z0 F{Z_TRAVEL_SPEED}
G90 ; Absolute positioning
M82 ; Extruder in absolute mode
{IF_BED}M190 S{BED}
M106 S80 ; Turn on fan
; Activate all used extruder
{IF_EXT0}M104 T0 S{TEMP0}
{IF_EXT1}M104 T1 S{TEMP1}
....
End G-code
G1 X0 Y0 Z130 ; Get extruder out of way. Uncomment to use!
; Disable all extruder
G91 ; Relative positioning
{IF_EXT0}T0
{IF_EXT0}G1 E-1 ; Reduce filament pressure
M104 T0 S0
{IF_EXT1}T1
{IF_EXT1}G1 E-1 ; Reduce filament pressure
M104 T1 S0
G90 ; Absolute positioning
G92 E0 ; Reset extruder position
M140 S0 ; Disable heated bed
M84 ; Turn steppers off
M107 ; Turn off fan
....
  • If you want to use the Preheat bed function of the LCD screen, you have to set the desired temperature in the configuration.h file of the marlin firmware :
    search for #define PLA_PREHEAT_HPB_TEMP 0 and #define ABS_PREHEAT_HPB_TEMP 0 and replace the zeros with the temperatures you want.


The Heatbed in place :
Headbed mounted.jpg

24V Power supply :
Psu24v.jpgPsu frame.jpg

Home made Power extender :

Heatbed pwe.jpg Power ext.jpg


Printing...

Headbed printing.jpg


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