3D Printing (Part 14)

Part 123456789101112, 13, 14, 15, 16

The heating plate is made of two symmetric printed conductive layers ~1.5 Ohm each. As printed on the heating plate you may wire them for use with 12 V or 24 V power supplies. As we need to add an extra power supply the choice for a 24 V power supply is trivial as less current will flow through the switch and the wires. As the minimum power rating for the power supply is 192 W, a 200 W power supply (and above) will do the job without efforts.

Nota: When choosing the power supply, check for the thickness. Many power supplies are 50 mm high which will prevent a proper cooling because of the insufficient air gap below the power supply.

This is the power supply that I bought:

  • Voltage in: AC 110 V/220  v
  • Voltage out: DC 24 v
  • Current out: 0 to 10 A
  • Weight: 0.5 kg
  • Dimension: 165*99*39 mm
  • Enclosure: alumina
  • Protections: over voltages, over-currents, short-circuits
  • Operating temperature: 0 to 40°C
  • Humidity: 0 to 95%

For a few euros I went for an off the shelf power switch. I found no reason why I should spend time to built a more expensive one.

This switch is driven from the heat bed output of the Marlin board. The switching part is fully isolated with an optocoupler. The marked wire is the goes to the + terminal on the main board.

Next picture contains the schematics of the Marlin main board where I circled the heater control output and the temperature input:

Best is to use MTA-100 series connectors (1 x 2 pins and 1 x 4pins). However if you do not not have such connectors you may use headers as the pins spacing is 2.54 mm.

Nota: the wire gauge is so high (in other words, the wires are so thin) that I failed to crimp the wires in the connector so that I add to solder the wires in order to achieve a reliable connection.

Next pictures illustrate the configuration that I choose for installing the power supply and the switch. The idea was to keep the wires as short as possible and to leave the aperture unmasked as I find it very convenient for cleaning the cabinet.

Save a sufficient cable length so that the wires will not suffer from being twisted back and forth down to breakage. Check my suggestion in the next picture:

Before connecting all pieces together, check the power supply voltage

and the heater resistance

Before running any print, you need to update the slicer parameters.

Go to the Cura pane, click on the Filament pane and set the appropriate temperature: 50°C (more or less) for PLA and 100°C (more or less for ABS)

Then you might want to update the G-Code which is executed prior and after printing:

Start G-Code

g28 ; home
g90 ; absolute positioning
g21 ; set units to mm
g0 z5 f5000 ; extruder above bed
g0 x150 y15 f10000 ; move fast to front right
m190 s{BED} ; set extruder 0 temperature and wait for it
m109 s{TEMP0} ; set extruder 0 temperature and wait for it
g0 z0.2 f500 ; up tray (slowly)
g92 e0 ; reset extr length
g1 e10 f50 ; feed filament
g92 e0 ; reset extr length
g1 x50 e10 f500 ; print wire
g92 e0 ; reset extr length

This start G-Code feature a short print which allows a proper priming of the extruder, a nozzle cleaning and a simple printing quality check.

End G-Code

g0 z180; down tray
g91; Relative positioning
g1 e-1; retract filament
m104 t0 s0; switch off extruder temperature
g90; Absolute positioning
g92 e0; Reset extruder position
m140 s0; Disable heated bed
m84; switch off steppers
m107; switch off fan

And here we are at last !

I checked the heated bed with Xmas decoration. Thin stars (0.6 mm, so as to say 3 layers) were subject to wrapping. They are now perfect using the default 50°C bed temperature


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