Once upon a time...

Once upon a time...
Christmas 2016

Monday 9 April 2012

Hot Bed Heat Up - Resolution

Thanks to the feedback from nophead, Triffid_Hunter & yngndrw on the forums, I have updated my wiring to overcome the short comings (pun intended) of the Sanquinololu.

The summary is as follows (based on the information gleaned from the three above):

The issues:

  • The molex connectors are rated for c.1A per pin.
  • The HotEnd's typically draw sub 2A
  • The heated bed draws about 11A
  • The pcb tracks are dubious
The solutions:
  • Use screw connectors instead of molex.  These are recommended by nophead anyway due to all the movement/vibration that these printer's undergo.  Triffid_Hunter seems to agree as his Sanguinololu also has screw connectors.
  • Bypass/supplement the PCB traces with additional trace reinforcement, suggested by Triffid Hunter
  • Connect the heated bed ground to the tab on the mosfet and the positive directly the the power supply using 13A wire, suggested by nophead.
  • Double up by using all 4 of the molex pins.  Mentioned by both nophead and yngndrw.
The implementation:
  • As I didn't have the parts (or the inclination to be soldering on my Sanguinololu), I elected to go for nophead's mosfet tab fix, as it is relatively straightforward
  • I also took the time to connect up the additional 2 pins on the HotEnd molex while I had the soldering iron out.


  1. Hi,
    Thanks for the excellent posts. I was wondering if you could help me since I add the same "melting" on the heatbed connectors.
    Is the nophead really that simple? you just use the - connector from the heatbed on the MOSFET and the + on any 12V on the PSU? Can it be any power part? My PSU is 600W rated at 34A on the 12V ATX, but can I connect it to any other power part?

    Thanks for the help.

  2. Hi there,
    Yes it really is as simple as nophead's solution. I have had my printer running as described in the post since April 2012 and have had no hints at a problem since then. It is My PSU is an old PC one rated at about 300W and handles it all fine. Make sure you use appropriately rated wire.

    Please also note that for my extruder I am using all 4 wires, i.e. 2+ve and 2-ve.

  3. That seems perfect, what kind of connecter you've used on the PSU side? I've noticed that on the Board you've used a Crimp Ring terminal, is it a 6mm? Thanks once again.

  4. I think it might be 6mm, just what I had in my toolbox. On the PSU side, I modded the PSU to have screw terminals, so on the PSU side I have the bare wire screwed down.