Heatbed wont turn on after converting Wanhao duplicator I3 from Melzi to RAMPS

Hi.  I've looked everywhere I could online to find an answer, and haven't yet.  I believe my issue to be in the software/configuration, so hoping someone here can help.

Background: I bought a Monoprice Maker Select v2 (aka Wanhao DI3).  With only minor tweaking, it printed PLA great out of the box.  I started my first ABS print after a month of PLA prints, and it was struggling to reach temp... took the bed a long time to climb to ABS temps... and then there was smoke from the control box.  I unplugged everything, let it cool, and found that the heatbed connectors to the Melzi had melted.

Rather than RMAing the whole thing (which would have been a lot quicker, but much less 'fun'), or just replacing the connectors, I started looking at DIY options.  Ultimately ending up with RAMPS 1.4.   I've done a full replacement of the Melzi.  I'm running repetier firmware and host.  I even picked up an separate heatbed mosfet (Trigorilla).

From the host, all the controls (x,y,z,extruder and hotend) and sensors (stops and thermistors) work as expected, except for the heatbed.  When I turn on the heatbed, the RAMPS led lights up, the power supply buzzes, and the temp on the heatbed doesn't climb.  I've confirmed I have 12V going into the 5A input (that powers the onboard heatbed mosfet), but there's only 5V coming out of D8 when the heatbed is turned on in Repetier... shouldn't this be 12V?

I was suspect of my RAMPS board.  I tried with a new RAMPS and the results were the same.  For good measure I even tried a new Mega, with the same result. ...I even switched out a a new power supply, bupkis.  

I have to think this is a configuration issue, but haven't seen a setting in the arduino's configuration.h that looks plausibly related to this situation.  

What should I check next? 


  • RAMPS has 2 power connectors. One of them is for the heated bed, the other one for all other outputs. Sounds like you do not have power to the bed connector so it does not get correct power. Just bridge a cable to second input to get it powered.
  • The 5A input is for the motors and hotend,  the heatbed needs 12/24V on the 11A input
  • I do have sets of power wires running from my supply to both the 5A and 11A input.  I checked voltage on those connectors, and they both read 12V.

    For what it was worth, when I had the heatbed connected directly to the RAMPS (before I had the off-board heatbed mosfet connected), the mosfets on the RAMPS would get blazing hot.  I did google some articles that suggested that my mosfet wasn't getting proper trigger voltage.  It kinda still feels like the same problem, since there's only 5V coming off the D8.  I just don't know how to confirm or fix it if it is the problem.
  • So if it works without your mosfet is is a electronic problem. Not my field but are you sure you wired it correctly. Descriptions gives me impression that polarity etc. matters, but otherwise they also say it should work then with D8 output.
  • The bed hasn't worked right since I took out the Melzi and wired up the RAMPS... so I could have wired something wrong... it could be a polarity problem.  I'm sure I have the polarity right on the heatbed connections, but could any other connections' polarities affect the mosfets?  I'll go through everything tonight and report back.
  • As fas as I know polarity is important to mosfets. They only work in one direction.
  • Quick update: I posted into the reprap formus.  If this is a hardware problem, they may be able to set me straight.  I'll post back soon.
  • Hey all.  My new best friend Obewan in Reprap forums helped me figure out it was my heated bed configuration settings.  It's heating now, at least with bang-bang. It's not quite 100%, but its functional; I do need to spend some time calibrating.  

    Is there a standard Repetier/ramps config for Wanhao di3?  Or does everyone come up with their own? 
  • We have no standard configs for any printer. We leave that to vendors to produce them.
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