Printer heat bed randomly stops heating

Hey all!
Let me preface this with an apology for the length of this post.
Sorry. I'll put a TL;DR at the bottom (too long, didnt read).

I got my 3d printer just before thanksgiving and FINALLY have time to play with it. It is the pre-assembled ABS version (model ROBOABS001). I'm using a windows 7 (64bit) operating system, with RoBo 3d Repetier-Host 3D Printer Software V0.90D, that I downloaded off the robo3d site. The driver was automatically installed with the software, and I'm able to send manual commands to the printer once it is connected, and after i hit the Home button.

I want to print the 25mm calibration cube (search calibration cube on thingaverse, and its the first result); but the problem is that the printer heat bed wont rise to temperature. I've made sure that when I sliced the model, I selected the ABS material (with the appropriate temp settings). When I go to the temperature curve, the heat bed starts rising, and some times will get as high as 87degrees...before it studdenly stops heating. The purple bars showing the desired temps are still in place, but the blue curve just starts declining. At this point no further commands are processed by the printer. I cant start/stop the fan, or anything else. During this process, the extruder line, the orangered one, does not increase. Once I have disconnected and reconnected by hitting "emergency stop", and regained control by hitting the home button; i can chose to manually control and heat the extuder....which rises to 220 degrees just fine. I am even able to tell it to extrude, which works quite well. With the extruder at 220, i have manually told the bed to start heating...and will not respond untill it has cooled to 30degrees, at which point it begins heating and will randomly decline (usually at or just before 70 degrees). I again lose control of the printer and am forced to use emergency stop.

I have tried using a different computer, with the same operating system and software; thinking it may be a USB problem. I even went and got a powered USB hub to ensure the microcontroller in the printer was properly powered. The same thing happens.
I have not yet tried to print PLA plastic ( a small batch was provided), but instead I had purchased a spool of white ABS plastic.

Can anyone advise me on what to do? Is there a malfunctioning part on my printer? I would like to find out soon, so I can sent it for repairs during the warranty period.
Thanks!

TL;DR: Printer is connected and responds to commands, but the heat bed randomly cuts out and stops heating. As such no prints will process since the gcode has them waiting until the bed reaches the correct temp. Whats wrong?

 

You need to add in a solid state relay. The problem is the RAMPS board has circuitry with a heat sensitive switch that shuts down when things get too hot. By wiring in a solid state relay directly from the power supply to the heated bed which is triggered by the RAMPS board means that power isn't going through the RAMPS board and heating things up.

Another option is to add a fan to cool the RAMPS board. Several people have had success at that.

Cambo3D has created a schematic/drawing of how to wire up the SSR. Make sure you use a good quality SSR.

http://forums.robo3dprinter.com/index.php?threads/heatbed-and-bed-leveling.841/page-2#post-5466

 

Thanks so much Melody! I'll look into it right away. Do you have any recommendation for the model of SSR? Cambo's diagram seems pretty clear, but I'm still a little apprehensive about my electronic circuitry skills. EE was never my strongest field, so I'm up for all the help I can get!

 

The SSR (SSR 25DD) that Cambo3D uses in the diagram is an excellent SSR. It can be found in Amazon.

http://www.amazon.com/gp/aw/d/B005X465KW/ref=mp_s_a_1_4?qid=1386653423&sr=8-4&pi=AC_SX110_SY165_QL70


Sent from my iPhone using Tapatalk

 

The other alternative is to replace the polyswitch on the ramps board with one that's higher rated. We're still testing it as a viable solution and would require desoldering skills. We'll know if it works tonight or tomorrow.

The SSR solution is a good one for no-soldering. Though be sure you have a fuse in line in case of a short circuit.

 

I changed the polyswitch and added a RAMPs fan. It worked for me.