Problem with ATX PSU for RAMPS 1.4 with Heated Bed



I’ve purchased a Ramps 1.4 + Arduino mega + heatbed MK2B Bundle from aliexpress and am trying to get it to work. First I used a “Led PSU” which could barely power the setup (it was a weak one, just for testing). Then I took an ATX PSU and did the necessary preparations according to this guide: . Now I have everything hooked up and am using the +5V 1.0-30A and +12V1 0.5-19A configuration. Problem is, that when I plug it in the RAMPS 1.4 connector, it turns on and everything lights up, but as soon as I want to draw power to heat the heatbed up, it shuts down, the entire PSU. Then after a few minutes, I can turn it back on again, but as soon as I want to draw power again, it immediately turns off. Since my skills with electronics are very limited, I was hoping that any of you could help me troubleshoot my issue and help resolve it.

Many Thanks in advance!

Here are Images of my PSU and the cables I’ve soldered to:


Hi Sd,

I’d really want to see where those leads from your PSU plug into the RAMPS. The RAMPS wants two 12V connections, providing a combined minimum 20A rating. What it sounds like is happening is you are providing 5V (which is what a USB connector might send). This will power the electronics just fine. As soon as you turn on the heatbed, you are demanding an additional 20A at 12V. If you don’t have that, the RAMPS trips its polyfuse(s) and shuts down until the fuse cools and resets.

So, make sure you are providing the necessary voltage and current to the two sets of power blocks on the RAMPS.



the rams itself needs 5-6 A (the right side of the connector)
the rest should be 14-15 A

the main problem is that the atx psu doesn’t provide the 15A on one single rail but on maybe 3 or 4.
You have to combine them.


Dear Stefan,

My 5V line is (afaik) connected to the socket labelled “PS” which I guess stands for power supply. The 12V line is connected to the second socket.
But if the Ramps trips its fuse, my PSU shouldn’t lose power as well, right? The thing is, the PSU shuts down as well…


thank you.



Dear Moorviper,

According to my PSU’s capabilities, I have the following options available:

and you suggest, I add another combination or two, to get to the required Power output. (how do I know I won’t fry my electronics?)

Thanks in advance,



Hi SD,

I think Moorviper and I are converging on the same explanation. It is most likely that you are not providing the RAMPS with enough current. The power supply will probably cut off if you are putting too high a demand on it (a good thing, as it will protect itself). Triple check how much current is being sent to the RAMPS under load.



Thank you Stefan, I will check and will of course let you guys know asap!

Many thanks to you too, Moorviper!


Is your ATX labeld Haswell compatible or Haswell ready. If not and by your issue description shut down as soon as a higher load is drawn you might have issue with an unbalanced 12V rail. Especially an issue with older ATX pre 2014
Regard Richard


Sometimes the heatbeds are out of specs my mk3 bed should draw around 200w and it draws 350-360w to much for my 12v 20A power supply.

Now the printer is running full with 24v and the supply can deliver 420w which is just a little to small but it works


Ugg, I forgot about that. Absolutely right. Check the resistance (ohms) of your heatbed. The RAMPS doesn’t want to go over 10-11 amps, which means that your bed needs to have a resistance of about 1.5 ohms. (MV, check my math!)



alex kenis has a great series of ramps related videos: