I had my 3D printer powered by dual 24 V PSUs wired in parallel and my heatbed was wired into the main using a SSR to help power it. I replaced the two PSUs with a single Corsair 750 W ATX. My printer runs smoother and there's much less wiring clutter to deal with but now no matter what the heatbed will not heat up.

The main connection of the ATX I purchased is an 8 pin connection so I tried using all 4 wires to power my printer and it didn't make a difference, I tried using the SSR again using 2 connections from the ATX leaving the other 2 to run the motherboard but that didn't work either. I even tried MOSFET and that also failed. I don't see why the Heatbed no longer heats up yet the thermistor is more accurate and working properly since my switch to the ATX, do I need to go up to a 1000 W ATX instead? I can't imagine what more I could do.

Schematic of PSU, bed, control board and SSR

  • 1
    $\begingroup$ i don't see how the ATX would connect to a main-powered heater, at all. You should be connecting the bed heater signal wire or the post-mosfet wire to the SSR; it only needs 5v and 0.02A to fully turn on. It's unclear how you have everything wired, a schematic or diagram would sure help. Keep in mind that an SSR that switches AC will not work with DC. $\endgroup$
    – dandavis
    Sep 18, 2020 at 8:22
  • $\begingroup$ The bed isn't connected to the GND in your sketch. The bed needs to be in the loop with the ATX PSU, it is not now. $\endgroup$
    – 0scar
    Sep 18, 2020 at 15:44
  • $\begingroup$ There is no ground on my board just positive and negative terminals. How/ where would I ground the connection $\endgroup$
    – LDF
    Sep 18, 2020 at 15:56
  • $\begingroup$ So I tried using one of the grounds on the ATX and grounding the power supply to the SSR but that didn't work either. Nothing makes this heatbed heat up but it worked before with the SSR when it was connected to 24V 360 W standard PSU. I don't see the difference it should work if I'm feeding more wattage through now. $\endgroup$
    – LDF
    Sep 18, 2020 at 18:50
  • $\begingroup$ First of all, make sure SSR is controlled. Unplug all the bed wires and test it first. Test the wiring. 1000% I give you, you made a mistake while wiring. $\endgroup$
    – Martynas
    Sep 18, 2020 at 20:34

2 Answers 2


You indicated that you were using 24 volts, implying you have a 24 volt bed. ATX power supplies do not have 24 volt outputs. The highest is 12 volts which would heat up the bed, but not fast or probably to full temperature.

  • $\begingroup$ So if I to use a 12 V to 24 V step up converter for the bed could work as a solution that would allow me to keep the ATX in place $\endgroup$
    – LDF
    Sep 19, 2020 at 1:28
  • $\begingroup$ @LDF, If you need to step it up, ensure that the mosfet is on the output side of the boost convertor. Flicking one of those on and off is going to produce some "explosive" results. $\endgroup$
    – user77232
    Sep 19, 2020 at 2:52
  • $\begingroup$ @user77232: actually the mosfet is likely just in front of ground, not the output; n-chan fets run cooler and work better. $\endgroup$
    – dandavis
    Sep 21, 2020 at 2:52

voltage = current x resistance

An ATX PSU is designed to only allow approximately 16 amps per pair of YELLOW and BLACK wires. The yellow is 12 V and the black is GND. If your bed were rated at 24 V then its resistance would be higher than that of the 12 V bed. The best solution for you would be to get a 12 V heated bed, as opposed to using a boost converter. Reason being is that you would need to get a boost converter that can tolerate over 200 W of power! It's just cheaper to replace the bed.

Finally, you need to consider the heat bed, the extruders and the steper motor's power needs before you purchase a PSU. If you had a multimeter with a current measurement, then you could accurately determine how much power each one uses and then purchase to size. Based on your bed size (600 mm) I think that 500 W should be enough.


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