Heat bed wires get hot (12 V connected to RAMPS 1.4 shield)


I'm using a 200x200 mm PCB Mk2B which connects to the MOSFET of the D8 pin on a RAMPS 1.4 shield. I used 12 V power source for heat bed so I connected positive to pin 1 and negative to both pin 2 & 3 of the bed. Heat bed worked properly. But the wires that connects power source to power supply pin on RAMPS were being heated badly. I think the problem is come from heat bed because when I unplugged heat bed, wires were cool down instantly.

Can someone helps me with this problem. I'm just a newbie in this area.


Posted 2020-03-16T03:19:53.250

Reputation: 31

Its normal for the wires in a 12v system to get hot. What was the bed temp? how long was the print? – user77232 – 2020-03-16T15:34:25.243

The bed temp is 60 degree. The wires were getting hot just after the print begun. But replaced the wire with a thicker ones had solved the problem – DrPortgas – 2020-03-18T09:33:23.557

What AWG did you use? (NB: it supposed to be printed on the cable) – user77232 – 2020-03-18T12:39:45.577



The PCB heatbed Mk2B has a reported resistance between 1.0-1.2 Ω. The current that is drawn from the power supply equals about 12/(1.0 or 1.2) = 10-12 A. Note that this amount of current requires cables that can carry that load, too thin cables heat up.

Note that you have wired the bed correctly for 12 V (see image below), the wires might have a too-small cross-section, try thicker wires. Personally I use AWG 12-14 silicone wires depending on the bed resistance.

Mk2B heatbed connections

AWG 12-14 size silicone, multiple threads (these are the best for the bed because they are more flexible), should be able to handle the load fine. Note that cables also have resistance; if there are heat spots in the cable or the connection, this indicates that the cable may be broken or the connection has too much resistance.


Posted 2020-03-16T03:19:53.250

Reputation: 25 570

1Yes, the heat spots were indicated in the cable. I will replace its with a thicker ones. Thanks for your help – DrPortgas – 2020-03-17T01:57:39.763

@DrPortgas, don't use that machine again until you replace that cable. – user77232 – 2020-03-17T12:38:46.957

yes, i had replaced the cable and its works very well. Thank a lot – DrPortgas – 2020-03-18T09:29:32.367


Check the diameter of the cable. The smaller the diameter the higher the resistance, thus the heat. AWG14 seem a bit small.


Posted 2020-03-16T03:19:53.250

Reputation: 11

Sure, i will check again the diameter of the cable – DrPortgas – 2020-03-17T01:58:32.267

114 awg should be sufficient. Moving to 12 awg won't really reduce the heat. – user77232 – 2020-03-17T12:37:14.280