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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.

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  • $\begingroup$ Its normal for the wires in a 12v system to get hot. What was the bed temp? how long was the print? $\endgroup$ – user77232 Mar 16 '20 at 15:34
  • $\begingroup$ 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 $\endgroup$ – DrPortgas Mar 18 '20 at 9:33
  • $\begingroup$ What AWG did you use? (NB: it supposed to be printed on the cable) $\endgroup$ – user77232 Mar 18 '20 at 12:39
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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.

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    $\begingroup$ Yes, the heat spots were indicated in the cable. I will replace its with a thicker ones. Thanks for your help $\endgroup$ – DrPortgas Mar 17 '20 at 1:57
  • $\begingroup$ @DrPortgas, don't use that machine again until you replace that cable. $\endgroup$ – user77232 Mar 17 '20 at 12:38
  • $\begingroup$ yes, i had replaced the cable and its works very well. Thank a lot $\endgroup$ – DrPortgas Mar 18 '20 at 9:29
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Check the diameter of the cable. The smaller the diameter the higher the resistance, thus the heat. AWG14 seem a bit small.

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  • $\begingroup$ Sure, i will check again the diameter of the cable $\endgroup$ – DrPortgas Mar 17 '20 at 1:58
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    $\begingroup$ 14 awg should be sufficient. Moving to 12 awg won't really reduce the heat. $\endgroup$ – user77232 Mar 17 '20 at 12:37

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