Some confusion about the current and the DC jack

[bliepp]

Hey guys, I'm currently having a look at the project and found something odd (maybe I'm wrong due to tiredness, it's 4 AM in my timezone):

TL;DR Doesn't matter what settings I use in any track width calculator, I never get to a point were the characteristics of the PCB heating track (2000 mm long, 1.4 mm wide and 1 oz/ft² thick) result in a reasonable current suiting the DC jack.

According to the "How-To - Designing a board" file the heating element is made using a 2000 mm long and 1.4 mm wide copper track on a 1 oz/ft² PCB, hence a resistance of 0.9 Ohms (I calculated 0.7 Ohms, but that's only a detail). Furthermore, the document states that the board can easily reach 200 °C at only 8.4 V. According to Ohms law this means the overall current is approx. 10 A (9.3 A for 0.9 Ohms or 12 A for 0.7 Ohms) for 8.4 V. The schematics show that the board is intended to be used with 12 V (so 13.3 A < I < 17.2A), but the barrel jack used is one rated for max. 5 A. Using any PCB track width calculator (KiCAD in my case) a track width of 0.4 mm (=> 2.5 Ohms) would be needed to stay below the DC jacks maximum rating for the same results.

How does that even work? The barrel jack chosen in the BOM should melt or at least get extremely hot due to its high load (which doesn't happen, as far as I can tell from videos and this community here).