This was my first time designing PCBs, so I apologize in advance if this sounds dumb...

I'm making an ATX PSU adapter for old computers that didn't use this standard. There wasn't much electrical engineering involved, it's pretty much a "converter" (i.e. re-routing) board. I had calculated my track widths based on 2 oz copper layers. Now that I got quotes back from PCB manufacturing houses, I'd rather use 1 oz copper layers because it's much much cheaper.

Here's what I'm working with:

  • 120 VAC: max 6 A power draw (per track). My tracks are 3 mm (120 mils) wide.
  • 5 V (motherboard): max 3 A (per track). Tracks are 2 mm (80 mils) wide.
  • 12 V (motherboard): max 5 A (per track, worst case scenario, probably less in real life). Tracks are 2 mm (80 mils) wide.
  • 5 V standby: 1.25 A, 1 mm (40 mils) wide.
  • "Molex" power connectors: I can't seem to find an actual max current spec, but 16 AWG can work up to 10 A apparently. The tracks are 2 mm (80 mils) wide.

Should I make my tracks wider or is this sufficient?

I've seen that temperature rise is an important factor. Bear in mind that the PCBs will be cooled by a massive fan.

Thanks in advance for your help.

EDIT: I already tried online calculators and obtained the following results (please check the widths I have vs. temperature rise). I don't know how much these can be trusted... 80°C for the HD connector doesn't seem right.


  • 1
    \$\begingroup\$ Use this tool 4pcb.com/trace-width-calculator.html \$\endgroup\$
    – G36
    Apr 14 '20 at 12:35
  • \$\begingroup\$ Thanks for your answer. Please see edited post for details. \$\endgroup\$ Apr 14 '20 at 12:54
  • 1
    \$\begingroup\$ Increase the HD track width to 100 mils and you should be fine. \$\endgroup\$
    – G36
    Apr 14 '20 at 13:14
  • \$\begingroup\$ Thanks a lot! I'll make that 3mm (120mils) and that should be more than enough. According to 4PCB, 8Amps with a 25 degC temperature rise corresponds to a 3mm track. What about the rest though? Is it ok? \$\endgroup\$ Apr 14 '20 at 13:25
  • 1
    \$\begingroup\$ For the FR4 board, such a temperature rise should not be a problem. And try to keep a distance between 120 VAC track at more than 2mm apart. \$\endgroup\$
    – G36
    Apr 14 '20 at 13:48

To calculate the trace with you can use this Calculator. You can set different parameters included maximum temperature rise.

You should also ensure enough trace clearance for the 120 VAC section!

  • \$\begingroup\$ Thanks for your answer. Please see edited post for details. \$\endgroup\$ Apr 14 '20 at 12:55

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