Having just installed resistors on those three heatsinks, here’s the results from that ATX power supply.
| Loads | +5V | +12 V | -ON -> Gnd | PS Tester |
| 0 | 4.94 | 11.76 | 13 | 17 |
| 1 | 4.81 | 11.82 | 70 | 72 |
| 2 | 4.79 | 11.92 | 129 | 130 |
| 3 | 4.77 | 12.02 | 189 | 192 |
Notice that the +12 V output increases under load, which turns out to be true because all the outputs share the same transformer: supporting the load on the +5 V output requires more flux, which tends to increase all the other outputs.
The last two columns are the input power from the AC line, with the -ON pin shorted to ground and with a black-box power supply tester that evidently draws a watt or three.
The resistors on each heatsink dissipate a total of 46.6 W:
- 1 Ω -> 4.82 / 1 = 23.0 W
- 6 Ω -> 11.92 / 6 = 23.6 W
The box sees 140 W with all three heatsinks powered up.
Three of those fans draw 1.1 A from +12 V, adding another 13.4 W.
Grand total: 153 W. Close enough!
Power supply efficiency at full load is 81% = 153 / 189. Not as good as you’d like, but it’ll suffice for my simple needs.
The drop across a single Molex power connector pin is 11 mV @ 5 A and 4.3 mV @ 2 A: call it 2 mΩ. They’re rated for 11 A with a 30 °C temperature rise, which means I really should use PowerPoles.
The Smell of Molten Projects in the Morning 