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I need a power supply that can output 60amps at 12 volts. Based on the sticker on this power supply 12v maxes out at 62 amps. Perfect. Unfortunately the 12 volt wires are 18 gauge, which after some googling seem to safely max out at around 7-10 amps. Even wiring the two together could only support around 20. How would I manage to get 60 amps at 12 volts from a power supply with 18 gauge wires?

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    \$\begingroup\$ There are a lot more than two cables. \$\endgroup\$ – Tom Carpenter Sep 1 '16 at 0:52
  • \$\begingroup\$ Have you looked at an ATX power supply? There are lots of parallel wires for power and ground. \$\endgroup\$ – user2943160 Sep 1 '16 at 0:55
  • \$\begingroup\$ I haven't ever done any type of electrical work before, but there are only two 12 volt cables. 12v 60a means 60a through ALL wires? \$\endgroup\$ – quelleck Sep 1 '16 at 0:56
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    \$\begingroup\$ @quelleck 15 in fact. And it is not 60A through each wire, it is 60A maximum capacity shared between different cables. \$\endgroup\$ – Tom Carpenter Sep 1 '16 at 1:01
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Because there are many more than just two cables. By my count that PSU has the following for 12V:

  • 24pin ATX - 2 cables
  • 2x 8pin PCIe - 6 cables
  • 1x 8pin EPS - 4 cables
  • 3x Peripherals - 3 cables

That gives at least 15 cables - or at 7A per cable, 105A cable capacity.

The point is, that total load is expected to be distributed between different connectors, not just through one of them. Each of those different connectors have a specific power rating - with the EPS connector being the highest.

Modern CPUs are power hungry so the EPS connector with 4 cables became the modern standard having been expanded from the earlier P4 connector which only had 2 cables for 12V to the CPU (and going even further back, just the 20pin ATX connector powered the whole motherboard).

Modern GPUs are even more power hungry, so multiple cables are chained together - the high end boards have both an 8-pin and 6-pin connector which allows 6 cables in parallel.

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  • \$\begingroup\$ In the early days mainboards did not create the CPU voltage out of the 12V, so the 3.3V and 5V line and amperage were a lot more important - that's why there are only 2 12V lines on the ATX board connector. \$\endgroup\$ – Arsenal Sep 1 '16 at 8:19
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A typical ATX supply uses multiple wires in parallel to provide the rated power. Multiple cables in parallel will have a better power delivery capacity compared to a single cable, do to paralleled resistance (it halves) and doubled heat carrying capacity. They do not carry all 60 Watts on a single wire. You have 10 on the motherboard connector, two on the +4, 1 on each hard drive connector, a few on the pci, etc.

At any given time, I would say there are at least 15 wires for 12V on a normal pc, but this is a guess from memory. A cursory look inside a pc case would confirm it.

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It's probably total lies, especially for the cheap unbranded ones. "Mine's bigger than your's." Yes there are several wires exiting the PSU. But the PSU circuit board is still copper clad PCB at what, 1oz? I would be interested in seeing the gauge of the wire on the transformer secondaries. That's the pinch point in a SMPS and probably a significant proportion of the cost.

When you see a PSU review, it's never tested to destruction (understandably). And how would you test it with computer parts anyway? A hard disk only uses 500mA. That's a 120 hard disks. I doubt many would hold a continuous 60A. You can weld with that.

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  • \$\begingroup\$ Power supplies are factory tested using special testers with controlled loads on all provided connectors, not some unspecified hard drives. Everything is tested, ripple level, overshoot and undershoot after sudden load change, and everything else to meet all ATX12V specifications. \$\endgroup\$ – Ale..chenski Oct 12 '16 at 2:12
  • \$\begingroup\$ @AliChen Is it tested on that equipment that tests the 5W output torches for $3? Or my x30 Triplet that magnifies 7 times? Or my Uno knock off where some of the headers fell out? \$\endgroup\$ – Paul Uszak Oct 12 '16 at 10:22

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