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I'm working on the wiring harness for a PC build that's going to include a bunch of (5050) LED strip lights.

The strips will be wired to fan connectors (more details at end). For testing, I've been running them off of a SATA to fan splitter (e.g. this) connected to a stock SATA power cable. However, I'm going to have a lot of wires to cram under the PSU shroud and the splitter and stock SATA power cable are adding a bunch of bulk (and TBH, the splitter feels a little sketchy). Since I don't need 5V anywhere, I'd like to build some cables that don't have unused wires.

My initial thought was to build a peripheral cable that would run PSU → SATA (for some case fans) and somehow chain fan connectors off the end of that. (Or maybe with the SATA at the end.) However, to do this I would have to double-crimp a bunch of fan pins, or build a 2x SATA cable and keep the splitter. And in either case, I would also need fan extension cables, and 100% of the total load is being carried by a single pair of wires.

Then it occurred to me... I'm almost certainly never going to be using more than 4 out of 6 of my EPS/PCI ports otherwise... and an 8-pin EPS connector is 4x 12V pairs (compared to a peripheral connector which has only 1x 12V pair). AFAICT, although the pin pairing is a little screwy, there are no paired wires in the EPS cables, and the PSU end is also 4x 12V pairs. Physically, I could wire up a custom cable that plugs into an EPS/PCI port and has 4 separate 22/2 stranded 12V pairs coming off of it. This would add a little bit of extra wire right by the PSU, but each pair can be made to length (no extensions!) with a fan connector on the end (no SATA → fan adapters!), and each pair is only carrying the load of one set of LEDs.

Practically... Is this a good idea, or a terrible, terrible idea that will turn my Corsair AX1000 into an expensive paperweight?


All that said, I have already run the entire 5 meter strip off the stock SATA power cable → fan splitter → 4" 22AWG adapter, so the PSU does seem able to take the load on a single 12V pair (nothing caught fire, not did I notice any melting... aside from the LEDs themselves which put out much more heat than I would have expected). However this was only for maybe 30 minutes, where the completed harness is probably going to run 24/7.

In any case, the strips themselves are going to be connected with 22AWG solderless connectors (e.g. these) that have had fan pins crimped to the other end. Strips will be connected with either similar connectors (where possible; the pre-made connectors are only about 10cm long) or soldered with 22/2 between strips. The longest connected run will be about 1 M - 1½ M. Total lighting will be less than the 5 M reel (but possibly a significant portion thereof). Allegedly (read: according to the product description), the entire reel draws 38W, but what I have left of the reel (about 80-90%) only pulls about 2.3A (measured), so probably closer to 30W. Thus, each of the four runs, individually, will not exceed 1.5A, and probably closer to 0.6A each.

p.s. This is sort of very, very loosely related to Is it electrically safe to use an ATX PSU's PCI output for SATA/MOLEX instead of graphics cards?. Unlike that question, however, I'm powering LEDs, not HDDs, and only need 12V.

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    \$\begingroup\$ This question seems to be rambling over a broad territory. Can you try to narrow it down to a specific question and include links to the datasheets for the LEDs and power supply? \$\endgroup\$ – Elliot Alderson Sep 24 '19 at 22:44
  • \$\begingroup\$ I explained where I am coming from and what I am trying to do. The actual question is fairly straight-forward: is it "safe" to power some LEDs via an EPS/PCI port as described? I don't know why the datasheet of the LEDs matters; they are a 12V load at such-and-such amps (less than 2A per run, but it will vary because each run has a different number of LEDs). Nor would I know where to find a datasheet. FWIW, I'm using these: amazon.com/gp/product/B07QNK81HH. \$\endgroup\$ – Matthew Sep 25 '19 at 15:48
  • \$\begingroup\$ I was also unable to find a datasheet for the PSU. Here's the product page if you think you'll have better luck: corsair.com/us/en/Categories/Products/Power-Supply-Units/…. \$\endgroup\$ – Matthew Sep 25 '19 at 15:48
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Break down the problem into smaller sub-problems.

  1. Define each PCIe/CPU connector port as a "load"
  2. How much power is each load going to draw? Break that load up into sub-loads.
  3. Determine the relevant rating of each link.
  4. Recursively break down each load to its subloads until you hit discrete components if need be

In your case, the assembly comprises:

A PSU which has Na ganged load connectors. Each ganged load connector has Nb sub-loads (LED strips). Each sub-load has Nc of its own sub-loads (discrete LED).

Calculate the load of each and work backward. If you can't find a datasheet, test it empirically.

Here are some more references on PCIe power connectors: PCI Express Auxiliary Graphics Power Connectors

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  • \$\begingroup\$ I'm not worried about the load in general. I'm worried whether I can supply that load from an EPS/PCI port on the PSU, whether said port is in fact giving me 4x 12V pairs, and whether I can apply a non-uniform load across those four pairs which would normally be connected to a single device. \$\endgroup\$ – Matthew Sep 30 '19 at 17:03
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    \$\begingroup\$ This is a valid question, as if you have multiple pins providing the same voltage but are not continuous, this could indicate you have discrete components sourcing those pins. The way to avoid this is to check whether the wires are continuous e.g. have continuity between all of them. If the wires have marginal resistance between them then they are on the same node with respect to Kirchoff's laws. \$\endgroup\$ – DeusXMachina Oct 1 '19 at 15:42
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I think the answer is "yes" (but feel free to jump in and contradict me if any of this is in error!).

In order to answer this, we need to address several sub-issues:

  1. Is the wiring adequate?
  2. Can the PSU, in general, handle the load?
  3. Can we pull four independent and non-uniform 12V loads off a PCI/EPS port?

We'll ignore the wiring; that would be a separate question. (AFAICT, though, 22/2 should be fine if each wire is only carrying 1.5A or less.) We're also way below the PSU's rated load (83A @ 12V), so no problems on the second point.

As for the third point... an 8-pin EPS connector is four 12V pairs. The stock EPS cable is passing these "straight" through, so the port is supplying four +12V pins and another four presumably neutral. Additionally, testing shows very little resistance (≈0.2Ω) between the various +12V pins (not just on a single EPS/PCI port, but also a pair of +12V pins on different ports), and likewise the various neutral pins, which suggests that in the guts of the PSU, everything just gets ganged together. (This seems to be pretty typical of modern PSU's, so no surprise here.)

So, as far as I can determine, I should be fine picking arbitrary pairs of +12V and neutral pins to run my LEDs.

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