Jump to content

Need some help with powering a PCIe extender card.

So, to make a long story short, I have a first-gen HTC Vive with the wireless kit, and I'm trying to figure out the best way to play with it in the living room without having to move my computer out of my bedroom every time. I've looked at getting an extension cable for the WiGig antenna, but everyone online says that, even if I were to get a good-quality cable, I can really only hope to get a about 6.5 feet max before the signal starts getting too degraded for the PCIe WiGig card to detect anything. So alternatively, I've been looking at getting a 1x to 16x PCIe riser card like this and giving it a go with a 20ft male-to-male USB 3.0 cable (as opposed to the ~2ft long one they tend to come with). I'll admit, it sounds like a very sketchy plan, but enough people on Reddit have reported success for me to be willing to try it out for myself.

 

The part I'm hung up on though is that I don't know how I'm going to power the riser card once it's 20 feet away from my computer and power supply. From what I've seen, molex and 6-pin PCIe connectors are the most common standards for powering these things, and just about every one comes with a SATA to 6-pin or SATA to molex adapter respectively. But short of literally just buying a used PSU off someone on OfferUp and jumping the 20-pin connector to take advantage of its molexes or 6-pins, I'm stumped as to how to deliver power via either of those standards. I've found some wall-to-molex power supplies like this on a few different websites, but none of them really inspire a lot of confidence in me, especially once I start sorting the reviews by most critical. And the ones I've seen that go wall-to-SATA weren't much better. So, does anybody have any pointers as to what I should try? The Vive WiGig card doesn't need a whole lot of power to function, but I A. don't want to buy a new one because I trusted a sketchy non-standard power supply, and B. don't want to just have a whole entire computer power supply just hanging out in the living room or hallway for no other reason than to power a little PCIe riser if I can help it.

Link to comment
Share on other sites

Link to post
Share on other sites

Those pcie riser adapters over usb do work and are mostly in use in mining rigs.

Only issue is that it gets limited to x1 speeds and gets latency from pcie to usb and back to pcie conversion, so some critical tasks wont run as well,

 

Also keep in mind that USB cables have issues at lenghts, and 5m gets problematic for some USB devices like printers. It might work really well, or be a complete belly flop.

I know i have few of these riser cards, i might test a gpu with 5m USB3.0 cable if i manage to find one and see if that works.

Link to comment
Share on other sites

Link to post
Share on other sites

No, pause... 

 

Those riser cards don't do any signal conversion, they just take advantage of the fact that the USB cable has enough wires to be support 1 pci-e lane worth of wires ... I think they need  8 or 9 wires and it just so happens that the usb cable has at least 9 wires (5v, ground, d- and d+ pair, for usb 2 backwards compatibily, superspeed tx pair and superspeed rx pair and at least another ground (should be two).

The construction quality of a USB is also good enough to work on low distances with pci-e signals. 

You could hack one of those cards to replace the USB cable with two cat6a ethernet cables and it would still work fine, because the wires would be very well insulated in the ethernet cable...

 

Pci-e is quite resilient, but the standard allows for up to around 15 inches of trace length (the distance from the pci-e controller chip -the chipset- to the chip on the card plugged in the slot), if you don't use repeaters, signal amplifiers or retimer chips. For pci-e 4.0 the recommended maximum trace length is 10-12 inches, and they say retimer chips are needed at every 10 inches, if the total trace length is longer than 12 inches.

 

Now this being said, you will probably be fine with around 1 meter of USB cable, probably even 2 meters... but more than that I would say absolutely not, at least not reliably. 

We all saw Linus  made a video about how many pci-e riser cables they could join together and still have a video card working, so it's quite possible to still have a functional card, even though you don't see how many transmission errors the pci-e controller logs, and how many times the data is retransmitted.

 

As for power ... most pci-e x1 wireless cards don't use 12v, they only use 3.3v ... typically they'll consume around 3-5w or so. Officially the pci-e standard says up to 10 watts is available in the slot. 

 

However, that particular riser card you linked to (1x to x16) is designed to take in 12v  and uses a DC-DC converter chip to convert 12v to around 4-5v  (the tiny chip near the inductor with 100 on it, between two capacitors) and then a 3.3v linear regulator is used to produce smooth 3.3v to put in the slot (the square-ish chip). 

The 12v is also passed through directly to the slot pins. 

If you're absolutely sure the wireless card doesn't use 12v, you COULD power the riser board with less than 12v - that dc-dc converter would probably produce that lower voltage of around 4-5v with something as low as around 6-7v 

 

You could also hack it by connecting 5v from let's say another USB cable directly on the input of that square linear regulator chip and basically ignore that dc-dc converter, not power it at all, and therefore you also won't have 12v at all in the slot (a wireless card that only takes in 3.3v won't care about it and will run happily)

 

You can take any existing adapter cable (for example sata - > molex , molex -> 2 x molex )  and extend the adapter to the length you need.  The molex connector is basically : 5v - ground - ground - 12v - 5v is red wire which you can ignore , ground is black wires, 12v is yellow. 

The riser cables often come with that small pci-e 6 pin to sata ... you can cut the sata part, and use 2 wires to extend, only the yellow and one black wires needs to be extended.

 

Link to comment
Share on other sites

Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

×