Six pin to 8 pin power adapters For GPUs?

[JerryTheC]

I've just acquired a refurbished 8 core xeon workstation as a relatively inexpensive intermediate upgrade from my ancient core 2 quad system, which should keep me going while I save up for an eventual new build.
according to the specs, it should be able to handle 1 or 2 GPUs up to around 300W total, though the current graphics card is extremely basic.

Looking at the power supply connectors, it has two six pin connectors available. Looking at mid to high end GPUs, it seems that most of them now use from 1 to 3 x 8 pin connectors.
Since the PSU isn't a standard size, replacing it with one with 8 pin outputs doesn't look like an option.

A quick look at adapters show a variety of types from 1 x 6 pin in to 1 or 2 x 8 pin out, and also 2 x 6 pin in to 1 x 8 pin out.

which ones would be sensible to use, if and when GPUs become available again?
Does it ever make sense to try and use 1 six pin from the PSU to feed two eight pin sockets on a GPU?
For a GPU with one 8 pin socket, when would it make sense to join 2 six pin from the PSU instead of just going from a single six pin?
Or is there a limit of 8 pin connectors that it's worth trying to drive from two six pin?

[Corky34]

IIRC the 2 extra pins on an 8pin are grounds and while you can use an adapter from 6pin, or even 2x molex/SATA power, into an 8pin it sort of depends on the PSU.

Again if i remember correctly the extra ground pins are used by the card to detect how much power it can pull so while an adaptor would work fine there's a chance you may overload the PSU or cable, i think 6pin is 75W max and 8pin is 150W so by the sounds of it your PSU should be capable (do you happen to know what model it is?).

My main concern would be the gauge of the wires and if they could handle the current draw (amps), 2x 6pin into an 8pin would be the better choice IMO because there's less chance of overloading the cables, hopefully someone with better knowledge than I can confirm that or tell me I'm talking rubbish.

[DanceswithUnix]

, hopefully someone with better knowledge than I can confirm that or tell me I'm talking rubbish.

Seemed pretty much spot on to me

6 pin connectors have 2 wires out, 2 wires back for the power loop. 8 pin have three wires out, three wires back. Adding 50% more power carrying wires doubles the official power handling capacity, which says to me there was some finger in the air estimation on what the people setting the two standards thought was safe.

So, winding back a bit:

Does it ever make sense to try and use 1 six pin from the PSU to feed two eight pin sockets on a GPU?

No, I would say it doesn't. That is splitting a 75W rated connector into a pair of 150W rated connectors. Even allowing for the 75W often being quite conservatively rated, 75 to 300 seems unlikely to work.

6 pin to a single 8 pin is often OK though. Check your 6 pin PCIe connector, it is possible that it only has two power (probably yellow) cables going to it, but most have three. If it has three, and the wires look beefy enough (which in a workstation they should be fine), then you can get a 6 pin to 8 pin cheap adaptor and you should be good for one 8 pin connector.

My son is still using an old Dell Xeon workstation as a desktop, so I've been through this. It took a couple of goes, you can get SATA power and Molex HDD connector to 6 pin cables as well, the PSU may not like some combinations and refuse to come up so it can take a few goes. Sadly that depends on your specific PSU, so hard to give you exact advice.

[JerryTheC]

I thought going from one six pin to two 8 pins would be a bit iffy

The PSU is the 635W one in a Dell Precision T3600. Label claims +12VA 18A, +12VB 18A, +12VC 18A, +12VD 18A, +12VE 18A, -12V 0.5A, 5VSB 4A, Combined output 635W max.
Dell model F635-EF0, Plex P/N DEL-D-0635ADU00-101 by Flextronics sales and marketing (A-P) Ltd, made in China, 80+ Gold
Both 6 pins have 3 x black and 3 x yellow, probably 16 or maybe 18AWG - print is a bit small, but they're noticeably thicker than 20 AWG. Same thickness as the ones in the 8 pin CPU power connector.

Dell's T3600 hardware spec lists video card support for "Up to 2 full-height, full length (maximum of 300 W)". that 300 is a total; detailed specs (and looking at the motherboard) give a 75W max for each of the two graphics slots, or up to 225W with the external power from the 635W PSU, though it's not clear whether that's with one or both of the 6 pins.

[DanceswithUnix]

Nice box, my son's PC is an older 6 core T3400 and still does him quite nicely.

Problem is the GPU they expect you to use in one of those machines is a Quadro, usually some underclocked low end Nvidia chip with a single slot cooler. I had one of those machines a couple of jobs ago, nice box. Mine had two GPUs in it because cards of that era had three outputs but could only drive two of them at once, so with three monitors I needed two of those stupidly expensive for what they are cards.

The motherboard can indeed supply 75W through each PCIe x16 slot, which if you add to a pair of 75W 6 pin connectors gets you a comfortable total of 225W to a card without going out of spec on anything. The 300W will be 75W from each of a pair of PCIe x16 slots, and 75W each from the pair of 6 pins for 4 x 75W total = 300W.

But hey, you seem to have a bunch of 12V rails that can all do ~200W. If those 6 pins are on the same 12V rail, then it sounds like with 6 to 8 pin adaptors you could squeeze a bit more out of them with a 200W rail plus the 75W from the mainboard. With 5 x 12V rails you might have each 6 pin on its own rail. So, it sounds like you can safely get a 225W single card, more than that and you should be able to pull in more power from HDD connectors or similar but it could be a faff.

Measure the machine for card length as well, I had to remove a hard disk tray on the T3400 and it's been a few years since I delved inside a T3600 so I can't remember if they are the same. With that gone it could take a nice long GPU, but as standard I couldn't get an RX 570 in there.

[JerryTheC]

I poked around a bit more - and found the release press point for the end-of-PSU shroud. The T3600 PSU is a slide in unit with PCB connections. and the 2 x 6 pin connectors turn out to be an 8 pin to 2x6 pin Y cable plugged into an 8 pin socket on a connector board under the end-of-PSU shroud. Card length shouldn't be a problem, since the T3600 only has a 2 drive cage next to the end of the PSU below the motherboard, and the optical drives mount above the slot level so there shouldn't be a problem with GPU length.

[abzycar]

In general I wouldn't recommend an adapter like that, as it could cause damage to the GPU and potentially other components if the adapter is low quality.

[elguapo]

I've tried it in the past and worked fine but wasn't pulling anything like the full 150W from the 8 pin.