mersenneforum.org Radeon VII @ newegg for 500 dollars US on 11-27
 Register FAQ Search Today's Posts Mark Forums Read

2020-08-03, 00:57   #298
S485122

Sep 2006
Brussels, Belgium

2·5·157 Posts

Quote:
 Originally Posted by ewmayer ... However, power extension cables with [6+2]-pin male plugs at each end are legion - could I simply plug the 6-pin solid block of one end into a 6-pin Peripheral&SATA power-out of the PSU, leaving the 2-pin bit dangling, and do similar at the other end to plug into one of the 6-pin female plugs of the Y-adapter? ...
Be careful : the "peripheral" end of power cables is standardised, but unlike fan cables the supply end is not. You might short your PSU through the powered item. The PSU will resist (their are fail safe circuits that do work), the item could be damaged beyond repair: fried.
One can not mix cables from different PSU suppliers without checking first that their layout is identical, even if the connectors are identical at the PSU end (if they aren't the cables will be difficult to plug-in :-)

Jacob

2020-08-03, 01:24   #299
ewmayer
2ω=0

Sep 2002
República de California

1151810 Posts

Quote:
 Originally Posted by S485122 Be careful : the "peripheral" end of power cables is standardised, but unlike fan cables the supply end is not. You might short your PSU through the powered item. The PSU will resist (their are fail safe circuits that do work), the item could be damaged beyond repair: fried. One can not mix cables from different PSU suppliers without checking first that their layout is identical, even if the connectors are identical at the PSU end (if they aren't the cables will be difficult to plug-in :-) Jacob
Unfortunately the only [6+2]-pin-male-plug-containing cables that shipped with my Corsair PSU are of the kind that have a pair of such plugs marked 'PCIe' at the device end, and a solid 8-pin male plug at the supply end. I briefly thought "genius! I'll make a Y-adapter out of it by reversing it and plugging the 6-pin PCIe plugs into a pair of PSU Peripheral&SATA power-outs and the solid 8-pin end into the F port of one of the power splitter cables feeding the GPU", but I bet that's also not workable - looking at the metal connectors inside the male plugs of the above connector, the PCIe-labeled [6+2]-pin ones all have metal connectors, but the unlabeled PSU-end soild 8-pin plug has just 7 metal connectors, the 8th is an empty hole.

I did find an example of a 6-pin male-to-male cable, but that one comes with a loud "NOTE: Compatible with ONLY CoolerMaster and Thermaltake power supply with PCIe 6 pin port !!!" warning illustrating what you say.

If someone manages to find a Corsair-PSU-compatible 6-to-6 cable like the above, I would be most appreciative for a link.

2020-08-03, 03:24   #300
LaurV
Romulan Interpreter

Jun 2011
Thailand

2×11×397 Posts

Quote:
 Originally Posted by ewmayer Unfortunately the only [6+2]-pin-...
Yuck!
Please QUADRUPLE check that with an ohmmeter (connection beep-beep). As S48' said, and he is right, there are at least 3 different ways, not counting the other 8 pins (like the 4+4 for the CPU) cables which look EXACTLY the same. A toy like this (which I bought long ago for just few bucks) could be extremely useful - you can connect all the cables to it, and you can't connect the cables in a wrong way, the "keys" won't match (yes the PCIe 8 pin, vs. CPU 8 pin cables also have a "key" , some pins are rounded in one side, and the space between pins is obstructed by a very narrow plastic bridge, if you look carefully).

 2020-08-03, 07:04 #301 ewmayer ∂2ω=0     Sep 2002 República de California 101100111111102 Posts So, the SATA cables that ship with the Corsair PSU have a 6-pin power plug at the PSU end, and a set of flat 15-pin male HD/SSD-style plugs along their length. The powered-riser cards I'm using for 1X-PCI-connected GPUs plug into one of the 15-pin plugs, and that connection gets transmogrified to a 6pin male power plug which plugs into a 6-pin F port on the riser card. The riser cards are not PSU-specific, which implies the 15-pin connection is standardized. The question is, is the 6-pin riser-card plug also standardized, or specific to this brand of riser? If the former, I could use 2 such plugs to feed the dual-6-pin end of the Y-power adapter cable that shipped with the Radeon VII.
2020-08-03, 13:08   #302
PhilF

Feb 2005

3×132 Posts

Quote:
 Originally Posted by ewmayer So, the SATA cables that ship with the Corsair PSU have a 6-pin power plug at the PSU end, and a set of flat 15-pin male HD/SSD-style plugs along their length. The powered-riser cards I'm using for 1X-PCI-connected GPUs plug into one of the 15-pin plugs, and that connection gets transmogrified to a 6pin male power plug which plugs into a 6-pin F port on the riser card. The riser cards are not PSU-specific, which implies the 15-pin connection is standardized. The question is, is the 6-pin riser-card plug also standardized, or specific to this brand of riser? If the former, I could use 2 such plugs to feed the dual-6-pin end of the Y-power adapter cable that shipped with the Radeon VII.
I guess I can't picture the riser cards and what they are using those flat HD power connections for, but you can't pull the kind of power that video cards require (especially R7's) through those flat HD power plugs. If those are the type of adapters you are looking for you need to change those plans.

2020-08-03, 21:17   #303
ewmayer
2ω=0

Sep 2002
República de California

2×13×443 Posts

Quote:
 Originally Posted by PhilF I guess I can't picture the riser cards and what they are using those flat HD power connections for, but you can't pull the kind of power that video cards require (especially R7's) through those flat HD power plugs. If those are the type of adapters you are looking for you need to change those plans.
I'm just doing outside-the-box brainstorming to try to find some way to connect from a pair of 6-pin Peripheral/SATA power-outputs on the Corsair PSU to the dual 6-pin female plugs on the Y-power-combiners that shipped with the Radeon VII. Don't worry, there will be no plug-and-praying unless and until I find a suitable cabling solution.

Here's a pic of the riser I'm using. Indeed, says 16W max current, not even close.

I'd been meaning to lay in a spare one of the Corsair RT850 PSU but Amazon was out of stock in the months since I bought my first one - over the weekend noticed they were back in stock for a just a smidge more ($135 vs$128) than I paid previously, so that is ordered. That will give me the option to replace the old PSU in my Haswell ATX-case system with a new one and thus be able to power the current pair of R7s plus the one I'm still trying to find a power solution for ... but I just think it would be really nifty to be able to power 4 R7s from a single 850-watt PSU. :) Plus there's simply no room in the Haswell system for a 3rd R7, so powering it from that would mean running both a long USB cable for a riser card and an extra-long 8-pin-power-to-dual-[6+2]-pin-PCIe cable from the under-desk Haswell system to the space between my desktop fan and the open-frame build. That might introduce another there-is-no-such-cable-available-for-your-brand-of-PSU problem.

Very annoying that Corsair seems to not make 6-pin-to-6-pin power adapter cables compatible with their PSU.

2020-08-03, 22:39   #304
kriesel

"TF79LL86GIMPS96gpu17"
Mar 2017
US midwest

440810 Posts

Quote:
 Originally Posted by ewmayer Here's a pic of the riser I'm using. Indeed, says 16W max current, not even close.
"16A peak current". Nominal max PCIe socket wattage is 75W. Some extenders are limited to 60W.

Last fiddled with by kriesel on 2020-08-03 at 23:04

2020-08-03, 23:07   #305
ewmayer
2ω=0

Sep 2002
República de California

2·13·443 Posts

Quote:
 Originally Posted by kriesel "16A peak current"
Doh! But does not state the voltage. Is there any kind of "this is the minimum wattage a SATA plug must be able to carry" specification in the SATA connector standard?

I see some tantalizing hints e.g. for this Monoprice 108494 SATA 8-Inch 15-Pin to 6-Pin PCI Express Card Power Cable, where a reviewer notes "This is a decent cable, but SATA power delivery is rated at 54W as opposed to 75W for the PCIe power spec".

So - LOL! - let's conservatively assume for grins that a SATA plug can handle up to 30W ... so the SATA cables that ship w/Corsiar PSU take a 6-pin power-out and divide it among up to 4 15-pin SATA plugs along the length of the ribbon cable. Use a pair of Two SATA 15 Pin Power to 6 Pin PCI Express Video Card Power Cable Adapters to recombine the power from those 4 SATA plugs into 2 6-pin PCIe outputs. Those plug into the 2 female 6-pin PCIe input plugs of one the pair of Y-adapters that shipped with the R7 GPU. The output of such a Y-adapter is a single 8-pin PCIe power-out. A second such Frankensteinian split-and-recombine plate of spaghetti plugs into a second 6-pin power-out of the PSU, and feeds into a second 8-pin PCIe power-out, all we need - in addition to the powered riser hookup for data - to power an R7. If each of the 8 15-pin SATA plugs being used can handle 30W, that offers up to 240W, more than a downclocked R7 needs. (And note my setup-multiple-R7s-and-run-PRP-tests bash script always does downclocking of all cards before firing up any code).

The one other question needing answered - besides "is ewmayer a certifiable loony or a mere obsessive?" - would seem to be "what is the wattage rating of those 6-pin power-outs of the Corsair PSU?" As long as each such is rated, say, 120W or more, it should suffice, though there is the issue of transmission+distribution losses in going through the above-described fugly series of adapters.

In interesting-coincident-timing news, I decided that my household really needs a pair of dry-chemical fire extinguishers, one for the kitchen and another for everywhere else, just took delivery of those over the weekend. :)

2020-08-03, 23:14   #306
PhilF

Feb 2005

1FB16 Posts

Quote:
 Originally Posted by ewmayer Plus there's simply no room in the Haswell system for a 3rd R7, so powering it from that would mean running both a long USB cable for a riser card and an extra-long 8-pin-power-to-dual-[6+2]-pin-PCIe cable from the under-desk Haswell system to the space between my desktop fan and the open-frame build. That might introduce another there-is-no-such-cable-available-for-your-brand-of-PSU problem.
No-such-cable-available is right, and there's a reason for it. Not only would a long cable like that introduce too much voltage drop, but it can also introduce too much inductance. That could cause a catastrophic self-oscillation that would probably destroy every device connected to that power supply.

A definite no-no.

Quote:
 Originally Posted by ewmayer In interesting-coincident-timing news, I decided that my household really needs a pair of dry-chemical fire extinguishers, one for the kitchen and another for everywhere else, just took delivery of those over the weekend. :)
Ha! That's called good Karma. <--- Me staying out of the way of exploding chips
--------- Ernst's R7's -----------> ^^^^^^^^^

Last fiddled with by PhilF on 2020-08-03 at 23:47

2020-08-04, 05:56   #307
ewmayer
2ω=0

Sep 2002
República de California

2·13·443 Posts

Quote:
 Originally Posted by PhilF NHa! That's called good Karma. <--- Me staying out of the way of exploding chips --------- Ernst's R7's -----------> ^^^^^^^^^
So I take it my Frankenstein-cable split-and-recombine proposal is theoretically workable, you're just gonna stand well back as I try it. :)

Four 2x-SATA-to-6-pin-PCIe adapters ordered ... seller was alas down to "1 left in stock", so ETA is 2 weeks from now - that gives us plenty of time to think on the error of my ways.

As Breaking Bad's Jesse Pinkman memorably said, "For science, yo!"

 2020-08-04, 07:46 #308 sdbardwick     Aug 2002 North San Diego County 68010 Posts Keep those fire extinguishers handy. If you keep the total power draw below 216W on the 12V lines, it might work, but it is right at the edge of the envelope. BTW, many (most?) PCI-E graphic cards, if they have PCI-E power cables, will draw almost nothing from the slot 12V line ('cause you don't want the card killing the motherboard if one of the main 12V lines fails and it tries to draw full load from the PCI-E slot). There is a good reason Corsair doesn't make 6 pin (peripheral) to 6 pin PCI-E cables. Those 6 pin peripheral cables consist of 1 pin 3.3V, 2 pins 5V, 1 pin 12V, and 2 pins ground. PCI-E cables consist of 3 pins 12V and 3 pins ground (an 8 pin connector to the PSU is 4 12V and 4 ground). IMO, you are asking too much of those 2 poor 12V pins. [Although the SATA connectors will probably fail first, sparing the PSU connector, as each SATA connector can only supply (4.5A x 12V) 54W under perfect conditions; a 2 SATA connector cable can load the 12V pin with 9A, which is exactly the maximum current rating for the Mini-Fit Jr. connector used. Better hope the both cable assemblies are exactly the same resistance.] Last fiddled with by sdbardwick on 2020-08-04 at 08:02

 Similar Threads Thread Thread Starter Forum Replies Last Post ET_ GPU Computing 1 2019-07-04 11:02 M344587487 GPU Computing 10 2019-06-18 14:00 jasong GPU Computing 0 2016-11-09 04:32 0PolarBearsHere GPU Computing 0 2016-03-15 01:32 firejuggler GPU Computing 33 2014-09-03 21:42

All times are UTC. The time now is 09:14.

Sun Sep 20 09:14:54 UTC 2020 up 10 days, 6:25, 0 users, load averages: 2.10, 1.69, 1.52