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Author Topic: 4 pin molex to 6 pin pci-e connector. Word of warning  (Read 102386 times)
P4man
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November 13, 2011, 04:14:37 PM
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I was running short on 4 pin molex plugs on my PSU. Going through my box of cables I came across a single 4 pin molex to 6 pin PCI-E connector. Just what I needed to get around my shortage. So I did some math

4 pin Molex  is rated for 60W, compared to 75W for PCI-E.
Motherboards supply up 75W.
One PCI-E connector is a proper one, 75W
One 4 pin to 6 pin: 60W

75+75+60=210W. SHould be plenty for a 5850, even with a decent overclock no?

Nope. After one day:



I massacred the cable by pulling it out, but there were and still are clear burnmarks. Dont skimp on this folks, its not worth burning your house down over a cable Smiley

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November 13, 2011, 04:18:26 PM
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Not positive, but I don't think they make these anymore for this reason. The standard now uses power drawn from two molex powers to one PCIe 6 pin.

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November 13, 2011, 04:22:56 PM
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I dont remember where I got that cable from. It was never used, still in plastic wrapping. I think it came with an old nvidia card (8800gt or so? or perhaps a card that draws only ~75W ).

Anyway, just wanted to show you shouldnt use them for a reason Smiley. I was surprised though, you'd think there is some safety margin on those specs, and 60W to 75W isnt that much a difference.  From now on Ill see those 8 pin PCI-E connectors as a selling point.

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November 14, 2011, 05:09:03 AM
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I dont remember where I got that cable from. It was never used, still in plastic wrapping. I think it came with an old nvidia card (8800gt or so? or perhaps a card that draws only ~75W ).

Anyway, just wanted to show you shouldnt use them for a reason Smiley. I was surprised though, you'd think there is some safety margin on those specs, and 60W to 75W isnt that much a difference.  From now on Ill see those 8 pin PCI-E connectors as a selling point.

Does not make sense, its an isolated case with a bad connector.

I'm using several connectors like this (provided with Sapphire 5850) and all works flawless.

5850 cant draw that much power. Your calculation shows more than what it needs.
 

Edit: i notice something odd with your connector. The 6pin misses the middle 12v wires?

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November 14, 2011, 08:03:52 AM
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Does not make sense, its an isolated case with a bad connector.

I'm using several connectors like this (provided with Sapphire 5850) and all works flawless.

Id have a good look at them, particularly if you are overclocking (I was testing at 900 MHz but only since a few hours and at stock voltage).

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5850 cant draw that much power. Your calculation shows more than what it needs.

Well, I would have more faith in a brown melting wire than my "calculations" Smiley. As it turns out, these cards usually only draw ~25-30W from the motherboard. That leaves ~120W for those 2 connectors at stock speed. Assuming the card pulls from each plug equally, thats the limit of the 4 pin molex spec at stock speed.

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Edit: i notice something odd with your connector. The 6pin misses the middle 12v wires?

Do you have 3 yellow wires on your plug? To be clear, this is a SINGLE molex to PCI-E adapter. Most (all?) new cards come with dual molex to PCI-E.


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November 14, 2011, 01:13:14 PM
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Edit: i notice something odd with your connector. The 6pin misses the middle 12v wires?

Do you have 3 yellow wires on your plug? To be clear, this is a SINGLE molex to PCI-E adapter. Most (all?) new cards come with dual molex to PCI-E.


  All of my official sapphire plugs have all 3 yellow wires there. And of course are dual molex. I've got a few old pci-e 6 pin that are lakcing the middle yellow that came with older 8x, 9x nvidia cards as well. Not so sure it woulda helped much in your situation but its probably not healthy if the card is looking to spred that draw over 3 pins on the card side is all.

If you're not excited by the idea of being an early adopter 'now', then you should come back in three or four years and either tell us "Told you it'd never work!" or join what should, by then, be a much more stable and easier-to-use system. - GA
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November 14, 2011, 01:22:34 PM
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 All of my official sapphire plugs have all 3 yellow wires there. And of course are dual molex.

Well, thats kind of my point. With dual molex you should be fine, its the single molex to PCIE cable that is a fire hazard. Not sure if there are 3 wire variants for single molex, but since the limitation is the connector rather than the wires (and the pastic connector has brown burn marks), I dont think it would improve much. Not going to touch single molex to PCIe anymore even if there are a dozen wires Smiley.

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November 14, 2011, 02:41:23 PM
 #8

That connector is all kinds of weirdness.  Can't believe anyone actually authorized that.

Worse is the fact that even IF the Molex connector could handle the current the PCIe 6-pin isn't rate even for 60W in a configuration like that.

The PCIE 6-pin is rated for 72W @12V = 6.24A.  This is spread across 3 power lines for 2.08A each.  With only 2 of the 3 12V connectors attached even at only 60W those leads are pulling 2.5A a piece

If you want to see the glass half full ... had the Molex side of connector not burnt likely it could have destroyed your graphics card.  Honestly whoever made that connector should be sued and if it was included with a GPU whoever included it should be sued too.

Standards exist for a reason.

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November 14, 2011, 03:42:16 PM
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Hmmm.. now you make me nervous. I just went through my box of cables, and I have plenty of those. Like this one, its a dual molex to PCIe, but also has only 2 red and 2 yellow wires:



If I remember correctly, that cable actually came with my 5870?

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November 14, 2011, 03:49:24 PM
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Sorry for the scare.  I went back and looked at the standard.

It looks like the 6pin connector does allow the middle connector to be unconnected.  However that increases the amperage on remaining two wires to 3.125A (max).   Why they hell they allowed that I don't know but I assume if the standard allows it then all components must be rated/tested to handle up to 3.125A per line.

Here is an example of a different way to connect them:


I guess looking at it further there really is no good way to connect 6pin to dual molex.  Dual molex gives you 4x grounds but only 2x 12V.  So while the middle connector above it is connected it is done by connecting two pins to a single molex pin.  That means the amperage on each of the 6pin connectors is <2.1A but one MOLEX is pulling 4.2A while the other is pulling 2.1A.  That isn't exactly optimal either but I would rather have lower load on the PCIe leads and more importantly the traces on video card connector.  Good news is as more and more PCIe capable power supplies are sold it likely is less and less of an issue.

Somewhat off topic:
For the record I hate when companies use nonstandard wiring.  Why use red wires (as seen in your photo)?  Did they have left over red wire to they used that instead of 4 black wires?
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November 14, 2011, 04:00:22 PM
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Im guessing they are pulling from 12 and 5v? 2 wires with 12v (yellow) and two from 5v (red) ? WHich wouldnt be a bad idea for old PSUs that likely have ample 5V power (and not enough on 12v)

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November 14, 2011, 04:01:59 PM
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  Still even if it is ok it makes me wonder WHY do it?  Why push >3.125A per wire when you can have enough connectors (both on PCIe side and on dual Molex side) to keep current below <2.1A?

  because capitalism rules!  10k units x 2" 16Ga wrapped copper wire @.08 to .38 per ft. = profits

  Edit; which is why sapphite cheats on their's. It is more dangerous to the traces on the board than to the 16ga wire. Sapphire takes advantage of this with the cables I got from them by only running 2 12v lines form the molex and then using a 1/2" wire to fill the middle pin from one of the other 2 at the 6 pin connector...

If you're not excited by the idea of being an early adopter 'now', then you should come back in three or four years and either tell us "Told you it'd never work!" or join what should, by then, be a much more stable and easier-to-use system. - GA
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November 14, 2011, 04:05:57 PM
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here is the entire cable:



Ive only seen one's like that TBH. Well, in so far I paid attention. Ill check my mining rig later.

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November 14, 2011, 04:05:59 PM
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Im guessing they are pulling from 12 and 5v? 2 wires with 12v (yellow) and two from 5v (red) ? WHich wouldnt be a bad idea for old PSUs that likely have ample 5V power (and not enough on 12v)

No they can't be.  That wouldn't work.  Can't supply 12V from a 5V lead without using some sort of converter (VRM, DC to DC switching,etc).  Looking at the connector the red wire (which does denote 5V) is actually connected to pin2 = ground.

On Molex peripheral connector with the "round side" down the pins are from left to right are
1) 12V (usually yellow)
2) ground (usually black)
3) ground (usually black)
4) 5V (usually red)

So they are connecting ground to ground however they decided it would be fun to use red wiring instead of black.  Maybe they have 10,000ft of spare red wiring to get rid of?  Still annoying IMHO (and a pet peeve of mine).
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November 14, 2011, 04:06:29 PM
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see picture above.

edit: oops you are right. I thought that 2/3 molex pin was 5v, but its ground. Why would you have 4 ground wires and 2 current carrying?

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November 14, 2011, 04:13:18 PM
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Funny, every single card I bought ~4 mo ago came with single molex to 6-pin adapters.  I was using probably 8 of these amongst my various rigs and never had an issue - the wires and connectors were never even warm.  The build quality seems superior to the one P4man posted, but still - why would they supply only single-molex connectors if this was a such a major risk?

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November 14, 2011, 04:14:50 PM
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see picture above.

edit: oops you are right. I thought that 2/3 molex pin was 5v, but its ground. Why would you have 4 ground wires and 2 current carrying?

  Its supposed to be 3 and 3. 2 of the ground wires join together at the center pin on the 6 pin connecter.

  Edit; likely they split that ground like that to compensate for any extra resistance that may be on one of the psu molex lines.

If you're not excited by the idea of being an early adopter 'now', then you should come back in three or four years and either tell us "Told you it'd never work!" or join what should, by then, be a much more stable and easier-to-use system. - GA
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November 14, 2011, 04:30:20 PM
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 All of my official sapphire plugs have all 3 yellow wires there. And of course are dual molex.

Well, thats kind of my point. With dual molex you should be fine, its the single molex to PCIE cable that is a fire hazard. Not sure if there are 3 wire variants for single molex, but since the limitation is the connector rather than the wires (and the pastic connector has brown burn marks), I dont think it would improve much. Not going to touch single molex to PCIe anymore even if there are a dozen wires Smiley.

Nope, all the connectors come with Sapphire xtreme are single molex.

I believe many others also use them.

They have 2 12v wires from the 4pin and convert into 3 wires at the 6pin.

This just shows your connectors are poorly made.

Has nothing to do with single molex, i overclock my cards as well. The 5850 realistically draws 150w

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P4man
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November 14, 2011, 04:37:38 PM
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Just went to check what I had on my rat rig. DeathAndTaxes, you are going to love this one.



Yep. BROWN cables Smiley. Same layout as the other splitters though. I just checked if they felt hot, and they werent. Cables seem cool enough

As an aside, this is the entire rat rig now;



DnT, you will love the blue/red fan extension cables!
Cheesy.

Ans yes, Im using 2 PSUs now. Didnt trust the antec 500W to power 5870@1Ghz + 5850 @900 Mhz + old P4 prescott cpu (yes, I know). It managed fine at stock speeds, but thought Id not push my luck, so I recycled an old 450W unit with a faulty fan, hotglued a spare fan on it. Its a rat rig after all Dont ask about power efficienciy, its not efficient, but hey, it works, and it does a good job keeping the storage room from freezing Smiley

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November 15, 2011, 09:34:03 AM
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Cable isn't a problem. According to the electrical engineering site here: http://www.rbeelectronics.com/wtable.htm - for cable runs of less than 3 feet (OK for GPU connections, surely), with 12V supply, 18 AWG is the recommended gauge for up to 40A or 240W. If you're using 16 AWG, that's the recommendation for 50A / 300W.

So according to this, the *cable* itself is good enough to supply an entire 5850 with ONE yellow wire and ONE black wire... and these are the 'recommended' gauges so I doubt the cable would ever get hot.

I've tried some rather dodgy practices in the past and never come across hot cables, except where a GPU was blowing its hot exhaust air onto the cable. Pure resistive heating? Not really ever seen a problem (other than my 10A rated 240V extension lead powering the Shelf Rig at 2.5 kW and getting VERY hot).

The problem seems to be with the connectors. As plastic says, the single Molex -> 6-pin connectors are very common and still supplied with many new cards. Even quality stuff like my Asus DirectCU II 6950s.

I suppose it depends completely on the thickness of the pins inside the Molex connector. As P4man demonstrated, the cables weren't at fault, but the crimping point between the cable and the Molex connector. If all Molex pins are the same, then there could be a problem... but if the GPU-supplied Molex plugs have thicker, uprated crimped connectors then things should be OK.

Personally I **much** prefer to use 6-pin Y-splitters, and power any twin-6-pin GPU using one 6-pin output from the PSU. The connectors themselves are rated higher than the Molex and, as pointed out above, the wire itself is NOT a problem. So every single card I use is powered from one 6-pin PSU cable, with a Y-splitter attached. Not had any problems yet.

However I will definitely test for hot connectors - since the cables shouldn't have a problem with 200-odd W, they won't get hot, but the plastic connectors most certainly can if not rated for 20-40A.

...so I give in to the rhythm, the click click clack
I'm too wasted to fight back...


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