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Author Topic: 4 pin molex to 6 pin pci-e connector. Word of warning  (Read 102412 times)
jake262144
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February 17, 2012, 10:57:41 AM
 #41

What a god-awful hack crimping two 20 AWG wires together at the molex(1) contact, where all the current will flow...
That sure is a fire waiting to happen.

And no matter what, don't ever use a sata-> molex adapter for powering anything more than a hard drive!
The SATA connector is rated much lower than that molex connector, at 4.5 amps max under ideal circumstances.



Notes:
(1) Actually, the four contact "Molex" connector should be called the 4 pin peripheral connector but everyone just calls it a molex.
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P4man
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February 17, 2012, 11:03:28 AM
 #42

Would it be safe to solder these things yourself?

I have an old spare PSU thats rated for 450W (350W on 12V, one 14A and one 15A rail) which should be plenty to power 1 5850 until my new PSU arrives.

Thing is, its old and has zero PCI-E connectors and only 2 molex connectors. And like a dozen SATA connectors.

If I were to cut my now defunct molex to PCIe adapter (keep the PCIe part), and cut some wires from the PSU (sata or maybe even from the motherboard or 4/8 pin CPU connector?)  and manually solder them.. would that be a good idea or drop dead stupid?

jake262144
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February 17, 2012, 11:23:46 AM
 #43

If you feel comfortable with a soldering iron in your hand, rock on.
Twist the copper wires together and don't skimp on the solder, give them as much as they will soak.
Just don't forget to put the shrink-wrap insulation in place before soldering the wires together Cheesy

PCIE 6-pin/8-pin plugs and contacts can be easily ordered online, you can make any kind of connector you need without that messy wire soldering.

Also, that 2*molex -> PCIE 6-pin you mentioned before looks up to the job.

EDIT::
Since you mention this is an old PSU, have you tested whether it will run with no load at 5V / 3.3V rails?
More importantly, won't it jump out of spec under the cross-load condition?
You might need to load the 5V rail with a power resistor.

Do you happen to have a multimeter lying around? Power up the card, and measure voltage on some other 12V cable connected to the same rail.
A double-rail design will likely have rail1 connected to the ATX12V connector (and perhaps the ATX 24-pin connector) and rail2 to all sata/peripheral connectors.
When in doubt and the user manual is inaccessible, open up the PSU and verify rail setup visually.
Measure again with the card having ran fully overclocked for a couple of hours. Better safe than sorry.
P4man
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February 17, 2012, 12:39:34 PM
 #44

If you feel comfortable with a soldering iron in your hand, rock on.
Twist the copper wires together and don't skimp on the solder, give them as much as they will soak.
Just don't forget to put the shrink-wrap insulation in place before soldering the wires together Cheesy

PCIE 6-pin/8-pin plugs and contacts can be easily ordered online, you can make any kind of connector you need without that messy wire soldering.

I already purchased a new PSU to be able to handle at least 3 cards. Since it wont arrive today, I just want to get through the weekend

Quote
Also, that 2*molex -> PCIE 6-pin you mentioned before looks up to the job.

Yeah, but I can only use 1 of those with this PSU, since it only has 2 molex connectors.  I need somthing to power the second PCIe connector.

I could use a second PCIe connector from another PSU, which is not up to the job of powering the entire card (on top the 5870s it has to deal with), but it might be enough for "half a 5850".

Intuition tells me its a terrible idea to power a GPU from 2 different PSUs, but Artforz claims it should be no problem... so now I have to decide whether to believe him (and potentially risk a card), or cut some wires (and potentially risk an obsolete PSU).

Quote
EDIT::
Since you mention this is an old PSU, have you tested whether it will run with no load at 5V / 3.3V rails?
More importantly, won't it jump out of spec under the cross-load condition?
You might need to load the 5V rail with a power resistor.

Ill hook up a DVD drive or something, I suppose that should do?

Quote
Do you happen to have a multimeter lying around? Power up the card, and measure voltage on some other 12V cable connected to the same rail.

I remember checking it a while back with another GPU, and it was okay-ish. 11.3V or so under load.

jake262144
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February 17, 2012, 01:06:47 PM
 #45

11.3V is already out of spec by 0.1V  Undecided
IDK how exactly you tested that PSU but do keep an eye on the voltage... it can be a sign that the unit is having a really tough time.
Let's cross the fingers and hope that the PSU can last a couple of days.

Not a DVD drive - the power utilization is nil when not actively reading a disc.

As it turns out, Art was correct - PCIE graphics manufacturers are prohibited from creating a galvanic link between PCIE power sockets.
Plug1 powers a set of voltage regulators and Plug2 - another set.
The VRM controller regulates those subsets independently and in general makes sure they behave.
bulanula
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February 17, 2012, 01:20:48 PM
 #46

Quote from: jake262144

As it turns out, Art was correct - PCIE graphics manufacturers are prohibited from creating a galvanic link between PCIE power sockets.
Plug1 powers a set of voltage regulators and Plug2 - another set.
The VRM controller regulates those subsets independently and in general makes sure they behave.


So what exactly does this mean in practical terms ?

Can mix and match PSUs on an individual GPU without problems ?

Thanks !
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February 17, 2012, 01:38:59 PM
 #47

If you feel comfortable with a soldering iron in your hand, rock on.
Twist the copper wires together and don't skimp on the solder, give them as much as they will soak.
Just don't forget to put the shrink-wrap insulation in place before soldering the wires together Cheesy

PCIE 6-pin/8-pin plugs and contacts can be easily ordered online, you can make any kind of connector you need without that messy wire soldering.

I already purchased a new PSU to be able to handle at least 3 cards. Since it wont arrive today, I just want to get through the weekend

Should be fine.  For short term you likely don't even need soldering just wire nuts.

Take that Molex -> PCIe adapter.  Cut the molex end off.
Take the PSU find some 12V and ground wires to match, cut the ends off.
Match and wire nut them.
Jumper PSU and check all voltage to ground readings w/ multimeter.

If you want to get fancy the "pins" in PCIe/Molex connector are available in most home improvement stores or radio shack.  Just rip one out of a bad connector and bring it in to match it up.  A pair of needle nose pliers will crimp them in a pinch and a drop of solder will make sure it isn't going anywhere. 
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Gerald Davis


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February 17, 2012, 01:51:52 PM
 #48

(1) Actually, the four contact "Molex" connector should be called the 4 pin peripheral connector but everyone just calls it a molex.

Yeah it bugs me too but if you don't say Molex nobody has any idea what you are talking about.  Molex makes a lot of connectors for example this one (Molex part #45559-002 and #45558-002)



Smiley

and most "Molex" connectors aren't made by Molex anyways (they are generics to save 0.25 pennies per connector).




P4man
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February 17, 2012, 01:59:56 PM
 #49

Should be fine.  For short term you likely don't even need soldering just wire nuts.


 Huh
How would that be any better than the adapter I almost set on fire?
I dont even see how my soldering would be better.

FWIW, here is a picture of the adapter after the facts:





(right click / view image for full res)

DeathAndTaxes
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Gerald Davis


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February 17, 2012, 02:11:41 PM
 #50

If I remember right that was due to reduced # of pins being used thus increasing the current on each pin and/or bad quality crimp at the connector.  Right?

I am just saying to use the connector from a Molex -> PCIe6 adapter simply as a source for the connector itself, unless you happen to have some PCIe 6 pin blank plugs laying around.

Wirenuts can handle high amperage just fine.  Most of the wiring in your wall has wirenuts and they can pull 15A per connector.  On a 6 pin connector w/ all 3 12V wires connected at most each conductor is handling ~2A.  That is nothing for the wire itself or any quality wire nut.

Just make sure the connectors are sold (no loose crimps or bad solder joints).

If you have a spare Molex to Molex adapter (sometimes used as Y connector for fans) or Molex to PCIE you can destroy it for more wiring which already has pins crimped.  If not you could always buy some pins and crimp them yourself.



P4man
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February 17, 2012, 02:40:13 PM
 #51

If I remember right that was due to reduced # of pins being used thus increasing the current on each pin and/or bad quality crimp at the connector.  Right?

The connector pin itself looks fine actually, its where the 2 cables are crimped (cramp, crump?) together that its molten. Thats why I wonder doing that myself would be any better.

Ill just go the *cough* new safe way of using 2 PSUs for 1 card and see what happens.

DeathAndTaxes
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February 17, 2012, 03:02:04 PM
 #52

If I remember right that was due to reduced # of pins being used thus increasing the current on each pin and/or bad quality crimp at the connector.  Right?

The connector pin itself looks fine actually, its where the 2 cables are crimped (cramp, crump?) together that its molten. Thats why I wonder doing that myself would be any better.

Ill just go the *cough* new safe way of using 2 PSUs for 1 card and see what happens.

Well 2 PSU is always an option.  Lets us know.  I was saying assumming you had enough 12V wires only use 1 wire per connector.

i.e.

12V from PSU ----- wire nut ------ pin in PCIe6 connector
12V from PSU ----- wire nut ------ pin in PCIe6 connector
12V from PSU ----- wire nut ------ pin in PCIe6 connector
Ground from PSU -- wire nut ------ pin in PCIe6 connector
Ground from PSU -- wire nut ------ pin in PCIe6 connector
Ground from PSU -- wire nut ------ pin in PCIe6 connector

If you didn't have enough individual conductors I would make all the connections in the wingnut to keep load on each pin down.

                           wire nut ------ pin in PCIe6 connector
12V from PSU ----- wire nut ------ pin in PCIe6 connector
                           wire nut ------ pin in PCIe6 connector

                           wire nut ------ pin in PCIe6 connector
Ground from PSU -- wire nut ------ pin in PCIe6 connector
                           wire nut ------ pin in PCIe6 connector
jake262144
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February 17, 2012, 03:03:16 PM
 #53

I have been running overvolted sapphire extreme HD5850s with this kind of molex adapters for months without problems.
Don't take my word for it, do your own math: the spec clearly says 1.5A per contact. Three contacts equal 4.5A per connector.
Moreover, the sata power connector was by a no means engineered for reliability. Instead, a lot of emphasis was put on ease of connection/disconnection.
You did notice this is a SATA - "molex" adapter, not a molex - PCIE adapter, right?
jake262144
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February 17, 2012, 03:13:00 PM
 #54

...
                             wire nut ------ pin in PCIe6 connector
12V from PSU ----- wire nut ------ pin in PCIe6 connector
                             wire nut ------ pin in PCIe6 connector

                             wire nut ------ pin in PCIe6 connector
Ground from PSU -- wire nut ------ pin in PCIe6 connector
                             wire nut ------ pin in PCIe6 connector

Did you mean:

                                      /------ pin in PCIe6 connector
12V from PSU ----- wire nut------- pin in PCIe6 connector
                                      \------ pin in PCIe6 connector

                                      /------ pin in PCIe6 connector
Ground from PSU -- wire nut------- pin in PCIe6 connector
                                      \------ pin in PCIe6 connector

(three PCIe 6-pin cables packed together at one wire nut)

Anyway, I don't see the advantage of choosing a wire nut over soldering... the latter pretty much eliminates the point of failure.
Both are 5 minute jobs...
jake262144
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February 17, 2012, 03:19:10 PM
 #55

The connector pin itself looks fine actually, its where the 2 cables are crimped (cramp, crump?) together that its molten...
The problem lies at the contact-wire interface.
Look at the difference wire gauge makes: 10 amps with 16 AWG wiring drops to merely 6 amps with 22 AWG.
A dab of solder might be to the connector what thermal paste is for CPUs.
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February 17, 2012, 03:20:22 PM
 #56

Did you mean:
(three PCIe 6-pin cables packed together at one wire nut)

Yes.  Thanks for the improved ASCII diagram.  No problem using 4 conductors.  Just be sure to use proper sized wirenut based on gauge and # of conductors.

Quote
Anyway, I don't see the advantage of choosing a wire nut over soldering... the latter pretty much eliminates the point of failure.  Both are 5 minute jobs...

He said he only needs something for the weekend and I wouldn't call a wirenut a 5 minute job. Smiley   Nothing wrong with soldering either but if it is a crap PSU and he is just looking for something to run the weekend I personally wouldn't waste the time soldering.  Maybe I am just lazy. Smiley

Now if it was some custom build (like using 3KW server PSU to power 10 GPUs) I would take the time to solder and inspect each joint.
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February 17, 2012, 03:21:31 PM
 #57

I have been running overvolted sapphire extreme HD5850s with this kind of molex adapters for months without problems.
Don't take my word for it,do your own math: the spec clearly says 1.5A per contact. 3 contacts equal 4.5A
You did notice this is a SATA - "molex" adapter, not a molex - PCIE adapter, right?

Sorry I think I need some sleep, I meant molex-pcie adapters, but SINGLE molex, as this is what sapphire supplied their 5850 extreme cards with. Not sure but I think the reason why P4man had his connectors burned was either:

a) he was unlucky to stumble upon a faulty adapter with congenital faults
or
b) there are numeours companies producing these adapters and some are of worse quality than others.

so far I only dared to connect a X600XT with sata adapter Wink
jake262144
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February 17, 2012, 03:27:16 PM
 #58

Sorry I think I need some sleep, I meant molex-pcie adapters...
No problem, I'm glad we cleared this misunderstanding.
Actually, thanks for giving me a reason to link the manufacturer's spec sheet for everyone to see.
P4man
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February 17, 2012, 03:39:28 PM
 #59

Sorry I think I need some sleep, I meant molex-pcie adapters, but SINGLE molex, as this is what sapphire supplied their 5850 extreme cards with. Not sure but I think the reason why P4man had his connectors burned was either:

a) he was unlucky to stumble upon a faulty adapter with congenital faults
or
b) there are numeours companies producing these adapters and some are of worse quality than others.

so far I only dared to connect a X600XT with sata adapter Wink

Now that you mention it, these connectors most likely came bundled with a sapphire 5850.
Its not likely I would have stumbled upon TWO faulty connectors, in the first post I describe one that burned, and now, x months later I tried with another one and burned it again.

Keep using them at your own peril. At the very least check them.

Anyway, card is working fine atm powered by 2 PSUs (and 2 times 2xmolex->PCIe).
Im not loading the 5v yet, but voltage seems decent (11.6v) and if the PSU blows up, so be it. I dont have a spare sata drive and all the other stuff I can think off needs 4pin molex. Maybe Ill cut a sata connector and solder a fan or bycicle light bulb to it, Ill see what I can find.

Thanks for all the help.

jake262144
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February 17, 2012, 03:47:49 PM
 #60

Anyway, card is working fine atm powered by 2 PSUs (and 2 times 2xmolex->PCIe).
Im not loading the 5v yet, but voltage seems decent (11.6v)...
Not broken (yet Tongue), don't fix. If the PSU works fine with no 5V load it's all for the better.
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