Safe to use molex to 8-pin on 4870X2?

That's_Corporate

[H]ard|Gawd
Joined
Sep 30, 2006
Messages
1,738
My PSU (Silverstone 750W Strider) does not have an 8-pin PCI-E output. Luckily, my Sapphire card came with a 2 molex to 8-pin adapter. I was going to use two separate molex outputs from the PSU into the two molex inputs of the adapter.

I can't imagine this would be a problem since Sapphire included it in the box, but will this provide adequate power? If yes or no, does anyone have any concrete proof?

Thanks in advance!
 

ta addict#2

Limp Gawd
Joined
Dec 8, 2005
Messages
487
a good quality psu such as you have equipped will do the job
I may get one and would still use the 3 year old 600w seasonic that is doing the job now and do it with an adapter
 

That's_Corporate

[H]ard|Gawd
Joined
Sep 30, 2006
Messages
1,738
a good quality psu such as you have equipped will do the job
I may get one and would still use the 3 year old 600w seasonic that is doing the job now and do it with an adapter

Okay.
Is the dual molex configuration theoretically able to provide the same juice as an 8-pin output? I believe the 8-pin does 150W max?
 

crawlgsx

[H]ard|Gawd
Joined
Aug 12, 2008
Messages
1,252
I'll tell you this much, I don't think the 6 pin - 8 pin is sufficient. I believe it is the cause for most of my X2 problems. Molex would obviously be different and I believe able to provide more power (2 molex to 1 8 pin)
 

BinarySynapse

[H]F Junkie
Joined
Feb 6, 2006
Messages
15,103
I'll tell you this much, I don't think the 6 pin - 8 pin is sufficient. I believe it is the cause for most of my X2 problems. Molex would obviously be different and I believe able to provide more power (2 molex to 1 8 pin)

what?
 

crawlgsx

[H]ard|Gawd
Joined
Aug 12, 2008
Messages
1,252
I have an adapter from newegg that goes from 1 6 pin PCIX plug to an 8 pin PCIX plug, I definitely do not think it is sufficient.

2 Molex connectors will definitely be better (more power from 2 molex connectors on separate rails than 1 PCIX connector), but I still wouldn't trust it.
 

Ste

Gawd
Joined
Nov 27, 2006
Messages
574
I use the adapter and Have had no problems.

Itll be fine.

I even monitered my 12V rail under load, and it never went out of ATX specs.
 

silent-circuit

[H]F Junkie
Joined
Sep 18, 2005
Messages
16,136
I have an adapter from newegg that goes from 1 6 pin PCIX plug to an 8 pin PCIX plug, I definitely do not think it is sufficient.

2 Molex connectors will definitely be better (more power from 2 molex connectors on separate rails than 1 PCIX connector), but I still wouldn't trust it.

The adapter isn't the cause of the problem, I can promise you that. All it does is ground out the other 2 pins in the 8 pin plug. Any half-way decent PSU manufacturer uses large enough gauge wire to carry /far/ more than 150 watts through a 6 pin PCIe connector, so it is not inability to draw that's causing your problems. If it were, the wires would melt. Simple as that.

You don't list your PSU make and model, your OS, your driver version, or anything else that might be helpful in diagnosing the problem from what I've seen, just go in to similar threads and complain that your setup is 'having problems' (which I've yet to see you detail, either). It's gone a bit far at this point.
 

crawlgsx

[H]ard|Gawd
Joined
Aug 12, 2008
Messages
1,252
I posted all my details in MY thread about MY problems.

Vista Ultimate 64bit
Tried 8.8 official, 8.8 betas, and currently on CD drivers from Visiontek.
MSI Neo2-FR p35
Toughpower 650w
q6600 @ 3.6
4gb of DDR2 800 @ 800
2 x 160gb 7200rpm SATA2 16mb cache in raid

I have had no problems with 2 x 4850's in CF
No problems with an extremely overclocked 260 GTX
Nothing but problems with my 4870 X2


To eliminate PSU I have already ordered a new one that is on the way, but I have my doubts.
 

BinarySynapse

[H]F Junkie
Joined
Feb 6, 2006
Messages
15,103
I posted all my details in MY thread about MY problems.

Vista Ultimate 64bit
Tried 8.8 official, 8.8 betas, and currently on CD drivers from Visiontek.
MSI Neo2-FR p35
Toughpower 650w
q6600 @ 3.6
4gb of DDR2 800 @ 800
2 x 160gb 7200rpm SATA2 16mb cache in raid

I have had no problems with 2 x 4850's in CF
No problems with an extremely overclocked 260 GTX
Nothing but problems with my 4870 X2


To eliminate PSU I have already ordered a new one that is on the way, but I have my doubts.

I read up on the Toughpower Qfan 650. If that's the same psu as the Toughpower 650 you have listed, then you have three PCIe leads. Two of them are on the same 18a (216watts) rail and thus wouldn't be able to provide to enough power to the hungry ass 4870x2. Try switching one of the leads out with the one you're not using.

EDIT: hmm, one of the PCIe leads is an 8pin that's not modular. So if you only have 6pins this may not be your PSU.
 

crawlgsx

[H]ard|Gawd
Joined
Aug 12, 2008
Messages
1,252
It's not the Q, its just the regular Thermaltake Toughpower 650.

Only 2 PCIX 6 pins (thought it had 4).
 

Putz

I have a custom title
Joined
Jul 8, 2002
Messages
5,413
if the 6 pin and 8 pin isnt native id just look into a new psu, using adapters isnt never wise, get a power supply built for the job out of the box :)
 

Mr. K6

Supreme [H]ardness
Joined
Mar 23, 2005
Messages
5,077
There's nothing wrong with adapters. Many times the FUD is a gimmick to get you to buy another power supply. I'd go with molex to 8-pin adapter if it was me personally though :).
 

silent-circuit

[H]F Junkie
Joined
Sep 18, 2005
Messages
16,136
There's nothing wrong with adapters. Many times the FUD is a gimmick to get you to buy another power supply. I'd go with molex to 8-pin adapter if it was me personally though :).

Considering the supply in question has a pair of 6 pin PCIe plugs and it's a multi-rail design I'd say they'd be better off using a pair of 6 to 8 pin adapters (or just jamming a wire to bridge the two sockets that the 6 pin plug doesn't cover, if you're feeling ballsy -- that's what the ones I have appear to do) as that'd put the GPU load where it's "expected" rather than sharing other rails with different components.
 

Mr. K6

Supreme [H]ardness
Joined
Mar 23, 2005
Messages
5,077
Considering the supply in question has a pair of 6 pin PCIe plugs and it's a multi-rail design I'd say they'd be better off using a pair of 6 to 8 pin adapters (or just jamming a wire to bridge the two sockets that the 6 pin plug doesn't cover, if you're feeling ballsy -- that's what the ones I have appear to do) as that'd put the GPU load where it's "expected" rather than sharing other rails with different components.
I don't know if I'm like most other users, but always have a free line or two coming from my PSU. It would be more than easy enough for me to commit that to an adapter and give the card the most stable power possible instead of "disabling" those two extra pins. My attitude is the design is there for a reason. To each his own, though.
 

silent-circuit

[H]F Junkie
Joined
Sep 18, 2005
Messages
16,136
I don't know if I'm like most other users, but always have a free line or two coming from my PSU. It would be more than easy enough for me to commit that to an adapter and give the card the most stable power possible instead of "disabling" those two extra pins. My attitude is the design is there for a reason. To each his own, though.

People regularly say that 6pin PCIe connectors are only capable of supplying 75 watts to the GPU each, as if it's a limitation of the wiring used. That's incorrect. The ATX spec only allows for 75 watts, but the wiring itself is good for something like 400 (as a previous poster pointed out). All the 7th and 8th pins in an 8 pine power connector do is provide further sources for ground, so as long as the wiring in place can take a load higher than 150 watts -- and you'd hope it can, otherwise you have a very shoddily designed PSU on your hands, a real fire hazard -- there's no real downside to using a 6 to 8 pin adapter.

There is however a potential downside to using a molex to 6pin or molex to 8pin adapter, since this could put the draw from the GPU on the wrong rails in a multi-rail PSU design. I'm not really seeing your argument, in light of that, unless we're talking about single rail PSUs only. In that case, it doesn't matter how you get the power to the pins as long as it gets there, because it's all coming from the same place anyway.
 

Mr. K6

Supreme [H]ardness
Joined
Mar 23, 2005
Messages
5,077
People regularly say that 6pin PCIe connectors are only capable of supplying 75 watts to the GPU each, as if it's a limitation of the wiring used. That's incorrect. The ATX spec only allows for 75 watts, but the wiring itself is good for something like 400 (as a previous poster pointed out). All the 7th and 8th pins in an 8 pine power connector do is provide further sources for ground, so as long as the wiring in place can take a load higher than 150 watts -- and you'd hope it can, otherwise you have a very shoddily designed PSU on your hands, a real fire hazard -- there's no real downside to using a 6 to 8 pin adapter.

There is however a potential downside to using a molex to 6pin or molex to 8pin adapter, since this could put the draw from the GPU on the wrong rails in a multi-rail PSU design. I'm not really seeing your argument, in light of that, unless we're talking about single rail PSUs only. In that case, it doesn't matter how you get the power to the pins as long as it gets there, because it's all coming from the same place anyway.
There's no doubt that the wires can supply the needed power, all I'm saying is that if you have 4 12V and 4 ground on a standard 8-pin PCI-E power, I'd like to use the same power setup. Kind of like how I plug in the molex connector on my motherboard on my family comp with a GeForce 7300 - is it necessary? Probably not, but why not? Besides, I've never used a multi-rail PSU that couldn't balance loads properly (hell, just look at the chart in the manual if you can't figure it out), but like I said in my last post, the wiring here is more of a personal preference.
 

BinarySynapse

[H]F Junkie
Joined
Feb 6, 2006
Messages
15,103
There's no doubt that the wires can supply the needed power, all I'm saying is that if you have 4 12V and 4 ground on a standard 8-pin PCI-E power, I'd like to use the same power setup. Kind of like how I plug in the molex connector on my motherboard on my family comp with a GeForce 7300 - is it necessary? Probably not, but why not? Besides, I've never used a multi-rail PSU that couldn't balance loads properly (hell, just look at the chart in the manual if you can't figure it out), but like I said in my last post, the wiring here is more of a personal preference.

The standard 8 pin PCIe connector doesn't have four 12v wires though. It only has three, just like the 6 pin. The extra two wires are ground and a 12v sense to tell the PSU how much voltage is being supplied at the connector. To the video card, that wire looks like a ground, so most PSU's manufacturers make it a ground instead of making the actual sense circuitry.
 

Mr. K6

Supreme [H]ardness
Joined
Mar 23, 2005
Messages
5,077
The standard 8 pin PCIe connector doesn't have four 12v wires though. It only has three, just like the 6 pin. The extra two wires are ground and a 12v sense to tell the PSU how much voltage is being supplied at the connector. To the video card, that wire looks like a ground, so most PSU's manufacturers make it a ground instead of making the actual sense circuitry.
Interesting, I didn't know that (I had assumed that the 4 yellow wires and 4 black wires were 12V and ground, respectively). I can see then that the adapter makes jack squat of a difference. That said, I wonder why they even bothered changing in the first place?
 

silent-circuit

[H]F Junkie
Joined
Sep 18, 2005
Messages
16,136
Interesting, I didn't know that (I had assumed that the 4 yellow wires and 4 black wires were 12V and ground, respectively). I can see then that the adapter makes jack squat of a difference. That said, I wonder why they even bothered changing in the first place?

I'd assume it was primarily a safety thing. First up, yes it's nice to have the built in load monitoring via the sense wire, but as the other guy said it's often unused.

More importantly, though, would be that there are a lot of fairly poor quality PSUs out there with 2 6pin PCIe power connectors on them that could /never/ power something like a 4870X2. Changing the cable makes most people think "Oh man I need a new PSU, I don't have the right kind of wire for that graphics card" and probably avoids a good many fireworks displays.
 
Top