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6-pin to 8-pin PCI-E adapter question

Last response: in Components
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December 2, 2012 10:46:24 PM

Hi everyone

I've decided to replace my old Gigabyte GTX 275 with MSI Lightning GTX 680.

This is my current setup:

Mother board: ASUS Rampage ii Extreme
CPU: Intel core i7-920 overclocked to 4 ghz (190 x 21, 1.25 vCore)
RAM: Patriot Viper Xtreme DDR3 6GB (3 x 2GB) 1600mhz (currently 1524mhz).
GPU: Nvidia Geforce GTX 275
PSU: Thermaltake Toughpower 750w

The problem is that the MSI Lightning uses two 8-pin PCI-E cables and my PSU only has one available. Is it safe to use a 6-pin to 8-pin PCI-E adapter?

The result will be one standart 8-pin cable connected to the card and another 6-pin cable connected to the card using the adapter.

Thanks in advance
a b ) Power supply
December 2, 2012 11:22:01 PM

Well i would by a new PSU. Dont risk with that as 8 pin needs more power than 6 pin
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December 2, 2012 11:34:57 PM

I considered doing so but if this is the right option then why does MSI include this adapter in the GPU package if it can't work properly?

edit: I did some research (I'm not an expert in power supplies) and it turns out my cable setup will generate 300w for the gpu (75w from the board + 150w from the normal 8pin cable and another 75w from the 6pin cable with the adapter), am I right?

If so, then will 300w be enough for a decent overclock without any voltage tweaks(the minimum is 195w)?

You probably want to ask why I'm not getting a new PSU along with the GPU so i can overclock it freely. The answer is that i want to get a PSU that will a support 2 way sli with overvolted cards, and I can't buy two expensive components right now.

I plan on buying Corsair HX 1050w for maximum stability. If it's overkill for 2 way sli then I'll be glad to recieve suggestions for a cheaper psu with less wattage.

Thanks
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December 3, 2012 12:16:36 AM

If its an Adapter from 2x 6pin to 1x 8pin that's fine

But if its from 1x 6pin to 1x 8pin it may not supply enough power

As 6pin PCIe plugs are rated to 75watts
8pin PCIe plugs are rated to 150watts
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December 3, 2012 12:20:03 AM

So if i use one normal 8pin cable and the other 2x 6pin to 1x 8pin will I have the same power supply as x2 normal 8pin cables?
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a c 78 ) Power supply
December 3, 2012 12:29:52 AM

Yes

6 pin = 75
8 pin = 150

While many power supplies will deliver 150 on the single 6 pin, you may just be asking for trouble(the 8 pin cable actually gives 2 extra ground wires as I see it.).

I have even seen single 4 pin molex to 8-pin adapters. Why!!!

In other news, I want a 8 pin -> 2 x 6pin to clean up my case :) 
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December 3, 2012 12:40:44 AM

Alright then. I think I'll just save up for both the GPU and the PSU. Regardless, I couldn't find 2 x 6pin to 8pin adapters anywhere.

Thanks for the replies!
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a b ) Power supply
December 3, 2012 12:47:41 AM

moshik94 said:
So if i use one normal 8pin cable and the other 2x 6pin to 1x 8pin will I have the same power supply as x2 normal 8pin cables?

The GPU won't be able to tell the difference.

Both extra pins on the 8pin connectors are GND, one of them used to tell the GPU's PWM that it can draw 150W from that rail. Were it not for the risk that the PSU's 6pin connectors and wire gauge might not be good enough to handle the extra current without excessive voltage drop or heating, you could cheat by using a jumper wire between the two pins.

The 680 should work fine with 1x8 + 1x6 without cheating.
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Anonymous
a b ) Power supply
December 3, 2012 1:00:36 AM

moshik94 said:
Alright then. I think I'll just save up for both the GPU and the PSU. Regardless, I couldn't find 2 x 6pin to 8pin adapters anywhere.

Thanks for the replies!

thats because there are non and well i see errors in some replies.

an 8 pin pci connection doesn't need more power connections than a 6 pin; the difference is it has 2 more neutral (black) connections "allowing" more power to the connection. take a look at the difference between a 6 and 8 pin connections and see for yourself: the same amount of positive (3 yellow).

what matters is the gauge of the wire being 16awg and the amps on the 12 volt rail(s). and seeing that TTTP has four "18 amp" rails it would look ok but the PSU will shut down at 14 amps.
http://www.jonnyguru.com/modules.php?name=NDReviews&op=...
Quote:
Test 6 says"OFF" in all of the cells because the PSU immediately shut off once I cranked the 12V rails up to 14A. Since the PSU would run for at least a minute when it was "cold" with this load on it, there's no doubt in my mind that this is an issue of overheating 12V rectifiers.


to provide 150 watts it would need to "continuously" provide 12.5 amps . .that may be cutting it close on that with doing it on more than one rail. not a bad PSU just not great design.


edit: crap InvalidError ninja'd me :lol:  - i was watching the game!
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a c 78 ) Power supply
December 3, 2012 1:11:15 AM

I have seen these 2 x 6 pin to 8 pin adapters. that should solve the issue of cable size(just like the dual USB plugs for external drives to get more power). The problem is these are all from random sites over seas and no clue if they are actually any good.

You can find LOTS of mis-built adapters on the net. Even Startech being a rather large company sells fan splitters with tach(yellow) cables connected. This is not right, but so many sell them this way. This can confuse the motherboard and I am sure its not good for the fans sensors to be running into one another(maybe the fans have that lead protected, best case it just messes with the speed readings.).
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a b ) Power supply
December 3, 2012 1:38:56 AM

nukemaster said:
This can confuse the motherboard and I am sure its not good for the fans sensors to be running into one another(maybe the fans have that lead protected, best case it just messes with the speed readings.).

There is no need for "protection" on the tach signal line since it is an open-collector (aka wire-OR) arrangement.

IRQ lines on the XT/ISA/EISA/VESA/PCI busses worked using wire-oring too. The #reset signal in all modern devices is almost universally managed with wire-or to accommodate all possible reset sources from hardware buttons to watchdog timers and power monitoring to system management ICs. The I2C bus used in the DDI interface for VGA/DVI/HDMI, SPD on DIMMs and countless other places also uses wire-ORing for signaling. Wire-ORing is a tool of the trade in electrical/electronics engineering.

However, you are correct that it can confuse monitoring software since one side-effect of wire-oring multiple asynchronous signals does have the effect of stretching pulse when one source kicks in before whatever previous source was pulling the line low release it, resulting in lost pulses. No (physical) harm done but it may cause system monitoring tools to report completely wonky RPM numbers.
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a c 78 ) Power supply
December 3, 2012 2:06:34 AM

I have to take your word for it :) . I just remove the extra wire.

I just not that feeding 2 outputs to one input is generally considered bad(audio/video).

If you have more info on open-collector's I would actually be quite interested, drop me a PM.
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a b ) Power supply
December 3, 2012 11:58:49 AM

nukemaster said:
If you have more info on open-collector's I would actually be quite interested, drop me a PM.

If you try searching on Google, you get millions of relevant results with schematics and probably more details than you wish for.

The reason why wire-or/open-collector is so popular for shared control/data signals is because it is simple, compatible across an extremely broad range of driving methods (bipolar, mosfet, SCR, relays, push-buttons, etc.), can easily be adapted between IO voltage levels and is intrinsically safe for all intents and purposes within reason. Whether or not it is functionally appropriate or desirable for a given application is a different story.
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Anonymous
a b ) Power supply
December 3, 2012 12:04:09 PM

:o 
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Best solution

a c 243 ) Power supply
December 3, 2012 1:49:28 PM

moshik94 said:
I considered doing so but if this is the right option then why does MSI include this adapter in the GPU package if it can't work properly?

edit: I did some research (I'm not an expert in power supplies) and it turns out my cable setup will generate 300w for the gpu (75w from the board + 150w from the normal 8pin cable and another 75w from the 6pin cable with the adapter), am I right?

If so, then will 300w be enough for a decent overclock without any voltage tweaks(the minimum is 195w)?

You probably want to ask why I'm not getting a new PSU along with the GPU so i can overclock it freely. The answer is that i want to get a PSU that will a support 2 way sli with overvolted cards, and I can't buy two expensive components right now.

I plan on buying Corsair HX 1050w for maximum stability. If it's overkill for 2 way sli then I'll be glad to recieve suggestions for a cheaper psu with less wattage.

Thanks

The 195 watts is the rating for the reference card, ( 2 x 6 pin connectors )
A GTX570 is rated at 219 watts ( 2 x 6 pins )
A GTX480 is rated at 250 watts ( 1x 6 pin , 1x 8 pin)
Many reviews show a system with the MSI using not much more power than the reference card during gaming ( even overclocked )

http://www.hardocp.com/article/2012/07/23/msi_geforce_g...

And, at it's stock clocks, less than either of the other cards I mentioned

http://www.guru3d.com/articles_pages/msi_geforce_gtx_68...

Unless you're looking to set some overclocking records and trying to burn the card up with Furmark you'll be fine with the 6 pin to 8 pin adapter

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a b ) Power supply
December 3, 2012 8:40:05 PM

delluser1 said:
Unless you're looking to set some overclocking records and trying to burn the card up with Furmark you'll be fine with the 6 pin to 8 pin adapter

Or just straight 6+8 without adapter.

The second 8pin connector is likely mostly there for people with multiple 6+2 connectors don't have dangling +2s since the extra 75W is clearly unnecessary unless shooting for the moon.
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December 10, 2012 10:30:07 AM

Best answer selected by moshik94.
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