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DPete27
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Help Choosing Flex-ATX PSU

Wed Sep 26, 2018 10:43 am

I'm looking at 2 options for a gaming PC:
1) FSP400-60FGGBA
2) Silverstone FX350-G

I like the Silverstone because it's cheaper while still providing the power I need and it's black with sleeved cables (FWIW). I don't like that it's only got a 6-pin PCIe connector. I don't currently need an 8-pin PCIe power for the GTX1060 I'll be using, but I'd like to leave that option open for future upgrades, just in case. Since I'll be shortening all the wires considerably (probably half the currently length), is it acceptable to turn that into a 6+2 pin by splicing off the main wires like this?:
Image

The FSP unit does have the 6+2pin PCIe running straight from the unit (I think) but it's a dual rail design and I'm a little cautious about the fact that it advertises 2 x 12V @ 18A = 430W and yet it's only listed as a 400W PSU. I would assume that the CPU/mobo and PCIe don't share the same rail, but I can't find any documentation to prove/disprove this and aside from best practice, there's no standards that say PSU manufacturers HAVE to divide their rails this way. It seems the industry has moved to single rail designs to avoid this potential pitfall/confusion which would make me believe the FSP is an older platform (yet still 80+ Gold so not terribly old)

Can anyone weigh in on this.
Main: i5-3570K, ASRock Z77 Pro4-M, MSI RX480 8G, 500GB Crucial BX100, 2 TB Samsung EcoGreen F4, 16GB 1600MHz G.Skill @1.25V, EVGA 550-G2, Silverstone PS07B
HTPC: A8-5600K, MSI FM2-A75IA-E53, 4TB Seagate SSHD, 8GB 1866MHz G.Skill, Crosley D-25 Case Mod
 
derFunkenstein
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Re: Help Choosing Flex-ATX PSU

Wed Sep 26, 2018 10:47 am

A single 12v rail, so I don't see why that would be a problem, unless you drew more power than it can deliver. If something uses both the 6-pin and the 8-pin leads, you could (in theory) tie up 225W just in those two cables, plus whatever the card draws from the PCI-e slot and all the other components (drives, memory, CPU, PCH, etc, etc.)
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DPete27
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Re: Help Choosing Flex-ATX PSU

Wed Sep 26, 2018 1:19 pm

Found this:
The PCI-E connecter has 6 pins. They are not all used for power. For the 6 pin connector, Pins 1 & 3 are 12V & each can carry 8 Amps. Pin 2 by spec is not connected, although some PSU manufacturers do add a 12V line there. Pins 4 & 6 are Com return lines. Pin5 is Com for sensing. Using 2 lines, you get 12V*8A*2= 192Watts, much over the required 75Watts. With an 8 pin PCI-E connector, 2 Com lines are added (4&8) not a 12V & Com. There, Pins 1,2,3 are 12V, Pin 4 is a Com for the 8 pin connector sensing, Pin 5,7,8 are Com return lines, & pin 6 is for the 6 pin connector sensing. Using that config, 12V*8Amp*3=288 Watts, much over the required 150Watts.

TL;DR one of the 3 positive wires is not used in a 6-pin powered GPU. One of the added negative wires on a 6+2 pin connector is there because 8-pin powered GPUs use that 3rd positive wire. It sounds like *typically that 3rd positive wire in a 6-pin plug is powered from the PSU (there are 3 yellow wires shown on the Silverstone product page, why run a wire if it's unpowered) so, especially given my extraordinarily short trace distance, I can safely do the conversion as shown above. Right?
Main: i5-3570K, ASRock Z77 Pro4-M, MSI RX480 8G, 500GB Crucial BX100, 2 TB Samsung EcoGreen F4, 16GB 1600MHz G.Skill @1.25V, EVGA 550-G2, Silverstone PS07B
HTPC: A8-5600K, MSI FM2-A75IA-E53, 4TB Seagate SSHD, 8GB 1866MHz G.Skill, Crosley D-25 Case Mod

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