PSU rail question

Toggle sidebar Toggle sidebar
S

seductivedream

Honorable
Nov 24, 2013
9
0
10,510
Hi, I have the atnec hcg 750 watt psu and I currently purchased a xfx r9 390. I am able to boot up and into certain games but some games crash before I get to the main screen. I installed the drivers on a new windows install so no driver issues. My question is regarding power getting to the card. I have the 8pin and 6pin connected to the card from one rail. Can I take a 6 pin connector from a free rail and connect that to the graphics card to provide more power? I have 4 rails at 40a and they have an OCP 53a(does this mean I can combine two rails and it will not allow more than 53 amp to travel to the GPU)?

Game crashed before logging into witcher 2, 3 and even killer is dead lol. I am able to boot up into some witcher 2 but turning down the settings and the same for witcher 3. It's sporadic though and everything worked fine when I had my gtx 760 installed a few days ago.

System setup info:
MB: ASrock Z97 pro4
PSU: Antec HCG 750watts
GPU: Xfx r9 390
memory: G Skill
CPU: I7 4790k
Display:Qnix 1440p 27"
IS: W7 64-bit
 
Sort by date Sort by votes
R

Rookie_MIB

Distinguished
Jul 27, 2013
1,970
10
20,965
Looking at it, you should have -two- 12v rails @ 40A each. That means each rail is capable of providing almost 500w of power - and since the PSU is marketed as a 'SLI/Crossfire certified' PSU, that means it should handle two high-end GPUs.

Average power draw for an R9-390 is about 200-250w with perhaps some spikes in the 300w range for a few ms or so (a power draw graph is quite interesting - it's not 'smooth' by any stretch of the imagination). Regardless, the GPU power draw is well below the single rail capabilities of the HCG-750 so I don't think changing it will be a solution.

You could try it. One thing you don't know is which rail the mobo and other accessories are drawing their 12v supply from. If by chance the main ATX and the GPU are pulling from one rail, you could be getting close to that 500w limit per rail which would explain the occasional hiccups.
 
Upvote 0 Downvote
S

seductivedream

Honorable
Nov 24, 2013
9
0
10,510


Thank you for your quick response. I literallly received the notification while I was moving cabling around in my case lol. Now when you say that the ATX and GPU are pulling from the same rail, that confuses me a bit. The MB, CPU both have their own separate cables that are feeding them directly from the PSU. I can only assume those are two of the 4 12 rails. I have two remaining cables from the PSU that are laballed PCI. I am currently using one to power the r9 390. I did however switch to the other unused cable ( incase as you stated both components were on the same rail) and tried to boot up witcher 2 on ultra and it crashed. I have seen this card run on an extremely similar PC setup to mine, the only difference was the power output from the rails. Their PSUs were ouputting in the mid 40s and 50s and mine only has 40 per. I will try to combine the two PCI rails, 1 8 pin and another 6 pin and report back what happens.
 
Upvote 0 Downvote
R

Rookie_MIB

Distinguished
Jul 27, 2013
1,970
10
20,965
To clear it up - the PSU has -two- 12v rails. This is according to the specs for the PSU. I'm not sure where you're getting 4 rails from. Anyhow, if you think about it, the 24pin ATX plug has 12v leads, those have to come from one of the rails. It -has- to. It also has the other 4pin (or 8pin depending on the board) 12v supply for additional board power. That has to be coming from a 12v rail. Then you have the PEG power connector for the GPUs - each one of those also taps into one of the two 12v rails. Just because they have their own cables doesn't mean they have their own RAILS. There is a 3.3v rail, a 5.0v rail and for your PSU two 12v rails. All 12v power must come from one of those two rails.

So - lets say that the ATX and the additional 4pin/8pin for the motherboard come from one rail, and then you're using a PEG connectors which happens to also be attached to that same rail. That means you're drawing all power from -one- of the 12v rails instead of splitting the power load between the two. Of course, you'd have to figure out which PEG connector goes to which rail, and that may be a matter of trial and error.

It also points out the advantages of having a single 12v rail design for the PSU. No guessing around needed.
 
Upvote 0 Downvote
S

seductivedream

Honorable
Nov 24, 2013
9
0
10,510


I found the information from the Antec website...
http://www.antec.com/product.php?id=705200&fid=5022035&lan=nz
"Quad High Current +12V rails with high maximum load for better graphics card compatibility"
+5V 25A ±5％ 38A 50
+12V1 40A ±5％ 53A 120
+12V2 40A ±5％ 53A 120
+12V3 40A ±5％ 53A 120
+12V4 40A ±5％ 53A 120
-12V 0.5A ±10％ 120
+5VSB 3A ±5％ 50
+3.3V
25A
±5％ 38A 50

I was able to get the card working fine by connecting the 6 pin from the free PCI cable that I had. Thanks for your help and responses. Much appreciated.
 
Upvote 0 Downvote
R

Rookie_MIB

Distinguished
Jul 27, 2013
1,970
10
20,965
Well, I stand corrected. I'm just not sure I see the wisdom in making a quad-rail design, but that's how they did it. As long as you're up and running ok, I guess that's all that matters. Still, I'd like to see the internal design because regardless of how they label it, the board -does- take 12v power from both the 24pin ATX and the 4/8 pin motherboard connector. Unless they have an additional rail specifically for the CPU socket and motherboard slots (the PCIe / PCI slots all provide 12v power) they have to be drawing it from somewhere. You may want to tag the PEG connector you took off the GPU to make sure you don't inadvertently reconnect it if you pull apart your build for any reason...
 
Upvote 0 Downvote
ko888

ko888

Titan
Feb 18, 2009
16,708
41
84,990
The PCI-E power connectors are on the +12V3 and +12V4 rails.

Each hardwired PCI-E cable has two (6+2)-pin connectors on them.

If the PSU adheres to proper wire color coding then each +12V rails' yellow colored wires should have a different color stripe on them (e.g. a green stripe or a blue stripe) to indicate which +12V rail they are connected to.

Antec_HCG750_PCIECable2.jpg

Antec_HCG750_PCIECable1.jpg
 
Upvote 0 Downvote
You must log in or register to reply here.

TRENDING THREADS

Latest posts

Moderators online

Share this page

COMPANY
RESOURCES
FOLLOW
Top Bottom