Split 12 volt rails, how best to utilize them?

[reallyscrued]

Just received my parts for my new budget gaming build and I'm confused how best to approach the massive amounts of power this damn video card needs with the number of splits in my 12 volt rail.

The power supply I bought is an Antec BP550 Plus, that's the Basiq model. It is a modular power supply (sadly) that's actually rated for crossfire so I figured it would be a good bet that this PSU could provide enough juice for my single 4890. It has three 12 volt rails.

Now, the 4890 I have requires one 8 pin PCI-E connector and one 6 pin PCI-E connector.

My PSU has one 8 pin that branches off of my main 24 pin ATX cable and a whole seperate port for a 6 pin PCI-e connector.

My question is:

Would it be a better idea to connect the 8 pin connector from a 2 molex adapter that is from a seperate port than my 24 pin ATX connector?

Here are my specs:

Gigabyte MA-790X-UD4P
Antec BP550 Plus
HIS Radeon HD 4890


I realize this is a very convoluted description, please let me know if I can clarify any further.

 

[HOOfan 1]

You have an 8 pin PCI-E connector and an 6 pin PCI-E connector already with the PSU...just use them.

From pictures I am seeing, the 8 pin PCI-E does not branch off of the ATX connector, but they may be sleaved together at some pont...

Edit: If I had to guess, I would say the ATX 24pin, and peripheral cables are all on 1 22A rail, both CPU cables are on another 22A rail and both PCI-E connectors are on the 25A rail.

considering that a 6pin and an 8pin connector shouldn't draw more than 19A combined...you should be absolutely fine.

 

[reallyscrued]

Hoofan, that's exactly what I wanted to know. Whether the ATX and 8 pin PCI-e are sharing the same 12 volt. Here is a picture of what the back of it looks to make it a little clearer:

Plugs


See how it says 12V1 (HDD), 12V3 (PCI-E/HDD), and the last one I assume is 12V2 (ATX/PCI-E) ?

This is the spec sheet for the power:

Specs

My 12 volt rail is digitally monitored at 11.9 volts. Before this video card arrived, I had a regular PCI one and the rail was read as 12.03 volts.

The other thing is, in the HIS box, it says STOP, DO NOT USE A TWO 4 PIN MOLEX TO 8 PIN PCI-E POWER ADAPTER, ...and then they supplied the adapter in the box.

Am I reading too far into this? I've been playing Doom3 for a half an hour and it's been fucking awesome, hasn't crashed.

Edit: Bad linking skills.

 

[HOOfan 1]

I doubt it...like I said, it is probably ATX and peripherals on 1, 4 pin and 8 pin CPU on another and both PCI-E on the third. I am pretty sure this is a Delta unit, and that is the way Delta has done the other Antec PSUs.

Just use the provided pins and you will be fine.

What do you mean be digitally monitored? digital multimeter?

 

[reallyscrued]

Digitally monitored? Sorry, should have been clearer. I mean done through the computer's BIOS, digitally monitored, not physically with a multimeter.

I've heard that it isn't accurate at all, but there was a noticible .1 volt drop in my 12 volt once I installed this card.

Previous post edited for clarification.

 

[Modelworks]

.1 volt drop is nothing to worry about. Valid range is 11.4 to 12.6 volts.

 

[theAnimal]

Originally posted by: reallyscrued
Just received my parts for my new budget gaming build and I'm confused how best to approach the massive amounts of power this damn video card needs with the number of splits in my 12 volt rail.

HD4890 is only 120-140W. Plug it in and enjoy.

 

[SparkyJJO]

Originally posted by: reallyscrued
The power supply I bought is an Antec BP550 Plus, that's the Basiq model. It is a modular power supply (sadly) that's actually rated for crossfire so I figured it would be a good bet that this PSU could provide enough juice for my single 4890. It has three 12 volt rails.

What's so sad about modular? It is very useful.

 

[reallyscrued]

Uninterrupted wire is best. Making a power supply modular just adds another point of contact where two wires are joined just by touching, (not fused or melted or soldered together) thus increasing resistance. I never would have bought this PSU because of it being modular but Newegg was selling it for like 60 bucks so I just jumped on it.

I remember when the first modular power supplies started getting popular. It was usually on flashy PSUs (junk) and somehow it caught on. I could be wrong though. I don't know why Antec started doing it, PC P&C still doesn't.

 

[MagickMan]

Originally posted by: reallyscrued
Uninterrupted wire is best. Making a power supply modular just adds another point of contact where two wires are joined just by touching, (not fused or melted or soldered together) thus increasing resistance.

This is pure FUD from PCP&C, quality modular units have no disadvantages compared to non-modular PSUs. On the contrary, eliminating unneeded cabling is actually better for your PC, overall. It eliminates cable clutter which improves airflow.

 

[PM650]

Originally posted by: reallyscrued
Uninterrupted wire is best. Making a power supply modular just adds another point of contact where two wires are joined just by touching, (not fused or melted or soldered together) thus increasing resistance. I never would have bought this PSU because of it being modular but Newegg was selling it for like 60 bucks so I just jumped on it.

I remember when the first modular power supplies started getting popular. It was usually on flashy PSUs (junk) and somehow it caught on. I could be wrong though. I don't know why Antec started doing it, PC P&C still doesn't.

PCP&C is the actually the only big-league mfg to produce strictly cabled designs - even though their exclusive OEM Win-Tact has a modular unit

 

[reallyscrued]

*Sigh* I have to stop listening to the marketing on company web pages.

All's well though, this new info only makes my power supply that much better

 

[HOOfan 1]

It certainly is true...you will have added resistance and some voltage drop due to modular cables. But the resistance is insignificant.
You will have just as much resistance by making the cables longer...but no one complains when the cables are longer...however people complain about cables being too short all the time.

In fact it is a trick by some companies when sending units off to 80plus, they will send it with shorter cables than the retail units ship with.

Instead of just rejecting units offhand because people read something like modular cables cause unneeded resistance, blah blah blah. People should instead be looking to the reviews at places like jonnyguru, PC Perspective and HardOCP. These reviews will tell you how well voltage is maintained via modular cables. General statements like "modular cables are bad" show absolutely no insight at all.