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One 12V rail vs two (or three)? | Antec 300 vs Cooler Master HAF 912?

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May 10, 2011 1:20:35 AM

I'm in the market for a new PC and I've got one major question along with another minor most likely based on preference.

What is the purpose of a PSU having more than one 12V rail? To the extent of my knowledge, only a MB uses a 12V rail while everything else uses PCIe, SATA power, or something of the sort.

Which case do you guys prefer, the Antec 300 (the Illusion special from New Egg is one I'm interested in when it becomes available) or the Cooler Master HAF 912? I'm stuck between the two. I'm looking to put a GPU in the range of a 6870 or a 6950 for some BF3 action along with a SSD boot drive. I know quality is Antec's middle name but what about Cooler Master?
a b ) Power supply
May 10, 2011 1:47:02 AM

Almost everything uses 12V nowadays. Get a good PSU (Corsair, Antec, Seasonic, etc) the number of rails doesn't matter. For a single HD 6950 you can get the Antec Neo Eco 620, Seasonic 620, Corsair 600 or 650, XFX 650. You can get away with a good 520-550W unit if you're on a budget. A nice 6950 is the XFX dual fan if you don't want to overclock it. Or the XFX 6870 dual fan.

Both cases are very good, depends on your personal choice. Look on YouTube for reviews, you get to see them in detail.
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May 10, 2011 2:17:00 AM

mosox said:
Almost everything uses 12V nowadays. Get a good PSU (Corsair, Antec, Seasonic, etc) the number of rails doesn't matter. For a single HD 6950 you can get the Antec Neo Eco 620, Seasonic 620, Corsair 600 or 650, XFX 650. You can get away with a good 520-550W unit if you're on a budget. A nice 6950 is the XFX dual fan if you don't want to overclock it. Or the XFX 6870 dual fan.

Both cases are very good, depends on your personal choice. Look on YouTube for reviews, you get to see them in detail.


Sorry, I don't think I made myself clear. My two questions are somewhat unrelated.

My first question is based on my lack of knowledge about PC components specifically related to PSUs. My question had nothing to do with how many rails I need it was a question of why are there PSUs with multiple 12V rails. My current understanding is that every PSU should be manufactured with only one 12V rail unless it is designed to power two MBs. Based on your response you make it seem like I need to plug a 12V rail into my GPU. I'm more than certain that is not the case.

For my second question I was looking for your opinion. I've researched both cases extensively but I personally like the Antec better based on it's looks (I'm not a fan of the raised portion of the HAF 912) and the fact that it is made out of some pretty thick material. However, I do like the sideways facing drive bays on the HAF 912 that might prevent a long card from blocking usage of bay ports facing in like on the 300.

You do however raise another question I've been meaning to ask. Is a dual fan configuration worth the extra $40? I mean, with an intake and an exhaust fan I can't see why you would need an extra fan that costs you $40 dollars unless you were planning on OCing. I don't really have any desire to OC.

http://www.newegg.com/Product/Productcompare.aspx?Submi...|14-150-527^14-150-527-TS%2C14-150-523^14-150-523-TS%2C14-102-921^14-102-921-TS%2C14-161-373^14-161-373-TS%2C14-121-437^14-121-437-TS

By my convention it would seem like the single fan XFX would be the way to go but for some reason it has gotten some pretty poor reviews. The next cheapest I would consider is the Sapphire card. Also, with the $40 I would save on the GPU, I could get a better MB/PSU.

Thank you for your response.
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a b ) Power supply
May 10, 2011 2:38:57 AM

Some stupid regulation in Europe. No more than XXX amps on a 12V rail or little Timmy might DIAF. That's the only reason for multiple rails. That and and the need for this on the modular PSUs where you use only the cables you need.

Sure you will plug a 12V PCIe connector in the video card. Same for the HDD (also they use 5V) and DVD writer and fans.

That dual fan is cooler and more silent, nothing else except for lifetime warranty (activated if registering the card on the XFX site within a week or so after the purchase. You can get that Sapphire, a good card.

Better state your budget and the parts you need, there are combo deals with discounts.
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a c 286 ) Power supply
May 10, 2011 2:51:37 AM

Almost all PSU are manufactured with a single 12V source, the rails however are just overcurrent set points on a grouping of wires to keep you from pulling too much current from the unit, this will trip in the event of a relatively higher resistance short, while SCP wont trip unless its a fairly low resistance short to ground so multiple 12V rails can help with that, but its primary existence comes from the old ATX spec that stated that for safety reasons no rail could have more than 240VA(20A @ 12V, 48A @ 5V, ~73A @ 3.3V), that restriction was intended to reduce the amount of power that could be dumped through a shorting component or into a person if they were part of the path to ground. That restriction has been lifted, as has the restriction that the CPU must have its own 12V rail to give it more stable power so there once was a mandate for multiple rails, it is now optional.
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a b ) Power supply
May 10, 2011 3:02:38 AM

Are you sure it was lifted? From what I know there's a Low Voltage Directive (LVD) in the EU that is still in place.
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a c 286 ) Power supply
May 10, 2011 3:07:38 AM

The Low voltage directive doesnt apply, the voltages are too low, in electricity low is a relative term, usually relative to high voltage lines. Low voltage usually refers to things that are high enough in power they could keep you from letting go, but low enough that it wont knock you back.
"The Directive covers electrical equipment with a voltage between 50 and 1000 V for alternating current and between 75 and 1500 V for direct current."
http://ec.europa.eu/enterprise/sectors/electrical/lvd/

Also, as of ATX V2.3 the 20A restriction for 12V rails was lifted from the ATX spec.

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May 10, 2011 3:43:22 AM

My GPU pulls ~200watts on the 12v and higher end multi-chip cards can pull ~400watts at 12v. Yes, the 12v rail(s) is used for more than just your motherboard.

As for multiple rails, on lower end PSUs, multi rails can be annoying as each rail has a limited total power and you have to be careful to make sure no single rail has too much load. In this case, one large 12v rail helps as it can usually supply your PSU's full wattage.

Higher end PSU's don't really have this limit on each rail, but they use multiple rails to help keep the power supply smooth. eg. My Antec 750 can supply 400+watts per rail and it has 4 rails. This means the total power would be 1200+watts. While it is a 750watt psu, they allowed each rail to handle the full load. This meant each rail was over-built with large caps and high end supply parts.

I don't have to be careful with which rails I use because each rail can handle anything I can throw at it, but at the same time I have multiple rails which lets me isolate each high power device from each other which keeps the voltage ripples to a minimum.

Seasonic tends to use a single large rail, which theoretically isn't as good as multiple rails, but it's much more power efficient and works just fine as Seasonic makes excellent PSUs.
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May 10, 2011 3:43:50 AM

mosox said:
Some stupid regulation in Europe. No more than XXX amps on a 12V rail or little Timmy might DIAF. That's the only reason for multiple rails. That and and the need for this on the modular PSUs where you use only the cables you need.

Sure you will plug a 12V PCIe connector in the video card. Same for the HDD (also they use 5V) and DVD writer and fans.

That dual fan is cooler and more silent, nothing else except for lifetime warranty (activated if registering the card on the XFX site within a week or so after the purchase. You can get that Sapphire, a good card.

Better state your budget and the parts you need, there are combo deals with discounts.


Well here is the current wish list:

Antec 300 - $70
ASRock Extreme4 P67 - $160
i5 2500 - $210
Sapphire 6950 1GB - $243
Corsair TX650 - $90
G.Skill Ripgaws X series 2x2GB (7-7-7-21) - $55
Hitachi Deskstar 7K1000.C 1TB 7200RPM - $60
ASUS DRW - $21
Total ~ $909

This does not include mail in rebates.

The main reason for this topic was to gain a larger understanding of PSUs in general.

Now about the connectors this PSU uses.

1 x Main connector (20+4Pin) - plugs into the MB
1 x 4+4 Pin CPU - plugs into the MB to power the CPU
8 x Peripheral - optical drive?
8 x SATA - HDDs (and SSDs?)
2 x Floppy
2 x PCI-E - GPUs

jonnyGURU reviewed the 750W version and wanted a second EPS12V rail. What purpose would that second volt rail serve?

Also, thanks for your replies and sorry for my confusion of the functionality of a 12V vs a 24 pin connector.

Edit: Of the connectors I listed above, I can't seem to determine which is the 'EPS12V' rail or if they even included that in the list:
http://www.newegg.com/Product/Product.aspx?Item=N82E168...

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a b ) Power supply
May 10, 2011 3:53:25 AM

I really hope the 300 Illusion comes back in stock this summer (I need another). I have one (see sig) and although it is definitely no frills and a little cramped in places, it does what I need and is very cool for a good price. If you have any specific questions about it, I can try to answer them. I will say though long graphics cards can be a bit of a pain. How long its that 6950? My 470 fit OK (a pretty long card).
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May 10, 2011 4:12:52 AM

A 6950 is 9 3/4 inches long. I'm ok with cramped but I wouldn't be thrilled with a blocked bay. Eventually I'd like to fit 2-3 HDDs and a SSD. Quality and upgrade-ability are my most important features when looking at cases. I'm not too wild about convenience like tool-less installation and the likes. I want a quiet case that will fit the components I want along with good airflow.
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a b ) Power supply
May 10, 2011 4:19:34 AM
a b ) Power supply
May 10, 2011 4:28:38 AM

That Hard drive is a good one (I have it and its RAID version, not in RAID though). I hope the quality doesn't go downhill with their recent purchase by Seagate.
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May 10, 2011 4:36:47 AM

mosox said:
The EPS 12V is the 1 x 4+4 Pin CPU.

Get this HDD
http://www.newegg.com/Product/Product.aspx?Item=N82E168...

Also the 2500K CPU if it's in the budget.

Cheaper good RAM CAS8
http://www.newegg.com/Product/Product.aspx?Item=N82E168...

Cheaper PSU
http://www.newegg.com/Product/Product.aspx?Item=N82E168...


I don't intend on OCing so I chose the 2500

With your new RAM recommendation it seems you're telling me $10 bucks isn't worth the upgrade from 8-8-8-24 CAS 8 to 7-7-7-21 CAS 7?
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May 10, 2011 4:38:12 AM

EXT64 said:
That Hard drive is a good one (I have it and its RAID version, not in RAID though). I hope the quality doesn't go downhill with their recent purchase by Seagate.


Are referring to the Hitachi drive?
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a b ) Power supply
May 10, 2011 4:49:31 AM

No, the Samsung. I've never had Hitachi, so I can't comment on them.
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May 11, 2011 2:31:38 PM

EXT64 said:
I really hope the 300 Illusion comes back in stock this summer (I need another). I have one (see sig) and although it is definitely no frills and a little cramped in places, it does what I need and is very cool for a good price. If you have any specific questions about it, I can try to answer them. I will say though long graphics cards can be a bit of a pain. How long its that 6950? My 470 fit OK (a pretty long card).


Did you ever have an issue with the front facing bay mounts? It seems that the longer cards would block some of the hard drive bays.
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a b ) Power supply
May 11, 2011 2:46:49 PM

Yep, it can be a bit tight. However I got a GTX470 and 2 1TB hard drives to fit fine. If you are planning for SLI/Crossfire and 2+ hard drives though, it could be a problem.
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May 11, 2011 2:49:39 PM

Alright, it seems like that would be frustrating when trying to add in new components. I think I'm going to do more looking around to find a case that has side facing bays.
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a b ) Power supply
May 11, 2011 9:33:19 PM

Wow, I had not seen that case before. Overall for the price it looks like a great choice. There are some minor flaws, but again for the price it is great. I'll be considering it for my new build as well.
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May 11, 2011 10:37:47 PM

Yeah that's what I was thinking. The only issue I could come up with is there is very little room around the back to route big cables from a PSU.
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May 12, 2011 3:17:16 AM

EXT64 said:
Wow, I had not seen that case before. Overall for the price it looks like a great choice. There are some minor flaws, but again for the price it is great. I'll be considering it for my new build as well.


I am actually beginning to lean more toward this Lian Li Lancool case because of its metal tool-less design, the ability to face the drive forwards or backwards for cable management, and the fact that I can actually remove part of the bay column to fit very large cards.

http://www.lancoolpc.com/en/product/product06.php?pr_in...
http://www.newegg.com/Product/Product.aspx?Item=N82E168...
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