PSU decision

Enclosures, modding, blowholes, and the power needed to run it all.

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PSU decision

Postposted on Fri Aug 31, 2012 11:07 am

I'm interested in a new power supply for a new build, but I'm a little confused about specs. Although it's a little more money, I've decided to go with a gold power supply for the high quality, high stability, and potential longevity.

Here's my question(s). Corsair offers 2 gold 750 watt psu's. An HX series and an AX series that are usually $20 to $30 difference, with the AX always being the more expensive.

Here's a comparison link. http://www.newegg.com/Product/Productco ... -010-10%23

The HX is listed as ATX12V 2.3 / EPS12V 2.91
The AX is listed as ATX12V 2.31 / EPS 12V 2.92
According to these numbers, I have to assume that the AX is better/newer version. Is that correct?

Thanks for any clarification and/or advice.
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Re: PSU decision

Postposted on Fri Aug 31, 2012 12:20 pm

Here's a pdf for EPS version 2.92:

2.91
Fixed error in 3.3V and 5V loading at higher power levels. Increased 3.3V/5V combined loading to 170W.

2.92
Higher power levels; 850W, 900W, 950W for dual GFX and 16xDIMMs. Increase 5VSB capability for 4A and 6A options. Add 12V5 and associated connectors. New efficiency specs. Update cross loading requirements; lower 12V min loading.

Here's Intel's guidelines for ATX12V 2.31

For ATX Form Factor with 12-volt connector power supplies.
12.1 Typical Power Distribution - RECOMMENDED
DC output power requirements and distributions will vary based on specific system
options and implementation.
Significant dependencies include the quantity and types of processors, memory, add-in
card slots, and peripheral bays, as well as support for advanced graphics or other
features. Figure 22 through Figure 26 shows the power distribution and cross loading
tables for power supplies in the range of 180 W to 450 W. These are recommendations
but it is ultimately the responsibility of the designer to define a power budget for a
given target product and market.


And here's more info on ATX 2.31. I was unable to locate a pdf.

The ATX 2.31 specification states that the overvoltage protection sense circuitry and reference shall reside in packages that are separate and distinct from the regulator control circuitry and reference. So no single point fault shall be able to cause a sustained over voltage condition on any or all outputs.
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Re: PSU decision

Postposted on Fri Aug 31, 2012 12:53 pm

What rig are you using this PSU for? If it's the one in your signature, that only requires ~600W. (meaning a 600W PSU would be at ~50% load when the system is at 85% load)

Here are the glaring differences I see:
- The AX has two 4+4 pin power connectors for rediculus overclocker boards like this whereas the HX only has one. (these are used to feed power to the CPU)
- The AX is fully modular, you can remove the 20+4 pin power connector if you wish. (not sure why anybody would need to do that, its hard to run a computer without power to the mobo)
- The AX has a slightly higher efficiency rating @ ">90%" (Since 80 Plus Gold is 90% and 80 Plus Platinum is 92%, the difference between that and the HX is small)
- The HX is a bit longer at 7.09" Not sure if this is the dimensions of the box or its just longer because of the 20+4 pin wires that stick out the back that can only be bent so far. 3/4" reduction for the fully modular AX seems like a reasonable explanation of the latter theory.
- The HX has a 140mm fan while the AX has an "ultra quiet" 120mm fan. The general rule says that the bigger the fan, the quieter it is; so I would imagine they would be acoustically equal.

Honestly, from what I'm seeing, I would go with the HX model. With the current $10 promo code, you'll get it for $115 after MIR. Sounds like a good deal to me.
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Re: PSU decision

Postposted on Fri Aug 31, 2012 1:27 pm

DPete27 wrote:What rig are you using this PSU for?

- The AX has two 4+4 pin power connectors for rediculus overclocker boards like this whereas the HX only has one. (these are used to feed power to the CPU)


It's for a new build for which I will be re-using my X58 motherboard that actually has two 8-pin power connectors for the cpu. I'm currently only using one 8-pin connector for the cpu, but its also not currently overclocked. I plan on a slight overclock and a gpu upgrade, and maybe more.
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Re: PSU decision

Postposted on Fri Aug 31, 2012 5:18 pm

It looks like you are getting way more PSU than you need. Can you post up the comlete specs so we can find the best fit for you?
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Re: PSU decision

Postposted on Fri Aug 31, 2012 8:33 pm

TheEmrys wrote:It looks like you are getting way more PSU than you need. Can you post up the comlete specs so we can find the best fit for you?


Staying with my x58, i7-950, and 12gb ram. Adding SSD, larger HDD, Sound Card, new version gpu or two.
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Re: PSU decision

Postposted on Sat Sep 01, 2012 10:31 am

The only thing you're doing that requires any real juice is the "new gpu or two". Unless you have a bazillion fans and drives, you can pretty much sum up your power needs as (CPU TDP + GPU TDPs)

Assuming you're planning on having capacity for 2xGTX680 or 2x7970, then you are right to be looking at around 750W. Even for two 200W+ GPUs, you don't need 750W but the headroom is useful for keeping your PSU running in it's most efficient load range and it'll be cooler/quieter if it's never working much beyond 50%. FYI, machines at 100% load and two high-end GPU's usually pull 450W from the wall, which means they are only being fed 400W from the PSU.
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Re: PSU decision

Postposted on Sat Sep 01, 2012 10:36 am

Chrispy_ wrote:The only thing you're doing that requires any real juice is the "new gpu or two". Unless you have a bazillion fans and drives, you can pretty much sum up your power needs as (CPU TDP + GPU TDPs)

Assuming you're planning on having capacity for 2xGTX680 or 2x7970, then you are right to be looking at around 750W. Even for two 200W+ GPUs, you don't need 750W but the headroom is useful for keeping your PSU running in it's most efficient load range and it'll be cooler/quieter if it's never working much beyond 50%. FYI, machines at 100% load and two high-end GPU's usually pull 450W from the wall, which means they are only being fed 400W from the PSU.


Then maybe I should just change my choices to HX650 and AX650. You're reasoning is sound, and I'm happy to save a few bucks, but I'm still unsure if I want the AX or HX. If the AX is a better component, then the extra $20 dollars is justified. Right?

*UPDATE*
The HX650 is bronze, not gold.
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Re: PSU decision

Postposted on Sat Sep 01, 2012 11:46 am

If you really think you might be going 2x gtx680s or HD 7970s, I'd go with an 850W psu. If planning to do heavy overclocking you could even go habit higher as I wouldn't be surprised if a pair of HD 7970s, pushed to the Max at over 1200 MHz could draw well in excess of 700W (total system power). (Although I wounder if you wouldn't be cpu limited with a pair of high-end cards- what CPU ate you using with the x58?) If staying with one gpu, then I agree, the 650W will suffice. Again, if planning to do some serious overclocking with something like an HD 7970, I'd take the headroom of a 750W psu.

Essentially, as stated already, a high end gpu (or 2) will take most of the power in your system. If you think there's a chance you may get 2 gpus, I'd go with the headroom of an 850W model, especially if planning to do some moderate overclocking. If only a single high end gpu, then the 650W.
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Re: PSU decision

Postposted on Sat Sep 01, 2012 2:32 pm

Just get the HX750 from the egg:

  • It's currently $10 off w/ promo code EMCNBGN37, ends 9/5 - so $115 with free shipping after rebate.
  • 650+ reviews and still 5/5 user rating
  • A bigger, slower-spinning fan
  • Those awesome flat modular cables are a joy to work with
The HX may be cheaper but it is more than adequate, certainly no flimsy unbranded POS - It's a quality CWT-manufactured unit and CWT is the common supplier for Antec. The AX is a re-branded Seasonic design. Either unit will be fine.

In a totally unrealistic stress-test-to-destruction, I would expect the AX to survive further past its ratings than the HX - but we're recommending a PSU that you'll run in the 15-50% load range, not some crazy, fuse-blowing, intentional overload bonanza.

The most important question is this: Do you prefer the blue label to the black and gold one? ;)
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Re: PSU decision

Postposted on Mon Sep 03, 2012 7:07 pm

^This. Chrispy_, I've been out of it for about two weeks, and as I've started to catch up I'm finding that I enjoy reading your posts. Keep up the good work!

To support Chrispy_'s points with first-hand experience:
The system in my signature was set up with a 2500k running at 4.8GHz on a 10% voltage bump, and had a pair of HD6950's running at stock speeds. I only have one SSD and one HDD, a WD Green at that, but there are three 120mm fans and four 140mm fans installed in the case; say two fans draws roughly what a single HDD might, if you need to make that association, though the draw is still near negligible.

With Prime95 loading the CPU and Furmark loading both GPUs, I was able to get the system to read 550w on a Kill-A-Watt, which results in about ~500w draw from internal components accounting for conversion losses within the PSU. With a Seasonic X-650 Gold, an older but quite nice unit I picked up used, I didn't feel that the system was wanting for more power, or would ever be during its serviceable life.
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Re: PSU decision

Postposted on Tue Sep 04, 2012 5:23 am

I wuv you too :P
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