How many watt do I need for this system ?

[Patroclus]

Hi, I need some advice.
What will be the minimum PSU required for this system (+ some headroom ):
- i7 medium overclk@4500
- HD5870 Crossfire
- 8 GB DDR3
- 3 7200rpm HD
- 2 SSD
- 1 DVDR/W
- 3 x 12cm fan

How many Amp of +12v should I be looking for (minimum) ?
Do you think Corsair CXM 650w (1x +12v @46A) or Seasonic SS-650JT (3 rails of +12v @19A) could handle this ?
Thanks

 

[TeknoBug]

With 2 5870's you want at least 60A on the +12 (5870 can get up to 350W under load and 2x that is 700W) so 800W to be safe especially that you're overclocking an i7 as well.

 

[lehtv]

With 2 5870's you want at least 60A on the +12 (5870 can get up to 350W under load and 2x that is 700W) so 800W to be safe especially that you're overclocking an i7 as well.

Whoa, what? No, a single 5870 can definitely not use 350W under load. 150-200W is more like it, which means 350W is not far from the truth for 5870 Crossfire. I'm not quite sure where you're getting your information from, or if you're just making that up.

What will be the minimum PSU required for this system (+ some headroom ):
- i7 medium overclk@4500
- HD5870 Crossfire
- 8 GB DDR3
- 3 7200rpm HD
- 2 SSD
- 1 DVDR/W
- 3 x 12cm fan

I'm guessing that's an i7-2600K... which means it's not as efficient as a newer Ivy or Haswell i7, but not the power hog that a first generation i7 would be.

How many Amp of +12v should I be looking for (minimum) ?
Do you think Corsair CXM 650w (1x +12v @46A) or Seasonic SS-650JT (3 rails of +12v @19A) could handle this ?
Thanks

For two 5870's, you need a unit with four PCIe connectors. Some 650W units have four, the ones you mentioned do not (assuming by CXM 650W you mean CX600M). I'd go 750W to be safe, you are running an overclocked system, after all. From a quality brand of course, with 5 year warranty as minimum, if possible within the budget.

What's your budget and where are you buying from?

 

[_Rick_]

I'd go 750W to be safe, you are running an overclocked system, after all. From a quality brand of course, with 5 year warranty as minimum, if possible within the budget.

A cursory glance at Euro-pricing shows the cheapest unit I would consider (i.e. equipped with 2x PCI 6-pin, 2x 8-pin and having at least 650W, and having that Intel certification for being Haswell compatible) to be the FSP Fortron/Source Aurum Gold 700W ATX 2.3 (AU-700) closely followed by the Sea Sonic S12G 650W ATX 2.3 (S12G-650).

Both have the five years warranty you would want, both are 80 plus Gold.
Downside: Both have widely varying prices on the market, with variations of more than 20%. The lowest budget in the Euro market at least for such a PSU would be around 85-90 euro. This should translate pretty much directly into the dollar price of the cheapest acceptable PSU for this use case.

Spending more will get you any combination of the following features, ordered by cost:
- 140mm fans
- modular cabling
- plantinum certification or gold certificiation with better actual efficiency
- an additional two years of warranty.

At the high end, there's Seasonic Platinum 660W at 130 euro.


I would expect all candidates to do well at 700W, 10% overcurrent can usually be sustained for quite a while by a quality PSU, but is unlikely to be reached, unless your CPU is munching through 225W, as are both GPUs. I would say that this is an unlikely scenario, and probably overestimates the load by around 10-15% on the GPUs.

Here's a list of 600-700W, that may be candidates. Have a browse: http://compare.eu/?cat=gehps&v=l&so...ower+States%7E1168_2%7E1167_4%7E1119_4#xf_top

 

[Patroclus]

I'm guessing that's an i7-2600K... which means it's not as efficient as a newer Ivy or Haswell i7, but not the power hog that a first generation i7 would be.

Yes it is.

Some 650W units have four, the ones you mentioned do not (assuming by CXM 650W you mean CX600M).

I always wonder whether it's okay to add 2 more molex --> Pcie converter if the PSU only provides 2 Pcie connectors. How do we know which molex to use to avoid overloading one of the +12v rails ? Does it matter ?

I would consider (i.e. equipped with 2x PCI 6-pin, 2x 8-pin and having at least 650W, and having that Intel certification for being Haswell compatible) to be the FSP Fortron/Source Aurum Gold 700W ATX 2.3 (AU-700) closely followed by the Sea Sonic S12G 650W ATX 2.3 (S12G-650). Both have the five years warranty you would want, both are 80 plus Gold.

Today, I was shopping around & looking for :
- Seasonic M12II-650 650W Modular
- Seasonic M12II-750 750W Modular
- Seasonic G-650 650W & G-750 750w
- Seasonic SS-750JS-BE 750W - Bronze
- Corsair CX-750M Modular

All no stock, except Seasonic G series 650w. The only Seasonic models in stock are either 500-650 watts of either the cheap ECO Power (upto to 600w), the X & Platinum series (too expensive for me). I was limiting myself to look for Seasonic M12 & G series because they're Haswell compatible, but alas only G-650 is in stock.
I called Corsair & Seasonic and they confirmed the models I listed are not in stock.
For Corsair CX/CXM series, I could only find the 600w models, which I'm not interested. Corsair distributor reassured me to get CSM-750 Gold series, because it is better than the older CX-750M Bronze (& still within my budget).
So.....amid my doubt to get Seasonic G-650, I ate the poison & bought CS-750M . :\

Feature wise, I find Corsair CS-750M fits my criteria:
- Big single rail of 12v : 62 Amp
- 4 Pcie
- Haswell compatible

But after reading some reviews of the CS 650watt models just now, I wonder if I made the right choice. Not many reviews yet for this CS series because it's new, but the I found 2-3 reviews of the 650watt models, and their conclusion is like "well okay it passed my test".
The CX-750M reviews sound better for me honestly.
Well, I've bought this one and I can only hope it is not really a "trashy" product from Corsair, esp. at $140.
Only 3 years warranty though. I still wish I could find Seasonic M12II or G-750

 

[_Rick_]

You shouldn't need to worry too much, despite the relatively short warranty, at that price point.
I would have probably settled for the Seasonic G-650, if it was sufficiently cheaper, especially because of the extra two years of warranty, and it meeting your specs well enough.

Newegg currently has the G-750 in stock for 130+shipping.

 

[lehtv]

I'm wondering why you're even concerned about Haswell compatibility when your CPU is Sandy Bridge? It would not make sense to upgrade the i7-2600K to a Haswell CPU, the performance gap is so small.

Also, if you did have a Haswell CPU, the PSU wouldn't need to be Haswell compatible. The fact that you have graphics cards drawing +12V power in addition to the CPU, negates the possibility of reaching a too low load for the whole system. If needed, you can also simply turn off the C7 sleep state in BIOS and any unit will be just as Haswell compatible as the next.

I always wonder whether it's okay to add 2 more molex --> Pcie converter if the PSU only provides 2 Pcie connectors. How do we know which molex to use to avoid overloading one of the +12v rails ? Does it matter ?

It really depends on how powerful the +12V of the unit is, and what the graphics cards are. In your case, using adapters would've been fine on a 650W Seasonic or similar quality unit, as long as it's a single rail unit. I wouldn't use adapters in multi rail units to avoid overloading a rail. Also I'd avoid overclocking the graphics cards if using adapters, just to keep peak load away from the maximum the PSU can handle continuously, to be safe.

Feature wise, I find Corsair CS-750M fits my criteria:
- Big single rail of 12v : 62 Amp
- 4 Pcie
- Haswell compatible

It's a decent unit I'm sure. As long as you're getting something within your budget that does what you need, without any serious compromises in quality or reliability, it's all good :thumbsup:

 

[_Rick_]

I'm wondering why you're even concerned about Haswell compatibility when your CPU is Sandy Bridge? It would not make sense to upgrade the i7-2600K to a Haswell CPU, the performance gap is so small.

Well, considering that these PSUs have 5-7 year warranties, I think having one that maintains good performance at low loads, and quick load switching is something that somewhat future proofs that investment.
Especially since future graphics cards are also likely to feature advanced power management features, especially in combination with on-die graphics.

While not essential for the present build, when getting a device with such a long lifespan, compared to the other components, which will likely see replacement in 2-3 years, I would personally prefer to have this extra feature present. On the other hand, most of the candidates have this capability anyway, so it won't exclude very many options, especially when buying new hardware.

 

[MongGrel]

A 650 continuous power unit would probably do just fine for that.

That being said I always go for some over kill myself and use a CP-850 myself with less than you have in there.

Just me maybe, I'd never go near a CX.

The Seasonics are good.