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6870 Crosssfire.. Which PSU?

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#1
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#2
that one would work with molex to pci-e adapters but i personally would get a psu that has 4 pci-e adapters.
 
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#3
Would it make a difference if the molex and pci-e connectors are all on the same rail?
I ask as i ordered 2 6870's for crossfire and only just realised when i noticed this thread that my hx620 only has 2 pci-e connectors but they are on the same rail as the rest of the modular cabling.

Is there a reason why it's normally suggested to use a psu with the right number pci-e connectors for however many cards you are using?
 
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#4
Would it make a difference if the molex and pci-e connectors are all on the same rail?
I ask as i ordered 2 6870's for crossfire and only just realised when i noticed this thread that my hx620 only has 2 pci-e connectors but they are on the same rail as the rest of the modular cabling.
I don't see why it would be an issue unless you're overloading that rail. So far as I know there is no reason why a PSU can't have one giant 12V rail that powers everything. It's just cheaper to have several lesser 12V rails.

Also I don't think you're correct on how your rails are divided. According to the internets your HX620 has 3x12V rails. Chances are one is going to the CPU/MOBO, one to the molex connectors and one to the PCIE connectors. Either that or one to the CPU/MOBO/molex and two for the PCIE connectors... Also the HX620 is a very high quality part and apparently has load sharing capability.

Is there a reason why it's normally suggested to use a psu with the right number pci-e connectors for however many cards you are using?
I can't think of an absolute reason but hopefully PSUs with 4xpci-e connectors are expected to work when all of them are plugged in. Unfortunately I know this isn't always the case. (Also it's nice not to buy adapters, eh?)
 
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#5
it doesnt exactly matter that you use molex to pci-e adapters but imo it offers more stability without having o use converters. i would use one pci-e and one molex to pci-e on each card if you dont upgrade your psu
 
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#6
it doesnt exactly matter that you use molex to pci-e adapters but imo it offers more stability without having o use converters. i would use one pci-e and one molex to pci-e on each card if you dont upgrade your psu
But if both the molex and pci-e connectors are on the same rail and both use the same gauge wire how would it make a difference? could the connection on the wires make any difference?
 
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#7
To save people from headache if psu is multi rail .A psu with 4 pci-e connectors =manufacturer calculated load on the rails and feed from different rails generally =no overload one rail if things done correct.
You can use molex to pci-e adapters but than you need to be careful which rail you are using (and which components that rail is powering ) ,user need a deep research and may have problem if overload a rail (resetting and/or freezing while gaming ) , single rail psus dont share this problem.
Would it make a difference if the molex and pci-e connectors are all on the same rail?
It is about max +12v power rail can supply, you should not exceed its limit ,if you do you ll get reset/freezing
Is there a reason why it's normally suggested to use a psu with the right number pci-e connectors for however many cards you are using?
 
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#8
To save people from headache if psu is multi rail .A psu with 4 pci-e connectors =manufacturer calculated load on the rails and feed from different rails generally =no overload one rail if things done correct.
You can use molex to pci-e adapters but than you need to be careful which rail you are using (and which components that rail is powering ) ,user need a deep research and may have problem if overload a rail (resetting and/or freezing while gaming ) , single rail psus dont share this problem.
Would it make a difference if the molex and pci-e connectors are all on the same rail?
It is about max +12v power rail can supply, you should not exceed its limit ,if you do you ll get reset/freezing
Good to know, i should hopefully be ok then (i'm assuming a phenom 965 and 2 6870's won't draw more than 54A).
 
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#9
HX620 is good psu and youll be ok i think 6870 is drawing 163w at max load according to w1zzard .HX620 is multi rail psu, 18A from one rail is first limit and 50A from all (3) rails is second limit to care ,btw i meaned rail limit not the total psu limit (18A=216w from one rail not 50A=600w combined +12v) because youll hit the wall before psu limit if you reach rail limit (downside of multi rail psus)
According to HWsecrets new hx620 models has 2 rails (and has 28A limit for first rail 27A limit for 2nd rail )
http://www.hardwaresecrets.com/article/Corsair-HX620W-Power-Supply-Review/371/7
Reverse i think it may suffice if you did not Oced to 3.7 with high voltage but cant be sure .If you need a new psu single rail one will be better choose , look to corsair psus if you need one

Good to know, i should hopefully be ok then (i'm assuming a phenom 965 and 2 6870's won't draw more than 54A).
 
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#10
HX620 is good psu and youll be ok i think 6870 is drawing 163w at max load according to w1zzard .HX620 is multi rail psu, 18A from one rail is first limit and 50A from all (3) rails is second limit to care ,btw i meaned rail limit not the total psu limit (18A=216w from one rail not 50A=600w combined +12v) because youll hit the wall before psu limit if you reach rail limit (downside of multi rail psus)
According to HWsecrets new hx620 models has 2 rails (and has 28A limit for first rail 27A limit for 2nd rail )
http://www.hardwaresecrets.com/article/Corsair-HX620W-Power-Supply-Review/371/7
Reverse i think it may suffice if you did not Oced to 3.7 with high voltage but cant be sure .If you need a new psu single rail one will be better choose , look to corsair psus if you need one
Yea i meant as 1 rail is the motherboard/atx 8 pin connector (i think? :laugh:) and the other for everything else i just grouped up the 3 x18A it says on the psu spec to cover the cpu and gpu's all together spread across both rails alhough i know its not evenly distributed so does not work out quite like that.
One of the reasons for getting the 6870's and not something more powerful is i was pretty sure my psu could handle it, i didn't want to upgrade my psu untill next year as i want an 800w+ and i really don't need that kind of power..... yet :D

I would assume that if loaded properley the 600w OCZ ModXStream Pro in the link would be fine with crossfire 6870's given that it's listed with 2 25A 12v rails.
Also the cards come with molex to pci-e connectors (or at least most of them do) so everything should be ready to go when you get your cards.
 
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#11
I plan on overclocking for sure..
 

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#12
A 550W should be enough. But best you get a 650W or 750W. :) Preferably Corsair.
 

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#13
650W or a decent 750W should be more than enough (2 6870 pull slightly more than a single GTX480)