Building a crossfire 7850 setup, need help with the psu

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Koen_S1

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Mar 18, 2015
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Hello,

I am planning on upgrading my system by adding another HD 7850 card. The problem is, my current card uses 2 6 pins PCI-E connectors and the card I want to buy only 1 (MSI R7850-2GD5/OC). However, I cant seem to find a PSU that has the amount of connectors I need. What would be a good solution? SATA/Molex to 6pin converters? Are they safe/are they safe enough to overclock the cards a little bit? Do I even need a new PSU or is my current one good enough (keep in mind I do wish to overclock a little bit)?
Any help is much appreciated!!

P.S. Why does my current card even need 2 6pin connectors? The max power usages is advertised to be 130W, and as far as I can find 1 6pin delivers about 75W and the rest should be deliverd by the motherboard?

My setup:
CPU: AMD Phenom II X4 965 (3.4GHz quadcore)
Motherboard: Asrock 970 Extreme3
RAM: 12GB Crucial Ballistix 1600MHz (2x2GB + 2x4GB)
GPU: XFX HD7850 2GB (AMD)
PSU: OCZ ModXstream Pro 500W

 
Solution
synphul
You shouldn't have to use molex to 6 pin connections, a proper power supply will have the necessary pcie 6+2 pin cables straight from the psu. I assume the adapters would work in a pinch but you shouldn't need them. Older cards were less efficient than the newer ones and they consumed more power meaning they had to get it from somewhere so they built them with a second pcie 6pin connection.

Something like a seasonic x650 gold, seasonic ssr-650rm, evga supernova 750 b2 should all be solid power supplies with 4 pcie 6pin connectors.
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Zerk2012

Zerk2012

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That's not a very good Idea you going to need a new PSU and buy the video card. Your 2nd card will be running at X4 speed with that motherboard.
My best advice is to save the money on the power supply sell your card and buy a RX 480 or GTX 1060. Both will give you overall better performance than SLI 7850's.
 
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Koen_S1

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Mar 18, 2015
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I do realise my CPU will bottleneck the setup, but I dont expect it to be a lot. Also I can get the 7850 basicaly for free and my plan was to use this for another year or so and then buy a completely buy a new system, hoping to re-use the PSU in that build. So apart from better options, anybody has a solution?
 
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Zerk2012

Zerk2012

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That's a fairly low quality PSU and will not power what your listing. Only 432 watts on the 12 volt rail and really what not to reuse in a new build. A general rule of thumb if your PSU don't have the connectors it's not made to power it. Sometimes it has the connectors and is still not going to power it. A lot of times if you get no extra answers it's because it's already answered but feel free to make a new post if you wish I'm off for the nite.
 
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Koen_S1

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Sorry should have been clearer, I mean use the new PSU for the new build
 
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synphul

synphul

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I wouldn't suggest crossfiring those on a 500w psu. For crossfire 550w is recommended on those cards and I'd probably go with a 600w if it were my system. When buying a psu it doesn't hurt to have a bit of overhead for breathing room so it's not maxed out (stress on the psu). Especially with the plan of using it further down the road, if a future situation calls for 600w or more and you only went up to 550w this time around you're stuck shopping for another psu again.
 
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Koen_S1

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Mar 18, 2015
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I was planning on buying a 650W PSU, and indeed it is better to spend a little money on it to be safe. However, I would still like to know if its safe to use the SATA/Molex to 6pin converters. I still dont even get why my current card uses 2 6pin PCI-E connectors
 
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synphul

synphul

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Mar 11, 2011
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You shouldn't have to use molex to 6 pin connections, a proper power supply will have the necessary pcie 6+2 pin cables straight from the psu. I assume the adapters would work in a pinch but you shouldn't need them. Older cards were less efficient than the newer ones and they consumed more power meaning they had to get it from somewhere so they built them with a second pcie 6pin connection.

Something like a seasonic x650 gold, seasonic ssr-650rm, evga supernova 750 b2 should all be solid power supplies with 4 pcie 6pin connectors.
 
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