External psu for power 2nd gpu!

Discussion in 'Mac Pro' started by redarc, Dec 11, 2011.

  1. redarc, Dec 11, 2011
    Last edited: Dec 11, 2011

    redarc macrumors member

    Sep 6, 2011
    Hi all again , after many research i take up and decision to put an external psu and bring inside the pci-e spot the x2 6 pin connector inside the mac pro , what i would ask now if every psu would work for give just the power to the second ati 5870 in this case i look at this


    so if i buy x 2 6 pin connector do i have just to put them in the psu then in the mac pro just powering up the psu ? or there would be any issue about compatibility?

    thank you as always for all the info.
  2. CaptainChunk macrumors 68020


    Apr 16, 2008
    Phoenix, AZ
    There are more elegant solutions available for what you're trying to do, such as this.

    It's a little more money, but if you're not using the lower ODD bay for anything, it would look 100x better than a PC PSU dangling outside of the case.
  3. BigJohno macrumors 65816

    Jan 1, 2007
    San Francisco
    How can you get the wires down to the card?
  4. redarc thread starter macrumors member

    Sep 6, 2011

    There is only 1 way to bring pin inside mac pro and you can from behind , removing the piece that access to pce slots for gpu.. i have a second optical bay.. so the more elegant way isn t possible for me , i just asked if that 1 would worked? or there is some better psu? small maybe? anyone can help me?

    thank you
  5. ghislain macrumors member

    Apr 22, 2009
    I have done this on my mac pro and it works quite well to power a second 5870. Most importandly, you can choose a silent external PSU whereas all PSu to fit in optical bay are rather noisy. However, you will have to use a trick to power on and off the external PSU in synchrony with your mac pro. This trick relies on powering a relay switch from an internal SATA power line and connect the output of the relay to the external PSU. Details of this trick are explained in details in other forums dealing with using 2 5870 in a mac pro.
  6. redarc thread starter macrumors member

    Sep 6, 2011
    it is that hard? u got any link? also link of you're silent psu ? thank you a lot for the help!!
  7. nanofrog macrumors G4

    May 6, 2008
    All you need is a 12V Normally Open 4 pin SPST Relay (most you'll find are 20A and up, which will be more than satisfactory), which you can find in an autoparts store. As per how it works and how to wire it up, take a look here; .pdf file).

    Connect the Yellow (+12V) and Black (Gnd) wires from a Molex 4 pin or SATA Power connector to the coil of the Relay. When you power the system on, this will activate the switch portion of the relay to closed, which will be connected to both the Green and Black wires in the Main Board Connector on the PSU (connecting these two wires is what turns the second PSU on).

    And voilà, power on the MP, and the secondary PSU will be activated (you will hear an audible click from the relay).

    As per a silent PSU, you can search for that yourself on the internet (and you should know better than the rest of us how much you're willing/able to spend on this ;)).
  8. redarc thread starter macrumors member

    Sep 6, 2011

    i have to thanks you as always nanofrog for you're help ,problem is that my technical/electric know is almost close to 0 and also english on specific word its quite hard to understand for me , so in most easy way... for avoid this.. if i just take an psu and i let the cable go behind from the spot close to pci-e , put the first 6 pin on gpu then use an x2 molex to 6 pin adapter for the 2nd 6 pin gpu , then i switch on the psu when i power on the mac pro? and switch off when i power off the mac pro? will this make any problem? i saw some photo about let this work"extra psu get on with power on of mac pro" but i would not touch any electric cable from motherboard or from original psu for warranty purposes , and for not well knowledge , maybe i'll try later.. but like this... brutal and not elegant would it work? it will be anyway estetic since i have mac pro close to the wall to my desk so i know how to hide the cables!!
  9. nanofrog macrumors G4

    May 6, 2008
    It's actually not that hard. Just take a look at pg. 9 in the linked .pdf file above

    If you've a friend locally that knows the basics in electricity (i.e. someone handy fixing car electrical systems), then they should be able to explain it (native language would probably help ;)).

    Just let them know the following (SATA or Molex power connector):
    • Yellow = +12V
    • Black = Ground

    Even if the external computer PSU has a mechanical switch, it still won't turn on the +12V voltages (what the graphics card cable uses).

    To get this regulator turned ON, you have to connect both the Green and Black wires in the Main Board Connector on the PSU (20+4 connector; it's the one with the most wires in it).

    You could just attach a switch and do it manually (turn the external PSU ON first, and OFF last). But it's a pain in the rear.

    The relay will do this for you automatically.

    Nor would I recommend using the Molex connectors to attach to a 6 pin graphics card connector, as there's no way to know how much current is already being drawn from that rail (could draw too much, and kill the MP's PSU :eek:).
  10. redarc, Dec 13, 2011
    Last edited: Dec 13, 2011

    redarc thread starter macrumors member

    Sep 6, 2011
    Nanofrog , you 're so generous and as allways very good to explain me everything... i won't annoy you and i hope to don t do it!! but i need you're help.. i need more easy way.. i would avoid this"no friend ... i only know peeps that like girls or tv ...nothing else..." watching some youtube video for how to dual psu rig an pc....and i find 1 that is using this adapter



    adapter http://www.frozencpu.com/products/5637/

    do you think it would work like an pci-e splitter?? it would be much easier i think... allways if i dont have missunderstand.. i'll wait you're word.

    allways if you can , could you give me youtube link that explain steb by step what i have to do on mac pro? "most important think where i find the motherboard connector :S?

    thank you very much apologize for my poor experience.

  11. redarc thread starter macrumors member

    Sep 6, 2011


    many tells that work with no problem.. there will be any problem? i think is the same thing of when you do it manually... or not?
  12. nanofrog macrumors G4

    May 6, 2008
    When both PSU's use standard connectors, this will work.

    Unfortunately, Apple's PSU wire harness is custom, so it's highly unlikely this adapter would work in a MacPro. :(

    Forget the Main Board connector in a MacPro (see above).

    You really would want to use the method described previously (relay using a Molex or SATA power cable).

    Fortunately, digging around, I discovered a ready-made adapter (has the relay already on it - just connect up the cable ends; Molex from the MacPro's internals and Main Board connector on the second PSU and you're done).

    Xoxide.com sells it here (not sure where you live, so this may be a difficult and/or expensive if you live outside of the US).

    But it will do the job, and you won't need to make anything (won't get any easier than this). :)
  13. redarc thread starter macrumors member

    Sep 6, 2011

    you really saved me...it seems very easy!! i live in italy and i bought the add2psu with more cheap expedition.. total 34 bucks.. so i need 15-30 days for let you know if everything will go well!!

    anyway i think there must be no problen and surely you couldn't explain me more easy then this :p , last thing just for know all at 100%, i need a molex from mac pro's psu , does mac pro have it free? where do i find it? wich 1 i have to use? i need splitter? after this... i just use molex from mac pro to add2psu molex and atx 24 pin from 2nd psu to the add2psu and everything done?

    also :) be chill with me and full of patience.. you think this psu that i bought is good? http://www.amazon.com/Corsair-430-Watt-Certified-Compatible-Platforms/dp/B004W2T2TM/ref=lh_ni_t

    and more it comes with 1 x6 pin , the 5870 need 2 of them , can i use 2 molex to 1 x6 pin pci-e adapter? like any of this? if not give me pelase link of what i have to buy!!! http://www.amazon.com/s/ref=nb_sb_n...tronics&field-keywords=2+molex+to+6+pin+pci-e

    sincerely thanks to you , as allways much apprecciated;)
  14. nanofrog macrumors G4

    May 6, 2008
    Which model of MacPro do you have?

    • 2006 - 2008 have Molex connectors for the optical bays.
    • 2009 - 2010 have a SATA backplane connector (data + power)
    If you've a model with a Molex connector (2006 - 8) and the 2nd optical bay is empty, then all you'll need is a long Molex cable (aka Molex Extension cable). If the 2nd optical bay is occupied, then you'd need a Molex splitter and a Molex extension cable (presume you can find one in the EU, if not locally).

    For a 2009 - 10 model, an empty 2nd optical bay will require a SATA to Molex Cable (pay close attention to the connector gender as it's important). Just plug it into the backplane cable (it will only fit over the power signals, leaving the data pins unconnected), and attach that to a Molex Extension cable to reach out of the case and to the relay adapter linked previously.

    If the 2nd optical bay is occupied, then it will be more complicated. You'd need to give me the details in this case, and we can go from there (usually does require some splicing <attach's 2 different cables together that don't have ends that just plug into one another>, but it's easier than the relay; just splice 4 power wires together by color).

    Given it's only needed for a single graphics card, and it uses a single +12V rail, it's going to be close (rated at a max of 336W on the +12V rail - the continuous delivery would be ~238W <Max Power divided by the square root of 2; in this case 336W/1.414 = 237.6W).

    Where I'm concerned, is with the HD5870's power draw (Anandtech tested it out at 354W at full load). PCIe slots can provide up to 75W of power, so that puts the load on the PSU as 354W - 75W = 279W, which is less than the continuous capability of the CX430 V2.

    The CX500 V2 however, can (barely). It's rated at 408W max on the +12V rail, which calculates out to ~289W continuous delivery on that rail (still a single +12V design). Which is just over what it would be required for an HD5870. ;) Just add a 6 pin PSIG splitter to the 6-pin from the PSU, and you've got power to the HD5870. :D


    Now if you want to be able to install a more power hungry card later on, then get a more powerful PSU now (i.e. CX600 V2 is the largest in that family, and is still a single +12V rail design; there is a way to use a dual +12V design, and that's just to skip the PSIG splitter and connect 2x 6-pin connectors from the PSU to the card, as they're likely on separate rails).
  15. redarc, Dec 13, 2011
    Last edited: Dec 13, 2011

    redarc thread starter macrumors member

    Sep 6, 2011
    OK nanofrog , 2 problem!

    1 ) i have 2009-2010 model... please make this easy for me.. like you done till now:D"if you can find any photo or video would appreciate it , sorry for stress mate:apple:
    2)on ebay i can see that the psu i bought is not sent yet.. so i may will have some chance to get refund without need to return , i'll buy the 600watt 1 , more i have already bought x2 molex to x1 6 pin pci-e.. doesn't it give enough power? or what? i would save this 10 more bucks + the no sense adapter i bought!!

    i'll wait you're info

    if needed i could remove 1 optical drive? i won't splice :(
  16. nanofrog macrumors G4

    May 6, 2008
    Do you have anything in the 2nd optical drive?

    If not, it's super easy...

    You plug this (or the other one linked), into the SFF-8482 connector located in the empty optical bay of your MacPro (it will only fit one way). Not all of the pins will connect (data), but it will get power to a Molex end that will power the relay adapter.

    I can't make it any easier than this... plug one cable into another. No cutting, splicing, ... of wires.

    Now if you have a drive located in that bay, you can get power without losing the data signal. I've seen backplane cables with the correct gender, but I'm not sure how easy you'll be able to find this, particularly in Italy (reverse genders of what's usually found on shelves). It also requires additional cables (becomes a mess).

    So in this case, you may have to make something that will do the job (and it really isn't that hard - match red to red, yellow to yellow and so on - it's really that simple). And this may not even be necessary. It also happens to be fairly clean vs. plugging adapter into adapter into adapter ...

    It's about whether or not the +12V rail/s can deliver enough power or not.

    In the case of the CX 430 V2, it doesn't from what I can see of the HD5870's power consumption at full load (would handle it for idle to moderate loads, but if you pushed it, would stop working properly).

    So stop the order, and get one that can generate enough power for certain.

    If you've already a second optical drive in the system, you could remove it and place it in an external enclosure (i.e. USB would be more than fast enough, and it will be able to boot under multiple OS's).

    But splicing a couple of cables is cheaper and cleaner (all hidden away inside the case). And it is not hard to do (just mate up the same color wires with wire nuts or insulated crimp connectors). Seriously, it really isn't that hard (about as difficult as turning a screwdriver).
  17. BigJohno macrumors 65816

    Jan 1, 2007
    San Francisco
  18. nanofrog macrumors G4

    May 6, 2008
    That pairing of cables is to get power to the relay adapter needed to trigger the second PSU (so it will turn on when the MP is turned on automatically). Not all that's needed. ;)

    Hope this clears things up. :)
  19. redarc thread starter macrumors member

    Sep 6, 2011

    nanofrog i have 2nd optical drive bay , i didn't explain my self well , if you think i can splice.. just tell exactly what to do , "red to red " yellow to yellow"

    SFF-8482 step by step mate , i take it out from optical drive then? i have to splice the yellow and red"it means remove right" "its hard? i just have to pull with strength?" this x wire where must go? in 2 psu? but where? not if i wrong but i remember to have seen an video where SFF-8482 of optical drive bay are all all blacks in mac pro? i wrong?

    also no chance of any adapter? u know i love them :p

    yes mate , i hope i can stop the order i made an claim and asked to stop.. but still no answer.... i'll return if bad luck... i need better psu how u sayd me..

    still sorry for many , many and many tasks/questions..thank you
  20. nanofrog macrumors G4

    May 6, 2008
    Use the following 2 cables:
    Notice the color of the wires for the power (single, colored wiring; black, red, and yellow). Just match them up, and connect them using wire nuts or insulated butt splice connectors (just fold the wire on the single side over = doubles it up so it crimps properly).

    Please note the sizes/colors of the wire nuts and butt splice connectors, as those are the right size. The wire nuts are easier to use, but a bit bulkier. The crimp connectors are thinner, so will lay flatter. But you will need a pair of crimp pliers to do it properly. Your choice...

    No adapter AFAIK (never seen it, and I've looked).

    Yes, the MP's wiring is all black. But the signals are all in their proper locations.

    It's either splice what I've linked above, or use a few different adapters connected together (which is a total mess and hard to fit in what limited space exists).
  21. redarc thread starter macrumors member

    Sep 6, 2011

    mate after u typed all this i started to watch what was going to meet.. i removed for my first time the optical bay.. took me 15 minutes or so... not the propely screwer "if this is the name" but.. when i removed the x2 sata i started to get scared.. i don't feel able to splice and etc etc.. sorry if i say this... since you gave me many and many details. but i'm not sure of my skill.. and also not sure to do all good...so i would prefer the most easy and easy way.. i remove 1 of 2 optical bay.. since i rarely use them.."extreme rarely i use 1 of them" . So another question i'm sure you're bored now to help me :p, just tell me how is called that adapter sata to molex that i have to buy if possible amazon link or don t know , anything!

    if i have understand i just have to remove 1 optical bay use the sata adapter with it and take molex into the add2psu relay all right?

    being crazy with it! already bought the corsair 500 watt mate , as you sayd me!
  22. nanofrog macrumors G4

    May 6, 2008
    Well, if you're willing to remove the second optical bay, then do the following (from post 16):

    Then plug the Molex Extension cable into both this cable (one linked in this particular post) and the relay adapter, and you're done.

    There is no easier way, nor can I come up with an even simpler way to explain it.
  23. redarc thread starter macrumors member

    Sep 6, 2011
    this is the female cable u says in post 15 , i guess u mean this right? + molex extension .

    last still last.. u says me to buy the splitter 6 pin pci-e but i have already bought 2 molex to 1 6 pin is it good or?
  24. nanofrog macrumors G4

    May 6, 2008
    It's just a single Molex off of the SATA end, while the other one has 2x Molex ends.

    Either will work just as well as the other.

    So it's up to you to decide which one to buy, as the second Molex could make things easier in the future without investing much in the way of funds.

    As the CX series all use a single rail for the +12V, it will work (didn't realize you were already buying cables before you understood what you actually needed).

    You got lucky on this one... :eek: :p
  25. redarc thread starter macrumors member

    Sep 6, 2011
    woohhhhh i'm lucky mate!!! 4i'm happy thanks for all!!!


    this 1 then m8?

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