How To Rig A 2nd PSU (For Modern GPUs or Adding a Second GPU) (w/& w/o soldering)

Discussion in 'Mac Pro' started by slughead, Oct 2, 2012.

  1. slughead, Oct 2, 2012
    Last edited: Oct 11, 2012

    slughead macrumors 68040

    slughead

    Joined:
    Apr 28, 2004
    #1
    Introduction

    Please note that even though this article is directed at Mac Pro owners, much of this info can be used for PC owners too.

    Even though the 1,000 watt PSU in the Mac Pro is perfectly capable of running a modern GPU or Two, in an effort to make the inside of the computer "pretty", Apple has routed PCIe GPU power through tracers on the motherboard. The limitations of this are the same damn reasons they put ancillary power supply inputs on video cards in the first place, but Apple likes to Think Different. For some daring people who have attempted to run "too much" current through these ports, the results have been disastrous (TL;DR: *KABLOOEY*, there went 3,000 bucks).

    For this reason, people like myself who don't want to have their computer stuck in 2010 or "on fire" have decided to add a second power supply. Unfortunately, again Apple makes life difficult by making a 2nd internal PSU like this one a pain to install (although some have managed to do it by modifying their case via tin snips [Great read!]).

    The way I have done it (twice now) is by using a standard ATX PC power supply and piggy-backing it on to my mac's power supply. Basically the principle is this: 1) Mac Pro's power turns on 2) Power goes from Mac Pro into a Relay switch 3) relay switch turns secondary power supply on 4) power supply runs current to video card 5) I play Borderlands 2 for 3 days straight and my girlfriend leaves me.

    Simple, right?

    [Edit: I've now written a shortcut where you can do this without soldering].

    Disclaimer

    Though doing the procedure outlined here correctly is assumed to be be safe (assuming the components you use are not faulty), neither myself nor Latewire.com are not responsible for any damage sustained to equipment during the execution of this tutorial. This is provided for informational purposes only. Proper precautions for protection of equipment from damage and persons from bodily harm are left to the reader to enact, and in no way shall Latewire.com nor the author of this article be held at fault for use of this information for any purpose. Latewire.com and myself do not recommend doing anything on this page under any circumstances ever.

    Ingredients

    The stuff to make this fantabulous contrapulation will vary based on what you have lying around and how versatile/convenient/cheap you want your end product to be. Before you get started, read this whole thing, sit down with a piece of paper, and figure out from start to finish what you need and how you're going to do it. I'm not wiping your butt for you, these are just some ideas.

    [edit: I've also created a non-solder method for those who absolutely refuse to do it.]

    1. A Relay

    [​IMG] [​IMG]

    A relay is a little switch that activates when you apply electricity. This dingus will be activated by your Mac Pro's power supply and then subsequently activate the 2nd power supply. I found this one at my local radio shack and it works just fine.

    2. A power supply

    There are several buying guides online for how to purchase a power supply. You can get a pretty decent one for around $50 on NewEgg. I purchased this 500 watt fancy thing for $45 and paid $6 for NewEgg's 1 year Warrantee. It has blue lights and they make me happy.

    3. Wire

    18 gauge: You need 4-5 inches of 18 gauge at the very least for this project (maybe a lot more.. keep reading). I like to use 2 conductor speaker wire (2 copper wires stuck together with insulation). If you need to extend your 6 pin cables (you may be able to get by without it), do so with 18 gauge wire -- you may use 24 feet of 2-conductor wire to extend your two 6-pin cables just 4 feet (double that if you are using 1 conductor wire).

    You will definitely need at least 4-8 feet of 20 gauge wire x 2 (either by 2 pole or just buy twice as much) to trigger your relay.

    4. 6 / 8 pin extension cable(s)

    [edit: There's been some question about how much power loss you get from extension cables, I've outlined it here (TL;DR: Not significant)]

    I modified my own extension cables to length because I'm an epic badass, but provided you don't want to spend all day soldering wire after wire (and believe, me: you don't), I'd recommend at least one 16" 6 or 8 pin extension cable. You definitely want at least 14 inches long--that'll work for every video card you can buy. This one looks very nice and will work with any configuration (6 pin or 8 pin). I think I would get 1 for each port just for some extra power (so for a card with two 6 pin ports or one 6 pin + one 8 pin, get 2 of these adapters).

    Keep in mind that if you modify your extension cable, you're going to need a heck of a lot more wire (use 18 gauge for this).

    This extension cable is necessary to get power into the case from the 2nd power supply. However, 16" is going to be barely enough to just go from outside the case to the card itself. If you want your power supply under the desk, you may need to buy TWO sets of extension cables and modify one set to be several feet long. Alternatively you can modify your PSU's 6 pin cables to be longer. I have done it both ways, they both work. Food for thought.

    5. Adapters to get 12v power from internal PSU to external

    You're going to need a 12 volt source from your internal PSU, and adapters to run the power to the relay.

    Take a look inside your case and see if you have 4 pin Molex (found in PCs and earlier generation Mac Pros) OR SATA power plugs (later generation Mac Pros). If you have 4 pin molex, PLEASE use that for your 12 volt source. It will save you SOO Much headache.

    For 4 pin molex people (PCs and Older Mac Pros i.e. 2006):

    [​IMG] [​IMG]

    Something like the above should work okay (one example). You see the ground and 12 volt line is already separated so you can take it from there. Also, it has a pass-through for your 4 pin molex so you can put it in-line with your drive. However you will need to extend the cable quite a bit. For a modern Mac Pro (Older = easier), you'll need at least 4 feet of wire (recommend 20 gauge as it will be easier to string it through) to get from the 5.25" drive bay outside the case. If you like, you can stop there, but I'd recommend reading the optional portion below to make your setup easier to work with.

    For SATA power people (Newer Macs):

    [​IMG]

    You need an adapter to go from SATA power to something you can solder on. I used this adapter and modified it to have a 12v line and ground going out of the case (actually I have a whole 4 pin molex coming out, but that's extraneous). For a modern Mac Pro (Older = easier), you'll need at least 4 feet of wire (recommend 20 gauge as it will be easier to string it through) to get from the 5.25" drive bay outside the case. If you like, you can stop there, but I'd recommend reading the optional portion below to make your setup easier to work with.

    **OPTIONAL BUT HIGHLY RECOMMENDED FOR BOTH SATA/4 PIN POWER**:

    [​IMG]

    Really you can use any plug imaginable (as long as it's 2 pole) to hook the relay to the internal PSU, but this "3 pin fan" plug moves nicely through the Mac Pro case as well as being cheap. I'd recommend buying something with a female "3 pin fan" plug so you can detach the PSUs from each other more easily (modular is better!). The linked part will work with those using the SATA adapter or a molex adapter mentioned above. Later in this article I will likely just assume you've done this. If you have a Mac Pro and you do NOT do this, you will have to string the wires through your case before you solder them. At least this way you can forego that headache.

    6. Solder, Soldering iron, Shrink tube (for 18 gauge wire), knowledge of how to solder, wire strippers (18 and maybe 20 gauge), wire cutters

    You're going to be "adapting" a few things. On a side note, these simple tools and even rudimentary knowledge of how to use them will save you boatloads of money in the future when fixing broken wires and such. Imagine having your vacuum cleaner power cord gets eaten by your pet wildebeest and you have to lug the thing to a freaking repair shop and pay $50 for them to spend 5 minutes and $2 on fixing it. This really is a life skill like changing a tire or flossing that it helps to not need to pay someone else to do it.

    So in short, if you you think you're about to close this page at this point saying "WAA THIS IS TOO HARD, WHO CAN I PAY TO BUY THE NICHE PARTS I NEED; DO NOT WISH TO LEARN TO SOLDER", then think again.

    7. A video card requiring power and a computer unable to power it

    Oh details, details.

    8. OPTIONAL: A multimeter

    This is a versatile battery-operated device that is really going to make your life better
     
  2. slughead, Oct 2, 2012
    Last edited: Oct 9, 2012

    slughead thread starter macrumors 68040

    slughead

    Joined:
    Apr 28, 2004
    #2
    STAGE 1: THE RELAY (link to non-solder method)

    Step 1: Test the relay

    [​IMG] [​IMG] [​IMG]


    If you're using the radio shack relay I recommended above, you do this by connecting a 12 volt DC source (yellow wire) and a ground (black wire) to the "coil" leads (see above pinout or read your relay's schematic… the coil leads are the ones with the little coil-looking thing). It makes NO difference which is PLUS and MINUS. Essentially, it's foolproof. The 12 volt lead in computer cases is yellow, except when it's red (for those using red/black 3 pin plugs, red = 12 Volt). You'll be quick to notice that you'll be hooking 4 wires to this thing yet there are 5 pins. The "extra" pin is will "close" circuit when voltage is released. Thus if you use this pin, your project will be on when the computer is off, and off when the computer is on (the opposite if what you want).

    Please test the relay with and without power to see if it's working as expected. I'd also recommend a multimeter set on the "COND" (conductive) setting. If you don't have a multimeter, you're going to have to put the leads in series with a case fan circuit or a light bulb or something be creative (or just buy a freaking multimeter you cheap bastard). If you connect it to a light bulb at 110 volts, keep in mind you can die if you touch the hot leads. 12 volt is safe as long as you don't put it in your mouth or connect it to your pacemaker/insulin pump/electric penis pump. You know what? If you don't know what you're doing just leave this site before you sue me.

    Testing the relay will ensure that it works, and also verify you know which leads to use.

    Step 2: Solder the Relay

    [​IMG]

    I soldered the coil leads first. Again, these coil leads are going to go to your 12 volt source. For these, I wanted a 4-5 foot long 20 gauge 2-conductor wire (I used 18 because I had some). I soldered that 4' length of wire to the 3-pin female plug mentioned in "ingredients". Polarity doesn't matter folks! Remember to put some shrink tube on there so you can heat it later to cover the exposed leads.

    [​IMG] [​IMG]

    The 2nd set of leads is a bit more tricky. You're going to want to solder your other 2 wires to the two leads on the relay that are OPEN (off) without power going to the coil, and CLOSED (on) when power is applied. These leads MUST be 18 gauge wire for the next step.

    [​IMG] [​IMG]

    After that you're going to attach the relay to the 16/20 pin motheboard cable. Tin (coat in a light layer of solder) the other end of the switched leads and shove one them into the GREEN plug and the other into the neighboring BLACK plug. You will likely need to use pliers for this. If you're having trouble, make sure your wire/tinning is nice and smooth. Alternatively, you could solder in those leads directly into the green and black wires. This will likely void your warranty, however, and using the way I describe seems to be very secure with good contact. (I was going to wrap the thing in duct tape, but it's just fine dangling there).

    [​IMG]

    On the other end of your coil wires/leads, cut off the 3 pin plug from your 3 pin "extender" -- use the end that will fit into the end you plan to solder onto your 12 volt line coming off the internal PSU (Female). Remember that on the 3 pin connector, the RED wire is 12 volt, black is still ground, yellow is worthless, cut it off. I don't care if you use female or male or if you're not even using the 3 pin plug at all, just make sure it plugs into the plug that's connected to the 12volts/ground leads coming off your computer's internal PSU, and that both pins make contact.

    Alternatively, you can solder these leads directly onto a 12 volt/ground leads from the internal PSU and skip the need for plug, but that would be incredibly annoying to "unplug" when packing up to move out of your parents' basement.

    STAGE 2: THE 12V SOURCE

    "In the course of human events it becomes necessary to disassociate yourself with the ties that bind" - Mojo Nixon, quoting somebody else

    Never in my life have I been as infuriated as I have been working ways around Apple's engineered non-scalability.

    Step 1: Tap That Lead

    FOR SATA USERS (Newer Mac Pro):

    [​IMG] [​IMG]

    I'm just going to assume you bought this extender I mentioned in the "ingredients" section. Long story short the reason you want this is because Apple, in an effort to make life "easier", has made it harder. If you look in your case like I told you to, you'll see what I'm talking about.

    [​IMG] [​IMG] [​IMG] [​IMG]

    You only need to solder the yellow lead and one of the black leads to your wires. If you're using 20 gauge wire, don't use the pictured method of joining 2 pieces of wire with a 3rd--just solder them all together or use a small 18 gauge segment for that. I'm sure 20 gauge will do enough amps for a single optical drive and the relay but let's have some Obsessive Compulsive standards people! If you're doing this in a Mac Pro, you need FOUR FEET of wire to get it outside of the case. That's 48 inches, 121.92 centimeters, 0.63 toise. Got it? You'll notice that I did all 4 leads so I could have an external Molex outside my computer. This is totally optional and you probably don't want to do that. I do it because I'm crazy. If you're just going to have the relay hooked up, use 20 gauge wire because you don't need the amps of 18 gauge and it'll be easier to string through the case. If you're going to do it my way, use 18 gauge for greater justice.

    Remember, if you're going to attach anything but the '3 pin' plug to the other end (such as the relay directly or 4 pin molex), to do it AFTER you string the wires OUTSIDE the case (see step below). If you attempt to pull a 4 pin molex through the Mac Pro case, I will mock and ridicule you until my face starts hurting and I lose my voice. The 3 pin plug seems to have no problems being fished through the tight crevices of Apple's "different" design.

    FOR 4 PIN MOLEX USERS:

    [​IMG]

    I didn't do this so I didn't have pictures. Simply take the red and black leads coming off the adapter here, cut them, and extend them 4 FEET. I'd recommend reattaching the 3 pin "male" plug on the end, as I mentioned before. Use 20 gauge wire for this.

    Step 2: String the wire

    [​IMG]

    Routing the cable is the fun part. I did it differently in my setup as you can see from the pictures, but there's no need. Just run the 4 feet of wire you added in the above step through the notch in the plate in the top of the case, route it around the plate and through the hole in floor separating the 5.25" area and the HD/PCIe area. If you have an allen wrench suitable to the task, you can unbolt the plate and it may make it easier.

    Once in the PCIe/hard drive area, string it over your PCIe Cards and out of an unused PCIe port. Don't have one? I have several methods of "adapting" existing PCIe cards to allow extra cables to leave the case (Scroll down).
     
  3. slughead, Oct 2, 2012
    Last edited: Oct 6, 2012

    slughead thread starter macrumors 68040

    slughead

    Joined:
    Apr 28, 2004
    #3
    How I did it (the silly way)

    [​IMG] [​IMG] [​IMG] [​IMG] [​IMG]

    Don't ask me why, but I love having access to Molex connectors outside my case. I was booted off a hard drive sitting on top of my computer for about 2 years (it had a nice little fan on it). This is totally unnecessary and I wouldn't recommend it. If you're wondering how I fit the cable through the holes, I shoved each wire through the cheese-grater one at a time and then stripped and soldered them once they were on the other side. If I wanted to remove this, I would have to cut the cable.

    STAGE 3: THE PCIe POWER CABLE (nightmare?)

    UPDATE: I have tried my external PSU with my Mac Pro 1,1 with a 6870 and had a problem where the card I was powering with the external PSU was not being detected. The problem seems to be that the motherboard initializes the card very early in the startup process--before the 2nd PSU has time to run current to the card. Therefore, I'd recommend attaching one of the motherboard's 6 pin plugs to each of your cards in these older Macs--it resolved the issue totally. My Mac Pro 5,1 had no such issue with the 6870 or the GTX670.

    If you have an open PCIe slot, simply remove the placeholder bevel and shove the wires through the open hole. If not, you've got some sacrificing to do.

    You've basically got to choose one of your other PCIe cards to "modify" the fancy bevel on so you can run the wires. It'll also depend on which cards have warrantees left to void, how much of a pain in the ass it'll be, and so on. Look at your cards carefully, try and figure out the best way with minimal effort.

    Method 1: Lucky with the vent design (4870)

    [​IMG] [​IMG]

    I got lucky with the 4870. I just took some wire cutters and my popeye spinach strength and cut off a small section of the vent. Put the wires in that notch and put the plugs outside of the case (through the PCIe slot opening in the rear) before securing the card in place. Works great if you can do it this way!

    By the way, ignore the 4pin molex to 6-pin adapter I used… I had an old PSU.

    Method 2: Not-so-lucky with the vent design (6870)

    [​IMG] [​IMG] [​IMG]

    This one was not so easy. I had to unscrew the bevel from the card before clipping it with my superman strength. There's probably a way of doing this than dulling my neighbor's borrowed dikes.

    By the way, ignore the 4pin molex to 6-pin adapter I used… I had an old PSU.

    Method 3: Attack it with a Dremel (my current setup)

    [​IMG] [​IMG] [​IMG] [​IMG] [​IMG]

    Like most limbs and sensory organs, most of the PCIe bevel is unnecessary. All you need is enough to structurally keep the card in place. These things are often made of really hard metal and so completely over-rated for the task of keeping wires from jiggling the card loose or keeping the card in the slot.

    I chose to carve up my RocketRAID 2314 card's bevel. I unscrewed it, carved out a chunk, and put it back into place. Notice I keep the line straight from the end that goes to the motherboard all the way over, instead of carving a notch like in the 4870's bevel. This is a matter of preference, but it helps me when I'm putting the card into place. Also make sure when you do this that you don't do it in a way that will make it not fit into the case anymore (in other words, if you're an idiot: DO NOT ATTEMPT). I kept the square tab at the bottom totally in tact, for instance. I also left the part where it screws into the case in tact, with a little piece left on the superior edge for stability. Use common sense, pick another method, or don't do it at all--at any rate, don't blame me if you mess up!

    STAGE 4: VICTORY

    [​IMG]

    I have tested this with a Mac Pro 1,1 with a pair of Radeon 6870 and a Mac Pro 5,1 with a Radeon 6870 and GTX 670, as well as 5,1 with Radeon 5870 and GTX 670. There was one small issue with the 1,1 (see above) that was resolved by changing the cord configuration, but other than that I have had no issues.

    Hopefully you found this helpful. I can't believe how much time I put into this ridiculous project. Below is a video of the latest incarnation of these methods.

    http://www.youtube.com/watch?v=tgKNTG6vAWw
     
  4. OrangeSVTguy macrumors 601

    OrangeSVTguy

    Joined:
    Sep 16, 2007
    Location:
    Northeastern Ohio
    #4
    [From other thread]
    I will post pictures when I get it setup.

    I think there's enough room to route through the front and under the logic board just above the SATA ports in front of the PCI-e bay fan. I don't want to be doing any cutting of the case.

    I have an E-Power 450w PSU that mounts in the optical bay. I'm stumped as to how I want to modify the cables as the 8 pin cables that were supplied with the PSU are jumpered 6pins. The PSU has 2x 6pin ports and 2x 8pin ports. It must provide enough ground through the 6 pins. I think the other 2 unused pins are for the EPS cable to since the cables are different but still plug into the same plug.

    I need to get a volt meter so I can confirm this. I don't want to be messing around as I'm not sure how the pins are setup on this PSU. I'll also need a PCI-e power to 4pin molex adapter as that's what I'll need to power on the auxiliary PSU using the extra PCI-e power in the lower slot.
     
  5. slughead, Oct 2, 2012
    Last edited: Oct 2, 2012

    slughead thread starter macrumors 68040

    slughead

    Joined:
    Apr 28, 2004
    #5
    Keep in mind that there exist TWO 8 pin plugs in standard ATX computers: 8 pin mobo plugs with 4 x 12v and 4 x ground and 8 pin PCIe plugs with 3x 12v and 5 x ground.

    This article explains the 8pin vs 6 pin thing

    I used one of those "jumpered" (parallel?) 6 pin + 2 extra ground in my GTX 670 for a week and it worked just fine. I think the extra ground is just a safety measure to make sure you have enough power reserved for the card to function.

    edit: according to the linked article, the extra 2 pins are normally apart from the regular 6 so that way the connectors can work with both.
     
  6. slughead, Oct 5, 2012
    Last edited: Oct 6, 2012

    slughead thread starter macrumors 68040

    slughead

    Joined:
    Apr 28, 2004
    #6
    After reading a lot about "rails" on power supplies and things like that, I thought I'd throw this in there:

    If you're like me, your greatest fear is thinking you're clever by jerry-rigging something and then finding out later that you messed up as your expensive hardware is sitting there smoking in front of you. For this reason I've been reading a lot about "rails" and the 6 pin / 8 pin specifications.

    Essentially, I've found that having multiple "Rails" pose no danger to your hardware. In fact, nowadays the only impact they have is actually *protection* of your PSU from too much power being drawn from any given lead. I was worried about drawing too much power from a single rail and damaging something, but the truth is: there's absolutely NO voltage variability brought upon by lumping all your current onto a single rail--unless of course it trips the OCP ("over current protection"), in which case your PSU automatically turns off. In short, if your PSU is still *on*, everything is okay.

    Therefore, when trying to find which 12 volt leads to put your 6/8 pin setup on, keep in mind that the worst thing that can happen is your new PSU shuts off and you have to un plug and try a new lead.


    Another factoid: the connectors and 18 gauge wire for 6/8 pin connector standard conducts wattage far UNDER what the connectors/wires are physically capable of. This means you should not have any issues with wires heating up due to over-powering.


    Final factoid: Some people see these 6 pin connectors coming off PSUs with this tiny 2 pin "extra" piece to add it up to 8. This is actually completely okay and is usually standard. In fact any 6 pin to 8 pin adapters should work perfectly fine as long as there are three 12 volt leads coming off the PSU through the 6 pin cable. Remember to CHECK to make sure this is the case, because otherwise your graphics card may get confused. The power supply I bought (above) came with a 6 pin plug with only two 12 volt lines (technically it was only 5 "pin"). This actually fits with the standards put forth between the manufacturers for "6 pin" cables, but obviously it will be inadequate for running 8 pin systems. I therefore grafted on another 12 volt lead from a spare 4 pin molex the PSU. According to my research, this should have no ill-effects. So far it's been running without issue.
     
  7. slughead, Oct 6, 2012
    Last edited: Oct 9, 2012

    slughead thread starter macrumors 68040

    slughead

    Joined:
    Apr 28, 2004
    #7
    I tried this with a Mac Pro 1,1 and a Pair of 6870's today. I had one small issue with the cord configuration (detailed above), but other than that, things are working great.

    Also keep in mind more GPUs = more need for cooling. I'd recommend this video on ways to boost the fan speed if you're going to run crossfire or SLI. If you're just having your extra card (like a helper) sit there while you play games, it shouldn't produce too much heat; SLI/Xfire however require a lot more cooling.
     
  8. MacVidCards Suspended

    Joined:
    Nov 17, 2008
    Location:
    Hollywood, CA
    #8
    Thanks for writing this up.

    This is the way for people to run multiple powerful GPUs (or GTX580s !!) in their Mac pro and have it last over the long term.

    Thank you again.
     
  9. slughead, Oct 9, 2012
    Last edited: Oct 9, 2012

    slughead thread starter macrumors 68040

    slughead

    Joined:
    Apr 28, 2004
    #9
    NON-SOLDER METHOD:

    After much cajoling, my grinch heart grew 3 sizes this day and decided to reveal the easy yet clearly "not hip" way of doing this. If you're totally opposed to soldering, you can forgo the relay and just have your 2nd GPU on continuously. You still have to shove a piece of wire (or a paperclip) into the motherboard connector on your 2nd GPU--connecting the green and black leads.

    [​IMG]

    When turning the PSU on, flip the switch on the back of the PSU and make sure it is powered BEFORE you insert the staple/wire whatever. The PSU's switch is kind of a "hard" start, where the green wire is more "soft". There seems to be voltage variability within the first 1-2 seconds of the hard switch being tripped. I'm not sure why, but the circuit on all the PSUs I've used need to "warm up" for a second prior to the "green wire" starting the computer. This issue was outlined in my Build Your Own RAID enclosure article. I'm not sure of the consequences of just using the PSU's switch very often, but it seems like it could cause issues. Note: It could be perfectly fine, I have no idea!

    The advantage to this method is you need NO 12Volt source and NO relay and therefore you can get by with NO soldering. The disadvantage is that the PSU will continue to run when your computer turns off. When turning the PSU off, you can just flip the switch on it. To turn it back on, you should first disconnect the "green" lead, flip on the PSU switch, and then reconnect it.
     
  10. jeffkrigstein macrumors newbie

    Joined:
    Oct 10, 2012
    #10
    Hi there, I am intending on copying this method (in a wimpier, less wire cutting/soldering way) with a corsair PSU and a GTX680 into my 2010 mac pro.

    I just wanted to ask whether there are any issues with a graphics card being on all the time, or being switched on before your motherboard (say if you've left the PSU on while your computer is off then turn the computer on, with power already being supplied to the GPU)?

    Also, if use the method in the similar thread that you've commented on... (http://forums.macrumors.com/showthread.php?p=16014053#post16014053) does this method still allow the motherboard to communicate with the GPU to control power allocation? Or does this method result in your GPU running at 100% power all the time (and all the resulting heat etc as a result).

    Sorry if any of this is newb questions, this is my first venture into modding a computer. :)
     
  11. slughead, Oct 11, 2012
    Last edited: Oct 11, 2012

    slughead thread starter macrumors 68040

    slughead

    Joined:
    Apr 28, 2004
    #11
    The PSU has a low idle power draw, but it should not be significant unless you're using the card. There is no direct communication between the PSU and the GPU, the GPU draws power as needed and the PSU provides. I think you're over-estimating the amount of communication the motherboard has with the PSU :). Just because it has that big cable doesn't mean there's anything that intelligent going on. Check out the pinout for the motherboard plug--apart from the toggled binary Green wire and the gray wire, there is no communication (gray wire only manages the +3.3 and +5VDC leads though, and the green wire is either closed or open (on or off)). The 12v rails, therefore, are a "dumb" circuit. The GPU/mobo simply close a circuit, resistance is reduced, and power flows in to power the circuit. Your cellphone charger shouldn't use much power with the cellphone isn't plugged in--same principle.

    As far as having the power hooked up all the time, it will not somehow force your GPU to be using a significant amount of power continuously (it may have some idle thing like a fan, but that's no biggie). I am not positive this will lead to zero issues, but I really doubt it will. Like I mentioned before, however, there will be a low idle power usage by the PSU just to keep "warm".
     
  12. slamz369 macrumors newbie

    Joined:
    Jul 4, 2013
    #12
    can i use the internal PSU 6 pin connector to send to the relay to power on the second PSU?

    then use the 2 external 8pins for graphics?
     
  13. OrangeSVTguy macrumors 601

    OrangeSVTguy

    Joined:
    Sep 16, 2007
    Location:
    Northeastern Ohio
    #13
    Should work. I can't think of the top of my head if it needs 5v or 12v to turn on the aux PSU. The 6pin only supplies 12v and ground.
     
  14. Dr. Stealth, Jul 4, 2013
    Last edited: Jul 5, 2013

    Dr. Stealth macrumors 6502

    Joined:
    Sep 14, 2004
    Location:
    SoCal
    #14
    Great write up!

    Great write up! Also interesting read at latewire.com
     
  15. slughead thread starter macrumors 68040

    slughead

    Joined:
    Apr 28, 2004
    #15
    LOL if steve jobs approved of a second GPU he would've added some cables for it and we wouldn't have to piggyback power onto a 1000watt PSU
     
  16. OrangeSVTguy macrumors 601

    OrangeSVTguy

    Joined:
    Sep 16, 2007
    Location:
    Northeastern Ohio
    #16
  17. Akira28.com macrumors member

    Joined:
    Oct 2, 2013
    #17
    Is this method wrong? And if yes, why?
    I read this simple method on a forum where someone had this problem to solve too. He said easily: ground the green 5V cable and when you power on the PSU it'll start.
    This is what i made on an old PSU and it works

    CUT:
    [​IMG]

    GROUND:
    [​IMG]
     
  18. slughead thread starter macrumors 68040

    slughead

    Joined:
    Apr 28, 2004
    #18
    This is basically the same as the "paper clip method."

    Nothing wrong with it at all, except using the PSU switch to turn the thing on and off is a bit of a "hard start." I doubt it makes any difference, I did that same thing for a long time.

    In my array, I put a toggle switch between the green wire and a black one.

    To each their own, your setup seems fine to me.
     
  19. haravikk, Nov 21, 2013
    Last edited: Nov 21, 2013

    haravikk macrumors 65816

    Joined:
    May 1, 2005
    #19
    It seems to depend on the PSU; I'm using a Seasonic Platinum Series Fanless 460W PSU which is great for several reasons, but one is that if you use this paperclip trick then you can just leave the paperclip in there and rely on the switch on the back of the PSU. It's not a cheap PSU, but it seems to smooth out the voltage really well so there's no issue with doing things this way. Also, for other PSUs I believe the PWR_OK pin provides a signal indicating that the PSU is ready to be switched on, but I'm not sure how you could use that to make more intelligent behaviour, not easily anyway. I actually have a spare power switch with LED so I might hook up the LED to PWR_OK and the switch to PS_On.

    The other advantage is that it's fully modular, so if you can get the pin-out diagram from the manufacturer (I have) then you can do the modification the connector on the PSU itself, rather than having to leave the long, chunky motherboard cable attached. I suppose that breaks the no-solder rule (though you can probably just use crimp connectors), but it's dead easy to do and while you're at it you can just as easily attach a simple two-wire switch, maybe even one with an LED for good measure.

    It's not the cheapest option, but there are cheaper modular PSUs if you are going to wire on a switch, if you just want to leave the two pins permanently bridged then a more expensive PSU is necessary to make sure it won't just fry everything when you switch it on :)
     
  20. AndreeOnline macrumors 6502

    AndreeOnline

    Joined:
    Aug 15, 2014
    Location:
    Zürich
    #20
    It's now 2015 and I'm researching the gfx/PSU issue. There still isn't a really elegant solution to this.

    I really appreciate all the work previously done, like in this thread, and I then found this video that also shows the concept clearly:

    https://vimeo.com/72823826


    So, shortening a normal PSU and hooking that up is VERY easy. Making it look beautiful/practical is the harder part I guess.

    Has anyone tried to remove the whole optical bay assembly to use that space to just "place" a PSU in? And then maybe make it auto start from the Mac Pro's power? Like with a 5.25" PSU that I can't find for sale anywhere anymore...
     
  21. mikeboss macrumors 65816

    mikeboss

    Joined:
    Aug 13, 2009
    Location:
    switzerland
    #21
    yes, there is an elegant solution. and yes, it has been done with PSUs in the optical bay. you'll find the solution in this thread: http://forums.macrumors.com/showthread.php?t=1852113 especially keep an eye on 666sheep's posts.
     
  22. Synchro3 macrumors 65816

    Synchro3

    Joined:
    Jan 12, 2014
    #22
    Or just buy a SWEX: http://www.hwtools.net/Accessory/SWEX.html
     

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