The World's Most Powerful iMac G4...so far...

Discussion in 'iMac Mods' started by rpster, Mar 8, 2017.

  1. rpster

    rpster

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    Jun 23, 2017 at 10:57 PM #11
    rpster

    rpster

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    @colingmo @68Electra Since there's really only two fans for the whole system, it isn't very loud. I opted for a 120mm fan at the top for better airflow at lower rpms (less noise). The 90mm Noctua fan on the CPU cooler is occasionally audible at high load.

    @Cang @aquelito Further explanation of the GPU power delivery: The 12V+ supply coming into the board needs to come from one source to prevent the power supply from feeding back onto itself. Since there are technically two 12V sources in the system, the motherboard's 12V regulator and the 12V PSU itself, I need to power the video card from only one of these sources. The relay here switches 12V feeding into the PCI-E connector & 6-pin of the GPU. It is triggered by the 12V rail on the PCI-E slot on the motherboard. The riser cable is the only thing modified.

    The riser cable is modified as such:
    -PCI-E Pins Side A 2,3 and Side B 1,2,3 on the riser are disconnected (Pinout available here)
    -These pins from the Motherboard side on the riser are spliced to feed into the trigger side of the relay
    -The same pins on the GPU side of the riser are fed from the 12V Output of the Relay.
    -The GPU is now powered via the Relay, not directly from the Motherboard

    Here's a visual overview of what's going on: [​IMG]
     
    Last edited: Jun 24, 2017
  2. aquelito

    aquelito

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    Jun 24, 2017 at 12:24 PM #12
    aquelito

    aquelito

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    That's great, thank you very much for the diagram : very clever :)
    Can you please let me know the reference of the relay you are using ?

    I've been toying with the same principle, except I used a MOSFET switch.

    Indeed, before using the Gigabyte GA-H110TN and a GTX 1050 Ti, I had an Asrock H110TM-ITX and a GTX 1060, fed by a single 230W 19V AC adapter.

    As the Asrock board only takes 19V for input, I had to power the GTX 1060 with a HDPLEX 250W.
    I used the internal 2-Pin as passthrough output to feed the HDPLEX with 19V+, which feeds the GTX 1060 with 12V+.

    I also used a powered PCB riser, which 12V line as been disconnected from the PCIe slot and is powered by the HDPLEX too.

    Both the riser and MOSFET switch have been designed and made by Qinx.

    To "sync" the HDPLEX with the motherboard, the same person which build the riser made a MOSFET switch to jumper the HDPLEX 24 Pin connector.
    The MOSFET switch is plugged into a FAN header on the motherboard, which triggers the MOSFET and starts the HDPLEX.

    [​IMG]

    [​IMG]

    [​IMG]


    I then moved to the Gigabyte GA-H110-TN, for several reasons. 12V input being a good one :)

    I am currently running a G4600T and GTX 1050 Ti, so I can power my whole system with a single 12V AC adapter.
    However, I'm going next for something more powerful, an i7 6700T and a GTX 1070.
    It would be a very thin brickless work station.

    To do so, I'm going to use a 275W open-frame 12V PSU from EOS, whith a switch triggered by the mobo.

    As I'm going to use my powered riser, I cannot use the PCIe slot 12V line to trigger the switch
    Do you think I could use a FAN header or the motherboard sata power connector instead ?
     
    Last edited: Jun 24, 2017
  3. rpster

    rpster

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    Jun 24, 2017 at 7:27 PM #13
    rpster

    rpster

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    I used an OMRON G4A-1A-E 12VDC 20A Relay

    I'm calculating that MOSFET to be dissipating about 1.4W @ 12.5A (150W @ 12VDC for a GTX 1070). It might be a good idea to sink it to a heatsink or to your chassis to keep temps closer to ambient.

    Not sure if you're planning to go fanless or not, but you'll definitely need a fan to get 275W out of that PSU. It's rated to only 160W when fanless.

    Yes. I believe that these all power on at the same time.
     
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  4. aquelito

    aquelito

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    Jun 26, 2017 at 5:34 PM #14
    aquelito

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    Thanks @rpster.

    Could you please take some pictures of the relay switch wiring ?

    I understand the principles but I have a hard time figuring how you soldered the three 12V+ from the 6-Pin to the relay poles.
    Did you use a single 14 or 16AWG wire spliced in three 18AWG wires going int othe 6-pin connector ?

    Did you use FASTON terminals or did you directly solder the wire the relay poles ?


    Also, the Meanwell-EPP300-12 has a built-in 5V standby and PS-ON fuction :

    I'm not sure if it's relevant but is it possible to use this function instead of an external relay ?
     
    Last edited: Jun 26, 2017
  5. rpster

    rpster

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    Jun 26, 2017 at 6:55 PM #15
    rpster

    rpster

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    @aquelito The area around the relay is pretty tight so there really isn't a clear shot of all the connections.

    To the left, beside the wi-fi antenna, is the relay. The FASTON connectors are pointing towards the camera, with the trigger side connections facing away.

    At the top you'll spot the 6-pin PCI-E going into the GPU. The (3) 18AWG +12V lines are spliced inside the FASTON connector plugged in at the relay terminal. Then between the relay and PSU I have a single 14AWG wire feeding +12V.

    In the middle, you can see the power output of the PSU. Power input to the motherboard and to the relay are terminated here with ring terminal connectors. +12V output on the left, GND on the right.

    If you want to do that, then you need another PSU to provide constant 12-19V to the motherboard. Otherwise, you wouldn't be able to power on the system at all :)

    Since i'm using only one PSU, I can't use the PS-ON function for switching power to the GPU alone. This would switch power to the entire system.

    The yellow 22AWG pair just to the right of the GND terminal is the PS-ON line going to the power switch on the back of the iMac. Note that the spec sheet is a little unclear on this: The PSU goes into standby when PS-ON is pulled to GND.


    [​IMG]
     
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  6. aquelito

    aquelito

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    Jun 27, 2017 at 1:21 PM #16
    aquelito

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    Thanks again for your explanations.

    If I sum up with a diagram, the proposed wire harness would look like this ?

    - Both GND wires and +12V from SATA Power are soldered to the relay coil poles (bottom side), right ?
    - Would you mind sharing the exact reference of both ring and Feston terminals you used ?
    - Which crimping tool did you use ? I have the Engineer PA-09 but I'm not sure it can crimp 3 x 18AWG wires one one terminal:)
    - How many wires (with a ring terminal) can you stack on the PSU screw terminal ?

    [​IMG]

    I'm finally going to use an Artesyn CPS-253M (92% efficiency vs. 88% for the EOS PSU).

    Yes that's right... I forgot this detail...

    Saying that, having a standard 120W 12v or 19v AC adapter powering the system, coupled to a 300W GPU-dedicated internal 12V PSU, would allow a fairly compact and powerful system, without having to "mess" with a relay switch.
     
    Last edited: Jun 27, 2017
  7. rpster

    rpster

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    Jun 27, 2017 at 9:38 PM #17
    rpster

    rpster

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    Correct. Soldered and heatshrinked/hot glued
    To be honest, I'm not sure. I have had multipacks of these laying around and just used them :p
    A random one I have :p It was difficult holding all three wires into place while crimping the terminal, so I soldered them together before crimping. Thinking back on this, it might be better to get bare ring terminals (Mine have nylon insulation), solder the wires in place, then add heatshrink.
    I have two ring terminals per post. The most wires I have on one ring terminal is 4 x 18AWG

    The specs for that PSU needs airflow of 300LPM in order to hit 250W. This is roughly equivalent to a server grade 40mm fan. Without a fan, you're looking at just 155W of useable power.

    I went with the Meanwell EPP-300-12 because it is rated to 200W when fanless, and 300W with a similar fan. There is also a newer Meanwell EPP-400-12 that is capable of 250W fanless/400W with fan :) Efficiencies are about the same as the Artesyn.
     
    Last edited: Jun 27, 2017
  8. aquelito

    aquelito

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    Jun 29, 2017 at 8:24 AM #18
    aquelito

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    Thanks @rpster

    Do you confirm that the wiring diagram is correct ?

    Funny you mention it : I have one laying around, that I was going to use for an other build with a standard mini-itx board and a 12V PicoPSU.

    For my tihin mini-itx build, I was leaning towards the Artseyn as it's both smaller and more efficient.
    Money will tell !
     
  9. aquelito

    aquelito

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    Jul 5, 2017 at 11:51 AM #19
    aquelito

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    @rpster

    Could you use this kind of 5v relay module instead of soldering wires to the relay ?

    [​IMG]

    I prefer to mount a PCB on my case for reliability issues :)
     
  10. rpster

    rpster

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    Jul 7, 2017 at 8:01 PM #20
    rpster

    rpster

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    @aquelito Yes, your diagram looks correct. Also, be sure to get an appropriately size relay if you intend to use one that is already PCB mounted.
     

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