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Thread: Extra ATX12V Sockets Optional?

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    Question Extra ATX12V Sockets Optional?

    I found this great spreadsheet of AM4 motherboards and I'm using it to find those that best suit my PM02 case (2 USB3 headers and 4+ system fan headers).

    I've noticed many list having a socket for a 4-pin or 8-pin CPU power connector in addition to the standard 8-pin and 24-pin.
    My PSU is the Bitfenix Formula Series 550W (as recommended in these forums ) only has a 24-pin and 4+4-pin when it comes to Motherboard cables.

    Clearly the extra connectors are to allow for CPU overclocking which I have no interest in doing (stability and longevity FTW!) but will such MOBOs throw a fit if not all their power connectors are filled?

    I don't want to filter the spreadsheet to only MOBOs with a single 8-pin connector if I don't have to as it looks like that would be quite restrictive - consistently pointing me to the Gigabyte X470 Aorus Ultra Gaming as the only option.

    I tried Googling but just got people asking about putting 4-pin connectors in 8-pin sockets :/

    Thanks!

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    For the current AM4 CPU's the extra 4 pins isn't really useful, except maybe for people who use subzero cooling and extreme overclocks. If you never gonna overclock, then the second 4 pins ATX12V connector is never gonna be useful because there won't be any AM4 CPU in the future who needs it.

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    Question

    Quote Originally Posted by -The_Mask- View Post
    the extra 4 pins isn't really useful
    By 'not useful' you seem to mean they are superfluous and I shouldn't favour boards with them.
    But that doesn't really answer my question which put another way is:
    Do boards with the extra sockets require power supplies with extra connectors?

    I plan to get a Ryzen 5 2600 and run it stock.
    Last edited by Zig131; 10-08-2018 at 05:41 PM. Reason: Add CPU info

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    No that 4 pins ATX12V connector on those motherboard is optional.

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    Ryzen processors don't consume enough current to "overload" existing 8 pin cpu power connectors.

    On regular air or water cooling, a regular 8 core Ryzen of first generation used to consume up to around 140 watts.

    The second generation of Ryzen have slightly tweaked process, which makes them slightly more efficient - they can achieve same frequencies of previous generation with slightly lower voltage required.

    They can overclock a bit better, so if you're generous, it would be safe to say a 8 core Ryzen 2xxx may consume 160-180 watts or so. With the losses in the dc-dc converter that converts 12v to the < 1.5v cpu wants, in the worst case scenario you can say a 8 core Ryzen may demand 200 watts from the 8 pin connector.

    That connector is mini-Fit series from Molex and they rate the metal contats inside the connectors at 9A per contact and the thickness of the wires allows for at least 10A through each wire (for AWG18, AWG16 wires are even thicker).

    For safety and other reasons, the people who made the ATX standards and standardized this EPS (8 pin cpu connector) say that the maximum current should not go over 7A on each pair of contacts (12v and ground).

    There's 4 pairs of wires in the EPS connector, so this means through the connector there can be maximum 4 x 7A x 12v = ~ 336 watts.

    If you ignore those recommendations and go by the next limitation which is the maximum of 9A per metal contact in the connector, then you could say the connector can handle up to 4 x 9A x 12v = ~ 432 watts.

    As you can see both these numbers are way higher than the 180-200 watts an eight core processor would pull. Your processor is a six core, which means it will peak at even less than this... expect around 15w per core less.

    So the extra 4 pin connectors on AM4 boards are kind of pointless.
    The benefits are very small. There's a couple more pairs of wires bringing 12v to the motherboard, so for example instead of sending up to 200 watts though 4 pairs, or 50 watts through each pair (~ 4.15 A per pair) you're not sending 33 watts through each pair, or around 2.75A per pair.

    This just means the metal contacts will be ever so slightly cooler and there's going to be just a bit less voltage drop and energy wasted in the cables between the power supply and the connector.

    For example, assuming 1 meter of AWG 18 wire between psu and connector, you know the resistance of AWG18 wire is almost 21 ohms per 1000 m , or 0.02 ohm per meter so you have 2 meters of wire (0.04 ohm) in each pair of wires going between connector and power supply.
    You have the formula Voltage = Current x resistance and Power = Current squared x resistance
    * at 4.15A current, you lose V = 4.15 x 0.04 = 0.166v and power lost in cable = 0.69w so if power supply sends exactly 12v, at the connector you have 11.834v
    * at 2.75A current, you lose V= 2.75 x 0.04 = 0.11v and power lost in cable = 0.3w so if power supply sends exactly 12v, at the connector you have 11.89v

    but in real world, you have less than 1m between psu and connector and on average the cpu uses way less than 200w so the actual losses are much much smaller

    Also your motherboard (and dc-dc converter that powers cpu) doesn't really care if it gets 11.8v or 12v, it's just as happy, so for the regular home user adding an extra cable to the motherboard would be just an inconvenience and extra cost and harder wire management.

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