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Thread: Corsair In Cable Capacitors (and others) - why located in motherboard end?

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    Default Corsair In Cable Capacitors (and others) - why located in motherboard end?

    I know this is probably obvious to many of you, but why are the in line capacitors located near the MB connection end instead of closer to the power supply?

    Edit: I think I just figured it out. Since the cable itself adds to unwanted power artifacts, having the cap at the end of the run is necessary for it to do it's job the best it can?
    Last edited by DWD1961; 03-22-2020 at 03:32 PM.

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    It is the mother board that varies the load, not the power supply, so that is where the capacitors should be.

    If the frequency of change is around 1 GHz then light can only travel 1 ft in a period (about the length of the power supply cable);
    computers these days run faster so the mother board itself is loaded with capacitors. In reality electrical signals run slower than
    light speed and the change happens over a half period. i.e. the power supply is too far away to be aware of voltage fluctuations
    in time.

    The speed of light limit is a real issue with signals, look at the wavy tracks on RAM modules so that all signals arrive at the same time.
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    Jon Gerow (03-22-2020)

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    Quote Originally Posted by ashiekh View Post
    It is the mother board that varies the load, not the power supply, so that is where the capacitors should be.

    .
    So if the cap was near the PSU or half way down the cable, it would still work, just not as efficiently?

    Also, highly interesting abut the wavy lines on the ram module and light speed. Very interesting.

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    Quote Originally Posted by DWD1961 View Post
    So if the cap was near the PSU or half way down the cable, it would still work, just not as efficiently?
    The farther from the load, the less effective the caps are.

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    Quote Originally Posted by Jon Gerow View Post
    The farther from the load, the less effective the caps are.
    So there really is no way to have these inside the PSU and do the same job, or would it just be more expensive? I know several PSU reviewers have said they don't think they are necessary and add bulk.

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    Quote Originally Posted by DWD1961 View Post
    So there really is no way to have these inside the PSU and do the same job, or would it just be more expensive? I know several PSU reviewers have said they don't think they are necessary and add bulk.
    There is no way to have the capacitors in the PSU and do the same job as the capacitors in the cables.

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    Quote Originally Posted by DWD1961 View Post
    So there really is no way to have these inside the PSU and do the same job, or would it just be more expensive? I know several PSU reviewers have said they don't think they are necessary and add bulk.

    Those decoupling/bypass capacitors are already on the mother board (closer to where they are needed) and so are not necessary in the cable; another problem is that large capacitors have significant inductance and so can't react quickly. So I agree that they are not needed in the cable or even very useful; on the mother board there are also smaller capacitors to tackle the higher frequencies (the lower frequencies can be handled inside the power supply itself).

    The clever supplies use Kelvin contacts which are sense wires watching the voltage at the end of the cable and the supply adjusts the voltage at its end to compensate for voltage drops along the cable. Of course one must be careful should the sense cables go wrong and the power supply try to over compensate.
    Last edited by ashiekh; 03-23-2020 at 09:46 AM.

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    I also noticed that the Corsair Sleeved ATX cable has the capacitors in the middle of the cable, not at the end. So, how much less efficient will that be vs the stock cables that have them right in the end?

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    It may make no difference for the following reason: large capacitors cannot handle high frequencies and it is only for the high frequencies that position really matters.

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    Quote Originally Posted by DWD1961 View Post
    I also noticed that the Corsair Sleeved ATX cable has the capacitors in the middle of the cable, not at the end. So, how much less efficient will that be vs the stock cables that have them right in the end?
    It makes a small difference. There's been a few reviews out there exposing this (OC3D, for one, I think).

    But the capacitors make so little difference in the first place... it doesn't really matter. Someone at Corsair decided to start doing it because EVGA was doing it.

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