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Thread: power supplies with minimal radio interferance?

  1. #241
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    I'm no expert, but shouldn't the wire go up in smoke if the amp carried in it is too high?

    What bothers me the most is I dont understand why the ATX standard uses several cables to carry the same voltage? My current understanding is that they are different circuits, carrying different "amp's." to the Board, so, what did I mess up by merging them together?

    My mainboard users a 20pin ATX connector so the only merged cables are 5V and 3.3V. (No 2nd CPU power cable or the extra 4 pins on the plug)

    I'm hoping its not a poor cable connection as it works fine when in the BIOS config screen so focus is on my merged cables. I'll see if I can fiddle around and figure it out.


    Update: I tested by limiting Windows to only use one core and powered the HD from a 2nd psu: Booted fine. Turned off the CPU limitation, did not boot fine.


    JJ

  2. #242
    Maximum Bitrate Mickz's Avatar
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    The wire will not burn if the current is insufficient for the cable to act like a fuse or over heated resistor. It will heat and melt over a period of time with a certain value of over current, you are not running the PC long enough for that to happen, however it will still drop voltage over it's length and on a 3.3V rail you have very little margin before under-voltage is detected and the PSU or PC resets.

    The wires are split to share the load as there can be very high currents involved and especially at lower voltages.

    IE: 100Watts at 3.3 V is around 30A , at 12V it's only around 8A. That's why you need to have 2 or 3 feed through caps in parallel, each with an individual cable to load share the high current lines.
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  3. #243
    Maximum Bitrate Mickz's Avatar
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    Quote Originally Posted by johnjore View Post
    My mainboard users a 20pin ATX connector so the only merged cables are 5V and 3.3V. (No 2nd CPU power cable or the extra 4 pins on the plug)JJ
    You did wire and connect the 4 Pin ATX_12v plug?
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  4. #244
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    Quote Originally Posted by Mickz View Post
    You did wire and connect the 4 Pin ATX_12v plug?
    If you're talking about the exstra 4 connectors on the ATX socket to make the atx cable 24pin: It's wired up, but not plugged into anything.
    If you're talking about the exstra 4 connectors (gnd and 12v?) that usually plugs into a separate socket close to the CPU, no i didn't. Nothing plugs into this on the m4-atx at the moment.

    Neither are used by my mainboard. (a very old Intel board with a dual core cpu)

    And ah, guess I'll need to run an extra 3.3V and/or 5V cable then. I thought the cables I used were sufficient (and the absent of smoke).

    Can the cables to the extra cap be merged on both sides with the other cables, or do I need to run a seperate cable from end-to-end?


    JJ

  5. #245
    Maximum Bitrate Mickz's Avatar
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    Some of these MB's will not boot correctly without the 4Pin +12v cable and depends various things including the PSU and the way it handles the standard connector supply current. Mine is simply wired to the M4 +12v ATX supply output line. I would give this a try first.

    They can be merged providing you are running a few wires back to the PSU supply plugs as each end (PSU and MB) This is needed as a single connection to the standard ATX 20 Pin or 24 Pin connectors can not handle the total current.


    EDIT: Just re-read you last post and it looks like you are saying that this 4Pin +12v socket does not exist on your old MB or is not used by that MB?
    Last edited by Mickz; 03-03-2013 at 02:41 AM.
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  6. #246
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    Hi and yes, that's correct: The extra 4pin/12V socket does not exists on my mainboard.

    JJ

  7. #247
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    Getting closer: Thanks to mickz suggestion, the mainboard can now be powered on, reliably, without crashing when Windows starts. (HD still needs to be connected via external PSU)

    Added: 1x cable on the 5V rail. (Adding additional cables to the 3.3V had no effect)

    Need to figure out if its 12V or an additional 5V to fix the HD power issue.

    Edit: An extra 12V was required to fix the HD


    JJ
    Last edited by johnjore; 03-03-2013 at 03:48 AM.

  8. #248
    Maximum Bitrate Mickz's Avatar
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    Great to hear, yes depends on the MB and how they use the various supply rails. - Just something to keep in mind with the feed through caps, there is a limit to the current they can pass with respect to noise. Put simply the more current each is called on to carry the less noise that cap will be capable of bypassing. This is why heavy current lines should be split over a few caps. (Unless you are using caps designed for the required current.)
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  9. #249
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    Ah. Well the mauser's didn't have an amp rating, thought that was because I was suppling my own cables going through the hole in the middle (and I used the same cables as the main feed into the M4-ATX. In my infinite wisdom, I used offcuts from the ATX cable between the different voltage bundles and the cap's, on both sides... Ops...)

    So what's the 1000pF vs 5000pF rating for, and does it matter for this purpose?


    JJ

  10. #250
    Maximum Bitrate Mickz's Avatar
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    The capacitance value effects bypass frequency. It's not the cable diameter or rating, its the construction, size and design of the device that impose current limits on the peak value of the RF (AC) component of the signal passing through the device.
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