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Thread: The "power supply FAQ"

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    Interestingly America has 220v; there is a 220v circuit in most American houses for the high consumption devices (clothes dryer, range etc.)

    HOWEVER
    There is one terrible disadvantage to the way 110v is often implemented in America, namely through a neutral line that divides the 220v into two circuits of 110v. Some devices in the house are on one circuit, some on the other. Now the problem: if that dividing neutral should ever fail due to a bad connection then some devices can be exposed to more than 110v and destroyed (it is almost paradoxical that the loss of a connection can lead to higher voltage).
    To be explicit, have a washing machine on one circuit and a PC on the other; disconnect the dividing neutral and the 220v now goes across the two devices in series and the voltage is now unevenly distributed across them.
    The following video illustrates it better than I can
    https://www.bing.com/videos/search?F...al&view=detail

    My point is that auto-switching PC power supplies might be able to survive an open neutral; unfortunately most of my PCs use manual voltage selectors

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    You could always make your own 220V circuit if you really wanted to by disconnecting that circuit's neutral off the neutral bar and connecting it to the opposite phase of the hot wire of that circuit.

    Not that I would recommend it...but you could. If you did though you'd want to know exactly what that circuit is connected to (preferably only the exact receptacles you intend to plug the PCs into), use a double pole breaker (same thing your baseboard heaters use), swap the receptacles for 250V rated ones if they are currently only rated for 125, tape the white wire either red or black depending on which phase you hooked it to, probably paint the new receptacles some kind of bright colour that invokes feelings of caution and danger like black and yellow stripes or red, add labels warning oblivious passers-by that they are dangerous 240V circuits (since any standard 120V power cord will still be able to plug into the sockets), and also cap them off. And also don't derp out and plug your monitor or power bar into it by accident...just the PSU.

    Again...just sayin'. Not recommended.

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    Quote Originally Posted by ashiekh View Post
    HOWEVER
    There is one terrible disadvantage to the way 110v is often implemented in America, namely through a neutral line that divides the 220v into two circuits of 110v.
    What you describe here sounds wrong. Either someone fed you false information or you understood it in a wrong way.


    Because normally you get one or more phases where one phase is shifted by a couple of degrees. For you yanks it should be 90°, for me as a European, it's usually 60° but we have 3 Phases. And that's why you have 220V or 400V between the phases but against neutral (wich is Neutral as the name says), you have the 'normal' voltage, in your case 110VAC/60Hz, in my case 230VAC/50Hz (though it seems it's more like 220VAC/50Hz as it was 40 years ago)...


    If you you break the Neutral line, your device doesn't work no more and you don't have a connection.
    However due to the way the devices are designed, what you are mentioning here does not happen because there is no circuit no more, thus nothing will happen. And since there is a seperate Earth wire for the cases you don't have any deadly voltage on the device there...

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    Actually what he said is correct, but the specific case he is talking about is when the neutral is broken somewhere between the panel and the transformer, not in an individual circuit.

    The power lines before the transformer are 3-phase where each line is 120° out of phase with every other one. Commercial and industrial buildings typically use 3-phase power (usually 600V/347V line-to-line/line-to-ground respectively in Canada, but I think they use 480V/277V in the US), but residential power only comes from a single phase, where it's stepped down to 240V. The transformer is center-tapped to give you your neutral and each of the two 120V sides are wired to be 180° out of phase with each other.

    If the neutral breaks in any given circuit, yes, the circuit will simply not work...but if it breaks before the panel and the load is not evenly balanced between the phases, then you could get, say 180V on one side and 60V on the other, but the circuits will still "work" (but one set will brown out and one will fry). It's rare, but it can happen.

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    Default 230V supply in North America

    Quote Originally Posted by bardacuda View Post
    You could always make your own 220V circuit if you really wanted to by disconnecting that circuit's neutral off the neutral bar and connecting it to the opposite phase of the hot wire of that circuit.
    This is actually acceptable if you:
    1. Reidentify the neutral wire as live by wrapping it with black electrical tape at each end. (as you already mentioned) and
    2. Use a NEMA 6 receptacle, which is keyed for 240V, rather than the more common NEMA 5.

    A second way, which is compatible with standard plugs, but requires 3-conductor (plus ground) wiring is to bring both phases plus neutral to a duplex receptacle and wire the hot side of the two outlets to different phases. Just break the tab connecting them.

    This is 100% to code, and actually commonly done in kitchens and workshops where high-load power tools are expected.

    Then build a Franken-cable by splicing two IEC cables together to connect the PSU to to the two hot phases, connect the grounds, and ignore the neutral pins.

    It would be safe, although strange, to omit the neutral connection to the receptacle so that the two outlets would be "dead" for 120V appliances. Since you need to run a separate cable for this special outlet anyway (you don't want the usual daisy-chain arrangement where one branch circuit feeds half a dozen receptacles), this is only helpful if you happen to have 2-conductor (plus ground) available but not 3-condutor.

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    Hmm didn't think of using a franken cable on a split phase plug, but I like that idea better. Much safer, and as you say, still up to code.

    You'd still want to make sure both phases are on a double-pole breaker though, or at least use a tie to link the handles of two single poles together.
    Last edited by bardacuda; 11-16-2017 at 04:10 PM.

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    Default FAQ

    Was wondering if the FAQ might benefit from a section on intermediate topics like

    dc-dc conversion
    flyback converter
    resonant converters
    forward converter
    PFC

    for people like me trying to keep up with some of the discussions here

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    Quote Originally Posted by ashiekh View Post
    Was wondering if the FAQ might benefit from a section on intermediate topics like

    dc-dc conversion
    flyback converter
    resonant converters
    forward converter
    PFC

    for people like me trying to keep up with some of the discussions here
    Sure. Of course.

    I personally don't have the time right now, but we can put together a discussion and sticky it as well.

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    Default

    Quote Originally Posted by arie_coolz View Post
    yupz.....
    my friends are going to buy new psu...
    it's best to recomend him to check auto clicker word unscrambler jumble solver this one
    The general rule of thumb is a high quality 500 to 550 watt power supply with sufficient current (amps) on the +12 volt rail(s) can easily power a system with any single video card made.
    Last edited by KAWTARY; 2 Weeks Ago at 06:15 PM.

  11. #20
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    Quote Originally Posted by KAWTARY View Post
    The general rule of thumb is a high quality 500 to 550 watt power supply with sufficient current (amps) on the +12 volt rail(s) can easily power a system with any single video card made.
    You're responding to an 11 year old post?

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