PSU's at limits causing lights to flicker

Discussion in 'Power Supplies' started by Ratzes, Jun 13, 2017.

  1. Ratzes

    Ratzes n00bie

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    I have a titan x (Pascal) running off of a corsair sf600 and noticed that in two separate circuits that the lights were flickering when under load. My other desktop is on a 1500W PSU with 2 titan x's and never had this problem. I swapped the 1500W PSU to the other box and had no flickering. Then I borrowed two more titan's from work, put 4 on my 1500W box under load and lights started flickering again.

    I've heard that lights flickering in a house is a sign of bad wiring and could be a fire hazard, is this concerning? It's surprising to me that this seems to be affected by how close the power draw is to the PSU limit and not just total power draw.

    Would greatly appreciate any feedback, thanks!
     
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  2. Luke M

    Luke M Limp Gawd

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    What kind of lights? Assuming incandescent, it's only concerning if they get brighter under load. Slightly dimmer is normal.
     
    Last edited: Jun 13, 2017
  3. GiGaBiTe

    GiGaBiTe Limp Gawd

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    1.5 kW is a huge load for a house breaker, it's no real surprise the lights are flickering, the circuit is sagging from the heavy current draw. If you stuck a volt meter in the socket in the same circuit, you'd probably see the voltage has dropped noticeably.

    Most standard breakers in the US are 15 amps, which gives you 1800W max.

    If you plan on continually drawing that kind of current, I would check each wall plug and light switch in the circuit to make sure they're not getting warm. If anything is getting warm, turn your machine off and get an electrician to install higher rated plugs or fire may ensue.
     
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  4. pendragon1

    pendragon1 [H]ardness Supreme

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    yup what GB said. youre hitting the upper limit of that 1800w max, so the light dims. I get this if I use my 1KW space heater on the same circuit as my pc.
     
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  5. Ratzes

    Ratzes n00bie

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    Both circuits are on CFL's and both just get dimmer so that's good to know.
    This makes sense, but I'm still curious why my 600W psu with titan x at load would also cause lights to flicker where the 1500W on one titan didn't. I rma'ed my sf600 before I knew about the 4 gpu flickering and just got a brand new one. I'm not sure whether to open it or not.

    Would it make sense if this flickering was just a function of the wattage getting close to psu limits and then demanding power from a poorly wired circuit? I would assume that a psu operating at it's sweet spot would pull a continuous amount of power and hence no flickering. I really don't know much about wiring at all, does wiring and power have aliasing issues?
     
  6. GiGaBiTe

    GiGaBiTe Limp Gawd

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    Your original post is confusing, but are you running two separate machines with three or four Titan X cards between them on the same circuit at the same time? Because it looks like you're not taking into account the power draw of all devices on the mains circuit.

    Three Titan X cards at full tilt will pull about 900W
    Four Titan X cards at full tilt will pull about 1200W

    This doesn't take into account the rest of the system(s) components, monitors, etc. You don't have a lot of headroom on your mains, which is why you're getting brownouts. If you're only running one machine at a time, you could be hitting some magic threshold of current draw where the mains starts to sag for various reasons. The more serious problems would be like I described above where the mains plugs / light switches aren't rated for the current draw and are causing problems. Since plugs and switches are usually wired in parallel, the load will go across each plug and any one of them can be a weak link, I've had this happen in my house before. Other problems like saggy pole transformers can also cause issues, another thing I have problems with.

    Unless you're using the PSU to drive a purely resistive load like a tungsten lamp or bank of high power resistors, there's no such thing as a constant load on a PSU. Switching electronic loads are always going to have some variability to them, which will appear on the mains input of the PSU as a variable current draw. The PSU itself is a switching load which further complicates power calculation. There are various sources on the internet which explain the differences between real, apparent and reactive power which is important to know if you need to calculate your true power usage.
     
  7. Ratzes

    Ratzes n00bie

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    No, just one system at a time. When all I'm running is the 600W with titan x, lights flicker, when I use my 1500W with one titan x, no flickering lights, I'm thinking maybe this really was just an issue with the PSU. It would be easy to explain the 4 titan flickering with the power sag issue you described.
     
  8. stormy1

    stormy1 Gawd

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    cfl bulbs are sensitive to lagging current which they actually create so they can self interfere.
    At a guess the dimming is a result of wiring issues and interaction of the cfl and power supply.
    That it does it when the power supply is near its limits makes sense. That is where the suppression circuitry is at its weakest and a more complex load is seen on the AC side.
     
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  9. Ratzes

    Ratzes n00bie

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    Thanks for the reply! Happy to hear there's some working theory to make sense of all of this. I'm going to go ahead and open my rma'ed sf600 and confirm that the issue wasn't the psu (oops).
    Thanks again for the 1800W info, had no idea this was something to consider.