The troubles with cheap PSUs

Discussion in 'General Hardware' started by Ripshod, Jul 22, 2012.

  1. Ripshod

    Ripshod Active Member

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  2. RDilus

    RDilus Active Member

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    that is some dangerous pasta lol!
     
  3. clawhamer

    clawhamer Ancient Guru

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    Usually the “experienced” are just that, they have either experienced or seen firsthand what can happen when electricity is running through low grade parts of cheap PSUs.

    More often than not, we make the recommendation based on possible damage to other PC components, but the reality can be much more severe.
     
  4. Mufflore

    Mufflore Ancient Guru

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    There are many reasons why you should use a quality PSU.

    They use better circuits, components, protection and have longer warranties (ie they should last longer).
    They are safer for your PC, and while they are not guaranteed to not damage your PC when they die, there is less chance of them dieing and less chance of component damage if they die.

    The rated RMS power is usually as specced or pretty close, lower quality PSUs often cannot manage to run at full power or can only do it for a short time before failing or they just stop working until you restart with lower power use.
    Running a PSU beyond its capacity can cause it to fail, this can be catastrophic (ie causes damage) or cause crashes.
    Power rail stability is better on a decent PSU, meaning there is less voltage drop under load and the rails have less noise.
    Rail instability and/or noise can cause crashes, especially if overclocking.

    Over time a PSU wears out in manner called derating.
    A general metric that is used is to reduce the maximum output capability of the PSU by 5% per year, more if you push the PSU hard a lot.
    The harder you push a PSU and/or the hotter it gets, the faster it will wear out.
    Electrolytic capacitors are what wear out the fastest and are the main cause of derating.
    Electrolytic capacitors derate over 'time' as well, so the older the PSU is the lower its output power.

    PSUs produce heat.
    The amount of heat is determined by the PSUs efficiency and the amount of power you need.
    As a PSU derates its efficiency drops, causing more of the power to become heat rather than DC power capability.
    A hotter PSU derates faster, causing it to get hotter, causing it to derate faster, causing it to get hotter ....

    Power requirements are averaged, the peak requirements are generally not considered by the user.
    A lower quality PSU will likely have a lower RMS and lower peak capability.
    If say you have a cheap 500W RMS PSU running a system that needs 400W RMS full load, you are pushing the PSU pretty hard (to 80% of its capacity).
    If your powerful PC is able to demand an extra 80W in a game for say 1/10th of a second, it can overload the PSU, causing a large drop in the voltage rail which will likely crash the PC or cause a graphics driver crash (or other recoverable error type) that will return you to the desktop.

    So as you use a PSU, you are wearing it out.
    It wears faster the hotter it is, the harder you push it and the lower the quality components/design used.
    If you push even some decent PSUs pretty hard, they can derate at 10% per year.
    For a 500W PSU, this means it is now a 450W PSU after 1 year, 405W after 2 years ...
    The lower the power output, the harder it is being pushed for the same load meaning it produces even more heat so it wears out even faster.
    This process can happen faster in cheap PSUs.

    As mentioned earlier, when you try to draw more power than the PSU can supply, the PSU can fail.
    The amount of protection you have depends on the circuits + design and quality of components, cheaper PSUs scrimp on these.
    A PSU failure can cause a voltage spike which can damage PC components attached to it.
    Some of the protection is to try and prevent damaging spikes getting onto the power rails.

    Many better quality PSUs have longer warranties, the Corsair AX series for example, have a 7 year warranty.
    When a PSU dies, you can get it replaced under warranty (if it is still under warranty).
    A PSUs warranty does not cover any other PC components that it kills though


    So you take quite a risk using a cheaper PSU, especially if you push your PSU hard.
    I try to keep my RMS power use about 50 to 66% of the max output of the PSU.
    This gives a lot of headroom so the PSU will last for years and gives a lot of headroom for peak power output too.

    That'll do for now :)
     
    Last edited: Jul 22, 2012

  5. Lethal Abz

    Lethal Abz Maha Guru

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    Rule is to never buy take a short cut when purchasing a PSU and Motherboard!
     
  6. FULMTL

    FULMTL Ancient Guru

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    The general rule is to not buy any computer component with Chinese letters on it.
    JK JK don't ban me.
     
  7. Lethal Abz

    Lethal Abz Maha Guru

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    If that's the rule I need to bin my whole PC.
     

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