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Thread: Burnt PSU, what happened?

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    Default Burnt PSU, what happened?

    There was a mild burning smell coming from my computer for a few days, and then it died and tripped my apartment's circuit breaker. No explosions or visible smoke or anything. Just a buzzing noise towards the end.

    The PSU is Zalman ZM460B-APS (460W) which was probably ~5 years old at this point. I only noticed this burnt coil thingy in there, but admittedly, I have no idea what other signs of damage would look like.



    Why could this have happened? Could dust be the only reason? I measured my computer's power draw once and it was only 230W under full load.

    Is it a bad sign that the PSU tripped the circuit breaker instead of shutting itself off when damaged? I already ordered a new PSU (Seasonic X-460FL2, hopefully that's a good one), but I'm worried the old one took my computer with it.

    Anyway I'm just trying to satisfy my curiosity here, hope that's OK. Never had this happen to me before.

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    Not an answer, just for your information.

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    Quote Originally Posted by buurn View Post
    Why could this have happened? Could dust be the only reason? I measured my computer's power draw once and it was only 230W under full load.
    Dust shouldn't have had anything to do with it. Your primary/APFC coil burned. Actually, it burned its insulation emulsion off. Most probably the insulation itself was not quite up to standard, and over time it gave way somewhere amidst the wire windings of the coil, allowing the coil to short out, overheat and burn. Without a working coil, the APFC won't work and the PSU is "dead in the water".

    Quote Originally Posted by buurn View Post
    Is it a bad sign that the PSU tripped the circuit breaker instead of shutting itself off when damaged? I already ordered a new PSU (Seasonic X-460FL2, hopefully that's a good one), but I'm worried the old one took my computer with it.
    There's no chance the PSU took anything with it at all. Since the primary and the secondary are galvanically isolated (i.e. no direct transport of electric current occurs, only an intermediate transfer of energy via magnetic fields and induction takes place), when the primary (AC side) "dies", the secondary (DC side, the one directly connected to PC components) "sees" this the same way it would "see" a sudden power loss (e.g. a blackout or flipping the power switch at the back of the PSU).

    There is nothing in place to protect from a burnt APFC coil simply because protections are there to prevent adverse effects of a shorted secondary or an overloaded primary or secondary. Burnt primary coil is a very rare event, and one that would be hard (expensive) to protect against, not to mention statistically insignificant. There might be a minimal chance of fire when something like this happens, but that too is rather unlikely.

    Quote Originally Posted by buurn View Post
    Anyway I'm just trying to satisfy my curiosity here, hope that's OK. Never had this happen to me before.
    Of course it's ok. We all learn from each other's questions and experiences, so threads like this are most welcome
    Careful what you wish for... You just might get it.

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    You should be happy. The PSU already had many leaking caps and probably high ripple, which kills your other hardware.

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    There's no chance the PSU took anything with it at all.
    I agree, as long as the PSU was not subject to physical abuse. That is, you didn't bounce it off the floor where something was knocked loose and came into contact with something else creating a short and problems when power was applied.

    Is it a bad sign that the PSU tripped the circuit breaker instead of shutting itself off when damaged?
    It is another indication the PSU is faulty, but not a sign it did damage to your computer.

    Burnt primary coil is a very rare event, and one that would be hard (expensive) to protect against, not to mention statistically insignificant.
    A simple and inexpensive fusible link could have been put in circuit to blow before burning up the coil and presenting a fire hazard. That would be significant, IMO, but not likely to save the PSU from its ultimate demise.

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    Faulty core. Heard that happened to some FSP Epsilon based PSUs around '07.

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    Quote Originally Posted by Digerati View Post
    A simple and inexpensive fusible link could have been put in circuit to blow before burning up the coil and presenting a fire hazard. That would be significant, IMO, but not likely to save the PSU from its ultimate demise.
    There already is a fuse in place, before the APFC section. The coil gradually draws in more and more current, and burns out before the fuse is tripped. Putting a smaller fuse exclusively for the coil would be impractical because of high transients. It would either blow on a "false positive" or not blow in time to prevent much of anything.
    Careful what you wish for... You just might get it.

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    The coil gradually draws in more and more current, and burns out before the fuse is tripped.
    Then it is the wrong fuse. Or poorly designed over-current detection. Or insufficient regulation/filtering/transient suppression.

    I do agree, however, that for most applications it would be impractical, or at least not cost effective. But in any case, if the fault results in smoke, burnt electronics, and trips the apartment circuit breaker, whatever overcurrent circuit was in there was either faulty, damaged, or insufficient from the start. A failed PSU should never draw so much currant as to trip the mains breaker. It should automatically shutdown before then.

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    You have a 400W unit, the load is 125W, how would you do the OCP primary??

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