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Thread: PSU makes hummin sound, when inverter is turn on

  1. #1
    Variable Bitrate
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    PSU makes hummin sound, when inverter is turn on

    hello. in my car i use, a modified sine wave to power my pc. the problem is, as soon as i turn on the inverter (no matter if the PSU is on , or off ) the psu makes a strange whining noise...
    not to mention that, when the pc works, it has allot of noise in sound.
    (To solve that, i have cut the ground wires from the psu to inverter)

    Any idea what could be causing this? cause i want to leave the inverter Always on, to remotely start the pc, but this sound makes me fear something is going on. would a pure sine wave solve it? or maybe a new PSU?

  2. #2
    Raw Wave
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    Yes - a poor quality inverter, else you have remarkable high frequency hearing.


    But I wouldn't use an inverter in that mode anyhow. Its standby power may be ~5-10% of its full load rating. Even if only 1A, it is likely to flatten your battery within 12-24 hours.

    Get a proper dc-dc converter, ie, an automotive ATX supply.

  3. #3
    Fusion Brain Creator 2k1Toaster's Avatar
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    Quote Originally Posted by OldSpark View Post
    Yes - a poor quality inverter, else you have remarkable high frequency hearing.


    But I wouldn't use an inverter in that mode anyhow. Its standby power may be ~5-10% of its full load rating. Even if only 1A, it is likely to flatten your battery within 12-24 hours.

    Get a proper dc-dc converter, ie, an automotive ATX supply.
    +1

    Poor quality inverter coupled with ATX supplies that are trying to do active PFC on the input line of a not true sine wave. It just isn't going to work. Get a real DC-DC PSU.
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  4. #4
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    well i have a dc-dc power supply, but i dont feel like burning any more motherboards. my last two dc-dc have both burned my motherboards, so i am not planning to use any again... so... i have to deal with inverter!!

  5. #5
    Fusion Brain Creator 2k1Toaster's Avatar
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    Quote Originally Posted by settra View Post
    well i have a dc-dc power supply, but i dont feel like burning any more motherboards. my last two dc-dc have both burned my motherboards, so i am not planning to use any again... so... i have to deal with inverter!!
    Once of my favourite quotes is "lo barato sale caro" which translated to English means "the cheap comes out expensive". If you buy a good DC-DC power supply, it will be rare for anything to happen to your motherboard. The M1 and M2 series are probably the worst I have ever seen other than the PicoATX brand that doesn't even regulate the 12v rail, it just passes it straight through!

    If you must go with an inverter, then you need to get a true sine wave inverter. Not a modified sine, or a triangular sine, or modified square, or any other fancy terms for not a true sine wave. These are more expensive than your standard inverter, but for good reason.
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  6. #6
    Raw Wave
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    Mr Toaster Esq, do modern PC supplies have PFC?
    If so, it's about time. That was something that amused me back in my UPS days - PCs required a clean AC supply and yet they were the ones causing the mains AC distortion. They often had crest factors of 3:1 and pf's of 0.5. The effect on building supplies was quite significant. (Same with CFC lighting etc, and the many products that later switched to SMPS instead of transformers.)
    Static (solid state) UPSs at the time could not handle the high crest factors - their rated loading had to be halved (eg, needed a 10kW UPS/inverter for 5kW of PCs).
    Not to mention equipment that suffered erroneous problems. (Premature failures, resets, noise etc. And in Queeensland Australia, domestic electric "off peak" water heating would switch on during the day (they were signaled via an ~1kHz injection on to the mains AC).)


    Otherwise, in principle, SMPS loads like PC PSUs should not care about AC sineage, all they require is sufficient voltage above a certain level for long enough - eg maybe above 80V or 130V for a 110VAC SMPS PSU.
    The same applies to the OP's PC, but much depends on its design - eg, noise rejection; hardening of components (the square "edges", or high harmonics if you prefer); and circuit design (early SMPS required AC, later AC SMPS can operate on DC).
    (I think his acoustic noise is simply electro-mechanical which may also reflect its (non) suitability for vehicle vibrations & shock. I doubt that it's a lower near-audible conversion frequency.)


    But an inverter - that's a cheap INITIAL method or for occasional vehicle AC loads etc. I look at that from an efficiency POV, plus practicality. And a (true) sinewave inverter probably costs as much or more than a good vehicle-DC ATX supply.
    Add the functionality you can get from a good DC converter - programmable off & on delays & low voltage warnings and shut down etc. Plus efficiencies in excess of 80-90% etc and low standby currents. (Some inverters also have low current standby modes, but old or cheap ones usually just idle the power electronics. And inverters with their typically lower than 80% efficiency coupled with the PC's AC PSU inefficiency... it's an extra dc-ac inversion that simply isn't needed.)


    As for dc-dc converters blowing motherboards, I can't see why - unless they were wired or set wrong, or were intended for regulated 12V DC instead of the highly variable vehicle 12V supply (eg, 8V - 16V).
    AFAIK the typical dc-dc converters used hereon (DS-ATX, M4 etc) do not have that problem, though the M4s are known for their various & bad noise problems.




    FYI and a clarification for some readers....
    "Modified sinewave" is really a modified square wave. Instead of a nice smooth wave, it switches between TWO voltage levels in both +ve and -ve directions, and off (0V).
    pf (power factor) is NOT cosφ. pf = W/VA (Watts divided by Volt-Amps). pf equals cosφ ONLY for (fundamental harmonic only) sinusoid waveforms which does not apply to typical non-PFC'd (non-pf corrected) SMPS.
    cosφ is the angle between the voltage and current waveforms. For resistive loads, pf = cosφ = 1.
    Inductive and capacitive loads lead or lag (whichever...) the current waveform by a certain number of degrees, hence pfs or cosφ's of 0.8 & -0.95 etc.
    Raw SMPS conduct current in phase with the voltage, hence no angle, hence cosφ = 1. But due to their crest factor (distortion) their pfs are typically 0.6 or less.
    (Crest factor is the peak verses average or RMS(?) value. EG - a normal sinewave crest factor is ~1.4:1. A crest factor of 3:1 means over twice the "normal" peak current.)
    That's all probably old knowledge - for me it's from over 20 years ago - but I still strike the occasional caveperson.

  7. #7
    Fusion Brain Creator 2k1Toaster's Avatar
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    To meet Energy Star 5.0 standards, all computer power supplies must meet a power factor greater than or equal to 0.9 at 100% of the rated output load. And big companies make them compliant to those standards because some locations require the import to meet those standards, so it is cheaper to just carry 1 product that meets global standards. Similar to RoHS compliance in Europe making it RoHS everywhere.
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  8. #8
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    well, i know a pure sine wave is the way to go, and i am planing on buying one, but on the meantime, i was looking for a solution that could "fix" it until i get a pure sine. a band-pass filter or something? i am more warried that, maybe it could do harm on the pc, leaving it with the inverter turned on for many hours?

  9. #9
    Raw Wave
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    I still reckon a good dc-dc converter is the way to go...

    But yes, a stepped wave "modified sinewave" does cause the front-end components of PSUs to heat more etc. That was one of the sales pitches the pure sinewave manufacturers or models pushed. I don't know if it makes makes much difference these days because PSUs are reasonable hardened - both due to mains distortion and that many use UPSs that are also stepped wave (although that is only during a power failure - not full time - and online UPSs are usually sinewave as opposed to combined inverter & rectifier (charge) offline aka standby types).


    And thanks 2k1Toaster for the update. I suspect the same market will cause the USA to go metric as it has in part already.

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