How to set your house on fire and burn it down...

  1. Posts : 432
    W10 22H2 19045.4355

    How to set your house on fire and burn it down...

    How to set your house on fire and burn it down...

    A while ago I was working on my computer and noticed a faint typical "burnt electronics" smell.
    Since the PC was working fine and I have a variety of other things around that are on power I checked them all.
    No indication anywhere of a pending or developing issue.

    When I was done with my work I got up and was about to leave.
    My PC, also the server runs 24/7 so I have remote access when I need it.
    I was ready to leave and walked back to my desk to grab the keys when I noticed an orange light inside the computer.
    Hmm... Well the orange light was constant and about the size of a surface mount LED.
    I never noticed it before since there are 2 other lights on the motherboard.
    I left and got into the car.

    But something bothered me about this light because I had my computer open a few times and never noticed it.
    So I went back up and when I walked into my office I noticed clearly this typical "burnt electronics" smell.
    it seemed to smell more intense closer by the computer.
    So I opened the side panel of the case to have a closer look to find out what that orange light is that has been glowing in there.
    😲😱 OMG!
    Fire in the box!
    An older four-port USB2 peripheral card I had installed a few years ago to which I connected low-speed USB devices was on fire! Component failure!
    How to set your house on fire and burn it down...-usb-fire-medium-.jpgHow to set your house on fire and burn it down...-usb-fire1-medium-.jpgHow to set your house on fire and burn it down...-usb-fire2-medium-.jpgHow to set your house on fire and burn it down...-usb-fire3-medium-.jpg
    the orange light being actually the fire of a continuous arcing on the PCB board!

    ( USB in fact is very dangerous as the power supply can deliver at least 20, 30 if not 40 A (mine is rated at 40 A).
    That's quite a high current! The problem with PCs in general and USB is, it's not fused so if the short-circuit starts throwing 30 A on a 40 amp power supply the PS keeps on pumping never shutting down! You can try that for yourself by short-circuiting a USB cable and plug it in and you will see the USB cable will get hot, the plastic melts and it starts glowing red orange!)
    Last edited by 3Bit; 21 Apr 2023 at 20:49. Reason: typos
      My Computer

  2. Posts : 9,792
    Mac OS Catalina

    Wrong on the amps. USB delivers mA not A.
      My Computer

  3. Posts : 432
    W10 22H2 19045.4355
    Thread Starter

    bro67 said:
    Wrong on the amps. USB delivers mA not A.
    Obviously you didn't read what I wrote.
    A) USB 2.0 is rated up to 1.5 A (1500 mA). Chargers are rated up to 1.5 amp output, some even more. nominal USB current is rated at 100 to 500mA depending on the revision cable rating type.
    B)the total maximum cable current specifications are less but higher for the power supply, depending on the size and rating can be quite high. In my case the power supply is rated with 40A on the 5 volt output. if you almost short-circuit that.... fireworks!
    So if you have a short-circuit, accounting cable length and wire resistance, you can easily draw 20-30 A without triggering a power supply shut down. In my case the short-circuit developed on the peripheral board. The arcing drew quite some current but the power supply delivered it. The carbonization of the PCB and epoxy aided that and it got bigger and bigger.

    Standard USB 2.0 cable for battery charging was 1.5A @ 5v (and devices not being charged were limited to 100 mA or 500 mA).
    Most use 28/28 gauge, meaning 28 gauge for data and 28 gauge for power, because they are designed to handle only 500 mA.

    Ref. USB - Wikipedia, USB 2.0 Specification | USB-IF
      My Computer

  4. Posts : 880
    Windows 10 Pro

    bro67 said:
    Wrong on the amps. USB delivers mA not A.
    Under normal operating conditions maybe, but this is a fault condition we're discussing and potentially the tap is wide open, the only limit being the over current trip on the PSU.
      My Computer

  5. Posts : 282
    Windows 10 Pro

    Change your username to Thermal Runaway....

    A Flock Of Seagulls - I Ran (So Far Away) (Video) - YouTube
      My Computer


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