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Featured Automagically destroy wiring in as many as eight places

Discussion in 'Prius, Hybrid, EV and Alt-Fuel News' started by ChapmanF, Oct 6, 2019.

  1. Lee Jay

    Lee Jay Senior Member

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    The reason for this is sound.

    The cost to repair or replace a car is generally far lower than the cost to repair and rehabilitate a person, not to mention the cost in suffering. And replacing a person is not even possible.
     
  2. Mendel Leisk

    Mendel Leisk Senior Member

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    Yes, but does it have to be one or the other? You don't compromise safety and It would be absurdly easy to make the front and rear "bumpers" a lot more durable/cheaper, for starters. And headlights on the Prime are over a grand apiece...

    Guess this is getting off-topic though.
     
  3. Lee Jay

    Lee Jay Senior Member

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    There are always compromises in engineering.

    Make the bumper stronger? Higher accelerations on the occupants, more weight, more cost.
     
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  4. I'mJp

    I'mJp Senior Member

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    I totaled my 2017 gen4, where someone ran a red light and smashed in my front end. All the airbags deployed, no one was hurt.
    The horn went off, and there was no way for me to shut it off.
    The fire department arrived, and I warned them that it was a hybrid, and had a high voltage battery.
    They asked me to pop the hood. I was surprised that the hood opened.
    Then a very muscular fire man stepped up with one of the biggest, shiniest axes that I've ever seen.
    He used that axe to chop off the positive terminal of the 12 volt battery, well .. the hole section of the battery and cleaved the cable as well.
    In one chop.
    The horn turned off.
    They weren't interested in anything else I had to say.
     
  5. Trollbait

    Trollbait It's a D&D thing

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    The concern when hybrids first arrived was in regards to extractions; when the fire fighters pull out the jaws of life and start cutting through the car's supporting structures.
     
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  6. kenmce

    kenmce High Voltage Member

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    I can see the value of cutting off stray voltage in a damaged car. I don't understand why irreversible little guillotines are somehow better than easily reset circuit breakers.

    This seems to be the people that make them, I'll go see if they have some kind of compelling reasons why their product is better: Pyroswitch – Pyrotechnical safety switches

    OK, they're a German company. This is where they list the advantages of their product: Protective Potential | Pyroswitch My summary of their list is that these little fellows are really, really, fast (milliseconds) and reliable. They get triggered with the airbags. Because they are fast, they state that damaged electrical lines can't start fires because their product shuts things off too quickly.

    At work we have a couple of 100 Amp 240 Volt circuits. They are easily strong enough to start fires, but we consider either replaceable fuses or resettable circuit breakers perfectly good protection. My chief gripe with these things was that I thought they destroyed the car in order to save it. Looking at the units I can't quite tell if you can just unplug a dead unit and pop in a new one. If you can, then I withdraw my objection - provided they put them where you can get at them without tearing the car to pieces.
     
    #26 kenmce, Oct 17, 2019
    Last edited: Oct 17, 2019
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  7. Lee Jay

    Lee Jay Senior Member

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    A circuit breaker works by thermally (slow) or magnetically (fast) opening the circuit from too much current, not by high-g forces.
     
  8. kenmce

    kenmce High Voltage Member

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    The pyroswitches are triggered electrically by the airbag system, the same as one would trigger a breaker. Them seem to be a variation on airbag igniters. Wouldn't a thermal breaker be called a fuse? If I can just unplug a dead pyro and pop in a new one, then I have no problem with it. It was the whole "entire new wiring harness" that got my hackles up.
     
  9. Lee Jay

    Lee Jay Senior Member

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    As I said, breakers are triggered thermally or magnetically, not electrically.

    No, a fuse is called a fuse. A circuit breaker pops thermally if it's a slow-blow type pop or magnetically if it's a fast-blow type of pop.

    Go watch this:

     
  10. ChapmanF

    ChapmanF Senior Member

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    That number is pretty well in the ballpark of what I've read too. It turns out the most immediately lethal effect is not when the heart flat-out stops, but fibrillates ... it's sitting there with all its fibers contracting on different schedules, which ends up not pumping any blood, and doesn't get sorted out by itself even after you're separated from the power source, unless there is somebody nearby with a defibrillator.

    Unexpectedly, higher currents (200 mA and up) can be less lethal, because they will clamp the heart to a complete stop, from which it can come back to a regular beat again once you're off the power source and get some basic CPR. Of course, higher currents can do other kinds of damage.

    Electrical Safety: The Fatal Current

    That doesn't agree as well with what I've seen; it seems easier to find references that put the risk of muscle tetany ("can't let go") higher for AC, in particular AC in a certain frequency range (say, 40 to 150 Hz, which unluckily contains the frequencies we conventionally use for home power). Three to five times higher than for DC, per some sources. Definitely more interesting and less cut-and-dried than we sometimes think.

    Physics 516 & 616: Intermediate & Advanced Undergrad Labs

    Electrical Injuries in Emergency Medicine: Background, Pathophysiology, Etiology

    CCNY article focused on "low-voltage" hazard (in a scheme where "high voltage" is defined as over 600 or 1000 volts, a Prius battery ends up considered "low")
     
  11. Trollbait

    Trollbait It's a D&D thing

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    They could have used automated switches.
    The cutters are faster.
    The switches would be more complex, making them more likely fail. They have the work during the forces of a crash. The blade is the only moving part on the cutter. In addition to the switch, there is whatever device used to flip that switch.
     
  12. Lee Jay

    Lee Jay Senior Member

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    There's an additional problem with using relays or solid-state switches for such an application - latent failures. In short, there's no way to know if the switch has failed unless you actuate it. Since you don't want to actuate it unless there's a crash, you can't tell if it has failed or not.

    That's why you want the simplest, most reliable system possible in life-safety situations.
     
  13. Lee Jay

    Lee Jay Senior Member

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    I've been hit by 120AC more times than I can count and by 320DC several dozen times (capacitor driven). What I remember about the 320 is that I couldn't let go until the capacitor drained. It was across my hand, not my heart, but I couldn't release my hand. It was brief (under a second) so this could have been psychological but there was the definite sensation of a muscle crap with my hand involuntarily clenching the device. With 120, I was always instantly able to pull away.
     
  14. ChapmanF

    ChapmanF Senior Member

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    My understanding of muscle fibers is that no individual fiber can stay tensed for very long; any sustained pull with a muscle is always a matter of continually stimulating some fibers to contract while earlier-contracted ones relax and recharge. AC right around the common power-grid frequencies is really good at doing that.

    Conduction of Electrical Current to and Through the Human Body: A Review

    Of course any one person's experience of any one shock can be different from what large-sample studies show, for any number of situational reasons. Maybe you were getting more than 300 mA across the hand in those cases. (Maybe there's more to the puzzle, with the hand's musculature really located in the forearm; I wonder what the current path was really?)

    And then there's the subjective part. I remember one time as a teen when I had my arms leaning on the top of a chain-link fence, and then my midriff came up against the pasture electric fence wire running parallel to it on this side. That fence was normally just an annoying zap, but the chain-link fence made a really good ground.

    Onlookers saw me flat on the ground instantly like a sack of potatoes. What I saw was me sizzling on the wretched fence for what felt like half a minute while about a dozen different explanations for what was going on all went through my head. One of them was that the neighbors might be secretly evil agents who had replaced the innocent pasture electric fence with some lethal prison-camp version. I actually had time to think all that before my shoulders hit the dirt.

    Then I just stared up at the sky for a few seconds and thought "oh yeah ... pretty good ground, that chain-link fence ....".
     
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