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Shocked from a tranformer

Discussion in 'Electronic Projects Design/Ideas/Reviews' started by goofeedad, Aug 8, 2009.

  1. giftiger_wunsch

    giftiger_wunsch New Member

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    I agree; personally I have a severe dislike for electric shocks and I usually take perhaps too extreme precautions when there is a known risk. I'm also quite new to electronics so until I have experienced exactly what's safe and what is not, I'm still going to avoid getting too close to mains transformers while plugged in, despite the heavy insulation and the fact that the secondary winding of the one I was testing is only 10V :eek:
     
  2. giftiger_wunsch

    giftiger_wunsch New Member

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    You misunderstand; we were discussing the way DC voltage causes a sustained contraction in skeletal muscle, which can often result in a prolonged shock as the victim is forced to grip the power source. The effect of AC on the heart never came up ;)

    Anyway, there are various 'advantages' and disadvantages to getting shocked by DC over AC and vice verca, but it may take a while to go through them all :p
     
    Last edited: Aug 11, 2009
  3. be80be

    be80be Well-Known Member

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    Ac is more likely to stop your heart
     
  4. dave

    Dave New Member

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  5. goofeedad

    goofeedad New Member

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    Wow! When I originally posted this thread my main concern was with someone other than me getting shocked. I am about to test a devise in a store and even though my electronics is enclosed and store employees can't easily access the electronics I wanted to know how I could reduce the risk of shock even more.

    I've bee told useing a switching supply would probably be safer but at the time I needed it I couldn't find one that had the output or the price I wanted.

    At this time I'm pretty happy with the degree of safety I have.

    Thanks everyone for all the responces, I will keep on reading all posts as I'm sure others will too.
     
  6. Hero999

    Hero999 Banned

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    This debate about which is more deadly AC or DC, surfaces every now and then.

    The fact is that AC is more deadly. I think the myth that AC is safer is very dangerous and wouldn't be surprised if some people have been killed because they believed it. Before you even consider the physiological effects, just looking at the numbers; common sense tells us that AC is more deadly because the peak voltage is Vrms√2, in fact I think its shocking effect is equivalent to the peak-to-peak voltage.

    Another myth is that the skin effect protects one from high frequency (100kHz to 1MHz) current; it doesn't. Human flesh has a higher resistance than copper so the skin effect is less pronounced, allowing the current to penetrate deep into the body causing nasty RF burns. In reality it's the fact that one's nervous system doesn't respond to high frequency current (>20kHz) so it doesn't have the same shocking as power line frequency AC or DC.

    EDIT:
    I disagree with that. I would consider a transformer to be safer than a SMPS because there's not voltage regulation circuit to fail (although this shouln't give deadly voltages) and there are no Y rated capacitors from the primary to secondary.

    I consider a transformer (this includes a transformer wall plug) to be the mose reliable and safest way to power a hobby project.
     
    Last edited: Aug 11, 2009
  7. BrownOut

    BrownOut Banned

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    Alot of what your're reading on here is fluff. It really doesn't matter if AC or DC is safer. The bottom line is to take all safety percautions. The suggestions on here are intended to lower the risk of shock. It can not be completely eliminated, and so it's good to know how to reduce it to a managable leve. If you use a grounded plug, insulate well and isolate the electronics with an isolated power supply ( it doesn't matter if it's a switching or normal power supply, as long as it's isolated ), make sure nobody goes sticking his hand inside the chassis, etc. then it should be fine.
     
  8. giftiger_wunsch

    giftiger_wunsch New Member

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    If the device has an insulated case, the transformer is well insulated, and the output is only 28VAC, your precautions are perfectly adequate.

    Edit: If you're still concerned, you could consider using an RCCB?
     
    Last edited: Aug 11, 2009
  9. Hero999

    Hero999 Banned

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    Generally I agree.

    What I'm talking about is risk assessment: if I were to work on something connected to a 50VAC supply, I would take more precautions than I would if it were connected to a 50VDC supply.
     
  10. bountyhunter

    bountyhunter Well-Known Member

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    Even an "isolated" secondary is connected to the primary via inter winding capacitance which can buzz you pretty good. If the transformer has a grounded shield between windings it will reduce this effect.
     
  11. kchriste

    kchriste New Member Forum Supporter

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    No matter what you are working with, it pays to be carefull. Think of what would happen if your wedding ring, or some other jewelery on your body, shorted the supply from a 12V car battery.
     
  12. giftiger_wunsch

    giftiger_wunsch New Member

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    That would indeed be rather dangerous, but generally the contacts on a car battery are too far away to be shorted so easily.
     
  13. Hero999

    Hero999 Banned

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    The problem is connections on other components such as relays and PCBs aren't that far away; they should be fused though.
     
  14. marcbarker

    marcbarker New Member

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    I dunno about all this health and safety mania, it all seems too risk-averse to me. I think a few occasional mild electric shocks are good for your survival, and creates a healthy sense of respect. It's a bit like riding a bike as a kid you learn not to jam your front brake on hard, rather than remove the front brake off the bike to remove the risk.

    The trouble is that if everyone does their best to eliminate all risk and increase 'health & safety' in every aspect of life, we lose any judgment of risk.

    Then one day when the 'completely de-skilled and over-protected' End User does "everything they are supposed to do to the letter", in a world of health and safety gone crazy,grabs hold of a live fridge door handle, we are then all in disbelief!
     
  15. giftiger_wunsch

    giftiger_wunsch New Member

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    You don't need to intentionally expose yourself to risk in order to learn how to avoid it. That defeats the purpose.

    Using your example of the front brakes on a bike, most people are warned what will happen and thus never do it, rather than being flung head-first from it before realising it's a bad idea ;)
     
  16. BaCaRdi

    BaCaRdi Member

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    Thanks for the explanation :)

    I used to live in West Orange, NJ shame on me.. I should know this..hehe

     
    Last edited: Aug 12, 2009
  17. be80be

    be80be Well-Known Member

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    Funny how I said that at the get go just shows how well people read
     
    Last edited: Aug 12, 2009
  18. giftiger_wunsch

    giftiger_wunsch New Member

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    The fact that you made your opinion known early on means we're forbidden from discussing the issue further then?
     
    • Like Like x 1
  19. be80be

    be80be Well-Known Member

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    Where did I say stop reading
    I said it's funny I posted this at the start and then it was like no one read it
    then two pages later some one posted the same as me and it's Like wow
    I didn't no that thanks for pointing it out
     
  20. giftiger_wunsch

    giftiger_wunsch New Member

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    Perhaps it helped that the later explanation was actually provided by the poster, rather than simply quoting wikipedia. Just a thought.
     
  21. marcbarker

    marcbarker New Member

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    It's about knowledge of risk, not the absolute prohibition of anything and everything deemed to be 'risky'. People who do dangerous sports understand the risks they expose themselves to, and they themselves are responsible for their own survival. On the other hand, people who never take risks are boring old people like bank managers and accountants!

    In a security system, the system administrators deliberately allow hackers to penetrate defenCes so that they can be strengthened. An auto-immune system allows 'germs' to attack the host, so that the adaptive immune system learns. I say the same goes for awareness of electric shocks, just like you have a rational fear of risky driving manauvres because of previous 'near misses' which teaches you a lesson.
     

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