transformless

Discussion in 'General Electronics Chat' started by guruji, Sep 22, 2008.

  1. guruji

    Thread Starter Member

    Nov 11, 2005
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    HI guys I am trying to modify a circuit from 18v to 12v and they told me it's too lethal even if this is sealed?!
    I cannot understand this.
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    Any fault in the capacitor places line voltage at the output. It is too dangerous, given the price and availability of wall transformers.

    Any transformerless power source is inherently lethally dangerous.
     
  3. KMoffett

    AAC Fanatic!

    Dec 19, 2007
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  4. Wendy

    Moderator

    Mar 24, 2008
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    The problem is isolation. The only component that truly provides it is a transformer, as there is NO direct connection between the high voltage side and the low voltage side. If something goes wrong you loose the transformer, which costs less than $2.

    On a direct connection, on the other hand, if something goes wrong you have the full line current/voltage where you are. We are no longer talking low cost components but your own very irreplaceable self. A big difference.

    Most of the old hands are nuts about safety. It is drummed into us at school, and there simply isn't anything to make us give it up in the field. What you are wanting to do isn't safe, no matter how you do it. If a company ever designed something like that and someone got hurt they would rightfully be put out of business and someone would be prosecuted for manslaughter.

    That isn't to say it hasn't been done, but this site is here for fun, and if someone were to advise you to grab a 100V+ line with your bare hands I suspect they would be banned and the post erased as soon as a moderator saw it. We take safety very serious here.

    Why are you so hot to go this route and not use a wall wart or internal transformer in the project?
     
  5. SgtWookie

    Expert

    Jul 17, 2007
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  6. scubasteve_911

    Senior Member

    Dec 27, 2007
    1,202
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    In school, they teach us that our primary duty as engineers is to 'protect the public'. So, how good is an engineer that tries to save two dollars at the cost of potentially killing a citizen who has no electrical knowledge?

    Steve
     
  7. guruji

    Thread Starter Member

    Nov 11, 2005
    29
    0
    HI Bill ok what you said is right but even if this circuit is sealed that no-one can touch.If something goes wrong only the bulb would blow up.
    I cannot understand so much fuss about this.:(?????
     
  8. scubasteve_911

    Senior Member

    Dec 27, 2007
    1,202
    1
    Sealed doesn't mean fool-proof. Example, someone drops it and it breaks, then picks it up and electrocutes themselves. The whole point is, the engineer is supposed to protect people from accidental death where it is feasible. Paying an extra few dollars for a safety device is definitely feasible. This isn't fuss, it is the way things should be done.

    Steve
     
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