Getting power from 220VAC switch

Discussion in 'General Electronics Chat' started by kammenos, Jun 4, 2009.

  1. kammenos

    Thread Starter Active Member

    Aug 3, 2008
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    0
    Hi there. I'm thinking of getting 5V power from the switch of a 220VAC, for dimmer and staff. I did some tests with a 10 Ohm resistor in series with the switch and got up to 6V. Bigger resistors gave me more voltage.

    But the light was on....

    The question:
    How could i get the same voltage when the light is off
    I do not want to use transformer as they are BIG to fit in a household switch case...
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    That is a very unsafe way to get power. The circuit will always present a lethal shock hazard. You are advised to use a wall transformer for safety.
     
  3. kammenos

    Thread Starter Active Member

    Aug 3, 2008
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    are there super small transformers for this? where can i find them?
     
  4. mik3

    Senior Member

    Feb 4, 2008
    4,846
    63
    What do you want to power with the 5V?

    Do you want 5V AC or DC?
     
  5. eimix

    Active Member

    Sep 2, 2008
    32
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    I suggest use PC power suply unit
    for DC it is powerfull - 5v -> 12-20A, 12v -> 5-12A
     
  6. kammenos

    Thread Starter Active Member

    Aug 3, 2008
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    Maybe i said it wrong.

    1. I do not want external power supply
    2. I will power 200mA
    3. I do not care for AC/DC. Whatever.
     
  7. mik3

    Senior Member

    Feb 4, 2008
    4,846
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    What device will you power?
     
  8. kammenos

    Thread Starter Active Member

    Aug 3, 2008
    127
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    But is it THAT important? Some 555, some other chips, some resistors, some capacitors. A circuit that i am researching right now. No motors. But why is that so important?
     
  9. Mike Mandaville

    Active Member

    May 27, 2009
    81
    1
    Is there some reason why you could not just use a nine-volt snap-on battery?
     
  10. Norfindel

    Active Member

    Mar 6, 2008
    235
    9
    Because taking 5v from the 220v line will likely leave the *live* wire on your supposedly low-voltage circuit, potentially killing anyone who touches the live wire and ground at the same time. Not safe to work.
     
  11. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    If you're going to be working with 555 timers and logic IC's, you will need regulated DC power.

    An inexpensive (and safe) way to do this is to use a "wall-wart" type power supply with a voltage regulator on the output.

    Look for a surplus "wall wart" supply that will put out 500mA to 1A at 8 to 12v. You can use a 7805 regulator with a large capacitor on the input and smaller caps on the output to provide decently regulated voltage for not much cost. A heatsink for the regulator is advisable.
     
  12. kammenos

    Thread Starter Active Member

    Aug 3, 2008
    127
    0
    Thanks a lot Sgtwookie.
     
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