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120 volt LED design

Discussion in 'Electronic Design' started by [email protected], Feb 25, 2008.

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  1. Guest

    Is it possible that I can add an LED in series with a 120 Volt AC
    circuit, this will light up to indicate that I have power when a load
    is connected. This LED will have to handle 15 amp load
     


  2. You got no brain. What planet are you from? Look up LED spec, see the current and do a little math will you? Don't expect people to put foods in your mounth. This is an easy job. Don't ask!



    --
    Service to my country? Been there, Done that, and I've got my DD214 to
    prove it.
    Member of DAV #85.

    Michael A. Terrell
    Central Florida
     
  3. sycochkn

    sycochkn Guest

    1500 leds in parallel.

    Bob
     
  4. Have you heard of current transformers? That is what I
    would use to connect a pair of LEDS in series with an AC load.

    Perhaps something like this one:
    ttp://www.netsuite.com/core/media/media.nl?id=3354&c=ACCT126831&h=467c29543fa58c37926a&_xt=.pdf
     
  5. BobW

    BobW Guest

    I don't think you understand what the OP is asking for.

    To me, it seems like he wants something that will light up when when a light
    load is connected to his "led box", and will also light and not blow up when
    a 15A load is connected to it, too.

    This is not such a trivial design.

    Bob
     
  6. Guest

    U can use a capacitor as a resistor for ac ccts. Cheaper than xfmr as
    long as u keep it safe.
     
  7. sycochkn

    sycochkn Guest

    Johns current transformer idea sounds like a good one a little amplification
    with an op amp and you have lots of range. or a hall sensor. current probe
    etc.



    Bob
     
  8. Guest

    thanks for the response, I do believe I will have to incorporate a CT
    (current transducer) I know that LEDs can't handle current and will
    now need advise on hooking up a very small CT to light up an LED when
    current is detected, on a 120 volt AC line. thanks for all
    responses. (And yes I do have a brain,)
     
  9. Guest


    A cheap way to sense current is to wrap a few turns of one wire around
    a read relay. mmm good for "bulb out" sensor on a car but not sure
    about Ac?
    Then use capacative reactance for Led supply.
    Mike
     

  10. You replied to a forged post by jackthehammer. I have never had an
    account with aioe.org.


    --
    Service to my country? Been there, Done that, and I've got my DD214 to
    prove it.
    Member of DAV #85.

    Michael A. Terrell
    Central Florida
     
  11. On Sun, 24 Feb 2008 20:37:43 -0800 (PST), the renowned
    No, that's not realistically possible unless you want to spend
    hundreds of dollars minimum and light up the room.

    A small metal core toroidal current transformer (run a wire through
    the core for the primary) can be used.



    Best regards,
    Spehro Pefhany
     

  12. 120V~
    | |
    | |
    | |
    | | +-----+
    | o | |
    | | | |
    | +-----+ | .-.
    | | |5V~ 120V~ | | |2k2
    | .-. +---. ,------+ .-----. | | |
    | | | )|( +-| ~/ |-+ '-'
    | | |.02R/5W )|( +---| / = |---+ |
    | '-' +---' '----+ '-----' | |
    | | | 100mA | V LED
    | +-----+ | -
    | | | |
    | o +---+
    | |
    | |
    | |
    created by Andy´s ASCII-Circuit v1.24.140803 Beta www.tech-chat.de

    For measuring or signaling current the best thing you can use is a current
    transformer. But this tend to be expensive things that are not always
    available.

    If you only want to signal the current in 10-15A range, the circuit above
    will do.
    Be sure to make proper connections between the 0.02R/5W resistor and the
    main line. A bad connection will become hot and fry itself. The resistor
    will become hot as well so provide enough ventilation.
    Connect the transformer directly to the resistor (so not to the line).
    The transformer can be a ordinary 100mA type. Even a 50mA type may do though
    it can become a little bit too warm. Mention its orientation.
    Use a low current type for the LED. A 2mA type will do.

    As the circuit is directly connected to the mains, use proper insulation.
    120V~ does not always kill but you don't want to be the exception... I guess
    :)

    petrus bitbyter
     
  13. I would put two big diodes in reverse parallel, and that goes in series
    with the load. Then use a transformer to step up the voltage across the
    diodes to a level that will light an LED. This will have the LED
    brightness only varying a little with load current, as long as the load
    current is enough to make the transformer light an LED.

    - Don Klipstein ()
     
  14. Bill Bowden

    Bill Bowden Guest

    Problem is, you might get a current spike that blows the LED when the
    thing is switched on or off. I tried to use an LED in a 1KW space
    heater as an indicator light, and just used a diode and resistor
    across the low voltage fan which was in series with the heating
    element. It worked for a few hours and then blew the LED. So I
    replaced it and tried again with same result. I finally just put the
    LED and large power resistor in parallel with the entire load and
    never had any more problems. The extra heat from the power resistor
    just helped heat up the room.

    -Bill
     
  15. OK, I would either add a bridge rectifier or use two inverse-parallel
    LEDs. A suitable dropping resistor is needed of course.

    With the transformer primary's voltage limited to a diode drop, I doubt
    anything bad will happen to the LEDs unless those primary diodes fail
    open or the power line is hit by lightning. (Put a fuse in series with
    the transformer primary in case those diodes open.)

    - Don Klipstein ()
     
  16. Bill Bowden

    Bill Bowden Guest


    Yes, it will probably work if the 15 amp power diodes are fast enough
    to respond to short current spikes. I think my problem was the
    inductance of the fan motor bumped up the voltage considerably when
    power was switched off.

    -Bill
     
  17. JosephKK

    JosephKK Guest

    Just buy a 120v LED indicator and wire it in parallel with the load.
    Then load current from 0 to blows the breaker does not matter.
     
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