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Indicator Light 12v

Discussion in 'Hobby Electronics' started by Mike Manuka, Sep 19, 2008.

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  1. Mike Manuka

    Mike Manuka Guest

    I have a 12v bulb 12w with a switch with only a positive wire and no chance of getting a negative wire to pick-up. It is an architrave switch so not a lot of room. Is there any way I can get an indicator light/LED to work.

    Is there some way of dropping the voltage slightly with diode and getting an LED or something to light.

    Many thanks in anticipation.
     
  2. Steve

    Steve Guest

    chance of getting a negative wire to pick-up. It is an architrave switch so
    not a lot of room. Is there any way I can get an indicator light/LED to
    work.
    I think that it's on a 12VDC supply. If so, a smaller resistor, about 560
    ohms, would be better.

    .... Steve
     
  3. Mike Manuka

    Mike Manuka Guest

    So I take it the LED would be ON the whole time the switch is off?

    If that is that case, 10mA an hour over 24 hours is nothing compared to
    leaving the light on all night which happens. Plenty of solar power to take
    care of the 240mA over 24 hours compared to minimum 8A if left on all night.

    Many thanks and appreciated.
     
  4. Franc Zabkar

    Franc Zabkar Guest

    If you are looking for a way to illuminate your switch in the dark,
    then connect an LED and 10K series resistor across the switch
    contacts.

    - Franc Zabkar
     
  5. Franc Zabkar

    Franc Zabkar Guest

    Yes, that was a typo. I was aiming for 10mA from 12V, so I should have
    specified 1K.

    - Franc Zabkar
     
  6. Franc Zabkar

    Franc Zabkar Guest

    Yes. I'm assuming your light is an incandescent type that provides a
    low resistance path to the negative terminal.
    You could experiment with higher resistances and high brightness LEDs.
    You could also try a flashing LED which would require less current to
    be effective, although the flashing may be annoying.

    Here are a few Dick Smith LEDs:
    http://www.dse.com.au/cgi-bin/dse.storefront/en/product/Z4044
    http://www.dse.com.au/cgi-bin/dse.storefront/en/product/Z4024
    http://www.dse.com.au/cgi-bin/dse.storefront/en/product/Z3982
    http://www.dse.com.au/cgi-bin/dse.storefront/en/product/Z4031
    http://www.dse.com.au/cgi-bin/dse.storefront/en/product/Z4033

    BTW, that's 240mAh and 8Ah.

    - Franc Zabkar
     
  7. Mike Manuka

    Mike Manuka Guest

    Franc are you saying the LED would take 240mAh and 8Ah?
    If it will, is there something else that would use substantially less?
    Can you get itsy bitsy teeny weeny LED's that use low power?

    Yes, it is a standard filament bulb.

    I don't imagine I would be to popular with her ladyship if I used a flashing
    LED.

    Many thanks and also for the links.
     
  8. Jasen Betts

    Jasen Betts Guest

    240 mAh to operate a LED at 10mA for 24h ,

    presumably 8Ah is the cost of leaving a 3W lamp running for 24h ???
    not sure.
    absolutely, leds will light with only the tiniest aount of current
    flowing through them (they only light the tiniest bit however, but if
    the goal is locating the switch in the pitch black that should not be
    a problem)

    best results are had with leds marketed as high-efficiency.

    1mA is sufficient to make an ordinary led (jaycar CAT. NO. ZD1694) bright
    enough for it to be visible in dark daytime shade, and to stand out in the
    dark.

    with about 0.2mA I get a glow comparable to those glow-in-the-dark
    bedlamp switches. With a high efficiency led you could go
    to even lower power usage.

    Bye.
    Jasen
     
  9. Franc Zabkar

    Franc Zabkar Guest

    Ampere-Hour is a measure of charge. If you draw 1A for 8 hours from a
    battery, then the battery will have lost 8Ah of charge.
    In addition to what Jasen has said, you could use several LEDs in
    series across the switch. Some high brightness LEDs have a
    significantly higher voltage drop than ordinary LEDs, so some
    experimentation may be in order. You might get away with 4 or 5 bright
    LEDs and a resistor that sets the current at 1mA. Just bunch the LEDs
    together, like an LED night light. That will give you 4 or 5 times as
    much light output for the same current.

    - Franc Zabkar
     
  10. Mike Manuka

    Mike Manuka Guest

    Many thanks. Bought a 3mm orange LED from Jaycar, 1k resistor and uses
    11mA. I may try the next resistor size up and see how bright that is and if
    it reduces the power v LED brightness.

    Many thanks for the assistance. Sincerely appreciated.
     
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