AC Supplies and LEDs

Discussion in 'The Projects Forum' started by trafficman40, Mar 7, 2013.

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  1. trafficman40

    Thread Starter New Member

    Mar 7, 2013
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    Hi All.

    I need a circuit that drives an LED and also creates a load of 10watts.

    I've also read that I would need to put a diode in reverse across the LED in the first instance when using ac.
    Would I put a load resistor in parallel to get the 10W current drop.?
    What would be the best type of resistor for the load and for the LED ?


    2 different circuits required...
    one for 48v ac
    and
    one for 230v ac

    What size and rated resistors LEDs Diodes etc. would I need.

    Thanks in Advance.
     
  2. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    mains powered LED's are against the forums rules.. sorry.

    Not to mention if you are having to ask questions you are not competent enough to be working with hazardous voltages.

    I suspect this is a 10W multichip LED correct?
    If so you should purchase a proper LED driver where you can simply plug it into the wall and outputs a constant current to supply your LED.
     
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  3. trafficman40

    Thread Starter New Member

    Mar 7, 2013
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    10W mulitchip...? No
    Competent...? Yes

    I am looking to simulate a 10W lamp load but using LEDs.
    It is for a test box and rather than using real fittings as these are large and cumersome and there are many lamps required for indivdual automated switching. 96 in total.
    I was querying the best size and type of WW based on heat issues etc.
    I am sorry that this type of post is not allowed.

    #rulebreaker :)
     
  4. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    Whats wrong with off-the-shelf LED bulbs already made to simply screw into a mogul base or whatever instead of trying to build something.

    Is the exact 10W draw important?
     
  5. trafficman40

    Thread Starter New Member

    Mar 7, 2013
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    Yes, the 10w is precise for circuit monitoring.
    It's for traffic signals and off the shelf Red Amber Green 10w lamps are not easy to come by.
     
  6. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    Just a 20+W resistor in the correct ohm range and you will be all set. 20W is a 2x safety factor.. You never want a resistor running at its limit. Ohms law will tell you what the resistance should be for each different test voltage.

    Going by the rules here.... an isolation transformer/bridge rectifier or AC/DC converter should be used if you want to add LED's also to the circuit. And since you say you are competent that should be no problem for you.

    Of course not sure why you can't just use the bulbs that normally go into the traffic lights and forget making something fancy anyways. Socket them and add alligator leads or whatever.
     
  7. takao21203

    Distinguished Member

    Apr 28, 2012
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    Large resistors are highly impractical.

    I am sometimes getting away with wire coils or toroid inductors.

    But normally you should use a LED driver circuit, or at least an electronic transformer. They often have +/- 10% adjust so if the voltage matches, you can match the LED.

    For different colors unfortunately this does not work.
     
  8. trafficman40

    Thread Starter New Member

    Mar 7, 2013
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    The reason I can't use the real thing is the intensity of the lamps are so bright it would be like a permanent radiation blast in your face with up to 36 signals staring you in the face in a test room environment.

    Thanks for your feedback.
     
  9. takao21203

    Distinguished Member

    Apr 28, 2012
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    Then run them at reduced current. For sure a ready-made box can not adjust current, but it is possible with the right kind of circuit.
     
  10. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    test them upside down.. 1/2" off ground.. :D:p


    Just use the big resistors. Its simple and perfect for a test jig. Then add 20ma colored LED's for visual indicators.
     
  11. Wendy

    Moderator

    Mar 24, 2008
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    As has been mentioned, line powered LEDs (direct off mains) is against the rules.
     
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