Circuit Design help

Discussion in 'The Projects Forum' started by jkfde, Sep 5, 2012.

  1. jkfde

    Thread Starter New Member

    Sep 5, 2012
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    I need help figuring out how to wire multiple light circuits. i want a switch that has these positions(off, light 1 on, light 2 on, light 1+2 on) but i want that wired into a dimmer switch. what potentiometers and resistors would i need. the power source is a normal wall outlet 110v 20 amp i think, and light once would be a normal light socket. light 2 would be 4 seperate light decorations that run on 3 AA batteries which would need to all be on light 2. i know this sounds a little confusing but can anyone help?
     
  2. #12

    Expert

    Nov 30, 2010
    16,247
    6,744
    Until you said, "run on 3 AA batteries" this was a simple job that an electrician could do. Now you want dimmable 4.5 volt lights wired to a switch that controls 120 volt power?
    Not legal. Not safe. Probably won't be allowed on this site.
     
    Last edited: Sep 6, 2012
  3. jkfde

    Thread Starter New Member

    Sep 5, 2012
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    pretty much the project is a cool looking lamp, built from scratch. so i need to be able to have a normal light bulb in the center. and lights on the side that run on a couple of volts. i want to be able to do the stuff in my other post.
     
  4. Wendy

    Moderator

    Mar 24, 2008
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    LEDs off main voltage is a direct violation of Terms of Service. A transformer or wall wart much be used to power these LEDs, or this thread is done.
     
  5. jkfde

    Thread Starter New Member

    Sep 5, 2012
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    Ya i want to know what i need to power the lights, resistors or whatever else i need.
     
  6. jkfde

    Thread Starter New Member

    Sep 5, 2012
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    I do not know the exact voltage for leds since i didn't receive them yet. so lets say each requires 5 volts, and all 4 lead to a transformer. would that transformer need to bring it down to 5 volts, or 20 volts to spread out equally among the 4 lights. how does the electricity disperse voltage? and amps?
     
  7. wayneh

    Expert

    Sep 9, 2010
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    3,025
    You can run LEDs in either configuration - series or parallel. A forward voltage of 3V is more typical than the 5V in your example, so lets say you need DC at about 3V for 4 parallel LEDs or at about 12V for 4 series LEDs. Most folks prefer the latter arrangement unless/until the LED count gets too high and you need too high a DC voltage.

    But it's a little more complicated.

    A transformer changes one AC voltage to another AC voltage. You need a rectifier (4 diodes) to convert this to DC, and usually some sort of filter to smooth out the ripple. A capacitor is often used for this. The final voltage will be roughly the transformer's AC secondary voltage times 1.4, minus 1.4V lost in the rectifier. (The primary voltage is the mains that you connect it to.)

    But here's the important bit: The LEDs need a certain current level, usually 5-20mA, to produce reliable light without burning out. You cannot just apply a voltage. Limiting the current is often accomplished by placing a resistor in series with the LED(s). So for instance instead of the 12V supply mentioned above, you might supply 14V and drop 2V across a resistor. You need to use Ohm's law to calculate the appropriate resistor.

    My advice is to start with just 5mA and only move up towards 20mA when you are fully comfortable with your circuit.
     
  8. jkfde

    Thread Starter New Member

    Sep 5, 2012
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    Would it be easier to get one of those generic ac/dc power supplies that will have it already brought down to a certain voltage that's dc.
     
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