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replacing 220V rated bulb for a 12V LED?

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  • replacing 220V rated bulb for a 12V LED?

    ok, so today i started on my custom faceplate for my control buttons..

    i got one of these in maplin..

    maplin illuminated button - code: N09AR

    anyhow the rating on it is for 240VAC.. after playin around with it i discovered there was a tiny bulb that could be removed..

    what i want to do is replace the bulb inside the button with a 12V led..
    then i plan to wire the power into the dash light 12V so that my buttons will be illuminated at nighttime..

    what i was wondering is...
    should this work ok or is there anything else i need to consider?
    i will be connecting up about 10 of these buttons for my control panel..
    should i wire lower voltage Leds in series, or just use 12V leds in parallel...

  • #3

    Ok, small electronics lesson....

    Typical LED needs 5-10 mA, If running from 12V you calculate resistor as follows:

    R=V/I = 12-1.6/10x10-3 = 1.04 Kohm (-1.6V for led volt drop)

    check power of resistor P=I^2xR = 10x10-3 ^2 x 1000 = 100mW
    (normal 0.25W resistor ok)

    Enforcer - I would never put LEDs in parallel as the will not current share correctly. If you want 2 LEDs, use 2 separate resistors. Although I dont see why you'd need to because if you drive them correctly, it will be workinh long after you are dead...



    • #4
      10-3 ? where the -3 come from? I know there are 10 LEDs but can't figure out the -3 part. Thanks


      • #5
        Ok, i was thinking series would be more likely way to do it...

        only thing is, if im working off 12V rail from the car dash light line, the voltage will surge (from 8 to 14v) when the car is cranking..
        trying to remember my electronics class..
        V/I = R, so if the voltage drops will the current surge and blow the leds?

        how can I regulate the voltage/current?


        • #7
          V= IR

          where V= the difference in voltage. If the LED is rated at 12 v and source is 12 v there is no resistor needed.

          With crank up to 14 v, v=2, I = .001 (assumed), R would in this case = 1000 ohms.

          I'd suggest a 12v lamp though. That way you don't have anything to worry about.

          '04 Canyon 4x4 pickup

          [---PC on hold----working on external fiberglass "tool" box---]


          • #8
            Enforcer - Thx for clarification, thats what i meant.

            Foxbat - Why post if you're not sure what you are talking about? [flame over]
            There is no such thing as a 12V LED. ALL LED's have a voltage drop of about 1.6V.
            The variation in current for the voltage variation is not a problem, since the LED has a wide current working range. It's crazy to use a filament lamp that will blow sometime, when you can use a reliable & cheaper LED!?

            Preachin' good electronics to the world!


            • #9
              oh, ok, starting to understand a little better now..

              so a bulb can survive the voltage surges better that LEDS?

              would this bulb be suitable so: (its about the right size i need...)

              filament typebulb, dia. 5mm, 12V, 008A, 096W


              • #11
                Ok, those were the ones i was looking at before actually..
                ill probly go the led way, as it looks the easiest, their tiny and cheap..
                will do up a little prototype to check if it works, then get the rest of the buttons..
                thanks for all your help.


                • #12
                  You simply wont have enough voltage to power all the 10 LEDs in series.

                  Assuming each LED drops 1.6v then for you to be able to pass a current on all of them you will need 16v (10x1.6) atleast.

                  Best to connect all of them in will need to connect a resistor on each LED and threat them as one 12V lamp, then just connect all those lamp in parallel.

                  Calculate the resistor value :

                  As enforcer said, yes you can get a 12V LED, its just basically an LED that can operate at 12V (with limiting resistor). Will save you hassle having to add a resistor on each LEDs.

                  + 12 V ---[ RESISTOR ]---|>|--- 0V
                  + 12 V ---[ RESISTOR ]---|>|--- 0V

                  Just connect all of them in parallel, add as much as you want, a much flexible solution this way. Although you can connect LED in series but you certainly cannot connect 10 and powering them with 12V.

                  If you are worried about the surge then just calculate the resistor such that the current being passed is still safe for the LED...calculate the limiting resistor for 16V not 12V. Just pass 20mA per LED at 16V to be on the safe side.


                  • #13
                    You can always get an extra bright LED, run a risister assuming 14v, so when the car is running at 12, it will be bright, just not as bright as it can be. LEDs last what, 100,000 hour? That should cover it.

                    I have no idea why the hell I would suggest a lamp. I love LEDs. I'm working on convincing my little sister that LEDs would make badass electrons for her 8th grade lead atom model.

                    '04 Canyon 4x4 pickup

                    [---PC on hold----working on external fiberglass "tool" box---]


                    • #14
                      no, no, no - filament lamps are not more tolerant to voltage variations. In fact it is the opposite, since an led has a linear range of current vs brightness.

                      Foxbat - I suggest you go and read a few books before you post stuff that is wrong & confuses people.



                      • #15
                        gonna try out the led solution, i can get my hands on those current limiting ones easily enough.
                        thanks for all the knowledgable comments.
                        even the bulb suggestion being shot down clarified the whole led v's bulb thing for me a little..

                        just a couple of other things im not clear about.. Heat..
                        what is the differences in heat output between Leds and filament bulbs. which is best to use? i dont wanna melt my plastic dash!