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need help asap with leds and such

Discussion in 'LEDs and Optoelectronics' started by ineedhelp, Jun 14, 2012.

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  1. ineedhelp

    ineedhelp

    6
    0
    Jun 14, 2012
    im trying to put some leds in my car i had them all wired up with no resistor. :( the were wired to a 12v power supply and then grounded to the car i started the car turned on the switch and the leds went on and then off right away im guessing i blew them out.
    i also tested them on a 3v battery before i put them in the car.

    so should i use a resistor. if so how many what kind ant where should i solder them in at.

    there is a wire from the power supply to a 20a fuse. then to the 14v dc push button switch(also has an led that still works)has three prongs. one for power in, one for power out, and then ground. power out- splits into four wires one going to the positive of each led then from all the negative of the led wire goes to the ground of the switch then a fifth wire from the ground on the switch is grounded. there are 4 led's excluding the one in the switch. please help asap. if possible texting me would be easier my number is 717-579-6639. thank you in advance.
     
  2. ineedhelp

    ineedhelp

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    0
    Jun 14, 2012
    the led's are 4.0v max also
     
  3. CocaCola

    CocaCola

    3,635
    5
    Apr 7, 2012
    First off yes, you popped the resistors since you didn't limit the current to them...

    Start here...
    https://www.electronicspoint.com/got-question-driving-leds-another-work-progress-t228474.html

    There are multiple ways to hook up the LEDs...

    If I was doing it and wanted 4 LEDs as I assume you do, I would use two series bundles that contained 2 LEDs each and a resistor and wire them parallel...

    The resistor value will depend upon your choice of how you wire them up...
     
  4. ineedhelp

    ineedhelp

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    Jun 14, 2012
    could you make a schematic for me if possible that would help me out tons
     
  5. CocaCola

    CocaCola

    3,635
    5
    Apr 7, 2012
    Sure I could but one isn't necessary once you understand the basics of Ohms law...

    What you described as the circuit is one way of doing it (so you already have the 'schematic') all you need to do now is limit the LEDs current so that you don't pop the LEDs...

    There is a schematic on how and where to put that current limiting resistor in the post I linked, please go read it... It's really counter productive for me to go and copy and paste it for you or paraphrase what is already written there...
     
  6. Raven Luni

    Raven Luni

    798
    7
    Oct 15, 2011
    I'd have to say that you really should not be attempting this if you don't know what you're doing. I'd go as far as to say that something on the scale of a car battery is probably the second most dangerous thing to working with the mains. 12 volts might seem harmless enough but those things can deliver an instantaneous current of well over 100 amps. This can generate massive ammounts of heat in a very short space of time - enough to shatter glass and an instant recipie for fire, and if you happen to be near the fuel line........

    If you want to mod your car, get it done professionally or not at all.
     
  7. ineedhelp

    ineedhelp

    6
    0
    Jun 14, 2012
    CocaCola thank you and Raven Luni i do know what i'm doing as far as connecting it to the car and i have gone through all safety precautions. i really only needed help with the resistor and where to put it. but thank you for your concern. oh and CocaCola from what i described could you tell me would that be series or parallel i'm a little confused on that.
     
  8. CocaCola

    CocaCola

    3,635
    5
    Apr 7, 2012
    What you described is 4 LEDs in parallel...
     
  9. ineedhelp

    ineedhelp

    6
    0
    Jun 14, 2012
    ok thank you
     
  10. ineedhelp

    ineedhelp

    6
    0
    Jun 14, 2012
    Ok so I got two different resistors a 1/4 watt 1k ohm resistor and a 1/8 watt 150 ohm resistor which one would work best
     
  11. CocaCola

    CocaCola

    3,635
    5
    Apr 7, 2012
    Work best? Why didn't you get the correct value?

    You have not given the spec for your LEDs except that they are 4.0v max, you need more info to get the idea resistor value... Did you read the page I linked you to? What value resistor did you come up with when you used Ohm's law or one of the many online calculators?

    Since this is an automotive application use 14.5 volts as the source voltage, not 12 as the car is rarely at 12 volts... 14.5 volts offers a safe margin of error...

    You stated the LEDs where 4.0v max, what is the recommend voltage? 3.2? 3.5? 3.8?

    What is the recommended current? 20mA? 25mA? 30mA?

    Plug those numbers into Ohm's law and you will get the idea resistor value...

    I can tell you right now that 150Ω is almost certainly too low and 1000Ω too high... The 1000Ω will likely work but the LEDs won't be as bright as they would with the proper value resistor... The 150Ω will also work but it will drastically shorten the life of the LED...

    Three of the 150Ω resistors in series would be closer to ideal values @ 450Ω, as would two of the 1000Ω in parallel @ 500Ω
     
    Last edited: Jun 15, 2012
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