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Multiple LED lighting — Parallax Forums

Multiple LED lighting

w4fejw4fej Posts: 264
edited 2013-01-23 07:04 in General Discussion
I want to use 16-18 white LEDs for background lighting on a wall hanger. Can I simply wire all the LEDS in parallel and power them with a 9VDC battyey or is there a better way to do this? The LEDs don't have to do any tricks, just glow. I will use a pot to adjust the brightness then replace the pot with a fixed resistor.

Thanks for reading.

Mike B.

Comments

  • Duane DegnDuane Degn Posts: 10,588
    edited 2013-01-22 14:10
    I've been told it's possible to use only one resistor for multiple LEDs if the LEDs are from the same batch and have matching electical characteristics but I don't think it's good idea to do it this way myself.

    The usual and safer solution is to use have each LED have its own resistor (wired in parallel as you plan). I'd suggest using the pot on one LED to figure out what resistance is needed to obtain the desired brightness/current and then use this same value for each of the other resistors.

    Edit: I agree with Martin and kwinn below as long as the voltage drop across the resistor will remains large enough to regulate the current as the voltage of the battery drops over time.
  • Martin_HMartin_H Posts: 4,051
    edited 2013-01-22 15:03
    I use the LED array wizard for designing multiple LED's at a voltage with the least number of resistors.

    http://led.linear1.org/led.wiz
  • kwinnkwinn Posts: 8,697
    edited 2013-01-22 15:05
    I would suggest putting 2 leds in series with a current limiting resistor, and putting 8 or 9 of those circuits in parallel to connect to the 9V battery. That way the battery will last longer. If you want to control the brightness use a 555 timer circuit to PWM the leds and make the battery last even longer. If the current draw is too high for a 555 to handle it will drain the 9V battery in a very short time.
  • NWCCTVNWCCTV Posts: 3,629
    edited 2013-01-22 16:24
    I will have to see if I can dig up any notes from a project I completed a few years ago to have lighting inside my model train tunnel. Basically I used one or to resistors with a transistor and I was able to run 9 LED's from one 9 volt battery. The LED's were quite bright and lasted for quite some time.
  • RDL2004RDL2004 Posts: 2,554
    edited 2013-01-22 18:05
    No matter how you wire it up, that 9 volt battery isn't going to last long at all. probably less than an hour (depends a lot on the type of battery and LEDs you use).
  • NWCCTVNWCCTV Posts: 3,629
    edited 2013-01-22 19:45
    RDL2004 wrote: »
    No matter how you wire it up, that 9 volt battery isn't going to last long at all. probably less than an hour QUOTE]

    My 3 Volt LED's lasted over 2 hours while playing on the train set with my grandson. They were still going, (albeit a bit dimmer) when I shut it all down.
  • homosapienhomosapien Posts: 147
    edited 2013-01-23 07:04
    Of the top of my head, I would say a bunch of LEDs in series w/ resistor at the end is more efficient, as the power dissipated by the resistor (wasted power in this application) is less.

    I would divide the LEDs into strings of LEDs in series that feed into one resistor at the end. The number of LEDs in each string will be dictated by the voltage drop across each LED and the source voltage. You want the voltage after the LEDs but before the resistor to be large enough so the resistor can adequately regulate the current (10mA usually works). If the power supply is not battery (ie wall supply) it is even better because you will not have to design around the voltage changing over time. Make sure the resistor is large enough to handle the power to be dissipated.

    If you need more specific info I would need to know the voltage drop of the LED at the planned operating current, voltage source type and voltage.


    Nate
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