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How to rewire 4 headlight bulb setup to 4 LEDS?

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  • Member since
    January 2007
  • 180 posts
How to rewire 4 headlight bulb setup to 4 LEDS?
Posted by Otis on Saturday, August 9, 2008 5:35 PM

I am converting to DCC a P2K SD38-2 that has 2 forward bulbs and 2 rear, each pair wired in series.  The original arrangement is just doubled to serve the headlight and number boards separately on each loco end.

I just paused to ask, should I also wire the LEDs in series (is that even possible?) or just double up the wires to give each of the forward and rear LEDs their own set?

Do I need 4 resistors too?

 

  • Member since
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  • From: Ontario Canada
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Posted by Mark R. on Saturday, August 9, 2008 8:57 PM

Actually LEDs work the same (almost) as bulbs in regard to series and parallel. In series - like bulbs - if one goes bad, they both go out .... but seeing as how LEDs have a much longer life, under normal circumstances, wiring in series work just fine - you just have to use a lower ohm resistor. I use two LEDs in parallel for my headlights and two LEDs in series for the number-boards - for no other reason than wiring convenience !

Here's the two LEDs wired in parallel for the dual beam headlight ....

Here's the two LEDs wired in series for the number-board lenses ....

 

Finally, this is how they are arranged within the roof of the cab ....

Mark.

¡ uʍop ǝpısdn sı ǝɹnʇɐuƃıs ʎɯ 'dlǝɥ

  • Member since
    January 2007
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Posted by Otis on Saturday, August 9, 2008 11:04 PM

Thanks, Mark.  Your photos seem tailor made to my question.  Cool.  I learned something today.

As usual in my case, I have only half a grasp  (or less) of the electronics side of things.

  • Member since
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  • From: Pittsburgh, PA
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Posted by dbodnar on Sunday, August 10, 2008 1:05 PM

Otis - I would strongly suggest that you use two separate current limiting resistors whenever you wire LEDs in parallel - if the LEDs aren't perfectly matched you will find one brighter than the other if you use only one resistor.

You may want to look over the information on wiring LEDs in series and in parallel in one of my articles:

LEDs 101

Please let me know if you have any questions.

dave

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  • From: Ontario Canada
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Posted by Mark R. on Sunday, August 10, 2008 6:15 PM
 dbodnar wrote:

Otis - I would strongly suggest that you use two separate current limiting resistors whenever you wire LEDs in parallel - if the LEDs aren't perfectly matched you will find one brighter than the other if you use only one resistor.

You may want to look over the information on wiring LEDs in series and in parallel in one of my articles:

LEDs 101

Please let me know if you have any questions.

dave

According to your linked article - in reference to parallel wiring ....

"Accepted practice is to wire each LED with its own current limiting resistor as in the diagram below.  Since each LED has its own current limiting resistor, which need not be the same value, you can mix different brands and colors of LEDs while having each retain its full brightness."

 I don't mix brands and colors and so don't have a problem with this. I have 43 engines all wired in this manner (front AND rear) and I'd challenge ANYone to tell me one headlight is brighter than the other.

Mark.

¡ uʍop ǝpısdn sı ǝɹnʇɐuƃıs ʎɯ 'dlǝɥ

  • Member since
    January 2007
  • 327 posts
Posted by locoworks on Monday, August 11, 2008 5:03 AM
 Mark R. wrote:

Actually LEDs work the same (almost) as bulbs in regard to series and parallel. In series - like bulbs - if one goes bad, they both go out .... but seeing as how LEDs have a much longer life, under normal circumstances, wiring in series work just fine - you just have to use a lower ohm resistor. I use two LEDs in parallel for my headlights and two LEDs in series for the number-boards - for no other reason than wiring convenience !

Here's the two LEDs wired in parallel for the dual beam headlight ....

Here's the two LEDs wired in series for the number-board lenses ....

 

Finally, this is how they are arranged within the roof of the cab ....

Mark.

that is some really neat and tidy soldering skills you have, a very good example.   wish i could get half as good.

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