Electronics and DCC

Hello,

I gathered up about five (5) bright white LEDs from broken flashlights (5mm) and want to use them in Engine Service Facility (HO).  I have a 12vdc power supply.  I am assuming these are 2.6v 20ma LEDs.

How should I wire them up?

Thanks for the advice,

Peter

modelalaska:

Hello,

I gathered up about five (5) bright white LEDs from broken flashlights (5mm) and want to use them in Engine Service Facility (HO).  I have a 12vdc power supply.  I am assuming these are 2.6v 20ma LEDs.

How should I wire them up?

Thanks for the advice,

Peter

Wire them with a 470 ohm 1/2 watt resistor in series with each one.  The resistor will drop the voltage down for your LEDs.  If they are too bright, try 560 or 680 ohm resistors.

12 volts - 2.6 volts = 9.4 volts to "drop".

At 10 milliamps of draw you want 9.4/10 = .94k ohms or 940 ohms

At 20 milliamps of draw you want 9.4/20 = .47k ohm or 470 ohms

Chose something between 470 ohms and 1000 ohms that gives the brightness that you want. They do NOT have to be all equal.

Power supply feeds a resistor in series with EACH LED.  Each LED/resistor pair in parallel across the supply.

(-) --------------------------------------------------------

        R      R      R      R      R      R      R

         |       |        |        |       |       |        |

        ---     ---     ---      ---     ---     ---      ---

         ^       ^       ^       ^       ^       ^       ^

          |       |        |        |       |       |        |

(+) --------------------------------------------------------

I know cra@@y drawing.

you guys are way to fast for me i went to do the calculations cam back 2 posts already.

yea like they said,wire in parallel with a resistor. also the + and - side do matter on the LEDs.the rester may go on either side. i usually try to always put it on the same side, for trouble shooting later on, all wired the same.

love that one Line diagram.

dan

 Wow, a resister for each LED... I was hoping one for all.  Don't the LEDs has some resistance themselves?

Anyway, thank you for the explaination and the equations!

Peter

I just wanted to confirm something.  Whether LEDs or incandescents:

Wouldn't bulbs wired "in series" only need ONE resistor TOTAL vs. "in parallel"; ONE resistor for EACH bulb?

Chuck, the way I interpret your post is that you need one resistor for each LED wired "in series".  Am I reading it incorrectly?  Thanks.

Tom

 It is better to wire lamps in parallel, so if one burns out, the others will tell you which one it is.  Series is used when a number of low voltage lamps are used with a high voltage supply, because it is cheaper and simpler to wire.

LEDs should have their own series load resistor.  Trying to run many of them through a common resistor will reduce their output, so a lower value of resistor has to be used to maintain decent current flow.  The flip side is that if a couple don't light because they don't get enough current, more current flows through the others and possibly shortens their lifespan.

Since resistors are pretty cheap, (cheaper than the LEDs) there is really no reason to try and scrimp on their usage.

The alternative is to build a multiplexing circuit, but that will need some room, and costs more than resistors too.

May I please jump in here? I now understand how to wire the resistors, but can someone show a wire diagram for wiring up LED lights to turnouts? One side GREEN for right away and maybe RED for turn out. Thank you.

If you're using tortoises it's easy.

Simply place the LED in series with one motor lead. (no resistor)

Otherwise a split power supply is best. Center to common, proper polarity switched power to whichever color you want lit at the time. (needs a resistor or two).

Thank you for your responce..Is it possible to get a drawling on the proper wiring? One thing though, I'm not using tortoises, I am using atlas. Also, not using DCC.