Installing an LED flashing beacon

[mlm682577]

I am going to attempt to install an orange LED beacon on top of an HO KATO SD45-2.  I have read the articles in MR, and DCC Projects 2.  I use NCE decoders.  I have ordered the resistors recommended by the paperwork that came with the decoders (1K ohm, 1/4 watt).  I have a couple of questions.  Please remember that I am a leyman when answering the questions.

 1.  I noticed that the LEDs can be defused and non-difused?  What is that?  Which one should I use as a beacon?

2.  Based on the orange (fake) lense on the cab, it appears to be approximately one scale foot (HO), or about 3.5 mm.  I am looking at purchasing 3mm, round LEDs.  Is that the correct size? 

3.  Some LEDs are labeled as "flashing"  I was under the impression that the flashing is powered by the decoder.  Should I purchase a flashing or standard LED?

4.  Is there a heigth measurement to an LED?

5.  If anyone has put a flashing beacon on an HO diesel, please make my life a little easier and tell me what you used.

 Thanks for your help.

Mark

[richg1998]

 This not an LED beacon but you can get an idea of what I did. The Details West plastic beacon has an ID that accepts a 1.2mm 1.5 volt bulb.

http://cs.trains.com/trccs/forums/p/163593/1801019.aspx#1801019

Rich

[cacole]

I've put flashing yellow beacons on several locomotives using 3mm LEDs with the flashing units built into them.  Simply wire them to one of the spare decoder function wires (green or violet) through the 1K Ohm resistor.  Notice that LEDs are polarity sensitive.  Most of them have one lead longer than the other.  The long lead is positive so you need to connect the blue wire to it.  The resistor can be connected to either wire. 

If you use a standard 3mm non-flashing LED, the decoder function output will need to be programmed to make it flash.

A 'diffused' LED has a slightly milky appearance.  A coating on the inside of the LED lens spreads the light out.  A non-diffused LED will be clear and acts as a pin-point light source.  For use as a beacon it doesn't make much difference which type you use.

 

[Silver Pilot]

I'm going to second Rich's suggestion of using a bulb instead of a LED.  I've installed numerous beacons using both style of rotary beacons made by Details West.  You'll get the best result by drilling out the lens and installing the bulb inside instead of trying to funnel the light using the plastic light tube cast on the beacon.  Using a bulb also allows you to use either the mars light or gyralight function on the NCE decoder.  Depending on the type of rotary beacon being modeled sometimes they give a better look that the rotary beacon effect, but because of the lighting effect the LED doesn't do it justice.

[WSOR 3801]

Silver Pilot

You'll get the best result by drilling out the lens and installing the bulb inside instead of trying to funnel the light using the plastic light tube cast on the beacon. 

 

The newer ones are already cored for a light bulb.  I believe Athearn uses these on the RTR and Genesis engines that have beacons.

 

[mlm682577]

Thank you.  Your information is appreciated.  I'm definately a little smarter now. 

In some of the other posts, they recommend using a regular bulb.  What is your opinion of this?  I also did the math that the books recommend to determine the resistor required.  My math shows a resistor of 395 ohms (quite a bit different than what the decoder manual recommends).  I used a multi meter to find the track voltage.  That showed 17.80 VAC.  The LEDs advertise that they are 2 VDC.  Th bulb current is .040.  The formula is Ohms = (17.8 - 2) / .040.  That is where I came up with the 395 ohm resistor. 

 In one of the posts, the individual stated that the larger the resistor, the lower the LED's intensity.  Do you agree with that? 

[rrinker]

 It depends on the decoder. Digitrax decoders do awesome light effects but they don;t work very well with LEDs. NCE decoders can be adjusted somewhat to work with LEDs, TCS decoders work very well with either, depending on how you adjust it.

 The 'problem' is it takes a bit more effort to make an LED appear to go between dim and bright due to their rather binary nature - above a certain threshold, they're on, below, they're off. What works perfectly for an ordinary incandescent bulb will result in an LED that either never goes off or goes off when it's supposed to be dim. Some decoders like NCE and TCS implement a more complex algorithm to control the function outputs and can be set to work just as well with LEDs as they do with bulbs.

                                                         --Randy