XMass Tree LEDs as Replacements in a HO Diesel

[cedarwoodron]

I have a box of 50 xmass tree LEDs, .02amp, that I have used successfully with a 470 ohm resistor in small structure lighting applications. Now, as I work on my first locomotive rebuild, I want to replace the existing bulb light with LEDs. Actually, I want to wire 2 of them, as the original design only included the one bulb. These LEDs have a concave end to enhance the brightness of the light as ornamental lights. In my structure applications, I sanded the top flat to allow for a more gentle "glow"' but in the diesel, there are two small lenses molded onto a flat plastic backing that each led would sit behind. So, how should I wire these? Do I use 2 resistors, one for each light? How should they be wired so that BOTH ends of the hood are lit whether the loco is moving forward or in reverse (my thought is that would be a safer practice, particularly in a switching yard)? As always, and advice will be greatly and gratefully appreciated! Cedarwoodron

[Hamltnblue]

You only need one resistor per led.  Start with 1k ohm and work down from there until you get the correct brightness. To get them to work with direction, just wire them the same way that the bulb was.  Usually the LED's from christmas lights are a bit large for HO scale headlights but if you can get it to fit and it looks good, that's all that matters.  Just know the LHS will probably have something much better for very cheap.

[cedarwoodron]

Actually these Xmass LEDs will sit BEHIND the existing two-lens original plastic light insert, so as to provide light thru both horizontally parallel lenses. Cedarwoodron

[cedarwoodron]

Also, forgot to mention that I am a frugal railroader, and that the box of 50 LEDs cost me $ 6.00 at Walmart, of which I have 45 left to use on the railroad. My shareholder (read CFO wife) heartily approves of my cheap instincts regarding my hobby spending. Cedarwoodron

[tstage]

If the LEDs are white and they are going into any steamers or early diesels, you will want to yellow the ends of the LEDs slightly to make them look more prototypical.  Otherwise, they will look too stark.

Tom

[cacole]

Most of the Christmas LEDs I've seen are called 'inverted cone' types that radiate their light to the sides as well as straight ahead, so you'll need to encase them with a couple layers of black shrink wrap or they'll light up the entire cab like the original Athearn bulbs.

 

[Texas Zepher]

cedarwoodron

Do I use 2 resistors, one for each light?

Yes.  Use 1 resistor per LED.

 How should they be wired so that BOTH ends of the hood are lit whether the loco is moving forward or in reverse

Just while the locomotive is moving or lights on all the time?

[cedarwoodron]

Actually, that's a good question! I would say that the lights would be on both front and rear, standing or in motion, as long as current is being applied (DC operation) to the track. This particular diesel, until I regear and repower it, is not known for it's scale slow speed handling. And, to guess the follow-on question, no- it's not a good candidate for DCC conversion, hence the repower emphasis. Cedarwoodron