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Advantages of LED Lights
Athearn produces a great variety of HO locomotives with outstanding detail and reliable performance. But one common complaint among modelers is that they continue to use 1.5-volt incandescent bulbs for the various lights on the locomotives, which can include a headlight, back-up light, classification lights, and ditch lights.
While incandescent light bulbs provide a nice color, they can burn out quickly. Fortunately, these locomotives can be converted to LED lights fairly easily. LEDs will last a lot longer and reduce the voltage draw—which can be significant if your layout includes a lot of locomotives.
These techniques will work on other brands of locomotives as well. While each installation can be a little different, the basic steps will be the same. The model shown in our example is an older Ready-to-Run SD40. For this installation, both LEDs and fiber optics will be used.
Tools and Materials You Will Need
Continue to 2 of 6 below.
- Soldering iron
- LED lights (T1 3mm "sunny white")
- 1k ohm 1/4 Watt resistors
- Heat-shrink tubing
- Wire cutters
- 0.40 fiber optic strands
02 of 06
Remove the Incandescent Bulbs
The first step is to remove the incandescent light bulbs. The small bulbs are held in place with glue on the inside of the shell. Just place a small drop of water on the water-soluble glue and let it sit for about a minute. You should be able to gently pry the bulbs loose without any problem.
Next, disconnect the wires from the PCB board. You can use the same tabs on the board for the new LEDs. If you are installing a DCC decoder, you can use the tabs on the board or just hardwire to the white, blue, and yellow leads on the decoder.Continue to 3 of 6 below.
03 of 06
Pre-Wire the LEDs
Unlike incandescent bulbs, LEDs are polarized, meaning that each light has a positive and negative lead. The positive (+) lead is called the anode, and if the LED has leads attached, the positive will be the longer one. The negative (-) side is called the cathode and will be the smaller of the two leads. Other LEDs, such as surface-mount styles, will have a flat spot or mark on the (+) side. It is important to wire the LEDs correctly, so be careful to distinguish the anode from the cathode lead.
You'll also need a resistor to reduce the voltage sent to the LED. You can wire the resistor to either the positive or negative side.
For most model train applications, the combination of LED and a resistor, as shown here, will work very well. The preferable LEDs are T1 3mm "sunny white." (To better mimic incandescent bulbs, look for a sunny or warm white LED; others will have a more bluish hue.) Pair these with 1k ohm 1/4 Watt resistors.
It is easiest to wire the LEDs for the headlight and backup light before installing them in the locomotive. You can greatly shorten the leads of most LEDs, just by clipping them to the desired length with wire cutters. Space is at a premium inside most locomotives, so use as little lead as possible.
Continue to 4 of 6 below.
- Place the LEDs back to back and solder the anodes together.
- Then, attach a short length of wire to connect the light o the PCB or decoder. If hardwiring to the decoder directly, attach to the blue lead.
- Next, wire a resistor onto each of the cathodes.
04 of 06
Wire the LEDs to the PCB
Next, the LEDs need to be connected to the locomotive. Again, you can use the PCB board in the locomotive or go directly to a DCC decoder. It is best to plan ahead and think about how you will connect the fiber optics to the LED and the LED to the board in a manner that will still let you get the shell on/off the locomotive.
For a PCB board, connect the anodes to the common post, and connect the two cathodes to the headlight and reverse light posts respectively.
For a decoder, use the white wire for the headlight, yellow for the reverse light cathode and blue for the anodes.
Slide a piece of heat shrink tubing over the wires before soldering the connections. Then position the tubing over the bare wire and use the edge of your soldering iron to shrink it around the joint. Use liquid electrical tape over the anode connection. Space is tight inside these models—don't take any chances with bare connections.
If you are adding additional lights (ditch lights, warning lights, marker lights, etc.) simply repeat these steps and use the appropriate leads.Continue to 5 of 6 below.
05 of 06
Attaching Fiber Optics
Use fiber optics to carry the light from the LEDs to the lenses. For most Athearn engines, .040 strands will work well.
This is where the installation gets a little more difficult. You'll have to plan ahead to determine the best way to go about the installation in your locomotive. For our example, it was easiest to test-fit the strands, install them in the locomotive, make the connections with the shell in place (keeping the dynamic brake hatch off), and then trim the fiber optics to length.
With some models, you may find it easier to first connect all of the fiber optics first, next attach the LED assembly to the body, and lastly make the connections to the PCB/ decoder.
Continue to 6 of 6 below.
- First, cut each fiber optic strand to an approximate length to run from the lens to the LED. Leave a little extra length.
- Bond the ends of the fiber optics together with more heat-shrink tubing. For paired lights, use a small band of tubing to first join the two leads together with their ends even. Then use a larger-diameter tubing to connect the pair and the LED. The tubing should fit snugly around the LED. Avoid using much heat on the tubing, as it could damage the fiber optics. (If necessary, you can take the strands off the LEDs and reattach as you assemble the model.)
- Paint the fiber optic strands black to prevent light from leaking through fans, cab windows, or other openings in the body.
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Finish the Lights
With the body assembled and everything connected inside, the last step is to finish the lights themselves.
Trim the fiber optics to length. Hold the tip of your soldering iron near the end of the strand and the end should flare out. If this gives you enough of a lens appearance, you're good to go. You can also use clear plastic lenses from Details West in the openings themselves. Trim the fiber optics so they end just inside the housing, then glue the plastic lenses in front. Use a piece of tape to hold and position the tiny lenses in place as the glue dries.
After you've done a few of these conversions, you'll find the process goes fairly quickly. Buying in bulk, the cost of materials for conversion is well under $2 per locomotive—about what you might spend on replacement bulbs each time.