how to install LEDs in a DC locomotive

[LLOYD]

Hi everyone.  I want to switch the original installed headlights on several of my DC locos.  I have read some articles in the forum on how to install them but they use electronic jargon which I don't understand and I need just a simple answer if there is one, Thanks

[Train Modeler]

If you're not comfortable rectifiers and electronics, this may be more than you want.

A simple and possibly cheap way is try and buy some used or leftover OEM DC boards with LEDs already installed.     Try Tony's Train Xchange for some and other shops that do DCC installs.    I would call them and discuss since this is not a normal request

http://www.tonystrains.com/

Richard

 

 

 

 

[Doughless]

Its easy.

The simplest way is to snip the existing DC bulb off of the wires, and solder a 1000 ohm resistor on to the black (positive) wire.  The LEDs come with two stiff wires, so solder the long wire to the resistor, and the short  wire to the red (negative) wire you snipped.  Of course, I always remove the black and red wires from the locomotive first, rather than trying to solder in the new parts while still on the locomotive.  You won't burn up the LED if you switch the wiring circuit, it just won't light.  You will burn it up right-quickly if you don't install the resistor.  Congrats, you've just installed an LED.

The more finicky part is sometimes physically fitting the new assembly into the spot where the old bulb was.  The LED's give you a lot of stiff wire, as do resistors, so measuring and playing with exactly how much, or little, stiff wire you need is sometimes the most frustrating part, having to bend and twist the wires to fit under the shell if you leave too much wire.  Trial and error is the only way, and each locomotive will be different.

Since LED's are sensitive to a lot of heat, I usually try to leave about 1/2 inch of wire still attached to the LED, so as to not have excessive heat travel back to the LED as I'm soldering the resistor and red wire to it.  I remove as much wire as I can from the resistor or even the exisiting black and red wires if the assembly would have trouble fitting in the locomotive.  

Also, I use a low wattage soldering iron, one that is suitable for soldering pc boards without melting them.  You can reattach the LED assembly back on to the locomotive the same way it came off. 

Minititronic Yellowglo White LED's look very nice.  Not too white (blue) and not too yellow.

I don't understand electronics jargon myself, so this is the only way I can explain it.

 

[farrellaa]

You can also use a 12 volt DC LED and not need the resistor, which I have done on a couple of my locos. The 12 V LED's come in bright white and yellow white (3 mm size) so you still have that choice. The only advantage in not using a resistor is space or lack of it. In my case this worked out just right. Just make sure you insulate the leads on the LED with some shrink tube so you don't get an accidental short.

    - Bob

[rrinker]

 How do you explain it without electronic 'jargon'? LED itself is an electronic term. LEDs need resistors to limite the current. Two more electrical words that have to be used in discussing this.

 FOr DC, a 1K resistor is probably too much, unless you spend all day runnign at full throttle. The problem is that with DC the voltage varies (I'm assumign the OP is NOT using an Aristo Train Engineer system here), and thus the LED current varies. A white LED drops about 3-3.2 volts, so it can't possibly even come on until track voltage reaches that level. A modern high quality loco will already be moving. Up it to 5 volts and unless this is a sound loco, most of which already have LEDs for headlights anyway, it should be moving at a good clip. With a 1K resistor this is less than 2ma to the LED (sorry, you cannot get away from knowing this basic stuff to find out WHY it works or doesn't work). Maybe the LED will glow at that low level, but it will be rather dim.

 Prepackaged LEDs liek the Miniatronics ones come with two resistors. One is mant for DC use (the smaller value one) so that the LED gets more current across the common range of DC track voltage where you actually operate. It puts the LED at or above the maximum current limit when the power is steady and 12V or more like it would be with a DCC decoder.

 Bottom line, LEDs aren't as suitable for DC as they are for DCC. You can do the same tricks with using diodes to drop the voltage to the motor that they do with constant lighting using light bulbs - like most Proto 2000 locos - however the LED is over twice the voltage of the 1.5V light bulbs they use, so you end up with a loco that works like most sound locos on DC - turn the knob over half way before the loco even begins to creep and from there it's only a slight bit more before it's running at warp speed.

                      --Randy