I have been out of the hobby for some time and am just getting thru trying to upgrade a bunch of locomotives to DCC. I just purchased a couple decoders and changed them out. One upgrade with a digitrax decoder went flawlessly with all working bulbs and direction/speed control. The other one using a lokpilot decoder was a Proto 2000 USRA 0-8-0 purchased about 20 years ago, i have the original packaging and the instructions say I should change the bulbs to 12volt/50milliamps and i should get them from the hobby store when i get my decoder. So i mentioned this to the fellow there and he says oh dont worry about that if there working now they will be fine. Well the conversion went well except the bulbs blew up when i ran it. So obviously this guy is not gonna be my best source for technical information.
Looking back in some posts on this topic there is mention of wiring in a resistor when replacing bulbs during a DCC upgrade. Others no mention of it.
So i guess i have 2 questions.
I am about to install another digitrax decoder in a different loco that has no instruction sheet stating the need for different bulbs. Should i be concerned or because it is a digitrax decoder will i be fine?
Or should a person always just preemptively change bulbs while inside the cab doing the work when doing upgrades as i was just lucky with the one that works?
It depends upon the type of locomotive and the brand of decoder.
Some locomotives come equipped with incandescent bulbs, usually 1.5 volt or 12 volt. Other locomotives come equipped with LEDs which almost always require a resistor on one wire to limit current.
If you decide to replace the light when converting a locomotive from DC to DCC, the new light needs to match the voltage capacity of the decoder light âfunction outputâ tab. Otherwise, you can instantly burn out the light, destroy the function output tab, or not produce enough current to operate the light, depending upon the type of light being installed. There are even situations where the heat from a light bulb can melt the locomotiveâs plastic housing. LEDs are often preferred to incandescent bulbs for a variety of reasons.
Just be sure to add a resistor to one leg of the LED. It doesnât matter which leg gets the resistor as long as one leg does get a resistor. Use a 1K resistor.
I had a similar problem with my old Life-Like/Proto 2-8-8-2. I had heard about the need for a resistor for the headlight, and put one in and it worked fine. However, the lights for the number boards burned out, even though the resistor was on the common wire both used. Perhaps the headlight was 3V and the numberboard lights were only 1.5V? Everything else worked fine so I havenât bothered to go back and fix it.
Anyway, an easy way to do LEDs is to use Evans Designs LEDs. Theyâre more expensive, but come pre-wired to accept any AC or DC power source up to I think 16 volts. Theyâre very bright so work well for headlights (I use the 3mm âwarm whiteâ ones). You can buy direct or thru Walthers.
I wont be surprised if i have to relocate the resistor as its current placement doesnât look to good for getting it into a tight spot in front of the boiler.
$17.00 for 30 of them (and thats Canadian bucks so even cheaper by most standards i guess.). I figured if they didnât work for the loco we can always use them to light up buildings and the such. Ill look into those Evans ones. If these dont work for me.
That pre-wired LED should be fine, and there should be no need to relocate the resistor.
To get it to fit into the housing, you may need to shorten the two wires.
Here is a TCS installation guide which may be helpful in installing the LED. The installation is somewhat different than yours, the locomotive photos may be helpful.
