I will soon be installing LED’s and 1.5v lights in various DCC-equipped locomotives (HO, by the way). I’m planning to use 1/4W resistors of various resistances, depending on the situation. I understand that heat generation is not a concern with LED’s, but it is with resistors and incandescent light bulbs. Just how hot do these things get, though? What are some good general precautions to use when installing and mounting light bulbs and resistors so I don’t melt any plastic?
Also, what is the best way to physically attach LED’s, light bulbs, and resistors in place? (Elmer’s glue? Silicon or latex caulk? What should NOT be used?)
Thanks in advance.
Stick with LEDs exclusively. They will essentially last forever, and generate minimal heat. Incandescent bulbs will burn out, and generate a lot more heat. When they burn out, you’re going to replace them with LEDs anyway, so save yourself the extra trouble.
For headlights, I strongly recommend the Yellow-White or Golden-White varieties. These have a warm glow which looks like a real headlight. LEDs, by the way, are very directional and cast most of their light in the forward direction, making them ideal for headlights.
If an engine doesn’t have a mounting bracket, you can press-fit the LED directly into the shell. You wouldn’t want to do that with an incandescent, because you’ll melt the shell. I glue mine in with a bit of CA if they won’t stay where I put them with a press fit.
For wiring, I use shrink tubing to insulate all the connections inside my locomotives. This makes a neater and safer insulation coating than tape, and it’s more compact, too.
LED’s are easy, if you are using the white varieties, you use a 1K resistor. At a 14V function output, that’s 0.014 amps, or 14 ma. That translates into 0.196 watts dissipating in the resistor, well within the realm of a 1/4W resistor. It will barely get warm to the touch, if at all. The LEDs will not even get warm. I wouldn’t use anythign strogner then Elmer’s glue to hold them in place, in case somethign goes wrong and you nee to repalce one. In most of the locos I’ve put LEDs in, I just put them where the blbs used to be, and maybe put a piece of tape across the wires to hold them in place. On an Atlas/Kato loco I repalced the single central light bulb with a pair of LEDs by cutting back the light bars from the middle and then attached the LED to the light bar with some shrink tubing.
For 1.5v bulbs it depends on the current rating of the bulb. Some are 15ma, some are 30ma. For the 30ma bulbs you will need a 1/2W resistor as more than 1/4W will be dissipated by the resistor. It will get a little warm. The nice low power Minatronics 1.5V bulbs will work well with a 1/4W resistor. The 15ma bulbs need twice the resistor value that the 30ma bulbs need.
I prefer LEDs - if I have to replace anything, I replace with LEDs. Golden White for first generation diesels, the Sunny White type is better for more modern units.
–Randy
Light bulbs and resistors both work in a similar manner, by restricting the amount of current that flows through them. This restriction creates heat. The more current restricted, the more heat generated. Reducing 12v to 1.5v is a lot of restriction. The bulb will only see the 1.5v, so it won’t get any hotter than it was designed for and shouldn’t melt the plastic housing. The resistor, however, will get very hot. If you go this route, you should take extra care to keep the resistor away from any plastic parts (good luck inside a loco shell!).
You’ve gotten good advice to switch to LED’s. Take the advice! A little extra work now will save you many possible headaches later. As has been mentioned, if the LED doesn’t just press-fit, a little CA will hold it in place.
Darrell, quiet…for now
Shrink wrap works great, and LED’s dont get very hot compared to traditional lights, and they have a very very long lifespan. Good luck! -beegle55
here is a great circuit for 1.5 volt light bulbs…you can install this in the roof of a locomotive shell with double sided tape…(click image to enlarge) chuck
Thanks for the quick responses, guys. OK… LED’s good, lamps bad… got it.
I do have several LED’s and generally planned on using them as head/tail lights. However, I do have 3 locos that I want to install working ditch lights, and the best way I can see to do that is to use the tiny Miniatronics 15ma, 1.5V bulbs (I’m not willing to tackle surface-mount LED’s at this time). The ditch light housings are all cast metal, but what should I use to atttach the bulbs? Would Elmer’s glue be OK so I could easily change them out if they burn out?
Good God, Chuck! [:O] I saw a similar circuit using the LM317 here:
http://www.tonystrainexchange.com/technews/install-lamps-decoders.htm
but it’s not as “parts-intensive” as the one in your drawing. I take it your diagram is for the DC version [:D]
Effects like flashing ditch lights and so forth generally work better with bulbs anyway. A small dab of Elmer’s should keep the bulbs in place yet be removable if they burn out. Plus it dries clear so you won’t really see it.
–Randy
Thanks, Randy, I’ll give it a try!
Golden-white LEDs look a lot better IMO than the pure white ones which look a little bluish. But you can get the pure whites much cheaper. I buy them 100 at a time with resistors and shipping for $11. 3mm or 5mm, you choose. Thats about 10 cents for each LED/resistor set. Buying small numbers of LEDs can cost you over $1 each and often dont include resistors. The solution is a bottle of tamiya clear orange paint. I got mine for $3 at my LHS. Dip your white LEDs in the paint, wait for it to dry and you have golden-whites for cheap![:)].
I use double sided tape most of the time to install them in case of course I have to remove them for some reason. And for those tiny lights, instead of little bulbs or tiny LEDs I use fiber optics if possible. The LED might be in the middle of the loco somewhere but the light comes out the ditch lights, marker lights, or whatever you need.
Some manufacturers use pieces of clear plastic to conduct the light from the LED to the lights on the loco. This system works but you lose a lot of light intensity. With fiber optics you lose hardly anything.
If you are doing marker lights on a cluster, like on the ends of a caboose, surface-mount LEDs are perfect. They are extremely small and are not directional like normal LEDs. Getting your hands on some is a little bit more difficult, but they are very useful in some cases.
I have used more LEDs than I could count and have never had one burn out. Unless I gave it too much voltage[xx(]. But thier long life, low heat output and high light output makes me use LEDs if at all possible. I havent used a bulb in quite a while and dont plan to any time soon.