Somewhat - you’d have to play around with the resistor values since the brightness change for the LED goes from mostly full brightness to not visible over a very short range. The logic of wiring that way is sound, and won’t fry anything, just might be hard to get the results you want. When a decoder supports dimming an LED, it doesn;t do the same as inserting more resistance in the circuit, it actually blinks the LED very fast and increases the percentages of “off” time which makes the LED appear dimmer. This is the same PWM used to drive the loco’s motor. The peak voltage is always the same, but as you increase the amount of “on” time, the apparant voltage rise and the motor turns faster.
Ya it’s a lot easier to just use a couple of CVs to get the lighting you want, rather than doing a rat’s nest of wires and resistors to do it “automatically”. Most all of my engines are set up so both headlights come on when I press F0, with the light in the direction of travel bright and the reverse dim. On some decoders, it only takes a couple of CV settings, on my MRC decoders it only takes changin one CV.
I’ve also set up F-units with two headlights so that the upper light flashes like a Mars light and the lower one is full brightness when going forward, and the lower light goes dim and the upper stops flashing when going in reverse. Again, just turning it all on and off with F0; set up by changing a couple of CVs.
Finally getting around to buying the LED’s for my locomotives. Earlier in this thread, Ed graciously gave me an ebay link to prewired LED’s with a 1k resistor. Specs also say for 12 to 16 volt environment. That chinese company no longer has LED’s on ebay. I’m having a difficult time matching that spec, several say 12 volts. Prewired with a resistor seems preferable for ease of installation.
However, I’m considering soldering my own, have not done that before, but chance to learn a basic skill. I found a firm that has very reasonable prices for LED and resistors.
They do sell a prewired 3mm LED but it only has a 580 ohm resistor. 48 cents for a premade versus 28 cents + labor to make my own. I only need 4 so the higher price is not cost prohibitive by any stretch. Is that resistor adequate? The size of the resister depends on the applied voltage, voltage draw of the LED, and desired current level.
Please check my math. The DCC system I’m buying has a 15 volt output and the LED’s use 3 volts, and max current is 20 mA (0.020 A). I have read that you want to set the target current at half the max current. Using these specs and ohms law (R=V/I), the desired resistor is:
(15v-3v)/0.010 amps = 1200 ohms
Assuming my calculation is correct, I should make my own since the prewired is only 580 ohms. Randy suggested that I use a TCS-T1 decoder in a different thread and has stated the 3mm LED fit P2K GP30’s. I found that TCS sells a T1-L
As to appearance - there is a definite difference. An old seller who is no longer around used to have a comparison picture with three of the same loco, one with golden white, one with sunny white, and one with bright white LEDs. Big difference. Sunny White is good for a modern loco, I am pretty much all first gen diesel so I only use the golden white ones.
Soldering your own is a worthwhile skill. You have the right solder - depending on the diameter. You want some thin diameter solder for fine wires and electronics, I use .015 diameter rosin core 63/37. I don’t use extra flux with decoder installs. For decoders and the fine wires associateds with them, if you don’t want to invest in a soldering station yet (which at around $50 for a good one isn’t a huge investment), you want no more than a 15 watt iron.
Several vendors sell bundles of decoder wire, the same wire that comes on the decoder harnessed. Get some of this, and maintain the color code - ie, if you need to make the blue wire longer, use more blue wire, not another color. And when you cut extra wires off - ones you didn’t need to hook to anything, save the leftover sections.
Your resistor calculation is correct, but 1K is fine - if you solve for amps and put 1K in, you get 12mA, still well within the safe zone for the LED. The resistors included in the TCS LED decoders, I’m not sure of the value, but they limit the current to well under the 20mA limit.
The decoder wire is around a #30 wire. You need some pretty small shrink wrap - places that sell decoders often have the right size, otherwise the typical assortments you get has a whole bunch that is far too large and not much of the really small stuff. I usually solder my resistor right to the LED, cutting the leads of both short. Make a good mechanical connection, then it should only take a second with the soldering iron. When doing it that way, you can’t put the heat shrink on first, but the smallest size that just barel
Heat shrink, I think I use 1/16" and 3/32" The only local retail store you might find this is a Microcenter computer stores. Mail order, the usual DCC stores and electrical supply stores have it or an assortment of by Soundtrax
I have had an intention tremor my entire life and lately it has gotten worse. I use helping hands: alligator clips on moveable arms. I position the shorted led lead and the resistor lead parallel and touching and overlapping. I tin both leads beforehand.
If all you are doing is adding LED’s I suppose any color is OK, I bought the collection of DCC colors from one of the above stores. 30 ga you can strip the insulation with your fingernails.