LED headlights hooked up to an LM-3S.

[faithie999]

to get started, I wouldn't worry about the ma rating of the LED's you've purchased.  when you get the led's and the resistors, wire a 1000 resistor to the negative leg of the LED and then touch the other lead from the resistor and the positive lead from the LED to your 15v track power to see if you like the brightness.  you can always add another resistor in series with the first one which will dim the light.

as for LED color--you can buy 'soft white' LED's which are more representative of incandescent bulbs in older prototype loco's. 

ken

[G8B4Life]

why do I need 2 different ones if I’m using 3 Volt LEDs on the railpro decoder.

You don't. You just need the ones that give you the brightness you desire. Let me explain as it seems you are a little bit lost. LED's are amazing devices but if they were intelligent beings they would not be very smart. Just like most dog's don't know when to stop eating if given an unlimited supply of food (as their instinct is "I don't know when my next meal is so I need to eat it all") LED's don't know when to stop consuming current and if it's not limited the LED burns out.

The two ways to limit the current are to drive the LED in it's spec'ed voltage range (which normally doesn't happen in the real world) or if we can't do that to add resistors to limit the current that the LED can consume, also within the spec'ed range for the LED.

White LED's are usually 3.2 - 3.6v and max 30mA.  A safe margin level would be 20mA but for many white LED's these days that would still be very bright and 15mA or less could be desirable. Ohm's law tells us what resistance we need to achieve 20, 15 10 or any mA. Some quick calculations for a 3.6v white led on an LM (~14.0v) give:

20mA : 560 ohm
15mA : 750 ohm
11mA : 1000 ohm

so the lower the resistor value the more current is available to the LED and the brighter it will be. Try each of the 750 and and 1000 ohm resistors to see which brightness you like best. You can also decrease the brightness using the HC as well.

as for LED color--you can buy 'soft white' LED's which are more representative of incandescent bulbs in older prototype loco's. 

There is an amazing variety of whites these days. There used to be a website (Richmond Controls I think) that had photo's of many of them side by side. There was Golden white, Sunny white, Bright white, some other white...

- Tim

[SWA737]

 Thanks Tim, I like that analogy. That makes sense. I have some of each so I will use that technique to see which brightness I like. I also got two colors of white so I can compare which one of the LED’s I like before the installation. I am getting a little bit more than, but I wanted to be prepared when ready to do the conversion.

[trainman605]

Don't get all caught up in this LED thing and trying to figure out all the math. First let me say LED's either work or they don't and they will do nothing to your module board that can damage it. Now I run G scale and I purchase mostly the 3mm, or the 5mm LED's on eBay with resistors, they are also rated at 12v on full power and I normally put the bright white in headlights and soft white in all other lights, interior, running lights, etc. So our RailPro modules are setup for 5v on the lights right, well guess what I run those 12v LED's on 5v and they burn just fine, yes the light is a little dimmer, but this gives me the light brightness that I want and if it's still to bright, I just add another 1K resistor. Many try to make the LED thing Rocket Science, which it's not, just buy in larger quantiles on eBay and test them out with the voltage you will be running, I use a old transformer and a test meter and set the dial with the meter to the voltage I want, I may even let the LED burn for 24 hours just to make sure it will work when installed in the engine, etc. I also do the same with any LED's regardless of size and voltage, just test them out, all they can do is go PUFF and smoke a little.

trainman

[KiloWhiskey]

If I remember correctly, the railpro module can dim the LEDs brightness similar to the way you can adjust the volume on individual sounds...

[KPack]

Warm white LED's with 1K oh, 1/4 watt resistors.  All my locomotives have these for headlights and ditchlights.  If they are too bright then you can just turn it down on the controller.  Easy.

-Kevin

[SWA737]

Ok thanks Kevin.

[SWA737]

The 3 Volt ones, correct Kevin?

[Tom]

Well, after reading this thread, I do not feel bad about staying with incandescent bulbs.  As an aside, on their longevity, I happen to have several Marx HO DC locomotives +/- 65 years old and lights are still working and have never been changed, maybe they do not make them like they used to.

Beyond that diversion, I dimmed one locomotive’s LED light to 20% and it is still too bright.  Too bad Ring will not allow dimming to near zero.

[William Brillinger]

"Too bad Ring will not allow dimming to near zero."

Tom, you can write your own light program that is as low as you want.

[ON28]

"Too bad Ring will not allow dimming to near zero."

Tom, you can write your own light program that is as low as you want.

How?

[William Brillinger]

Page 34 in the RPA manual has instructions for creating lighting effects.
http://ringengineering.com/RailPro/Documents/RailProAssistantUsersManual.pdf

[ON28]

Thanks, Bill.