Direction controlled White LED headlights for Large Scale Engines
This article is about how to build your own LED driver for bright white LED headlights. I designed this circuit for use in my Large Scale Diesel Engines to replace the incandescent lamps typically used by Aristo-Craft and USA Trains in their engines. Many people who use white LEDs just tap off of the existing headlight power and add a resistor to reduce the power for use with white LEDs. The problem I found with this method is two fold, first, you don't know for sure if adding a resistor is sufficient to protect the expensive LEDs and second, the LEDs should be pretty darn close to white with very little blue tint. I have found that by driving the White LEDs properly, with their own circuit, there is almost no blue tint. I don't know which method will provide a longer life for the LED but I have found that the blue tint comes from either an under powered OR WORSE, an overpowered LED. I discovered this when I first started trying to replace the stock bulbs with the newly available white LEDs a couple of years ago.
I like to try new things and ran across the RAM-Track white LED headlight modules at the Queen Mary Show in Long Beach. These were pretty reasonably priced at about $20 so I bought one to try and it showed me the light, White LEDs should actually be WHITE, and VERY BRIGHT! I bought a few more to install in my engines. Being fully capable of making my own circuits, I analyzed the RAM units and made my own. Later I thought that a dual circuit, for directional control, would be much better, so I designed one, it worked well but the voltage regulator (even on the RAM unit) get pretty warm. Then, George Schreyer posted an article on his web site that described a simple circuit design using the LM317 variable voltage regulator as well as one that used the 7805 fixed voltage regulator (which is what RAM uses). I liked the LM317 for the stable and clean output you get for this type of circuit. I also discovered why the 7805 was getting hot, being a fixed VR, it had to dissipate excess power in the form of heat, the LM317 does not because it only has to consume the power it is asked to provide from the components it is driving and LEDs use very little power.
Being a glutton for punishment, I thought that this design was good enough to mass market. Then I figured it was not worth the trouble, at least not yet, so I decided to write this article and let anyone who has the desire to make one, use my design for free. I retain the copyright (March 2001) to the design but feel free to make as many as you want for you personal use but not for commercial purposes (do not sell them).
Lets get started.
I won't speak about theory or why I selected the resistor or capacitor sizes I use, if you want to know more of the technical aspect of the type of driver, George Schreyer does an excellent job on his web-site. I will just describe the steps to make and install my design. For the purposes of the article I will be using an Aristo-Craft SD45 for the photos but the principles are the same for all Large Scale engines. I have converted RS3s, GP7/9s, SD40s, U25Bs and SD45s with no problems. Each of these engines use four LEDs to replace their headlights but you can use more or less without any change to the circuit. Radio Shack has everything but the LEDs, I prefer Digikey or Mouser because I by enough for 5 or 10 at a time, The LED Light has the best and brightest white LEDs I have found. I will reference their web-sites at the end of the article. You can make one of these systems for under $12 with prudent shopping.
