General Discussion (Model Railroader)

I am trying to locate someone online that sells high quality 5mm and 3mm white led lamps to be used as headlights in HO scale locomotives. I would also like to find some 2mm if they are available anywhere. The last time I purchased some they were on ebay and they were very poor quality and burned out very quickly. Some never even passed the test before I installed them.

Thanks in advance for the help.

George

I would check Digikey or Mouser, I'm sure there are others.....

But.....if you had multiple LEDs burning out quickly, the problem is probably not the LEDs.  Even cheap ones just don't fail, at least not like that, unless it was a batch was just faulty.  So, I have to ask...how did you hook them up?  Did you use a current limiting resistor?  They are a little trickier than bulbs to hook up right, so it need to be though about.

George,

What period locomotives will you be installing these in.  Steam?  Early diesel?  Modern diesel?  If they are the former two, I'd encourage you to consider the golden-white or sunny-white LEDs.  They cost more but they will put out a much truer and prototypical light for your headlights than the regular white LEDs.  I usually pick my 3mm golden-white LEDs at the following establishments:

Empire Northern Models

Litchfield Station

Jeff is right.  If you didn't use a resistor or one that wasn't "resistent" enough, it doesn't matter who's LED you wire in: It ain't gonna last long because you are trying to push 12 or 14V through a 1.5 or 3V LED.  The result?

Most of time, you need at least a 1K Ohm resistor for a headlight LED.  (At least in HO scale.)

Hope that helps...

Tom

The engines I am installing them in are all Athearn SD-45's, SD40-2's. SD40T-2's, GP50's and 60's. I did use a 1000 ohm resistor with the bulbs and they still burned out. I had a problem with the resistors that were originally sent with the bulbs. If you trimmed the leads off, it changed the resistance and the bulbs would burn out. That led me to believe that there may be a problem with these bulbs as well. I solder one lead of the resistor to the top of the motor and then from the resistor to the positive lead on the led. Then run a ground from the other lead to the frame on the engine. I have done this before with other leds I purchased at Radio Shack and have never had a problem. The only thing I did not like was that they charge over 5 dollars for one 5mm led.

George

Her's another good source for 3 and 5 mm LEDs.

SuperbrightLEDs.com 

That is exactly what I am looking for, the golden white led's. They do look much better than the bright white I had been using. Broadway Limited has those in the steam engines I purchased and they look great. I will be ordering some over the weekend. About the resistors though. I have seen a 1K with 1/4 watt and also a 1/2 watt. I had not noticed that before. Which do you use or does it make a difference?

Thanks again,

George

A good source of super bright and inverted cone LEDs is http://www.moreleds.com

frisco1519 wrote:

The engines I am installing them in are all Athearn SD-45's, SD40-2's. SD40T-2's, GP50's and 60's. I did use a 1000 ohm resistor with the bulbs and they still burned out. I had a problem with the resistors that were originally sent with the bulbs. If you trimmed the leads off, it changed the resistance and the bulbs would burn out. That led me to believe that there may be a problem with these bulbs as well. I solder one lead of the resistor to the top of the motor and then from the resistor to the positive lead on the led. Then run a ground from the other lead to the frame on the engine. I have done this before with other leds I purchased at Radio Shack and have never had a problem. The only thing I did not like was that they charge over 5 dollars for one 5mm led. George

George,

I will assume this is used in a DC locomotive.

Connecting an LED in this manor may fail, irregardless of the type because, of the reverse current applied to the LED when the locomotive's supply current is reversed or because of the spike-laden back EMF from the motor flowing through the LED. In any case it is wise to use a noise filter or snubber as well as a diode placed in series with the LED to block reverse current. White, yellow-white and blue-white LED's are less tolerant to reverse current or spikes. The Radio Shack LED's are more tolerant than some others, but safe practices are always recommended.

I did buy some new 1/4 and 1/2 watt 1K resistors yesterday and tried again with the bulbs I already had. I have been turning them off and on for quite a while and they appear to be fine. Maybe I had some bad resistors sent to me also. I will try installing one of these again and see what happens. So far so good. Thanks for all the help.

George

Frisco1519 wrote: 

The engines I am installing them in are all Athearn SD-45's, SD40-2's. SD40T-2's, GP50's and 60's. I did use a 1000 ohm resistor with the bulbs and they still burned out. I had a problem with the resistors that were originally sent with the bulbs. If you trimmed the leads off, it changed the resistance and the bulbs would burn out. That led me to believe that there may be a problem with these bulbs as well. I solder one lead of the resistor to the top of the motor and then from the resistor to the positive lead on the led. Then run a ground from the other lead to the frame on the engine. I have done this before with other leds I purchased at Radio Shack and have never had a problem. The only thing I did not like was that they charge over 5 dollars for one 5mm led.

  That's the problem.  With the locomotive going one way, the LED is forward biased and glows.  When you reverse the locomotive you reverse the polarity of the track power and your LED is now reverse biased (dark)  with 12 volts across it at full speed.  Most LEDs are speced to only withstand 5 or 6 volts of reverse bias. That's why a lot of your LEDS magically transformed themselves into Darkness Emitting Diodes (DEDs) when you reversed the locomotive.    

   You need to add ONE regular silicon diode to protect the LED from reverse bias.  Either place the protection diode in series the the LED or in parallel with the LED, either way works.  For a series connection,  make the protection diode polarity the SAME as the LED.  For parallel make the protection diode polarity OPPOSITE of the LED.

   Most of the "white" LEDs are very blue, as blue a a fluorescent bulb or an arc welder.  They look odd on trains.  A coat of yellow paint has been said to improve the looks of the average "white" LED a lot.

dstarr wrote:

You need to add ONE regular silicon diode to protect the LED from reverse bias.  Either place the protection diode in series the the LED or in parallel with the LED, either way works.  For a series connection,  make the protection diode polarity the SAME as the LED.  For parallel make the protection diode polarity OPPOSITE of the LED.

Or use an LED pointed the other way in parallel as the reverse light, still only need the one resistor, and the voltage drop across the LEDs will never be more than a forward LED drop.

Wow thanks for the links guys. Very helpful info too.

keep up the good work :)