Everything on model trains, model railroads, model railways, locomotives, model train layouts, scenery, wiring, DCC and more. Enjoy the world's best hobby... model railroading!
Converting Analog Bulb To LED
Len models HO and asks:
“Three of my locos have led driving lights, but I have a small switcher engine that still has an analog bulb. Can the switcher bulb be converted to LED, and can I do this without making the LED too bright?”
See the comments below.
7 Responses to Converting Analog Bulb To LED
Leave a Reply
SUBMIT YOUR QUESTION
Download Your Free Catalog
Use Tiny Railroad Micro Controllers
Model Train Help Ebook
Just add thge LED and a 2 or 3K resistor in the same line as the bulb was in.
Just add the LED and a 2 or 3K resistor in the same line as the bulb was in.
You will need to put a series resistor in-line with the LED, and possibly a rectifier diode to ensure that the correct polarity goes to the LED. The resistor should be sized to allow ~20ma current to flow in the diode, and be a limiter to prevent too much current which would burn-out the LED.
Len,
Yes you can convert your incandescent bulb to an led. First thing is to ascertain how many volts are going to the bulb. Most are 12 volts but some are 3 volts. You need to know what you are dealing with prior to planning changes. To keep the light not too bright look at getting YeloGlo led’s which simulate incandescent bulbs fairly well.
Next you will have to calculate the size of resistor you need using the formula Resistor = Voltage drop divided by desired current. Typically a white LED needs 3.4 volts and 10 mA. This gives you the following on a 12 volt power supply (12-3.4)/0.010 = 860 ohm resistor. This is the minimum resistor you should attach in series on the cathode (-) or short legged side of the led. If you want to reduce the brightness further you can increase the size of the resistor. Polarity is critical with LED’s. Some decoders allow you to adjust the brightness of the lights by changing a CV value. As long as you have the minimum resistor size you can tone down the brightness this way to what you are looking for. Remember a led is not forgiving, too much voltage and it goes out in very quick flash.
Robert, a number of weeks ago I sent in a question about stand alone power supplies that could run LED switch lights and other acessories like Atlas Snap machines. I am wondering if you did not get it? Thanks
Jim, if it has not been published please resubmit your question using the ASK A QUESTION link. There was a problem for a couple a few weeks ago where questions were not getting delivered.
Attached basic circuit for loco LED head and tail light on DC.
Brightness will vary with track voltage. Resistor value can be changed to adjust brightness.
(Minimum about 500 Ohms.)
If you want only the front headlight, replace the rear LED in the circuit with an ordinary diode.
(This protects the LED from too high reverse voltage)
White LEDs are available in Cool White or Warm White. Warm White imitates the light colour of an incandescent filament lamp, so is appropriate for older locos.
Standard LEDs are available in 5mm, 3mm, and some smaller sizes.
The very small SMD LEDs are useful in tiny spaces, but require some skill for soldering.