I need suggestions for white LED lamps and appropriate resistors for installation in an N scale locomotive using a DCC decoder. I’ve found some small LEDs but I don’t know how to properly choose a resistor to couple to them.
Chris:
First of all, What is the maximum output of your L.E.D. in Volts and also Amps? Without that information I can’t answer your question.
Your Welcome Chris. DCC systems put constant Voltage on the rails whether trains are running or not. You’ll need to install a resistor between the LED and the decoder to drop the voltage. I know the white LED’s from Minitronics include the resistors necessary to drop the voltage.
Most of the small white LEDs I found appear to have max voltage of 3.6 volts and draw about 20mA of current. Not sure exactly what DCC decoders put out for voltage (assume fully duplexed by using the blue and yellow wires) but appear rated for about 100mA for the common power circuit. Thank you for your help.
I’m doing the same thing with some non-DCC Atlas GP-7’s. To determine the value of the resistors needed, use the following formula: (Supply Voltage) - (LED Forward Voltage) / (LED Power Usage). Using your numbers, it would be 12 - 3.6 / .020, or 420. You would need at least a 420 ohm resister for the LED if your power supply was 12 volts.
If you’re planning on doing this, you should stop by Radio Shack and pick up some of the basic electronics books by Forest Mims. They have all of the basic formulas and are about $0.99!