JRPI am trying to install 2 (two) 1.5 V micro bulbs for the front headlight of a GP35. I'm using the Soundtrax LC series decoder. The bulbs of course each have two wires (one to the decoder white and one to the decoder blue) and the one connected to the white wire requires a 560 ohm resister. The LC instructions say that each bulb requires a separate resister. Okay, I understand that, but with only one white and one blue wire for front lighting on the decoder , how do I wire two bulbs (really 4 wires) so they don't short out. It's happened already when I thought I had this connected correctly. Can both bulbs work off just the one resister? Can the white decoder wire support two bulbs and two resisters? I just can't see how else this can be wired. Very frustrating.... JRP
Here's the correct skinny:
First issue: How many milliamps does the decoder support on the lighting function. I'm not familiar with the LC decoder, but you do need to look the answer up. How many milliamps does each light bulb draw - typical would be around 30-50 milliamps. So if the LC decoder won't support at least 100ma (2*50) on the lighting circuit, you'll end up blowing the decoder lighting function by using 2 light bulbs.
Second issue: The resistor is there to drop the voltage down to the 1.5 volt range from the decoder lighting function's output of 12 volts. Running both light bulbs through one resistor throws off the calculation, and will reduce the brightness of both bulbs. To make the circuit work as intended, each bulb needs its own resistor.
Wiring: One lead of the bulb goes to the resistor. You now have the bulb and resistor wired correctly in series. Each bulb/resistor combination connects the 2 wires of the function output. So one wire of the decoder lighting goes to the unused lead of both resistors, and the other wire goes to the unused lead of both light bulbs. You are wiring the bulb/resistor combinations in parallel with each other.
Hope this helps
Fred W
John:
I'm assuming that the milliamp draw of each bulb requires a 560 ohm resistor. Hook one lead from each bulb to a resistor. Connect the other ends of the resistors together and connect to either the blue or white wire. Connect the remaining leads from the bulbs together and connect this to the remaining decoder wire. This is called parallel wiring.
Joe