LEDs and Grain of Wheat bulbs with DCC


W

WVrailfan

Member
Is there a relatively simple formula, or even better, a chart, to help those of us that are math and electronically challenged to know what size resistor we need to use when using 12v or 1.5v bulbs or 1.5v LEDs, which are powered by the 14v track output?

Soundtraxx recommends starting with a 570 ohm resistor when using a 1.5 v bulb with their decoders, but what if I want to use a 12v bulb?

Thanks in advance for any help.

Jim
 
Use a 22 ohm resistor with 12v bulbs but keep it away from all plastic parts as it will get hot. Better yet use 14v bulbs and still use the 22 ohm resistor. The bulbs will last a lot longer.
 
WVrailfan said:
Is there a relatively simple formula,
Click to expand...
The simple formula for the bulbs is Ohms law. E=IR Where E is the voltage. I is the current. R is the resistance. 14v track - 12v bulb = 2v that the resistor must deal with. Take the current draw of the bulb. Transpose the equation. E / I = R. Substitute 2 / I bulb and solve for R.

The Soundtraxx recommendation has assumed some value for the current, that may or may not be correct for the specific 1.5V bulb one has chosen.

Diodes are a different story as they are not voltage driven things. They are controlled by current. When the diode gets 1.5V it will start conducting, from there it becomes a short circuit and it will act as such. The resistor is to make it not a short circuit. I usually recommend starting with 1000 ohm resistors and increasing if it is too bright.
 
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