Help with Multiple LEDs in circuit/s

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1

Hi there,

Newbie here.

I am building a model railway layout and have built the control panel. I have 16 signals on the layout, and mimicked on the control panel. There are 4 banks of 4 DPDT switches with corresponding red & green LEDs which mimic the LEDs on the signal heads. The LEDs on the panel are ALL wired in parallel - (I think - not sure after getting other advice elsewhere) - with “K” leg going to -ve and the “A” leg going through the switches. All in all there are 68 LEDs - yes 68! I have calculated that I need a 7.1324Ohm resistor, however the wattage of the resistor is 13.192 Watts! I know 16 x 4 does not equal 68! But here are master switches controlling street lighting, buildings, etc. That is where the other 4 LEDs come into play.

BTW the voltage is 12VDC. I also have point controls - turnouts to those in Nth America - that will be supplied from 15VDC. Would I be better off using 4 sets of resistors - 1 on each bank of switches. Online calculator tells me that the resistor value would be 30.1325Ohms @ 3.104 Watts and would it be better to have the resistor before or after the LED?

I am attaching files of the control panel and the wiring diagram. On both files the bank of 16 switches are circled in RED and the 4 extra switches are circled in BLUE.

2

The standard practice is for each LED to have its own resistor.

If you try to run multiple LEDs through one resistor, then the brightness will change as you switch them in/out of the circuit. Your LED calculation seems to assume all LEDs are on at once, and they all share current equally. That assumption is not safe since the majority of current could potentially go through a single LED and then !poof!