Need some help with wiring LED lights - Model Railroader Magazine

88gta350

If I'm understanding correctly, I can think of wiring my LEDs like wiring my DCC track. I can run bus wires around under the layout and run feeder wires to each LED as needed. Each feeder wire will need a 1k ohm resistor. Then each LED is getting the same voltage and the resistor will keep the LED from burning up.

You have it right about the wiring pattern. However, as Paul mentioned, there is a limit to how many LEDs you can put on your power supply. The specific number depends on the output of the power supply. As a general rule you should only go to about 75% of the rated power output. Running a single bus for structure lighting will work up to a point, but once you start to exceed that 75% rule you will need a second bus, and maybe a third etc. etc..

How much power each LED draws depends mostly on the size of the resistor. Your particular LEDs may specify a draw somewhere around 20 - 30 ma (Milli Amps, or 1/1000th of an amp). However, that draw is reduced as the resistance is increased so, for example, if you are using a 1000 ohm resistor the draw will only be about 10 ma.

In other words (geez I keep using that phrase. You must be sick of it by now), if you have a 1 amp power supply @ 12 volts, and you want a maximum of 3/4s of that rated load, you can safely draw 750 ma, or about 75 LEDs with 1000 ohm resistors. Keep the size of the resistors in mind always. If you were using 470 ohm resistors you would be limited to about 30 LEDs on the same power supply. If you were using 3000 ohm resistors you could get about 150 LEDs on the circuit. Ed's suggestion of a fuse in line with the LED bus is a good safety feature in case you accidentally connect too many LEDs to the power supply.

If you are going to use a lot of LEDs, i.e. several hundred, you might consider buying a larger power supply with multiple channels. These are typically used for closed circuit TV cameras. You can get them with built in resettable fuses, one for each channel. This one is probably larger than most modellers would need, but having a few extra 12 volt circuits available could be handy for animation etc.. Ignore the Canadian pricing. They will be much cheaper in the US:

Dave