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Woodland Scenics LEDs

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  • Member since
    July, 2010
  • 28 posts
Woodland Scenics LEDs
Posted by slammer406 on Sunday, April 15, 2018 8:14 AM

I have 3 W/S led bldgs (HO). I am using a 12vdc bus and wanted to find out what resistor values I needed. I contacted W/S and told them I was using a 12vdc bus. I went back and forth with them to find out what resistor values I needed. First they told me that I could use my 12v bus as long as I used their 'hub' and it was hooked up to 16v.(huh!)?? Didn't make any sense to me so after some more discussions they finally told me that they could not tell me what the resistor values were as that info was proprietary for their product and that I had to use their 'hub'. Outside of just replacing the LEDs/resistors with ones I know, does anyone know what resistors I may need. Bldgs are:Emilio Restaunt(BR5055)/2 LED, 30ma; Dugan Paint((BR5053)/1 LED, 25ma;Theater (BR5054) 2LED/50ma. 

Thanks in advance for your help.

 

  • Member since
    February, 2002
  • From: Reading, PA
  • 25,075 posts
Posted by rrinker on Sunday, April 15, 2018 11:14 AM

 What's missing is the voltage, however it's unlikely that a company like Woodland Scenics has had some LED company make a custom LED, so it is probably safe to assume they are standard white LED's in regards to chemistry and so drop 3.1-3.5 volts. Since they give the current, which is most certainly an absolute maximum, we can calculate a reasonable resistor for each building. The other assumption is that since the current is higher on buildings with 2 LEDs, they have them wired in parallel, not series. 

SO for the first one, 30ma. 12V supply - 3.2V for the LED = 8.8V  8.8V / 30mA is aboout 300K (30mA is .030A). I would not use a resistor less that 470 ohms, which works out to about 19mA, unless it really would make the lights too dim, but I doubt it. I would start with the usual standby - a 1K resistor, that results in about 9ma and if it ends up bright enough, great, because it's way below the rating of the LEDs and they should last virtually forever. If not quite bright enough, you can try lower values step by step, but not lower than the 470. 330 ohm is going to push the LEDs at pretty much that full 30ma rating and if they are anything like any other white LEDs they will look like small nuclear reactors at that power level, far too bright to represent the lights in a building.

Bottom line - try 1K at 12V, as a starting point. It's high enough that it should be fine. That value will actually work as a starting point for all of them, although the one rated at 50ma may need a slightly smaller resistor. 

                                                 --Randy

 


Modeling the Reading Railroad in the 1950's

 

Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.

  • Member since
    December, 2004
  • From: Bedford, MA, USA
  • 18,050 posts
Posted by MisterBeasley on Sunday, April 15, 2018 11:20 AM

These are WS "Just Plug" models, right?  They want you to buy their overpriced hubs and wires.  I'm surprised they are so stingy with information.

Resistance = Voltage / Current  (Ohm's Law)

LEDs themselves have a very low resistance, so they need a "limiting resistor" to keep from burning out and becoming "Darkness Emitting Diodes," or DEDs.

Neglect the resistance of the LEDs, to first order.

Resistance = 12 volts / 0.025 amps = 480 ohms.

Since these things are pricey, I would first try it with a 2K resistor (2000 ohms) and see how you like the light.  If it's too dim, go down to 1K.  Remember that the D in LED stands for Diode, and they will only work with positive and negative connecte the right way.

Almost all my LEDs are wired with 1K resistors, and that's probably where you'll end up as well, but you'll give yourself a safety margin if you start with 2K.

It takes an iron man to play with a toy iron horse. 

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