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Railpro lights circuit

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Carter:
Can anyone give the Railpro lights circuit voltages on the decoders? I want to install LEDs forward and reverse. Also recommendations on resister values if needed. And LEDs recommendations.

Thanks Carter

G8B4Life:
We discussed this in this thread. https://rpug.pdc.ca/index.php/topic,189.msg1014.html#msg1014. It's about half a volt lower than the power applied to the LM from the track, so if your supplying 14.5v from a PWR-56 then the outputs will be ~14v.

A suitable resistor would be simple to find using Ohms law.

Assuming ~3.5v voltage drop across a white LED then 14v - 3.5v = 11.5v. 11.5v / .02 (20 milliamps) = 525 ohms. Closest value that is larger is 560 ohms so 560 ohm 1/2 watt would suffice - just. Go a larger value (in ohms) for more headroom, your LED's will only be slightly dimmer.

Generally I just use 1k (1,000 ohm) resistors regardless as modern white LED's are plenty bright enough with them and it gives a good margin for power fluctuations.

- Tim

Alan:
A little testing of resistor values prior to installation is advised. Depending upon the application, many LEDs are way too bright when operated at near full forward current. For instance, number boards in a loco. They shouldn't beam like headlights. Don't be surprised to find you may have to go way up in resistor value to get a realistic lighting level. I have some LEDs using as high as a 22K resistor. Also be aware different color LEDs of the same family may have different brightness with the same resistor value.

Carter:
Thank you Alan and Tim for your reply.

I just ordered some diodes SMD 0402 Warm White. Tim from your reply I am guessing the LM-2 light circuit is track voltage + - some.

With that information It really is what brightness one likes for headlights and ditch lights etc etc. I do have plenty resistors and will play around with the LEDS.

YOUTUBE IS WHAT GOT ME STARTED WITH HEAD LIGHTS. AT 1.02 MINUTES IN. i CANNOT FIND THESES ON EBAY? LOOKS EASY TOO.
t=61s

Carter

Alan:
0402 are really small to solder to. Pre-wired is much easier to work with as was discussed on another thread. Have a look at these: https://www.ebay.com/itm/172046338387 I ordered some a while back. Expecting their arrival soon.

Personal preference of course, but I see a lot of pure white LEDs (6-6.5K) installed in model locomotives that would have been built before the advent of luminaries capable of producing such blue white light. Most locomotive lamps should be a littler warmer temperature to be accurate (4.5-5.5K). Look at a real locomotive headlamp on a sunny day. Compared to sunlight the loco lamp is a redder yellower color yet on so many models I see intense blue white sunlight temperature lamps. If that sort of thing matters to you.

Do the current calculations once you settle in on a resistor value. You may be able to use 1/4W or even 1/8W resistor for a more compact installation.

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