LEDs & resistors

[Neil4915]

I want to replace all the old bulbs with LEDs in all of my Athearn blue box locos.  They've all been DCC converted and I originally bought prewired 12v LEDs and resistors from evil bay which didn't work.  What do I need to get in order to make them light correctly.

[Prof Klyzlr]

Dear Neil,

 

The "what you need" is one question, but I'd submit the better question is "why did the pre-wired LEDs you already purchased _not_ work?"

Did they literally audibly/visually  "go pop" (IE they weren't "12V LEDs", and/or the built-in resistor wasn't appropriate),

or was it a deployment/wiring issue?
(IE is the "fault" such that, even if you did use "different LEDs and seperate resistors", the outcome would likely be the same "no visible light"?)

 

Assuming that the wiring _is_ correct,
(DCC "Blue" wire = Positive Volts
the appropriately-colored "Function Output" wire = Negative Volts)

 

and it _is_ just a case of "getting LEDs and resistors which work",

 

I would ask:
- where are you located?
- are you open to online ordering, or more a "buy in person" kinda guy?

 

For myself here in Australia, SatisLED.com do Warm White 3mm LEDs (suitable for most HO scale locos) at a great bulk price
http://www.satisled.com/3mm-water-clear-round-ultrabright-warm-white-led-1000pcsbag_p1762.html

 

While you're looking at SatisLED.com , I'd pickup some 1K Ohm (1000 Ohm) resistors
http://www.satisled.com/resistors-1k-ohms-14w-5-carbon-film-1000pcs_p996.html

 

They won't give the absolute brightest-possible result out of those LEDs on either Analog or DCC,
(if you do the electrical calcs, the _absolute_brightest_ result with those LEDs requires a 470 Ohm resistor per LED)

but still well-bright-enough for most modellers,

(Indeed, many modellers prefer a _far_less_lumens_ LED light appearance than a current-era high-efficiency LED can provide!
US outline headlights are typically more "dull lamp" than "supernova"!))
 

and provide a significant electrical "safety margin" to handle both "correct" and "reverse-polarity" wiring conditions...

 

I hope this helps...

 

Happy Modelling,
Aim to Improve,
Prof Klyzlr

[RedgateModels]

as the good prof said, 1k ohm resistors will be fine. This diagram extracted from a forthcoming article in BRM should help too 😉

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Note the blue positive wire should always connect to the longer LED lead, or the one attached to the smaller side of the internal structure as seen above 🙂

Edited July 29, 2022 by RedgateModels

[skipepsi]

I knew I had read something useful.