# Adding LED lights to a dc locomotive.



## Bonz85 (Sep 16, 2019)

Have a few blue box Athearn that don't have lights and would like to add some, I know there are some leds that will work on dc just wondering if anyone has suggestions. 

Thanks


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## MichaelE (Mar 7, 2018)

They all work on DC.

The problem is limiting the voltage at higher throttle settings and still have the LED lit at lower settings. The resistor you need to keep it from burning out at higher throttle settings will prevent it from lighting at all at lower settings.

You will need a voltage regulator circuit to make this work.


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## vette-kid (May 2, 2020)

Many DC locomotives already have LEDs in them. I have some N scale Katos with them. At low throttle settings they don't work well, they flicker. About half throttle they start working fine. 

I think if you had multiple LED together they seem to work better than 1. Lower resistance required to keep them from burning out maybe? Not sure exactly but that seems to be the case. One engine has one bulb, it requires more power to function than the one with multiple lights (separate ditch lights).

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## MidwestMikeGT (Jan 4, 2021)

I have been successful using pre-wired LEDs with resistors. Keep in mind LEDs are directional. If you want it to work both ways, you can use either a system of two LEDs or using a bridge rectifier. Adding a capacitor helps eliminate flicker as the vehicle moves over joints, etc.


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## gunrunnerjohn (Nov 10, 2010)

MichaelE said:


> The problem is limiting the voltage at higher throttle settings and still have the LED lit at lower settings. The resistor you need to keep it from burning out at higher throttle settings will prevent it from lighting at all at lower settings.


Actually, an LED that lights at a higher voltage setting with a current limiting resistor will also light at almost any voltage until you get below the operating voltage of the LED. It won't be as bright, but it'll light. The real question is, what is the range of operating voltages? If you're talking from 6 VDC to 12 VDC, for instance, a white LED with a 470 ohm resistor will work at 12V no problem and still be pretty bright at 6V.


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## Bonz85 (Sep 16, 2019)

Thanks for the help everyone.


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## MichaelE (Mar 7, 2018)

gunrunnerjohn said:


> The real question is, what is the range of operating voltages?


Exactly- If you are running a locomotive at scale speeds of 20-35 MPH, is there enough voltage at 470 ohms resistance to have the lights on? I don't know what voltage would be required for the locomotive to run at those _realistic_ scale speeds.

If you are running it around the track at 80 scale MPH, I would imagine it will be lit.


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## MidwestMikeGT (Jan 4, 2021)

I have replaced my bulbs in my vintage Bachmann F9s with dual LEDs, wired reversed polarity, and it has worked well even at very low speeds. The LED comes on before the locomotives start moving. I used, in those cases, a 3v LED with a 0.5W, 5% 680 ohm resistor, if I recall correctly.


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## vette-kid (May 2, 2020)

The one that bugs me the most is the Ditch lights. A few of my kato c44s have flashing led ditch lights. They do funny things at low power, flash fast, solid on, flickering etc. Is all factory installed, so I hadn't messed with it at all. 

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## MichaelE (Mar 7, 2018)

Well, an LED is a passive device. It only responds to whatever the characteristics are of the voltage/current being applied. Whatever is causing those strange actions is farther up the chain.


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## vette-kid (May 2, 2020)

It's just the way it is. 

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## ncrc5315 (Jan 25, 2014)

I use these for LED's: CL25N3-G Microchip Technology | Integrated Circuits (ICs) | DigiKey
They work from 5 volts, to 90 volts


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## Lemonhawk (Sep 24, 2013)

They output 25 ma, so the LED's will be bright. The CL2 version outputs 20 ma, a little better. To dim the LED's when connected to these current generators means you can't just put a resistor in series with the LED as the device will push 25 ma thru the led no matter what the resistor! Instead, if you have to have 2 LED's on put them in parallel so each will see half the current (I think this will work, sometimes one LED will fire and the other one will not) or put a resistor in parallel with the LED so it splits the current. Usually 20 ma makes the LED's way to bright.


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## ncrc5315 (Jan 25, 2014)

The way the original post is written, I'm assuming these will be ran on DC, therefore dimming wouldn't be an option anyway.


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## vette-kid (May 2, 2020)

Not sure what your comment means, the problem is that dimming and flickering is usually associated with LEDs on a DC layout. 

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## Lemonhawk (Sep 24, 2013)

The cl2 and cl25 are constant current drivers. Independent of the input voltage (once above the trigger point) they output a fixed current so the LED's will be bright as they are running at either 20 or 25 ma. As a result you have to do some fiddling to if you want them dimmer. They are great for use on a DC layout because of the way they work. Think of them like a voltage regulator, except in this case, they regulate the current to keep it constant.


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## vette-kid (May 2, 2020)

Interesting... the voltage change won't affect it? Do you need a resistor as well? 

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## Lemonhawk (Sep 24, 2013)

No voltage change will not modify the current to the LED nor will a resistor in series with the LED modify the current, the CLx limits the current which will prevent damage to the LED. Actually if you do put a resistor in series with the LED, you will only accomplish making the voltage needed to generate the current be higher before the CLx triggers. I've only used them with rectified DCC voltages so I'm not sure what they do with low voltages that will not allow them to produce the spec'ed current. In my case I used a CL2 to power 3 LED's in a shorty passenger car. Since they were too bright I used a resistor in parallel with LED's to siphon off some of the 20 ma available.


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