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Bi-directional LEDs

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  • Member since
    December, 2018
  • 6 posts
Bi-directional LEDs
Posted by Lewis A. Clark on Monday, February 11, 2019 1:00 AM

Would like to use LEDs in my Athearn Blue Box diesels and Rivarossi steam locomotives because of their longevity and thermal properties. However, I would also like for the front lamp to remain lit regardless of direction. Have not found anything on the net nor a quick glance at the Forum pages to provide a solution to this. Any suggestions would be greatly appreciated.

Tags: LEDs , Lighting

The American people are a very generous people and will forgive almost any weakness, with the possible exception of stupidity.  

Will Rogers

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Posted by RR_Mel on Monday, February 11, 2019 9:36 AM

I take it that you are operating a DC system.  For the reverse headlight its normal for an LED to work directionally with the correct polarity to the rails.  A white LED operates between 2.8 volts and 3.6 volts DC and you will need to use a resistor in series on 12 volts, about 1,000Ω.  I would also use a small diode in series with the LED to prevent flickering on reverse voltage.
 
For the forward headlight you need either a bridge rectifier or four diodes.  I use DB107s for this purpose.
 
 
 
 
 
 
 
 
Mel
 
 
My Model Railroad   
 
Bakersfield, California
 
I'm beginning to realize that aging is not for wimps.
 
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Posted by gmpullman on Monday, February 11, 2019 2:23 PM

IF you have enough room you could sandwich two small LEDs together and aim them out the headlight opening. I have some small, I believe they're 1.2 mm warm white that would probably fit into a side-by-side arrangement. Or you could get pre-wired SMD LEDs and place them side-by-side.

Then one LED would be lit in forward and when backing up the other LED would light but since they're aimed out the same opening no one would notice thet they are two different LEDs.

Evan Designs has LED's pre-wired with the rectifier as Mel shows if you want to make it easy:

https://www.modeltrainsoftware.com/collections/hobby-leds/products/universal-solid-leds-for-transformers

 

Good Luck, Ed

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Posted by Lewis A. Clark on Monday, February 11, 2019 10:04 PM

Yes. Quite right.I did leave out the fact that I am running DC. The salesperson at my train shop also said the same thing. But the salesperson at the electronics store sold me a voltage regulator instead. Did not know this until you presented a part number for the BR. Looked up the part # for my device and that is what it turned out to be. Sounds like a revisit to the electronics store is in oder. Thanks for the recommendation.

The American people are a very generous people and will forgive almost any weakness, with the possible exception of stupidity.  

Will Rogers

  • Member since
    December, 2018
  • 6 posts
Posted by Lewis A. Clark on Monday, February 11, 2019 10:29 PM

That solution did present itself to me. I can get that to work in the BB diesels just fine. The narrow confines of the headlight housing in the steamers may take a little more thought. Both solutions have merit. Being that I am probaly going to relight quite a few locomotives, cost may figure into the one recommendation or the other or a combination of the two.

By the way do you know of a white/red bicolor LED? Was planning on using that on the back end of my diesels. Have wired up a couple of red and white leds, but it can be cramped in places. Internet search turned up two places. Both are an entire ocean away and in opposite directions. Figures.

The American people are a very generous people and will forgive almost any weakness, with the possible exception of stupidity.  

Will Rogers

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Posted by mbinsewi on Tuesday, February 12, 2019 8:57 PM

I use the LED's that Ed links to.

https://www.modeltrainsoftware.com/products/chip-nano-pico-leds

I get the 7-19v universal AC/DC or DCC supply.  They have a 7-19v AC/DC rectifier plus a resistor, wired in. 

I use the chip LED for ditch lights, and wire them right to the power supply of the loco, when track power is on, the lights are on.  Put the loco in reverse, the head light goes out,  rear lite goes on, and the ditch lights stay on.

I would think you could use the same thing for the head light.  The head light would be on as long as the track power is on.

Mike.

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  • From: Mpls/St.Paul
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Posted by wjstix on Wednesday, February 13, 2019 12:26 PM

Generally, diesels wouldn't have a red light in the rear headlight, since even though they do have a front and back they are often used in both directions (except for say F units or E units). Some may have a separate light or set of lights that could show red for certain situations.

 

Stix

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