Powering LED's off Track Power (Lighted Car)

[KB02]

I building a lighted caboose (shoving platform, actually) and would like to power the lights off track power. Testing the LED's directly seems to work fine, but when I put them in the car, they only seem to work if the car is facing one direction. Is this a polarity issue or is my set up flawed? It still needs a great deal of refinement as the power going to the LED's is not great or constant, so it could be that, but before I scratch my head too hard, I figured it would be good to know if I'm fighting polarity and not just my janky wiring, you know?

[G8B4Life]

Without a sketch or something of how you've wired things up it's hard to say but I'm going to go out on a limb and say from your description your fighting polarity, vis the lights only work when the car is facing one direction but not that other. Not knowing what you've done I'm going to assume what you haven't done. To make the LEDs work regardless of which direction the car is facing along with the LEDs and dropping resistors you'll need a bridge rectifier and a small capacitor would be good too (to help with flickering). It's quite late so I'm not going to look for circuits to show you right now... However even though I said that this is essentially what you need to do:

https://www.coursehero.com/qa/attachment/3974530/

The AC side (the wavy bit on the left side) is the track pickup on your car. The polarity changes changes depending on which way the car is facing. D1 to D4 is the bridge rectifier. Load is your LED's and resistors. C is a capacitor to help smooth things out (will reduce flicker). Depending on how many LED's are in the car you could make the bridge rectifier out of LEDS (they are diodes after all). I could draw that one out later if you wanted but right now it's the day after I stared typing this post and I'm out of here.

- Tim

[gregeusa]

you can buy the entire full wave bridge in a single small package to save space... it will have the ~ and + and - markings

the cap might help flicker, if it's big enough (mfd capacity)

but remember you need to calculate a current limiting resistor since the LEDs by each run at about 3.6 volts and 20 ma max...

Since you say it works at least in one direction, you may have that done already.

So the full wave bridge in this case is used to provide a continuous output polarity, regardless of track polarity.

[KB02]

Thanks! Yes, I already have a 1k resistor in place. My knowledge of electronics is limited once you get into resistors and capacitors and what not.

What I have so far is pretty basic: Wipers on the wheels going up to the LED's with a resistor on one side. It should, in theory, work great on a regular ole DC layout. That's not what I've got though, and I do know that.

Thanks for the responses! Now I have a better idea what I need to do.

[LVRR1856]

To keep things even simpler ... I use LEDs with built in resistors, since it's in a caboose, just use to bulbs wired opposite.

[gregeusa]

So where you would use one LED, you use 2?

How's that working for you in marker lights?

To me, add ONE component, a 4 terminal full wave bridge for a buck fifty, is easier and simpler than paralleling a bunch of LEDs throughout a car, and I have never stuffed TWO LEDs into a marker light..

But YMMV..... Greg

[LVRR1856]

Yea - not ideal for marker lights, just thought you were doing single light in caboose.

[gregeusa]

Sorry, my mind is often stuck in G scale, we have to use multiple lights in cars, and I like that since it "evens out" the light, no single "hot spot".

Of course in HO, one LED might be ok, although 3, 1 in cupola, 1 at each end would be even nicer... of course in G scale we even put smoke units in cabeese! (yes we are sick puppies!)