Lighting Rolling Stock with DCC Track Power

[mlehman]

Bob,

The 3-unit LED segments are rated at 12v pretty universally (and similarly any unit of 3 x  however many you're likely to squeeze in in most scales), so that's why they work for you like that.

What's going on is that the LEDs are seeing the current constantly reversing, so they are actually flickering on and off, since LED require they be fed with a specific polarity and they don't light when they see reversed polarity. What explains why you see the flicker only sometimes is that it's happening so fast your eye typically won't perceive it, something like how your eye reacts to a movie as a moving picture.

It's possible that you could exceed the tolerance for reverse current that all diodes, inc. LEDs, have as a limit with such an unregualted set-up, but then again, what works, works. Adding the resistors helps limit that possibility. If you add the caps that further dampens things and will take the flicker out, as it will feed the LEDs with the correct polarity when the circuit reverses each time.

[TheWizard]

It could also be that, without any caps, the car loses power for a second which causes the flicker. I know none of my $80 Superliners have caps in them, and it's really obnoxious for such a premium product.

[farrellaa]

mlehman

If you add the caps that further dampens things and will take the flicker out, as it will feed the LEDs with the correct polarity when the circuit reverses each time.

Is that all I  would need is adding a capacitor?

  -Bob

[mlehman]

Basically. Look at the previous diagrams. Note that the voltage regulator is also required to provide + and - power. Caps are typically polarized, so connect the cap accordingly, + to + and - to -. The cap will keep supplying power when the DCC wave reverses many times a second, doing away with the flicker.

[hon30critter]

Bob:

Like Mike said, a voltage rectifier is required. Otherwise you will be feeding the capacitor AC which it is not designed for. They are not expensive. These guys are quite small but still easy to work with. The pins are marked but you might need magnification to read them:

http://www.digikey.com/product-search/en?keywords=MB12S-TPMSCT-ND

Dave