Hi gang:
I'm in the process of building a Walthers 90' turntable kit. I would like to add a couple of lights to the bridge, specifically, one for the interior of the control cabin and the other as an overhead street light type lamp to illuminate the end of the bridge where the control cabin is.
What do I need to run the LEDs off of DCC track power? I'm guessing a bridge recifier and appropriate resistors. Is that correct? Is there anything else I need?
I'm feeling rather dumb here. With the number of LEDs that I have installed I thought I should know the answer but I'm drawing a blank.
Thanks folks.
Dave
I'm just a dude with a bad back having a lot of fun with model trains, and finally building a layout!
While it is possible to run accessories from track power, I personally prefer to reserve track power for the trains and use a separate power source for everything else.
Lackawanna Route of the Phoebe Snow
If you are installing 2 LEDs - wire than back to back with a resistor in series with the pair. That's all you need. The back to back pair prevents one from seeing too high a reverse voltage. One LED will light ont he positive half of the DCC signal, the other on the negative half, and since the frequency is so high it will appear that both are lit up all the time. Resistor as usual to limit the current, 1K at least but if you are using high brightness LEDs a larger resistor may be needed to keep them from being glaringly bright.
By "back to back" you connect the + of one LED to the - of the other, and the - of the first LED to the + of the second. They don't have to be right next to one another, you can have a length of wire make the connection so you cna put one in the bridge and one in the cab. One junction connects to one side of the DCC power, the other junction connects to the resistort and the resistor to the other rail.
In most cases I would say not to do it from track power, but in this case it will be much less than 10ma, you have greater current drain in your bus wiring.
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
Phoebe Vet While it is possible to run accessories from track power, I personally prefer to reserve track power for the trains and use a separate power source for everything else.
This is generally true, but here the OP is wiring lights which are actually on the bridge of the turntable. The only convenient power is from the track.
It takes an iron man to play with a toy iron horse.
hon30critterI'm in the process of building a Walthers 90' turntable kit. I would like to add a couple of lights to the bridge, specifically, one for the interior of the control cabin and the other as an overhead street light type lamp to illuminate the end of the bridge where the control cabin is.
Hi, dave,
We're on the same page as far as wanting to see a gooseneck light on the turntable.
(The "halo" is a little Photoshop enhancement, but the lamps are lit)
When I installed my Diamond Scale TT almost twenty years ago, about the only thing available for light poles were the klunky Walthers ones. These are probably 14 or 16V GOW lamps. I just directly wired them to the bridge rails. IF I were to do it again, and someday I might, using LEDs I'd probably wire them the same way with maybe a 1KΩ or 1200Ω resistor.
I have wired many locomotive number board lights directly to the DCC pickup using only a resistor.
I made sort of a test rig where I have five resistors wired to an alligator clip 600, 1000, 1200, 2400, and 4800 Ω and another clip to hold the LED. I just clip it right to the rails when the DCC power is on. This way I can start at the highest value and work down to see what brightness looks best. If I need to tweak the value at least I have a close starting point.
Maybe there's lots of reasons why I shouldnt have an LED across the buss like that, but—they work. I often use a homemade "hot-rail" checker that's nothing more than a 1K resistor and a big red LED on short test leads so I can look for dead spots.
The turntable I used to play with at the B&O roundhouse didn't have any light in the operator's cab but sometimes we modelers like to have a little extra pizzazz in our night scenes.
Good Luck, Ed
A few years ago I did a couple of these with a 1k, 1/4 watt resistor.
As Randy said, 1k will alllow about 9 to 10 ma. I did LED current measurements some years ago and saw that.
Sometimes in the past, I used a 2.5k pot to select a close resistor value for certain brightness.
That might be necessary today with some super bright LED's.
Some say to use a diode for PRV but I never found a need for one.
My NCE Power Cab panel uses a 3mm, red LED with a 1k, 1/4 watt resistor to indicate DCC power to track.
Rich
If you ever fall over in public, pick yourself up and say “sorry it’s been a while since I inhabited a body.” And just walk away.
Hi everyone!
Dave - As MrB mentioned, getting power to the LEDs on the bridge would be difficult without using track power. There isn't room for a second set of wipers on the bridge shaft. This will be the only place on the layout where track power is being used for structure lighting, and as was pointed out, the draw will be peanuts.
Randy - Thanks for the two - LED wiring hint.
Thanks Rich and MrB.