I have a manual turnout at the end of the yard. I have just added a siding that will feed into that turnout. I want to add LED lights to be thrown manually with a simple SPST switch to indicate the path to me. Here is my question.
Can I take the power from the Bus Wires and if so would I need a resistor in the circuit?
Harold
You can power an LED from the DCC bus but you must include a resistor (1K or so) in series with the LED.
Joe
Don't you also need a rectifier?
Richard
JoeinPA You can power an LED from the DCC bus but you must include a resistor (1K or so) in series with the LED. Joe
Rich
Alton Junction
yeah, you'd need a at least an additional diode (or possibly better yet, bridge rectifier) in there so as protect the LED from the reverse-voltage generated by the "AC" coming from your DCC system.
other than that, there's nothing stopping you from pulling power off the track bus for indicator power.
-Dan
Builder of Bowser steam! Railimages Site
Personally, I leave the DCC bus to the trains, and I run all of my signal and control panel LEDs off of a DC power supply.
I'd also try to keep my DCC bus for trains only, but a single LED isn't going to use much power.
Is this a DCC installation? The OP did not specify his control system. If it's DC, the polarity will be direction-dependent and might require a different solution.
What kind of turnout is it? If it's power-routing, then you might be able to take advantage of that to control the signal rather than doing it manually. If you're using Caboose ground throws, consider one with contacts so that throwing the turnout will also flip the signal.
It takes an iron man to play with a toy iron horse.
Now I am getting confused. Isn't DCC a squared off DC power not AC.
The switch is a Custom Atlas (insulated Frog) I run all my turnouts and LED's from a DC power source. As I only wanted to add LED's and not change the control I figured I might be able to steal it from the track. I am going to look into that cabosse control.
If this idea can not be done simply I will just wire it to the DC.
DCC alternates about a common 0 base point, going both positive and negative relative to that base.
The ~10ma draw of an LED with a 1K resistor will not materially affect the train running current. You change it by 10ma every time you turn the headlight on and off in a loco with an LED headlight, and by 15-30ma when you turn the light on and off in a loco with an incandescent bulb headlight.
Just don't make a habit of it and start driving all your structure lights off track power just because it's convenient. 100 such LEDs and now you're sucking up 1 amp of DCC power. And a booster is a lot more expensive than a plain power supply.
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
OK
Let me then be clear.
Two LED's in series with a 1K resistor are fine? Nothing else.
LION nose little of DCC. It is not exactly squared off DC. The track power is in fact AC (I think) but is also overlaid with a digital signal (I think that is DC) and it is very much squared off as that is where the 1s and 0s reside. Thousands of signals per second to address every function of every decoder on the pike.
EWE *can* power an LED or more with that bus but you save nothing and can cause problems. LION would leave the DCC alone. Well, LION has no DCC, only DC, but like DCC layouts the power is always on. The Left Rail is GROUNDED and the right rail provides the power (+=forward; -=reverse) but him has no thorttles or reversing switches. Subway trains do not run backwards, you know. Resistors and gaps imbedded in the tracks provide contol to the trains.
But I digress, even with big 12 amp regulated supply to the tracks, LION would not tap pwer from it for other applications. GROUND wire (NOT FLAOTING COMMON) is available everywere on the layout. A secong +12v dc circuit is availabel for all LED and other applications. It is cheap and was installed to placate the Tortoise switch machines anyway.
Thes LION tells ewe, PUT an utility bus on your system, it is cheap and you are done with it.
ROAR
The Route of the Broadway Lion The Largest Subway Layout in North Dakota.
Here there be cats. LIONS with CAMERAS
hwolf OK Let me then be clear. Two LED's in series with a 1K resistor are fine? Nothing else. Harold
Nope.
You've got voltage flipping between +14 and -14 (or thereabouts) contsantly. All you'll get with two LEDs wired back to back (both anodes wired to both cathodes) is that both of them will always be lit.
Brain's not engaging entirely, and I can't remember how you end up figuring the reverse voltage that the LED sees if it's not lit, given a pair wired together with both anodes connected to both cathodes ... I THINK it's the same as the forward voltage allowed through the lit LED (e.g. 3V) ... but it could be as high as 11 or the full 14V ...
edit -- I mean something like this:
...A>|K---{ }----(resistor)--- (layout wiring)...K|<A
The NCE Power Cab has a 3mm red LED with a 1k resistor in the panel that you plug the cab into. The LED and resistor are right across the DCC signal output to the track. No diode. I traced out the circuit.
Been working fine for some years.
The Power Cab puts about 13.6 VAC to the track. My multimeter and digital Scope both agree on the voltage.
You can put a diode in series if you prefer. Cheap enough.
A bipolar green/red LED, both diodes with be lit.
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.
Adding a diode. Just use a 1k resistor. Found this picture some time ago.
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This is starting to sound like work. (Not taking about the doing but the number of differnt answers.). I think I will just wire it to DC power source.
It is not work at all. Put the LED, 1k resistor and diode across the rails. Many have done that. Cannot get much simpler.
Rich:
I couldn't agree more. It's really interesting how we can take a simple question and complicate it to the point of confusion of the questioner.
Yeah, the bridge rectifier and capacitor is over kill. If someone wants to power an electronic circuit, then a stand alone power supply is usually a better way to go.
The issue I see is some don't understand electronics and it can get confusing with too much info. Us old times sometimes don't know when to stop. lol
I forget I have been doing electronics since 1953 and have kept up with the times.
richg1998 The NCE Power Cab has a 3mm red LED with a 1k resistor in the panel that you plug the cab into. The LED and resistor are right across the DCC signal output to the track. No diode. I traced out the circuit.
Actually, it doesn't have it inline with track power, it's in-line with the input DC rail from the power connector (which just happens to also connect with some of the pins on the RJ45 connectors on the board). Just traced the leads from a panel I have sitting on my desk here.
Also, there's a blue resistor standing on end in between the two front ports, in series with the LED. Can't read the color bands though, since the one power leg is in the way, looks like it's 1k +/- 1%, but the bands don't stand out enough to call it for certain.
NeO6874 richg1998 The NCE Power Cab has a 3mm red LED with a 1k resistor in the panel that you plug the cab into. The LED and resistor are right across the DCC signal output to the track. No diode. I traced out the circuit. Actually, it doesn't have it inline with track power, it's in-line with the input DC rail from the power connector (which just happens to also connect with some of the pins on the RJ45 connectors on the board). Just traced the leads from a panel I have sitting on my desk here. Also, there's a blue resistor standing on end in between the two front ports, in series with the LED. Can't read the color bands though, since the one power leg is in the way, looks like it's 1k +/- 1%, but the bands don't stand out enough to call it for certain.
I would not say that it is "in-line" with either, since in-line usually means in series (the LED and resistor are in series with each other, but certainly not with the power input or DCC output). Regardless, however, unless NCE has changed it, I am pretty sure the LED and resistor are across the DCC output.
I have a cantalever signal with two LED's, one red and one green, and they are powered with a 3 volt coin cell (watch battery) in a single cell holder. I wired it through a toggle and manually switch the signal from red to green. I don't know how long the battery will last but it may work better(last longer) with a AA or AAA alkaline battery. Just a simple way to power an isolated LED.
-Bob
Life is what happens while you are making other plans!
AA alkaline cells are 1800-3000 mAH. So if the resistor is chosen for 10ma LED current, a single AA would last between 180 and 300 hours if left on continuously. If used say 3 hours a week for an operating session and turned off otherwise - a year or two. Not bad.