Hey Everyone!
I kind of remember an aritcle in MRR that described how to wire LEDs in passenger cars for a DC layout using a resistor (to not burn out the LEDs) and a capacitor (to help with continual power over turnouts).
Does anyone remember when that article was? Otherwise, what are your thoughts on the following wiring possibilities.
1] Power + to resistor to LED +, LED- to capacitor to power-.
or
2} Power + to resistor to capacitor to LED +, LED - to power -.
Thanks much in advance!
dan.
In both your 1 and 2, you show the capacitor in series with the LED and power. The capacitor will block DC and pass AC, so it must not be in series with the circuit at all.
Power +, to resistor, to LED +, then LED -, to power -. Then the capacitor is connected to LED +, to power -. You can leave out the capacitor but the LED may blink on dirty track.
However, I also think there should be a resistor connected to the capacitor.
You really need to find that article because electronics is a specific science.
Elmer.
The above is my opinion, from an active and experienced Model Railroader in N scale and HO since 1961.
(Modeling Freelance, Eastern US, HO scale, in 1962, with NCE DCC for locomotive control and a stand alone LocoNet for block detection and signals.) http://waynes-trains.com/ at home, and N scale at the Club.
i'm not familiar with your particular article. Could it be one of these from the Magazine Index?
i believe the circuit drawing on the left below illustrates what you tried to describe. It shows the track connections on top and bottom, a resistor in series with two LEDs. Since you said this is for DC, two LEDs are needed, one for each track polarity (forward and reverse).
The capacitor is like a very small battery. It would need to be in parallel with the LED circuit, so that when there is dirty track and no track power reaches the LED circuit, the capacitor would supply current to the LED. When there is track voltage, the capacitor would be charged up to the track voltage. No resistor is needed nor desirable in series with the capacitor.
But a large capacitor would be needed and large electrolytic capacitors are polarity sensitive. I don't see how you could place one in the circuit on the left because the capacitor would have the wrong polarity for either the forward or reverse direction, would overheat and pop.
A small 12 volt lamp would have none of these problems. It would simply be wired between the track voltage and require no resistor.
The circuit on the right is more complicated. It uses a bridge rectifier so that the the voltage across the LED and resistor circuit is always just one polarity regardless of the track polarity. Because of this, only one LED is needed and an electrolytic capacitor can be used. The capacitor polarity is marked with a "+".
the bridge rectifier reduces the track voltage by ~1.4V. The LED also needs ~1.4V (if not more). So several volts would be needed before the LED would even start turning on.
The article your looking for may have fewer limitations, but may have more expensive components.
greg - Philadelphia & Reading / Reading
It is more complicated than that, for you must consider the voltages and capacities of your capacitor.
First think of the capacitor as a battery in the circuit: it supplies power when the track is dirty.
But like a battery it has a + side and an - side, and so the circuit must be protected from reverse polarity when the train backs up.
Ergo the full wave rectifier show above (previous post) . Track power goes in on the AC terminals, what comes out is stable DC for your lighting system.
Now, if all you want the circuit to do is prevent flickering all you need is a 12 Volt capacitor at the highest farad number that you are willing to pay for and will fit in your equipment.
LION wants, on the other hand, for the lights to stay on while the train is stopped in the station.
Him needs to do more thinking, but him can find 3 volt, 4 farad capacitors that will fit in, but these must be limited to 3 volts, so a power regulator will need to be included in the circuit. Fortunately LEDs will run on 3 volts, but I'll need a different value resistor.
NOW! WHO will tell LION the value of Resistor kneaded four circuits.
ROAR
The Route of the Broadway Lion The Largest Subway Layout in North Dakota.
Here there be cats. LIONS with CAMERAS
BroadwayLionLION wants, on the other hand, for the lights to stay on while the train is stopped in the station. Him needs to do more thinking, but him can find 3 volt, 4 farad capacitors that will fit in, but these must be limited to 3 volts, so a power regulator will need to be included in the circuit. Fortunately LEDs will run on 3 volts, but I'll need a different value resistor.
I've added a circuit that I hope is similar to what you had in mind.
If the regulator voltage is less than the maximum voltage of the LED, no resistor is needed. There are adjustable regulators that can be adjusted for the LEDs.
I know you said you can get 3V caps that could be in parallel with the LED, but if you place a 12V capacitor (4 - 3V 4F capacitors in series) on the input side of the regulator, the capacitor(s) will be at a voltage greater than the regulator, will store more charge and will be able to provide charge for a longer period of time, until its voltage is less than the regulator voltage.
An electrolytic capacitor rated for a Voltage 3 or 4 times the applied Voltage is recommended by most electronics circuit designers. For 12 Volts track input a 35 Volt capacitor is recommended as the minimum.
i don't know much about supercaps. I see one rated at high as 100F 2V. This is probably what Lion is referring to, and why it would need to be parallel to the LED on the regulator output side. See circuit on right below
But as grandydancer suggested, I wonder if there needs to be a resistor in series with the input from the track, otherwise it will draw too much current until it is at least partially charged.. This would delay the LED becoming bright, but once there is enough charge on the cap, it would take just as long to dim during a station stop. Lion may want to hold the passenger car(s) on a track with power until the lights comes on before attaching an engine.
interesting stuff
Supercaps are generally no more than 5V, so to use them on DCC voltages, you have to wire multiples in series. If you look at something like the TCS Keep-Alive module, you will see it is made up of multiple capacitors in series, and perhaps more than one group in parallel.
Capacitors in series have the same capacitence but the voltages add - so if you can;t find a 100uF 35V capacitor you can use a pair of 100uF 16V ones if you have room.
Capacitors in parallel add capacitance, so if you can't find a 1000uF 35V capacitor you cna use two 500uF 35V in parallel. Etc.
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
rrinkerCapacitors in series have the same capacitence but the voltages add - so if you can;t find a 100uF 35V capacitor you can use a pair of 100uF 16V ones if you have room.
are you sure? Capacitors in Series and in Parallel
I have used the R/S 272-1032 cap for passenger car lighting with good results.
Jim
Minor correction, in series it's half the capacitance at double voltage.
So for 1000uF 35 volts you'd need a pair of 2000uF 16V, resulting in 1000uF, 32V.
Your question leads me to believe you need to do some research of basic electronics.
The below link has possibilities.
http://www.awrr.com/lighting.html
Also, do a Google search for flicker free dcc lighting. There are many links out there to store in Favorites. I have others but this will give you some experience in searching which can help a lot in model railroading. A few here who like a following don't like hearing that.
I am hearing a lot of positive results about the TCS decoders with stay alive.
The below link has many good links about lighting and stay alive.
http://www.members.optusnet.com.au/nswmn/index.htm
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.
You guys are veering off course .... the OP is looking for DC lighting help ....
Mark.
¡ uʍop ǝpısdn sı ǝɹnʇɐuƃıs ʎɯ 'dlǝɥ
I did this once. It's a bit more complicated. I found a "supercap" 0.47 Farads at 5 volts from All Electronics. You need this much capacitance to do any good in reducing flicker. The usual electronicing capacitors are rated in MICRO farads, and simply do not store enough juice to do any good. Until you have something in the farad range, you are wasting your time. The super cap is roughly the size of a silver half dollar coin.
First off, the capacitor is polarized. It only capacitates when connected plus to plus, minus to minus. If reversed, it stops capacitating and goes poof. Operating the reversing switch in your power pack reverses the track polarity and will make your capacitor go poof.
This can be fixed by installing a bridge rectifier in front of the capacitor to keep plus connected to plus, minus connected to minus at all times. The capacitor still needs help. Anything more than five volts will pop it. So you need a five volt regulator after the rectifier and before the cap. I like the color of incandecent lamps, so I used a pair of 1.5 volt bulbs, and a 1.5 volt regulator to give 'em the right voltage.
This rig would keep the lamps burning off pure capacitor power for 20 seconds after I turned off track power. All the stuff fit inside an HO caboose. (it lit the marker lamps).
One other bit of advice. Pick up track power with axle wipers. Wheel wipers have too much friction drag. I learned this after coupling a wheel wiper version to a friend's long coal drag. Even with a hefty Bowser steamer on point, it could no longer make the hill due to the drag of the wheel wipers.
David Starr www.newsnorthwoods.blogspot.com
Thanks Mark!
Yes, the original question is about DC lighting which I am doing for a neighbor. It is my first attempt at creating my own circuit.
When it comes to my layout, I will be interested in the DCC information. But not yet.
Thank to all of you for replying and helping this novice! The LEDs are arriving on Monday and I will need to look at getting a bridge rectifier. If I can figure out how to post a picture of my work, I will give you an update.
I don't know what brand of cars you are using but Walthers makes the "drop-in" passenger car LED lighting boards in DC and DCC versions for there cars and you may be able to adapt them for you particular brand. I've had no problem with flickering lights in my DCC layout even with dirty track. I believe the last batch I purchased directly cost $12.95 + shipping.
Funny thing is, it is for Walthers cars with the contacts in place. Sadly, Walthers does not offer the the $12 part anymore, but they do have one for $30.
I have purchased a curcuit learning book from Radio Shack, along with a breadboard, leds, wires, etc. So I will be playing with resistors, capacitors, transistors, etc. Then I will make it work for HO scale.
Thanks again to everyone who replied!