I asked a few posts ago about using LED’s in the observation cars. I was advised to use a string of lights coming from the train power rather than try & make pickups for each car. I like the idea so I’m going forward with this one. Question: Do LED’s have a negative or a ground side and a hot side? If so, or if not, can I use the metal of the car body as the ground and simply string the hotwires together? Also, what type of plug in would a person buy for the little wires on the LED’s so the cars are not tethered together, but can be unplugged from one another? Thanks to all & sorry so many questions in one post! Jake
What they have is a cathode and an anode, like the semiconductor diodes that they are. Your circuit can indeed use the car frames as one side of your circuit and run only a single wire between cars. Because of the fairly low voltage that the trains run on and so as not to require that you always use the same number of cars, I recommend that the circuits within each car be in parallel with all the other cars. In other words, the single wire will originate at the locomotive pickup and deliver the track voltage to each car in the train.
What you do within each car will depend on how many LEDs you want and in what colors. You could put a couple of LEDs in series within the car; but the light would vary less with track voltage if you wire each LED individually or in anti-parallel with the others in the car. Have you read my article on LEDs in the September CTT? If not, why not do that to get some background and then come back for more discussion?
LED’s do have a positive lead & negative lead. If you are using cars that already have lights, then i’d just replace the lights with the led. Don’t forget to use a series resistor(and a diode too)-- 820 or 1000 ohms for each one. Connect the negative leads together, then connect to the diode. The banded end of the diode connects to the outside rail track power. The positive leads from the LED’s go to the center rail track power connection.
The only minature connectors I’ve ever seen are sold by Miniatronics, and cost about $9 each. hopefully, someone else can be of more assistance than me----
If he’s using more than one LED per car, there’s a better way to wire them. You connect them in what is called “anti-parallel”. This means with the cathode of each LED connected to the anode of the other. Then you don’t need any other diodes to protect against reverse voltage–the LEDs protect each other.
The resistor value and power rating needs to be calculated based on the desired average current and the maximum voltage that will be on the track. The article gives details of this.
For a single wire, there is an easy way to make connectors using loose connector pins soldered to the wires and covered with shrink tubing.
I bought the units already wired with everything, ready to go into the system. I touched them to the track to see if they light and they do, no matter what lead you touch to the hot or negative track side, they still work. I’ll read your artcile again Bob and see if I can figure it out from there. I cannot tell from the wiring which is anode and which is diode. Doesn’t seem to be anything marking them but maybe I haven’t check in the right place. Jake
There’s not much need to figure that out if you have LED assemblies that already contain the ballast resistor and reverse-voltage protection, Jake. However, wired the way they probably are, they draw current only in one direction. For one light, this is not a problem; but a whole train of them all installed the same way might be more DC than your transformer can deal with. You never said how many you are putting into each car. If it’s more than one, and if you can see any difference between the connections to the assemblies, I recommend connecting half of them one way and half the other, to balance out the DC currents.
You also didn’t say what color they are. If they are white, they may be the very bluish white that is normally found in “white” LEDs. If that’s so and it’s okay with you, go ahead of course. My preference is the imitation-incandescent LEDs like those sold by Richmond Controls, since the prototype cars would have been lit with incandescents (or something with a similar color temperature).
Are these assemblies rated for your maximum track voltage?
They are rated for 5-18 volts. I will probably put two in each observation car. I’ll need to take a closer look at these I guess to see what wires are what & where. Thanks much, Jake
In your closer look, the LED will have a flat edge. This is your negative side. Also you can use a CR 2023 3 volt battery to determine polarity, since it is covered with shrink tubing. I keep afew around for testing.
Three volts may be a little low to light up a white LED. A 9-volt battery would probably work better.
Another way to find the right connection to balance the load is to connect two LED assemblies in series, then touch the loose ends of that pair to the track. If they don’t light, reverse one of the assemblies. If they do light, connect the loose ends to one side of your circuit and the ends that you connected together for the test to the other side of your circuit.
Would you like to have some pins to use for the connectors? I have lots of nice gold-plated pins and can easily send you however many you would need. I recommend putting a female at the locomotive, so that you can run it without fear of a short circuit from the dangling pin, and then a male-female pair on each car.
Bob, that would be great if you have some pins you can cut free. Put a bill in with them or let me know how much and I can PayPal you if you are set up for that. Thanks so much for the help, Jake
Address is as follows:
Jerry Andrews
R.R. # 5 Box 21A
Moundsville, WV 26041
Bob, by any wild chance would you know what might activate this K Line controller for the dump car? I’m at my wits end on this one, it’s brand new, battery is new, etc. I take it there is NOT a battery in the dump car somewhere? Thanks for any info on this one, Jake
Tell me how many you actually need. I’ll throw in a few more as spares. Don’t worry about money–they’re not worth the postage (unless you need them and don’t have them!).
I don’t know anything about the MTH car. Sorry.
Probably 10 pairs would do it Bob. Who sells them in case I need more? Does Radio Shack carry anything like that? Thanks much, Jake
They sell tin-plated Molex-type pins. The pins that I have are gold-plated and very sturdy. I got a large number that were surplus at my work many years ago. This is about the only use I have ever had for them. You would have to get them from a distributor like Mouser. They are for military-type circular connectors.
Thanks Bob, so kind of you to do that. I connected some of the LED’s today just testing them out, there doesn’t seem to be a wrong way to connect them. No matter what you do to them, they will light up just fine. What do you make of that? Thanks, Jake
That’s to be expected, Jake. They can’t tell the difference between the two wires of the AC circuit because the voltage alternates. Swapping the wires gives them the same voltage, just shifted 1/120 second in time.
The reason I advised connecting them in a particular way is that each of them draws current only in one direction, when the AC voltage momentarily has the polarity that that assembly wants. This amounts to drawing a component of DC current from the AC transformer. A little of this is okay; but a whole train of LEDs drawing current from the same half-cycles of the AC waveform may be hard on the transformer. So the idea is to connect half of them to draw current on one half-cycle and the other half to draw current on the other half-cycle. Then their DC currents cancel each other; and the transformer doesn’t know the difference.
Try lighting two of them in series as I suggested and see whether you can connect them so that they both light and so that neither one lights.
OK, I’ll give em’ a try and see what goes. Thanks for the help on this. Merry Christmas, Jake
Jake, I mailed you a dozen pairs. I soldered wires to one and insulated it with heat-shrink tubing as an example.
Thanks Bob, is there anything at all I can send you? Need any wood of any kind? Thanks again, Jake