What kind of light/LED [and resistor?] to use in a caboose?

I bought some Kadee Bettendorf trucks with electronic pickup today and I want to try them out in my caboose, but I am unfamiliar with the technicalities of track-supplied power for lighting. I have an LED that I have painted with a nice soft gloaming amber for the lantern (and fire?) in a caboose. The LED has a resistor built in. Is that okay to use for this purpose? I have used them in structures powered by a 12Volt WeHonest board, so I am assuming the LED will get the same voltage from the track. Help?

Thanks,

-Matt

You donā€™t mention if you are supplying DCC power to the track or is it DC variable?

If it is DC the LED will only light in one direction. The answer here is to have two LEDs with cathode and anode wired to each rail so one or the other will illuminate in whichever direction.

With DCC the LED will illuminate but you ā€˜mightā€™ want to add a little more resistance. Iā€™ve found that many of the prewired LEDs with resistors use a value that provides maximum brightness on DCC voltages. You can try adding a 1KĪ© resistor in series and place it on your rails to see what kind of brightness you get. You want it pretty dim for a caboose. Adjust higher or lower from there.

Some DCC systems can provide anywhere from 10.5 to maybe 13.5 volts (HO setting) to the rails. The LED will be ā€˜seeingā€™ about half of that, but wil still be pretty bright in most cases.

Good Luck, Ed

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Hi Matt,

I added lighting to my eight car fleet of Algoma Eastern cabooses and it was pretty easy. I am working with DCC.

I added marker lights and an interior light (more on that later) and I used a home made keep alive circuit.

Here is the keep alive circuit compliments of Mark R:

I added a magnetic latching reed switch to Markā€™s circuit so the lights can be turned off when the caboose is not in use. I used Utah Pacific marker lights with 3mm LEDs. Why 3mm? I could have used 0402 LEDs but the problem with those is that the light only shines out one side of the LED. If you put a 0402 LED inside a marker light, one lense will be very bright but the othe two will have very little if any light showing.

To make the 3mm LED fit, I mounted it in the chuck of a drill with the dome sticking out and then, with the drill running, I used a file to cut the tip of the LED down to the right size. You have to be careful to not cut too far down towards the base of the led or you might hit the ā€˜flagā€™ which will then give you a DED (Dark Emitting Diode!).

I also filled the marker lamp with epoxy to help distribute the light. Canopy cement would work too.

One note about lighting the interior of the caboose: I believe that the interior of the caboose would have been dark during night time running in order to protect the crewā€™s night vision. Instead of lighting the whole interior, I made a small box resembling a conductorā€™s office and only illuminated that area. The light only shines out of one window. I donā€™t know how prototypical that is, but it makes sense to me.

Cheers!!

Dave

Hi Dave,

Just curious: Why install a reed switch if the LEDs are powered by a cap?

According to your attached notes from Mark, the LEDs will stay lit for ~3 min. Given that reed switches will more than likely fail before a cap, I would have left it off.

ā€¦Or (and this thought just occurred to me), ā€œwhen the caboose is not in useā€ means when itā€™s sitting on the layout but not attached to a train. If so, then I get the rationale.

Tom

Woops, sorry. My layout is both DC and DCC, but I almost never switch it to DCC. And youā€™re right ā€“ of course youā€™re right ā€“ the caboose only lights in one direction. I hadnā€™t expected that. I wired it up with that amber LED last night. The color is perfect, but yes, itā€™s so bright that the glow shows through the styrene walls and the cupola looks like the top of a lighthouse being pulled along the tracks. Of course, it gets brighter with speed, and I run most of my trains pretty slow, except milk trains, hot shots and passenger trains, but itā€™s still awfully bright.

-Matt

i donā€™t understand this circuit. Wonā€™t the LEDs limit the voltage of the cap so that when the track voltage drops the cap will only supply current for a very short time.

Edā€™s circuit make a lot more sense because the cap will charge to near track voltage and will provide current down to near the diode voltage for a longer period of time

@Dave, Tom and Greg, unfortunately I am not versed in reading circuitry so Markā€™s illustration doesnā€™t make much of a picture in my head, and I donā€™t understand Tomā€™s confusion about the cap. But thanks all for responding. If I get that far Iā€™ll ask for clarifications. I like the idea of creating a ā€œconductorā€™s officeā€ and keeping the light to a minimum, or maybe shining in one window on each side.

-Matt

an LED with built-in resistor that works at 12V should work fine on a DCC layout although will be half as bright because it gets power only half the time.

a inexpensive small bridge rectifier, as in hon30critterā€™s diagram is needed on a DC layout

that same bridge rectifier could also be used on a DCC layout so that the LED gets power all the time. (you only need one rectifier even when using multiple of your LEDs

Hi gregc,

Markā€™s circuit does work. The caboose lights stay lit for quite a while after the power is removed. I donā€™t think they stayed on for three minutes but it has been a while since I tested them.

One thing worth mentioning is that the lights donā€™t come on as soon as the power is applied. It takes a few seconds for the cap to charge up before the LEDs have enough power. It is very important to remember that when you test the circuit or may think that it is not working.

Cheers!!

Dave

Hi Matt,

Iā€™m not much of an electronics guru either but I can assemble a simple circuit if I have a diagram to work from (note that there is usually some head scratching involved [swg]). I would encourage you to give it a try. Iā€™m sure that lots of folks on the forums would be willing to help. We can tell you which components to buy and how to assemble them.

Cheers!!

Dave

Hi Tom and Matt,

I believe the latching reed switches are hard to find these days so they probably wonā€™t be used anyhow. It is important to use ā€˜latchingā€™ reed switches. They stay ā€˜onā€™ when the magnet is removed. Regular reed switches are momentary. They will not stay on.

Tom, you are correct. The reed switches are there to allow the lights to be shut off when the caboose is on the layout but not in use.

Cheers!!

Dave

Hi gregc and Matt,

I donā€™t think that the LEDs with a built in resistor can be used in either Edā€™s circuit or Markā€™s. The circuits are designed to deliver 3 volts to the LEDs so an LED that requires 12 volts wonā€™t light. Somebody correct me if Iā€™m wrong please.

Cheers!!

Dave

An update: Reading through your responses, I decided to try the easy things first, the stuff I could make sense of. I understand about adding a resistor to dim the light, so I did a test and introduced a 30 ohm resistor between one of the wires coming from the hot trucks and the LED wire. The LED already has a resistor built in right at the head, but I added this second one. The LED shone as brightly with the additional resistor as without it, which made no sense to me. Maybe 30 ohms isnā€™t enough?

Another thing I did was add another LED into the circut with the red and black wires reversed. When I turned up the track voltage, one light lit, and when I switched the direction, the other one lit. So Iā€™m happy about that. Iā€™m not too worried about keep-alives at this point. Really what I want to do now is build some walls inside the caboose to restrict the glow to one window on each side of the caboose.

This is all DC, by the way. So now at least I can have the caboose lit regardless of which direction itā€™s facing.

-Matt

30 ohms and a thousand ohms are a bit different values.

I just installed what is probably my 50th ā€˜keep aliveā€™ circuit (see Gregā€™s post) in another passenger car last night. I can safely say the circuit stands the test of time. Plus I donā€™t think the inrush current has any negative effect on the DCC circuit breakers. I may have 2 dozen or more lighted passenger cars on the layout at any given time and there is rarely a problem with CB resets.

Iā€™ve recently begun using the LED SMD strips which have built-in resistors and are designed for a 12 V supply. They work just fine however are exceedingly bright. I add a 1/4 watt resistor (less chance of overheating) somewhere in the 680 ohm range.

Iā€™ve found that with the Walthers Proto cars I can aim these LEDs toward the inside of the roof and with a foil tape applied as a reflector I get a very nice, even lighting throughout the car.

Car Lighting LED by Edmund, on Flickr

The above photo shows the circuit I use, plain and simple. The two 1/4 watt resistors are there, in series, as I adjusted the resistance to meet the level of b

the built-in resistor is probably ~1k so adding 30 Ohms doesnā€™t make much of a difference

thatā€™s right because both Mark and Edā€™s circuits have external resistors.

Good point Ed.

Itā€™s been years, but I still remember seeing SCL freight trains at night and almost always, the caboosesā€™ yellowish (incandescent) lighting was barely visible through the side windows and cupola.

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