My model railroad project sort of "build thread" for railroad project has reached a step I don't really know how to do. I need to add some streetlights. There are some "plug and play" options, but they are stupid expensive and don't really match what I'm trying to model. I've found some el-cheapo knock off brand lights which came with no instructions. In addition to the lights, they also came with what appears to be a packet of resistors. Reading some reviews on line, it sounds like the lights needs a 3 amp resistor when attached to a 12v power source. The problem is the resistors are substantially larger than the light poles, which means I either have a mounting problem because I have to drill a hole substantially larger than the light to feed the resistor through OR I have to attach (and likely solder) the resistor under the table, which would be . . . not optimal. To make it even more awesome, the leads on each light are really short. Bear in mind that my knowledge (if you can even call it that) of electronics dates back to high school physics, some 30 years ago. So here's my proposed solution.
Step one: Extend the leads on each light to a workable length. I'm assuming I'll need to learn to solder fine wire. I'm hoping that isn't as hard as it seems.
Step two: Purchase something like this:
Step three: Connect to my power source and put the 3 amp resistor in the lead between the "bar" above and the 12v power source.
Step Four: Connect all lights to the power bar above.
Am I a genius, an idiot or do we need more information to decide that issue.
It sounds reasonable to me. Basically, your streetlights are an LED that runs on less than 12v. The resistor is there to knock it down. So you just knock it down before the bus and everyone is happy.
Alternative: source a power supply that outputs the voltage you need. You could probably pick up a cheap wall wart. Grab a multimeter and one of those resistors and measure what you actually get.
3 amp is a big resistor, so I am assuming all the lights go in parallel to each other and that group goes in series with the resistor. If that is correct, your plan looks good, assuming that is a distribution bar rather than just terminals. If terminals then everything is the same but you make a bunch of jumpers.
Regardless, modifying the power at one location and then taking little wires into the landscape is a good approach.
This Wally gem seems like it belongs here:
Also: The item I pictured above says it's a "Distribution board", I guess I'll order one up.
Do you happen to know the resistance of the recommended resistor? 3A is the power handling capability. Even a picture of one would help, they wear their rating on their sleeves so to speak.
Here's the package. They have no writing on them, but I assume the color/stripe pattern means something?
Left to right, the bands are brown(ish), black, black, brown, brown. (Although I guess "left to right" depends on which way you hold it!)
Resistor power handling is rated in Watts. Their resistance value is rated in Ohms. You need ohms law to figure out the correct resistance, then calculate the power dissipation and make sure your resistor is big enough.
If the LED needs 4 volts and runs at 50mA (.05 amps) and your power supply is 12V, then your resistor has to drop 8v and R=E (volts)/I (amps) or 8/.05 = 160 ohms. Power = Amps * Volts = 8V * .05 amps = .4 watts so you would want at least a 1/2 W resistor.
I'm guessing your Br/Bk/Br would be 100 ohms and the typical LED runs at about 3 volts so I would try two of those in series from a 12V supply. Should work fine depending on the current requirements of the LED.
EDIT: Google tells me most small LEDs run at more like 10ma, so you would need more like a 1,000 ohm ressistor. Don't suppose you have a voltmeter to measure yours?
Colors are exactly what we need. It is indeed a code. There should be a gap between the 4th and 5th. So is it brown/brown/black/black - gap - brown or brown/black/black/brown - gap?
Also, there are some white-ish cubes in the pic that look like resistors with high power handling.
A volt ohm meter is a handy thing to have for projects like this and they go for about ten bucks on Amazon.
The sequence brown, brown, black (SPACE) black, brown.
That's not where there's supposed to be a space :) jwagner is right, if you have a multimeter the easiest thing to do is just plain measure the resistance. It's probably a 1.1k.
If they are 3v LEDs - probably - then the easy option is to just use one of these with no resistors.
https://www.amazon.com/SMAKNÂ-Premium-External-Supply-Adapter/dp/B00R5BT2O2
Or, if you want to spend the big bucks and spend $16, one of these. Easier to hook up because it comes with a wire terminal.
https://www.amazon.com/Belker-Universal-Adapter-Supply-Speaker/dp/B07N18XN84/
Keith Tanner said:
That's not where there's supposed to be a space :) jwagner is right, if you have a multimeter the easiest thing to do is just plain measure the resistance. It's probably a 1.1k.
If they are 3v LEDs - probably - then the easy option is to just use one of these with no resistors.
https://www.amazon.com/SMAKNÂ-Premium-External-Supply-Adapter/dp/B00R5BT2O2
Or, if you want to spend the big bucks and spend $16, one of these. Easier to hook up because it comes with a wire terminal.
https://www.amazon.com/Belker-Universal-Adapter-Supply-Speaker/dp/B07N18XN84/
So, with the first option, strip off the output plug, figure out the positive/negative leads, hook them up to the power distribution board, plug/wire each light positive and negative to the power board, plug it in and good to go?
With option two, same as above but use the "wire out" adapter option rather than stripping the plug, and have some degree of output adjustment for brightness on the LED's?
jwagner (Forum Supporter) said:
A volt ohm meter is a handy thing to have for projects like this and they go for about ten bucks on Amazon.
I might even have one (completely unused 
) in the tool box.
kazoospec said:
Keith Tanner said:
That's not where there's supposed to be a space :) jwagner is right, if you have a multimeter the easiest thing to do is just plain measure the resistance. It's probably a 1.1k.
If they are 3v LEDs - probably - then the easy option is to just use one of these with no resistors.
https://www.amazon.com/SMAKNÂ-Premium-External-Supply-Adapter/dp/B00R5BT2O2
Or, if you want to spend the big bucks and spend $16, one of these. Easier to hook up because it comes with a wire terminal.
https://www.amazon.com/Belker-Universal-Adapter-Supply-Speaker/dp/B07N18XN84/
So, with the first option, strip off the output plug, figure out the positive/negative leads, hook them up to the power distribution board, plug/wire each light positive and negative to the power board, plug it in and good to go?
With option two, same as above but use the "wire out" adapter option rather than stripping the plug, and have some degree of output adjustment for brightness on the LED's?
Yup. Although if you go too high the leds go poof. If they're 5v LEDs, that second one gives you an option. And no goofy resistors.
kazoospec said:
jwagner (Forum Supporter) said:
A volt ohm meter is a handy thing to have for projects like this and they go for about ten bucks on Amazon.
I might even have one (completely unused ) in the tool box.
Be aware they are battery powered and if it's been in the tool box a long time...................
I don't like connecting a power supply directly to the LED. Once the LED hits the forward conducting voltage the current goes up really quickly so it's easy to overcurrent them. (Google "LED VI curve") A power supply and a resistor allow you to set the current to what you want and it won't vary much.
Decided I should probably stop in and update this thread. I ended up taking one of the leads I had from the Woodland Scenic "Just Plug" system as the power supply. This puts the street lights on the same power supply and switch as the building lights I already installed. I installed one of the resistors from the light kit in the positive lead and attached it to the power distribution block.
It looks like this:
I'm waiting on some fine gauge wire to finish wiring in all but the closest light. I hooked that one up directly to the distribution block because the leads were just long enough. That one appears to be working pretty well. The only remaining question is whether having all 8 lights on the bus bar will put too much load on it. I've "bench tested" is successfully with several lights without any appreciable drop in light output, so I'm hoping I'm good.
Light output is currently about perfect, it doesn't look like it in this pic just because I couldn't figure out how to take a decent pic with my phone.
I'd add that a good multimeter > cheap multimeter.
