i am new to wiring my layout. i bought some very nice LED street lights that are set to operate at a 3v current. i have a 16v power supply and was going to solder some resistors, but i would rather not go that route if i dont have to. can i purchase a 3v power supply and connect the LED lights directly to the power or would there be a risk of damaging the bulbs? if anyone has an answer or suggestion as to what may be a better solution, please help.
Since you bought the streetlamps, there should be some information on the packaging on the best way to wire them up. They *should* it seems to me that they would have the resistor built in
The thing with LEDs is that the voltage is not as critical as the current: thus the need for a resistor.
I get LED's from Walmart, and they are marked as 3 volt, but I run them at 12 volts. The 3 volts is the minimum voltage that will light the circuit. More, as long as the current is not too high will work just fine.
Is your 16volt supply DC or AC. LEDs run on DC current (other threads hereabouts notwithstanding). Connect one to your variable DC out put and run it up to see what happens.If it does not light up, turn it around as LEDs act as rectifiers and will pass electricity in only one direction.
Since you are not buying LEDs in bulk it would be a shame to "waste" one just to see what happens. But LEDs are LEDs. 12 Volts with a 1000 Ω resistor will work just fine. As I say, I run 3v LEDs at 12 V without any problem, and onboard trains I run them at 5 volts.
ROAR
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You have two options.
1. You can purchase a 3V power supply and wire the lights up in parallel just fine. I would get a resistor and wire them in series before the current gets from the power source. A small resistor value would work fine.
2. With the existing 16V power supply, you can wire up 5 LEDs (if you want bright streetlights but a slightly reduce service life) or 6 LEDs (at a slightly reduced light brightness but with longer life) in series with the power supply (and a very small resistor value).
BroadwayLion Since you bought the streetlamps, there should be some information on the packaging on the best way to wire them up. They *should* it seems to me that they would have the resistor built in The thing with LEDs is that the voltage is not as critical as the current: thus the need for a resistor. I get LED's from Walmart, and they are marked as 3 volt, but I run them at 12 volts. The 3 volts is the minimum voltage that will light the circuit. More, as long as the current is not too high will work just fine. Is your 16volt supply DC or AC. LEDs run on DC current (other threads hereabouts notwithstanding). Connect one to your variable DC out put and run it up to see what happens.If it does not light up, turn it around as LEDs act as rectifiers and will pass electricity in only one direction. Since you are not buying LEDs in bulk it would be a shame to "waste" one just to see what happens. But LEDs are LEDs. 12 Volts with a 1000 Ω resistor will work just fine. As I say, I run 3v LEDs at 12 V without any problem, and onboard trains I run them at 5 volts. ROAR
If you attach an LED to a variable source to test, DO NOT turn that variable source above 3.5 volts without a resistor in the line or it will be bye-bye LED. It can also be dangerous .... I've actually had LEDs literally explode sending small pieces of plastic all over !
The streetlights you have are just a white LED which has a nominal working voltage of 3.0 to 3.5 volts. It no doubt doesn't give you the current rating, but you could safely "assume" about 20ma. A 3 volt wall pack would have to have a high enough rating to handle the total number of LEDs you want to use. Five LEDs at 20ma each would require a MINIMUM of 3 volts @ 100ma. General rule of thumb though .... your power supply should always be greater than the required current. If you NEED 100ma, use a 125ma or 150ma supply, otherwise the supply might be stressed.
A quick word on walwarts .... don't use walwarts that are intended for a specific application (cordless tool chargers, etc.) - those are designed for a specific load based on its application. If that specific load is not met, the walwart will not provide the voltage / current it's rated for. You need to use the generic power supply variety that provides a regulated output.
You could wire five of them in series (six might be too dim) - but then you would have the Christmas Light scenario .... something happens to one, they all go out - and it's not as easy to determine which LED is shot !
The best approach would be to have an appropriate resistor on every LED. Even on a 3 volt supply, a 10 ohm resistor will act as a protection buffer again current insurges. Good practice even though few people would bother.
Mark.
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