Resistors and LEDs

[Slufoot]

I am building a coal mine loadout building and plan on using small LEDs to illuminate it inside and out. The LEDs I have require a 1K ohm resistor when powered with 12vDC. My question is this: must I use one resistor on each LED or can I use only one resistor in the power supply line for all LEDs.  I have 1K 1/4 watt resistors but I have limited room inside the building. Plus, soldering so close to the plastic could be an issue. I wondered if I could use just one resistor of the same 1K value but a higher wattage (like a 1 watt or larger) at the power source to run the lights. It certainly would make the wiring easier. Any thoughts/advice will be greatly appreciated.

Thank you,

Kevin

[rrinker]

 One resistor per LED. It is the easiest and most straighforward way, and avoids any potential problems.

The wiring is no more complex - just wire up resistor/LED pairs ahead of time, and then install them as simple 2 wire devices. Of if you need them in a line down the middle underside of a roof, you can cut off strips of perf board that you cna get at Radio Shack and wire the LEDs and resistors to those with 2 wires for the assembly coming off the end or middle of the board, whichever makes routing the wires easier.

             --Randy

 

[nedthomas]

If you plan parallel wiring then one resistor per LED is the best way to go. If you parallel the LEDS and use one resistor then the leds need to be well matched. At 12vdc you can series wire 5 or 6 leds in a string with one resistor per string. This may make your installation easier.

[jrbernier]

  Not a good idea.  The resister most suggested is to drop the remainder if the 12v based on  'load' of 20-30ma(typical for a LED).  Adding more parallel  LED's to circuit would have allow for the additional current of each LED.   Every time you added a LED, the voltage dropping resister will need to be changed.  Small 570-1000 ohm resistors are cheap

  You can buy cheap 3vdc wall warts for under $5 each:

http://www.allelectronics.com/make-a-store/item/DCTX-331/3VDC-300MA-WALL-TRANSFORMER/1.html

  Or you can buy these 44 cent voltage regulators for LED's:

http://www.trainelectronics.com/LED_Articles_2007/LED_104/index.htm

Jim

[cedarwoodron]

I agree with my fellow Minnesotan, Professor Bernier: I have used only one parallel wiring situation with LEDs so far, where they share a single resistor- that is where there were two headlamp holes that were spaced in such a way that two LEDS were more practical than one trying to light both openings. In that situation, the proximity of the holes and the need to conserve space with the wiring made a two LED parallel circuit the better answer. But, that was only for two of them. If there is sufficient space, such as in a structure, wire away with series wiring of each LED. I get 100 count batches of 470 ohm resistors from China on EBay- I am now generally using 3mm round and flat top warm white LEDs for most lighting projects. If a structure space needs more lighting, I use a 1000 ohm resistor with a 5mm flat top LED. Cedarwoodron

[hdtvnut]

While it's true that 20 ma. current is usually suggested for common 3mm LED's, most work well with less current where the full brightness isn't needed.  Try one of the high-brightness types at 5 ma. (iIf the supply voltage is 12, this means a resistor of about 2K ohms).  Even 2 ma. may work OK for many purposes.  Talk about flea power!

I run loco headlights at about 5 ma because they are plenty bright.  The efficiency comparison to filament bulbs is amazing.

Hal

 

[mlehman]

Here's a handy calculator for dealing with parallel and series wiring of LEDs. I stick with parallel circuits for nearly all my multiple LED installs.

http://www.quickar.com/bestledcalc.php

Don't be afraid of adding more resistance tio the calculated value, as far too many times you see LEDs bright enough to burn your eyes out, when a lower level of light output may be more realistic.

[hon30critter]

Kevin:

Keep in mind that there are some very small SMD (Surface Mount Device) resistors available. Here are some examples from Digi-Key:

http://www.digikey.ca/scripts/dksearch/dksus.dll?FV=fff40001%2Cfff800e9%2C80003%2C1c0002&k=SMD+resistor&vendor=0&mnonly=0&newproducts=0&ptm=0&fid=0&quantity=0&PV1=2358

Also keep in mind that you can get away with only one wire for each LED if you build your structure with brass and use the structure as the common ground. By doing that your negative lead needs to be only long enough to get to the nearest part of the structure.

The resistors don't need to be close to the LEDs as long as you can run a wire between the resistor and the LED. You can hide the resistors in all sorts of places. 38 ga magnet wire can be easily hidden against the structure. Just be careful about shorts.

Dave

[HaroldA]

Maybe I should make this question a separate post - but, are there some good books regarding wiring leds and other kinds of electronics as they pertain to model railroading and that also explain the nomenclature and symbols?  I have seen some very good diagrams but I don't have a clue what some of this is telling me.

[JoeinPA]

Harold:

Take a look at the following link. It lists all the common electronic components.

http://web.gps.caltech.edu/~als/IRMS/course-materials/lecture-1---electricity/circuit_symbols.pdf

Joe

[HaroldA]

JoeinPA

Harold:

Take a look at the following link. It lists all the common electronic components.

http://web.gps.caltech.edu/~als/IRMS/course-materials/lecture-1---electricity/circuit_symbols.pdf

Joe

Thanks for the info,  Are there are resources that explain how to wire these things up, make the necessary calculations, develop circuits or other information.  I have tried using resistors and lamps but still managed to burn out the lamp so i am assuming somewhere there is a resource that would help guys like me get started.

[JoeinPA]

Harold:

This link gives some good info on calculating the proper resistance for led circuits. It is directed to DCC decoder applications but the same principles apply to non-DCC applications.

http://www.mrdccu.com/curriculum/Lighting/LED.htm

The are many good references that can be found on the web. Just start Googling various words and phrases and you'll be surprised at the results.

Joe

[mlehman]

HaroldA

SNIP

...are there some good books regarding wiring leds and other kinds of electronics as they pertain to model railroading and that also explain the nomenclature and symbols?  I have seen some very good diagrams but I don't have a clue what some of this is telling me.

A friend of mine has a book out on using LEDs. He covers some pretty exotic apps using those tiny SMD LEDs, but also the basics for both structures and rolling stock:

http://www.quickpicbooks.com/MMR/Electric/SMLED_1/SMLED_Book.html

[HaroldA]

Joe and Mike

 

Thanks - I know there are resources and these will help.

[GGOOLER]

here is a good calculator for designing led

just add the info and it will draw the circuit for you to see.

http://led.linear1.org/led.wiz

later

g