# LED's & resistors....



## breezy8 (Jun 21, 2012)

Folks, Sound tracks instalation guide suggests 680 ohem resistors for LED's. The package of LED's I have say 10-16 volt system uses a 470 ohem resistor....My question is....which would be the right one to use..??? I am not an electronics type guy...LOL...


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## alman (Oct 22, 2012)

*Led resistor calculator*

Google ... 
LED Resistor Calculator


Sorry I don't know how to send the link.


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## NIMT (Jan 6, 2011)

I don't bother with any of the calculations I just use 1K ohm 1/8 watt.


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## Guest (Dec 1, 2012)

1K works. So does 500 ohms. LED's don't really care about the voltage as much as current.
You'll spend a lot of time calculating, ordering, and installing, when you just plop in a 500 or 1K.
I ordered out a bunch of 600 somethings years ago for a conversion job, still have a bunch.
I have an LED tester, adds resistance in stages (where you plug them in), and you won't really see any discernible difference in brightness over a huge span of resistances.
Dave


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## alman (Oct 22, 2012)

ScaleCraft said:


> 1K works. So does 500 ohms. LED's don't really care about the voltage as much as current.
> You'll spend a lot of time calculating, ordering, and installing, when you just plop in a 500 or 1K.
> I ordered out a bunch of 600 somethings years ago for a conversion job, still have a bunch.
> I have an LED tester, adds resistance in stages (where you plug them in), and you won't really see any discernible difference in brightness over a huge span of resistances.
> Dave




I M O, if you want your LEDs to work properly and last.

Then use the calculator.

Just because something works , does not mean it works as intended.

But then what do I know , I"m just an old curmudgeon. :retard:


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## breezy8 (Jun 21, 2012)

Thanks guys, I will try to figure out the values and calculate the resistor......or just drop in a 680....Thanks for the calculator link......


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## gunrunnerjohn (Nov 10, 2010)

I'm like Sean, I just wing it for resistors. Typically, I use higher values for markers because they shouldn't be as bright, then lower values for headlights for higher intensity. 

Rule of thumb for most common LED's, you need a minimum of 50 ohms per volt of power to be dropped. So, if you have 12 volts DC and a white LED, you need to drop 9 volts, that would be a minimum value of 450 to run the LED at maximum intensity. Fortunately, there is a standard value, 470 ohms that is readily available. You can go up from there to reduce the light output.


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## NIMT (Jan 6, 2011)

I have been known to use up to 5k ohm resistor to dim down an LED.


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## T-Man (May 16, 2008)

The calculator gives a value but the parts have some play. The numbers are just average values to caclulate. When a resistor or LED is made the values have a percentage of accuracy. There is a margin of safety built in. I would say 470 is the lowest. You may not see a difference until you use a 1000 ohms. You will not ruin anything by going higher except for the brightness.

That is the best layman's description I have.


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## gunrunnerjohn (Nov 10, 2010)

NIMT said:


> I have been known to use up to 5k ohm resistor to dim down an LED.


I have some markers with 12V on them and a 4.7k resistor, so I'm close.


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## mackdonn (Sep 26, 2012)

To throw my 2 cents in....I just bought a Walthers Cornerstone Lighted Station Platform and it comes with LED's. They also included 750 ohm, 1/4 watt resistors and 1amp, 50 PIV diodes with instructions "not to exceed 6-18 volts AC or DC or damage to the LED's and/or circuit will occur" if this info helps in figuring out what resistors to use.......


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## gunrunnerjohn (Nov 10, 2010)

If you have AC, you need diodes to protect the LED against reverse voltage. If you're running on single polarity DC, no diodes needed, just current limiting resistors.


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## Guest (Dec 2, 2012)

alman said:


> I M O, if you want your LEDs to work properly and last.
> 
> Then use the calculator.
> 
> ...


Oh, ya know, I started out in electronics in....1964? maybe. Done a lot with pushing 'trons around. Funny how some folks get hung up on doing all them calculations.
I suppose, thinking back, the only LED I ever popped was trying to get a POS Bachmann yeller LED bright enough. I think I got down to 20 ohms before it popped.
Most of what you get is LEDs from PRC, and they're gonna die long before 7.2 ohms of improper current limiting will do any harm.
But, we can scare the newbies with boogeymen and horror stories, so they figure the exact resistor, order out a dozen, pay 10 times what they cost for shipping, keep 10 around for 5 years before they throw them out...'cause you couldn't use those with the NEW LEDs ya got that require 26 MORE ohms by the precise calculations......

Tell me about the old curmudgeon retard bit...sounds interesting


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## Guest (Dec 2, 2012)

NIMT said:


> I have been known to use up to 5k ohm resistor to dim down an LED.


I had to think about that one for a bit.
And, I concluded, never, as in ever, did a customer ask me to dim his LED for him.
Yeah, I could, and have to show how it's done....but never had it asked of me.

Brighter? All the time, in which case I plop in a GOR or GOW.
When we run night ops outdoors, like now, when it's really dark, you don't want a 2CP marker light. You want to make sure the bozo coming up behind you actually sees them.

Dave


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## alman (Oct 22, 2012)

ScaleCraft said:


> Oh, ya know, I started out in electronics in....1964? maybe. Done a lot with pushing 'trons around. Funny how some folks get hung up on doing all them calculations.
> I suppose, thinking back, the only LED I ever popped was trying to get a POS Bachmann yeller LED bright enough. I think I got down to 20 ohms before it popped.
> Most of what you get is LEDs from PRC, and they're gonna die long before 7.2 ohms of improper current limiting will do any harm.
> But, we can scare the newbies with boogeymen and horror stories, so they figure the exact resistor, order out a dozen, pay 10 times what they cost for shipping, keep 10 around for 5 years before they throw them out...'cause you couldn't use those with the NEW LEDs ya got that require 26 MORE ohms by the precise calculations......
> ...






I am a self confessed old curmudgeon , because I am 70 soon to be 71 
(Dec 24).
I am retired but still maintain my electricians licences.

The reason I was trying to promote the use of the LED / RESISTOR CALCULATOR is.... for a novice, it may save a few burnt LEDs.

Retarded!!! Not yet. Just Retired!

I have always been old school, I guess, therefore, if there is a tool that can be used to make the job easier , then why not use it !!!

What's to lose ??? (not Lautrec) :laugh:


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## gunrunnerjohn (Nov 10, 2010)

You can use a calculator, but I can assure you if you follow the simple guideline I posted of 50 ohms per volt, you won't kill LED's because of overcurrent. Remember, there are other hazards to LED's, specifically excess reverse voltage, which requires diode protection in addition to the proper resistor.

Using more than 50 ohms per volt will most certainly not harm the LED's, it just makes them dimmer.

This advice applies to almost all generic LED's that have a maximum current rating of 20ma. Another important thing to keep in mind is most colored LED, like red, yellow, or green operate at 1.5 volts typically, and white or blue LED's normally have a 3.0 volt operating voltage. You can also string LED's in series to minimize the number of resistors required if you have multiple LED's to power from the same power source.

I'm old school too, and truthfully, figuring out that to drop 9 volts for my LED I have to multiply 9 * 50 just isn't that difficult for me.


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## Guest (Dec 2, 2012)

alman said:


> Retarded!!! Not yet. Just Retired!
> 
> 
> (not Lautrec) :laugh:


Funny....when you reply and quote, that emoticon you used doesn't show as an emoticon, rather just as I quoted....it says "retard".
Go look.....apparently we have some names for our emoticons that aren't pretty!


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## gunrunnerjohn (Nov 10, 2010)

ScaleCraft said:


> Funny....when you reply and quote, that emoticon you used doesn't show as an emoticon, rather just as I quoted....it says "retard".
> Go look.....apparently we have some names for our emoticons that aren't pretty!


I think it fits the emoticon that was quoted, go look at the original... :retard:


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## Guest (Dec 2, 2012)

Looked like someone with Bell's Palsy to me.


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## NIMT (Jan 6, 2011)

ScaleCraft said:


> I had to think about that one for a bit.
> And, I concluded, never, as in ever, did a customer ask me to dim his LED for him.


Well I've been doing installs for over 15 years and running an LED at full brightness in all situation would not work for me or my customers.
I don't want to make cab fryers out of my installs. 1940's engines didn't come with halagen or HID headlamps, so running them at full intensity would not look right either.
I can't see a 1857 steamer running a headlight at full "electric" intensity.
They also need to have the right color for the headlight and the marker lights. Most just use standard LED's that are way too blue to be anywhere close to right!


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## breezy8 (Jun 21, 2012)

Thanks guys, Great info......I will remember the 9 x 50 formula....I am going to model 1960 and back....steam to diesel period....so I am using the "yeloglo white" LED's Their package says 470 ohm resistors....Guess I will try that.....Again, thanks for all the info....


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## Guest (Dec 3, 2012)

NIMT said:


> Well I've been doing installs for over 15 years and running an LED at full brightness in all situation would not work for me or my customers.
> I don't want to make cab fryers out of my installs. 1940's engines didn't come with halagen or HID headlamps, so running them at full intensity would not look right either.
> I can't see a 1857 steamer running a headlight at full "electric" intensity.
> They also need to have the right color for the headlight and the marker lights. Most just use standard LED's that are way too blue to be anywhere close to right!


I never, as in ever use LED's for headlights on older engines. Unless oil fired lights, they came with incandescents, and that's all I use.
As far as cab lights, that's really a joke. When moving at night, they NEVER had a cab light on....it would blind them.
Most folks who know that have NO cab light.
1857 steamers.....only time I'd use one of the cheap Bachmann yellow LED's.
Since I don't do modern stuff......the joke always was the 1960's Bach 45 tonner with arc weld blue LED's.
Our engines with incandescents....you can see the railroad, read your waybill, see the switches and cars....and we've run through 5 major power outtages.


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## NIMT (Jan 6, 2011)

Well people that use DC are limited to having things on all the time.
I on the other hand I do DCC installs and have the ability to shut off the lights when I want to.


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## gunrunnerjohn (Nov 10, 2010)

I have actually built myself a small circuit that senses the motor voltage so that I can turn the cab lights on when the locomotive is stopped. I use the same circuit to turn on smoke units only when the locomotive is running. As far as using LED's for headlights, I use warm white for diesels and either warm white or yellow for steamers.


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## NIMT (Jan 6, 2011)

Excellent work around John!:thumbsup::thumbsup:


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## gunrunnerjohn (Nov 10, 2010)

The circuit was created initially to turn off the fan driven smoke on a little Dockside switcher I have, there wasn't a separate smoke output from the little TMCC board. So, when I'd stop on the tracks, the sucker would just smoke you out of the room! 

After I created the circuit, I realized that I could just reverse the function and use it to control cab lights. It's basically a bridge rectifier and an opto-isolator in the simplest form, for smoke units I added a small relay to control the power. Isolation is required as you can not depend on any ground reference for the motor power.

For cab lights, I use it to short out the LED with the open-collector opto when the motor is running, hence turning off the light. As long as the dropping resistor is properly sized, it just uses a few more mills while running, and us O-gauge guys don't notice that kind of power draw.


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## mgwsy (Aug 14, 2012)

I usually stick with a 1K resistor for LEDs.


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## gunrunnerjohn (Nov 10, 2010)

mgwsy said:


> I usually stick with a 1K resistor for LEDs.


I vary the value, depending on the effect I wish to accomplish.  Bright = lower value, dim = higher value.


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