I am burning out LED's right and left

[Mister Bill]

This is my first rodeo with LED’s.
I am trying to luminate an LED from my DC track with wheel wipers. I guess the voltage could be 6 to 12.
I bought a package of Miniatronics Yeloglo White 3 mm LED’s, and after burning out the first one (used the 270resistor), the second one worked fine and is in use (used the 470 resistor).
I tried to build two more using the same procedure and promptly burned out the LED each time.
I was holding the resistor in my bare hand and it might have taken 20 seconds to fiddle with the solder so I got asolid connection. Could I have burned out the resistor with 15-20 seconds ofheat?
My soldering iron is 18 watts.
On the good one, I cut the long leg ofthe LED. On the ones that burned out, I did not cut the long leg.
Does it matter which end of the resistor is soldered to the long leg?
Does it matter which LED leg the resistor is soldered to?

I appreciate all of your advice, but this came as a kit, so I though that the resistor selection should have been thought out by the manufacturer.

Bill

 

[Iron Horseman]

I am trying to luminate an LED from my DC track with wheel wipers. I guess the voltage could be 6 to 12.

Sounds about right if there is a locomotive or other load on the track. If it is "no load" power (no loco on the track) the voltage could go as high as 18V.

after burning out the first one (used the 270resistor), the second one worked fine and is in use (used the 470 resistor).

Even 470 ohms sounds a bit low to me. I'm thinking 680 ohms minimum, 1K a lot safer.

I tried to build two more using the same procedure and promptly burned out the LED each time.

As above I think you got lucky with the 470. Increase the value.

I was holding the resistor in my bare hand and it might have taken 20 seconds to fiddle with the solder so I got asolid connection. Could I have burned out the resistor with 15-20 seconds ofheat?

That is always a possibility. Heat is the enemy of all electronic components.

On the good one, I cut the long leg off the LED. On the ones that burned out, I did not cut the long leg. Does it matter which end of the resistor is soldered to the long leg?

no

Does it matter which LED leg the resistor is soldered to?

no

But having said all that. How do you know they are burnt out? Since this is a DC layout are you certain you have the polarity correct? An LED will not light when the power is reversed.

 

[MikeOwnby]

I was holding the resistor in my bare hand and it might have taken 20 seconds to fiddle with the solder so I got asolid connection. Could I have burned out the resistor with 15-20 seconds ofheat?

Bill

Actually, you may very well have also burned out the LED if you applied heat that long. I get nervous if my solder joint isn't done within 2 seconds, though that's just me being overly cautious. If I don't get it joined fairly quickly, I make sure to let it cool completely before trying again.

 

[gregc]

if your not sure about the resistor value, I would use clip leads (or something temporary), to connect the resistor to the LED and then a lead connecting the resistor to power and a 3rd lead connecting the LED to the other side of power. (doesn't matter which LED lead is used).

start with a larger value (1k) and then try smaller values. if nothing works, try reversing the power leads. This should be a quick and easy way to determine the polarity and resistor value for the brightness you want.


when I solder, I "tin" (solder the lead "to be" soldered) each lead separately. So one LED lead and one resistor lead. I then clamp the LED into something (a 3rd hand or small vice) and then holding the resistor with both "tinned" leads together, I heat both together and remove the soldering tip, holding the still while the solder cools. Once tinned, you don't need to add solder when heated together.

 

[Rico]

One more thing to consider is that once installed the LED will only light with the power in one direction.
I once put one in a DC loco backwards and couldn't figure out at first why it lit in reverse but not forward.

 

[Mister Bill]

Thanks, guys, problem solved.
I was the problem.
I put my last LED in a clamp and touchedthe iron to it for about ¾ of a second and got a good bond instead of trying todo it with my fingers.
I was applying too much heat for toolong and burning things out.
I now have a nicely lighted tender.

Bill

 

[Railrunner130]

When I first started using LEDs, I bought some off Ebay that came with a tutorial and resistors. I knew I was paying extra, but figured I could justify it because I was learning and this would hopefully save me $$ in the long run.

The tutorial contradicted what Iron Horseman answered to the long end of the LED. It stated that the resistor must be connected to the long end of the LED. I don't know if it really matters, but I haven't blown an LED yet. (knock on wood)

As for the resistors, I think it came with 485 ohm resistors or something close to that. A single resistor is bright, so it may not only save bulb life but may be more prototypical to add another resistor to tone it down.

 

[Mister Bill]

Railrunner,

Do you mean I just tack on a second below the first one?

Thanks for the advice. Yes, it is a little bright but better than my old incandescents (sp).

Bill

 

[goscrewyourselves]

Every instruction I have read regarding LED's + Resistors have stated that the resistor must be connected to the long leg (+ leg) of the LED. As said, that is what the directions have stated and I am yet to burn out an LED. Almost all the LED's I have attached have been attached using 470 ohm resistors attached to the long leg of the LED without an issue.

With regards the heating of the LED/Resistor when connecting them, I have always tinned both the LED leg and Resistor and have applied heat to both prior to applying the solder. I never really paid any attention to how long I heated the resistor ends or the LED legs but I know, without any hesitation it was a lot longer than just a few seconds. I do admit that I dipped the ends of the resistors and legs of the LED's in Flux first, so perhaps that may have prevented any potential heat damage.

Like rail runner said, you can ADD additional resistors if you find that one is not enough to "dim" the brightness of the light. Essentially, you could join 2, 3 or more 470 ohm resistors (for example) end to end. Or, you could add a combination of resistor values together as well. For example, if you use a single 470 ohm resistor and feel that the light is still a little bright, you could add a 270 ohm resistor to soften it a bit more and so forth. The only thing that will do is add more resistance which, in turn, will reduce the brightness of the light.

One thing you might consider is using 1 470 ohm resistor then adding a second if you think the light is too bright. If 2 470 ohm resistors make the light too dull, remove one of the 470 ohm resistors and replace it with something about the size and look at the light again. Although it is trial and error, you can work out the best size resistor to use.

 

[gregc]

The tutorial contradicted what Iron Horseman answered to the long end of the LED. It stated that the resistor must be connected to the long end of the LED. I don't know if it really matters, but I haven't blown an LED yet. (knock on wood)

it doesn't matter which lead of the LED the resistor is on. It's not like pressure builds up on one side and is less on the other.

if you're not sure, use some clip leads and try connecting the resistor to both sides of the LED. you'll see it works the same either way.

 

[Mister Bill]

Tony and Railrunner and all,
You guys are great.
I added another 270 resistor, and it toned the bright light down nicely.

I live in a small town and just don't have access to good information like that.

A week ago, I did not know a dang thing about resistors. I have watched some you tu.be, but you all are better.

Bill

 

[goscrewyourselves]

Bill,

Great news, glad you got it sorted out to a brightness you like. From now on, instead of buying 470 and 270 ohm resistors, you'll only have to buy single 780 ohm resistors which'll make less work for you in the long run.

Now, just to complicate things a little for you (which is so much fun for us) the light in your structures can be "seem" brighter or duller depending on the structure. In other words, using a 780 ohm resistor (for example) might look as you want it to in some structures but in others will be too much resistance giving the appearance of a duller light.

So now you are thinking "oh crap" - it isn't that bad. Of all the structures I have on my HO layout, there is only one or two that I have had reduce the resistor size to get a similar light appearance to all those structures that I have used 470 ohm resistors in.

The thing is, while a 780 ohm gives the light effect you like, it may not always do that depending on the structure. I will bet my bottom dollar though that if you light 20 structures, only on of them might look a little different to the others.

 

[josephbw]

One thing I used to do back when I was building electronic projects, was to use a potentiometer. I would hook the power to the pot, then hook the pot to the LED or light. Start out low and adjust the pot until you get the illumination you desire. Then disconnect the pot without changing the knob, and measure the resistance. Find the closest resistor to that reading, or combine resistors, and proceed with the project.

Joe