Is color of LED dependent on voltage?

When up apply to much voltage to and LED it will change color to blue/purple. So from what you state, you killed that one LED. I believe you must put resistors on all the outputs for that decoder.

Can we get more information Ed Kelly?  Like what manufacturer is the loco made by?  Is this decoder install being done by you?, etc?

Somewhat agreeing with Bruk.  Generally, any LED will need to have dropping resistors wired in line with the lighting function outputs of the decoder.  If you don't do this, the LEDs will light once, but only for a very brief moment.  After that, they are burned out.  I have seen diesel locos from Atlas O (2-Rail) where the headlight and backup light were 1.5 volt light bulbs and the marker/class lights were red colored LEDs.  The only way to know for sure is to remove the shell and verify.  I'm not understanding the different colors you are reporting.  You may have bi-colored LEDs.  I'm not entirely sure how these bi-color LEDs work--the color change may be done through polarity switching.

Let us know what you find out.

Kindest Regards,

Brian Huang

Bruk, Brian, et al,

The model is a 45+/- year old brass steam engine.  The DCC was installed by a knowledgeable friend.

The LEDs still light but with a green and blue color and not warm white which is what they should be.

Is the color dependent on the voltage?  if I change the resistor, which I will have to buy an assortment of, will that give me the warm white I am looking for?

BTW, what resistors should I buy?  What LEDs should I buy?  Please be specific.

Thanks,

Ed

I have heard that bi-color LEDs work by changing the polarity.   I think I have seen some that have 3 leads also  and you power one or the other to get a color.

But I have never seen  what you describe.    You need to talk to  your knowledgable friend since he put the stuff in.   He should be able to tell what they are and how they work.    I assume he has done this before and might know how to fix it.

Ed Kelly:  Since you are using the Soundtraxx TSU-4400 you should be able to use 1000 Ohm resistors with the LEDs.  The FX3 function outputs for lighting effects will put out 12 volts.  As for LEDs, probably either 3mm or 5mm diameter, white or golden-white in color for the headlight/backup light.  If the model has class lights probably go with the same colors.

Personally, I'd go with the larger diameter LEDs it they fit.

@Ed Kelly posted:

Is the color dependent on the voltage?  if I change the resistor, which I will have to buy an assortment of, will that give me the warm white I am looking for?

The short answer is no.  All that adding current (LED's are current mode devices), will do is make them brighter.  Now, you may seem to see a slightly different shade of whatever color the LED is based on the current through the LED, but it won't change colors.  The material that the LED is made from determines the color, not the current flowing through it.

Obviously, if you really put way too much current through them, you'll briefly see white or maybe even blue as they burn up!

Obviously, if you really put way too much current through them, you'll briefly see white or maybe even blue as they burn up!

Gunrunner, mine seem to get a really nice deep yellowish red before they wink out!!  

As to the size, I prefer the 1.8 mm as it looks like a bulb.

Peter

There are two lead LED's that are bi-color,  bi-polar.

Reverse the polarity, change color.

@Peter E B posted:

Gunrunner, mine seem to get a really nice deep yellowish red before they wink out!!

Yep, I don't certify the color of the flames as you over-drive your LED's, only that you'll get flames!

@Mike CT posted:

There are two lead LED's that are bi-color,  bi-polar.

Reverse the polarity, change color.

FWIW, the multi-colored LED's also have multiple light emitting diodes, one for each color.  Any given light emitting diode is only designed to emit one color of light.

Mike, there are also all kinds of multi-color LED packages, you can also get them that blink, change colors automatically, and flicker, just to name a few.

Normal operating currents generally produce insignificant changes in the perceived color of a white LED, easily confirmed by examining the manufacturer's data sheet (if available.) Changing the current limit resistor will not help.

I have found that many so-called warm white LEDs produce a greenish color cast, especially when not viewed straight-on. This was particularly true for pre-wired warm white 0402 LEDs I procured from Amazon. The solution for this is a better quality LED or, at times, applying a thin coat of transparent orange paint such as Tamiya.

White LEDs come in a wide range of color temperatures. Buying one that claims to be "warm white" might mean any color temperature from 2400K to 3500K, (the latter way bluer than we would want for any lamp on a steam engine.) I purchase my LEDs from industrial electronic suppliers such as Digikey and Mouser, because then I can order specific color temperatures such as 2700K which is appropriate for an 100 watt incandescent lamp.

I recently discovered that some 1206 package chip LEDs have an orange-yellow silicone window that can be instantly damaged by certain chemicals including ACC. After gluing one to a piece of 0.010" white styrene for a diesel number board I was surprised that it turned blue. So I wired another LED to my tester at 6 mA. It was a nice incandescent color, rated at 2700K. While viewing the LED I applied a dab of ACC to the window of the LED and it instantly turned bluish, more of a daylight color.

One chip LED I tested with ACC was a Lumileds L130-2790001400001 procured from Digikey. Lumileds published an assembly and handling application note which enumerates a non-exhaustive list of chemicals that will damage the silicone window. Included in the list is rosin flux, although it doesn't mention ACC specifically. After reading the note I switched to 0.015" diameter solder with no-clean flux cores. I'm experimenting with UV cure glues, although the jury is still out.

Also important for those who want to wire their own chip LEDs is that many have shifted from ceramic to plastic packages for cost reduction. The plastic melts at normal hand soldering temperatures such as 650F. I found that to be successful I needed a temperature-regulated iron set to 500F with a needle-sharp, clean tip. A variable-power iron would melt them. This temperature is the peak recommended for reflow soldering. I use thin double-stick tape to hold them to a slab of steel or aluminum; the metal acts as a heat sink during the procedure. Both the wire and LED are pre-tinned so that a joint can be made in about one second.

Regards,

Thanks to all.  I really appreciated the explanations as to what was happening.

Regards,

Ed

@riogrande491 posted:

One chip LED I tested with ACC was a Lumileds L130-2790001400001 procured from Digikey. Lumileds published an assembly and handling application note which enumerates a non-exhaustive list of chemicals that will damage the silicone window. Included in the list is rosin flux, although it doesn't mention ACC specifically. After reading the note I switched to 0.015" diameter solder with no-clean flux cores. I'm experimenting with UV cure glues, although the jury is still out.

Regards,

Thorlabs is a vendor of optical grade UV adhesive.

https://www.thorlabs.com/newgr...m?objectgroup_ID=196

Pete

@riogrande491 posted:

Also important for those who want to wire their own chip LEDs is that many have shifted from ceramic to plastic packages for cost reduction. The plastic melts at normal hand soldering temperatures such as 650F. I found that to be successful I needed a temperature-regulated iron set to 500F with a needle-sharp, clean tip. A variable-power iron would melt them. This temperature is the peak recommended for reflow soldering.

FWIW, most SMT packages recommend 260C (500F) maximum temperatures for soldering for a maximum of 10 seconds.  That's why I keep beating the drum for a quality soldering station for any SMT work.

Gunrunnerjohn -

I fully agree with the importance of a reasonable and adjustable temperature regulated soldering iron, good no-clean flux solder, and the right iron tip for the job, the iron temperature adjusted for the job at hand. A reasonable iron isn't very expensive and should last a modeler's lifetime, or until replacement tips are no longer available and those pre-purchased have been exhausted after being properly maintained. There are many expensive models that can be easier to use and have extra features such as automatic temperature set-back to extend tip life, or auto shut off after a period of time.

That said, an iron in a fancy stand with just a knob, instead of a temperature dial, is just a cheap iron hooked up to a light dimmer. Mostly worthless.

I largely agree on temperature, although for soldering most SMT (surface mount package for those unfamiliar) such as 1206 resistors and SOIC chips to circuit boards I've found 650F to work just fine. I never need to heat the part and pad for more than 1 or 2 seconds when they are clean and fluxed, always with eutectic leaded solder. With a clean pad, flux, and a proper chisel tip it is easy to place thin solder 2/3 the width of a 1206 resistor, against the part and pad, slide in, slide out all within a second or two. Nothing gets up to the tip temperature except the far extremities.

For me, today as a hobbyist and no longer a practicing EE, my notable soldering exception is the modern plastic-package chip LED about which I wrote. You are absolutely correct, the standard data sheet specified reflow oven max temp is 260C/500F and dwell time at that temperature 10 seconds max. That's not the temperature profile the all parts can handle, but a standardized temp profile that can solder the weakest parts without massive carnage. During that dwell, there is really very little mechanical stress on a plastic package SMT LED as it floats in two puddles of molten solder paste. But we are hand-soldering, not using a reflow oven.

Back in the day of ceramic packages, I enjoyed using a homemade version of an LED soldering fixture sold by Ngineering. It had two flat tipped copper alligator clips soldered to a bit of sheet brass. One clip held the LED, the other a wire to be attached. I found that pressure from the clip on the sides of a plastic body 1206 LED caused it to "squish" and be destroyed when heat was applied.

Regards!

I'll tell you if you solder the flickering thru-hole LED's with 650F, you are very likely to lose 10-15% of them in the process.  I make a flickering firebox board with four of the flickering LED's on it.  When I was soldering them using 600F, I'd have a consistent failure rate of more than 10% of the LED's.  Once I dropped the temperature to 500F, I haven't lost a single LED in the 40-50 I've soldered onto the modules since.