LED Ditch Lights for the FVM GP60M

[craigolio1]

I get cool white 0402 LEDs from eBay. Then I tiny them with clear orange Tamiya paint. Works great. Soldering them is difficult but not impossible. That double alligator clip think you see on the photos is a soldering helping hand old by Ngineering. That's worth the purchase.  But the LEDs from eBay are the way to go for sure.

The insulation on the wires is actually an epoxy coating it can be scratched off with a knife or it will come off by simply touching a glob of hot solder to it, which tins it at the same time. No further insulation is required. As you saw in the tutorial the soldering connections need to be insulated but that's normal. I've always used liquid electrical tape but now I see yet another application for Tacky Glue. I have to get some of that.

Craig.

[wazzou]

I model an era prior to the use of ditch lights Jim but I wanted to thank you for taking the time to compile this tutorial for the benefit of others.

[jereising]

Thanks for the comments, folks. 

I used Ngineering because I wanted to spend the time working on the locos, not sourcing LEDs.  I know they are substantially more expensive but am willing to pay for the convenience of knowing exactly what I will get and when I will get them.  And the eBay references are for 0604s, what I use are 0203s.  Size matters.

I may be retired, but my layout time is precious to me (and never enough) what with honeydos and generally life outside the layout.

Daryl, see my reply to Bill on page 1.  Although the decoder is capable of two functions, hence flashing ditch lights, BNSF doesn't do flashing.

Working on a couple of Swooshes now...

[JanesCustomTrain]

And the eBay references are for 0604s, what I use are 0203s.  Size matters.

Fair enough but they are 0402 (no such thing as 0203). For others, do a ebay search for 0402 warm white and the results will be similar, yes also with wires already on.

Jane

[Mark W]

...I wanted to spend the time working on the locos...
...my layout time is precious to me (and never enough)...

The two greatest arguments for not trying to solder your own micro LEDs. 

Here they are, 8 bucks cheaper for twice as many LEDs, pre-wired so you can complete the project in 1/10th the time. 
http://www.ebay.com/itm/T0402WM-20pcs-Pre-soldered-micro-litz-wired-leads-Warm-White-SMD-Led-0402-NEW-/261552594821

Anyways, not trying to undermine your skill in any way.  Excellent project regardless of which LED's are used!

[jereising]

Aw Geez!

They are indeed 0402, me eat crow.  The Ngineering description says they match their 0203 but that was referring to color, not size...

Funny thing, I've gotten real good at soldering those wires on - don't even use magnification anymore.

Thanks for the info and links - all info is good info if you use it correctly

[peteski]

Excellent writeup Jim!

Here is a handy chart of SMD components sizes: http://www.resistorguide.com/resistor-sizes-and-packages/

Actually, the SMD size convention is quite easy.  The 4-digit size name is actually the footprint dimensions of the SMD component. Each 2 digit pair is one of the dimensions (in decimal fraction of the inch). So a 0402 package's footprint is 0.04" X 0.02". 0603 is 0.06" x 0.03".

When one buys a pre-wired LEDs you have no control of how the leads will be soldered to the LED. When you roll your own, you can solder the wires any way you want.

Jim, the only comment I have is that I do not recommend wiring LEDs in parallel before the series current-limiting resistor. While in most cases this will work fine (especially when the LEDs are identical (same manufacturer, same batch), safer way is to have a resistor in series with each LED.  It is safer that way (for the LEDs).  I know that finding room for individual resistors is tough. I often use SMD resistors rather then leaded type. I usually use 0805 SMD resistors (they have power dissipation rating of 1/8 W). Or if needed, I go up to 1206 size (1/4 W).  Either one is much easier to conceal than small leaded resistors.

[Mark W]

Either one is much easier to conceal than small leaded resistors.

I beg to differ! 

[peteski]

I beg to differ! 

A 470 ohm resistor current-limiting disguised as an air tank?!  Very clever! I like it!   

[jagged ben]

Jim, the only comment I have is that I do not recommend wiring LEDs in parallel before the series current-limiting resistor. While in most cases this will work fine (especially when the LEDs are identical (same manufacturer, same batch), safer way is to have a resistor in series with each LED.  It is safer that way (for the LEDs). 

If the resistor only limits current to the max for two LEDs, then it's not a good idea.  But if the resistor would protect one LED by itself, then it probably doesn't matter so much.

[peteski]

If the resistor only limits current to the max for two LEDs, then it's not a good idea.  But if the resistor would protect one LED by itself, then it probably doesn't matter so much.

Ideally, each LED (or series-connected string of LEDs) should have its own series-connected current limiting resistor.  In this writeup I see both ditch light LEDs hooked up in parallel, then a single resistor is wired with those parallel-connected LEDs.  If the LEDs are identical then this will work as expected (each LED will pass 1/2 of the current going through the resistor. But if the LEDs aren't identical, one burns out or gets disconnected, then the single remaining LED will pass the full current (roughly twice the current of when both LEDs were functioning properly).

[craigolio1]

I usually go oversize for resisters, to keep the power draw/heat down, so in my case if one of my LEDs failed the remaining LED would still not draw more than the recommended amount of current, as long as I chose a large enough resister in the first place, correct?

I know that's very vague but the logic stands correct?

Craig

[peteski]

I usually go oversize for resisters, to keep the power draw/heat down, so in my case if one of my LEDs failed the remaining LED would still not draw more than the recommended amount of current, as long as I chose a large enough resister in the first place, correct?

I know that's very vague but the logic stands correct?

Craig

Yes, you're correct.  If the absolute maximum forward current of the LED is 20mA and you chose a resistor which passes 10mA of current total (5 mA through each parallel-connected LED), then if one LED is disconnected the total current going through the remaining LED will only be around 10mA.  Still safe, but much brighter than in its original configuration.

I guess I'm just a stickler for adhering to the best-practice rules of powering LEDs.

[jereising]

And here's the last of them.  A very enjoyable project.

[Seligman Sub]

Looks great!  Is it just me or did FVM correct the yellow striping on the swoosh scheme locos? I have early run GEVO swooshes and I know people complain about the dark orange but to me it's the yellow stripping that looks the worst on those.  These look correct to my eye but it is a photo.  Either way great job!