# Ditch Lights for SD40-2's



## TheFishGuy (Feb 1, 2011)

Hi all, I'm looking for suggestions on what size LED lights to use and how exactly to wire them... Meaning what diode to use.

eBay has a seller selling 5mm lights. That seems to be a good size... 

 I could care less if they're directional, as far as I'm concerned they can come on when the cab light comes on.

I use track power. 

I'm not an electronics expert but I'm also not a complete noobie either. lol

Thanks in advance!
Jonathan


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## TheFishGuy (Feb 1, 2011)

Here's some info on the lights I'm considering...

Brand: Everest.
Size: 5mm Led, The wire about 30cm(L).<LI style="MARGIN: 0in 0in 0pt"> Forward voltage:12V~18V(1000 Ohm resistor in series), AC or DC Compatible.​ Forward current (typ/max): 20mA/30mA.​Light Color: Warm White.<LI style="MARGIN: 0in 0in 0pt"> Package Included: 20 Pre-Wired leds.​ ​ ​ Not too clear on these specs:​ Forward voltage:12V~18V(1000 Ohm resistor in series), AC or DC Compatible.​ Forward current (typ/max): 20mA/30mA.​ Think they'll work?​


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## ewarhol (Mar 3, 2014)

Jonathan-

Are you looking to have the ditch lights on top of the walkway or below?What is your track power rated at? 

5 mm is a pretty big LED. How comfortable with a soldering iron are you? I use 0603 warm white LED's I purchased off of eBay. Very small and fit into places very well. Use magnet wire for hookup with the small LED's. 

Here's a link to a thread I started with a SD40-2 I'm working on. http://forums.mylargescale.com/15-model-making/43890-latest-project-upgrading-usat-sd40-2-a-2.html Post number 11 has info on the LED's I used. There's also a link to my Flickr page that has a video of the LED's in action. The 0603 LED's were used in the beacon, ditch lights, and step lights. The LED's from DigiKey I mentioned are part number CLM3C-MKW-CWAXB233CT-ND hookup wire for these can be 30 AWG.


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## Paul Burch (Jan 2, 2008)

1/29 ditch light castings from Ozark with 3mm warm white or yelo-glow leds. Done it many times.
http://www.ozarkminiatures.com/scripts/prodView.asp?idproduct=732


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## TheFishGuy (Feb 1, 2011)

I'm neither here nor there on the placement of the ditch lights... I suppose I edge a little towards having them on the walkway in little boxes...

My track power is a 10 amp train engineer from Aristocraft. It's old lol

I'm decent with a solder gun, I've got a very nice one from snap on. 

I like to tinker but I'll check out the link


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## ewarhol (Mar 3, 2014)

What wattage is your soldering iron rated at? Mine is 25w and is a little to strong at times for the small 0603 LEDs. I end up ruining some of the LED leads. Considering a 15w iron for some of the delicate electronic components. 

As far as the verbage you're not clear on. Forward voltage is the voltage it takes to light the LED. LEDs are typically around 3 forward volts. The ones you're looking at must include resistors. The 12-18 volts is the range it takes to light them. Below 12 volts they'll be dim or won't light, above 18v and you could damage them. 

mA stand for milliamps. This can be seen as 20mA or .02A. Again most LEDs are around 20ma.

I'm not familiar with the Aristocraft 10amp system. Is it a variable DC output?

Also are you familiar with Ohm's law and how to figure out your resistor value?


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## TheFishGuy (Feb 1, 2011)

Ok, I'm going to do my best to answer these questions lol 1, my solder gun is actually a butane torch with a very fine tip, it's really very awesome for tight spots and heats solder almost instantly! I'm good with it so I'm not worried about ruining anything lol

The trains are powered through the track with a walk around remote, I would assume 12v variable DC. The system can be used with HO trains too, which is what I'm familiar with... These are just three times the size! Lol

Here's an example of what I'm planning on getting off eBay: http://pages.ebay.com/link/?nav=item.view&alt=web&id=111113229078 

I want to get some 10mm and 5mm. But don't know what resistors to get in order to get them to light?? I'd like to go through my insane roster of engines and change out the head lights to make them as bright as possible to actually light up the track. I work a lot so train running happens at night most of the time...

I thought I'd just goto radio shack and get what ever resistors were applicable but have no clue where to begin...

Now... I do have what we call FankenEngine created from spare parts and some LEDs out of smoke detectors for directional lighting and I did get a handful of 10mm LEDs from eBay a while ago to use for headlights. I've got a video on YouTube of it. I stole the resistors out of the mother boards of the old smoke detectors to get them to light up! I just used the resistors that were in line to the LEDs I stole off the detectors motherboard... But obviously have no clue what they are? Are they color coded? I notice that resistors are labeled on motherboards and they also have stripes of different colors on them... WAY confusing... 

I'll try and post a link to FrankenEngines video...


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## TheFishGuy (Feb 1, 2011)

Hope the link works


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## TheFishGuy (Feb 1, 2011)

Awesome! It worked! Now to find the correct resistors for the rest of my engines! Help! LOL


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## ewarhol (Mar 3, 2014)

Welcome to Resistors 101 

Resistors are measured in ohms. The higher the resistor value the more resistance meaning the dimmer the LED/Bulb. Like wise it is also flip flopped; the lower the resistor value, the less resistance, means the LED/Bulb will be brighter.

The colors on the resistors help to identify the value of the resistor. I attached a photo of the back of resistor pack from RadioShack. Lets go over an example of a common resistor for LEDs, 470 ohms. The colors for this are Yellow, Violet, Brown. 

So, using the package the first band is yellow which has a number of 4. The next band is Violet which has a number of 7. The third number is brown which has a number of x10. So put the first and second band together and you get 47. Then take 47 and multiple it by the third band, so 47x10= 470 ohms. 









The fourth color is usually gold, sometimes silver. This is the tolerance of the resistor. I usually use gold band resistors at 5%.

Now we'll switch to Resistor 102, figuring out the value you need. 

This is where Ohm's law comes into play. R=V/I R=Resistance, V= Voltage Difference, I= Amps. Follow along as we figure out the Resistance. I'll be using your track power and LED's. 
R= (12-3.2)/.02 12 is the track voltage, 3.2 is the forward voltage of the LED and .02 is the amps for the LED.

R= 8.8/.02
R= 440 So a 440 ohm resistor is needed. Closest you'll probably find at Radio Shack is 470 ohms. Remember to go higher with a resistor value not lower. If you use a resistor below 440 you could damage the LED.

Now, to figure out what wattage of resistor is needed. This is W=V*I

W= (12-3.2)*.02
W=8.8*.02
W=.176 So a 1/4 watt resistor (.250) would be fine. If you were close to .250 or higher then you need a 1/2 watt resistor, .500. RadioShack sells both 1/4 watt and 1/2 watt resistors.

Hope this helps.


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## TheFishGuy (Feb 1, 2011)

WOW Eric!! That was brilliant! thank you! Now I need to print out your post and pretend I'm in school and study it like my life depended on it! Thank you! Thank you! Thank you!


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## ewarhol (Mar 3, 2014)

TheFishGuy said:


> WOW Eric!! That was brilliant! thank you! Now I need to print out your post and pretend I'm in school and study it like my life depended on it! Thank you! Thank you! Thank you!


LOL

Forgot to mention that each LED should have a resistor. Hook it up to the Cathode (negative) side.


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## Paul Burch (Jan 2, 2008)

There are several websites with led calculators. Just search it. Here is one.
http://ledcalc.com/


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## Greg Elmassian (Jan 3, 2008)

Can't say I like that calculator, it recommended a 1/4 watt resistor up to 224 milliwatts... common rule of thumb is double the real wattage...

I can tell you a 1/4 watt resistor at .224 watts will MELT plastic.

Greg


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## TheFishGuy (Feb 1, 2011)

I know I could have googled all of this and found the information I need but I'd much rather someone explain it to me like they have, with experience...

Greatest part is after a little more looking around on ebay I've found pre-wired lights with the resistors ready to go for my trains! lol but I'm glad I've learned something and am thankful for that and this forum and the people on it and their experience along with the willingness to share it. This forum is great, better than any "fish" forum I've been on.


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## TheFishGuy (Feb 1, 2011)

Well, I ended up getting a bunch of 3mm pre-wired LEDs and am slowly changing out all the headlights in the entire rostor. I'm also adding ditch lights to all of the engines lol here's a video of my GP9

https://m.youtube.com/watch?v=d7y0n5wQq7I&feature=em-upload_owner


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