Strasburg 89 from a Bachmann 2-6-0

[N Scale Train Boy]

What an awesome journey this project has been so far! Just had a great time reading through this thread, can't wait to see more work as it continues! Great work so far Ed!

[Ed Kapuscinski]

The current status as of last night.

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I'm trying to decide if I should grab the decoder out of my BLI NW2 that I converted to loksound but continues to be cursed or just pony up for a new one.

Hmm.

[Ed Kapuscinski]

Newark, DE, right off of Kirkwood

Well no *****.

I didn't realize we had another  in the area!

[Ed Kapuscinski]

It would be nice if I could do one install without blowing up some LEDs.

I got a set of Evan Designs picos for inside the rear headlight. It said they were 3v so I used a 480 resistor.

Apparently they were NOT 3V. And neither was the stock Bachmann one, again even though everything I read said it was.

Replacing the rear one is pretty easy. That front one is gonna be fun though. Ugh.

That said, I loaded up the appropriate sound file, made a ton of tweaks and I'm pretty happy.

[peteski]

It would be nice if I could do one install without blowing up some LEDs.
I got a set of Evan Designs picos for inside the rear headlight. It said they were 3v so I used a 480 resistor.
Apparently they were NOT 3V. And neither was the stock Bachmann one, again even though everything I read said it was.

What exactly does "Apparently they were NOT 3V" mean?  You burned them up?

Ed, LEDs aren't rated for certain voltage (unlike incandescent bulbs). They are designed for certain operating current. They are diodes which develop a voltage drop across their leads and the series-connected resistor is used to control the current flowing through the circuit (and through the LED).  Yes, this sounds complicated, even if it really isn't.

The actual electrical specs for LEDs (not the often-misleading info provided by vendors selling LED to modelers), specify the voltage drop across the LED when it is operating at its nominal current. For white LEDs, that Forward Voltage (Vf) is around 2.8-3.2V (so looking at it from that perspective, 3V is sort of correct).  The resistor value can be calculated using the decoder's "blue" voltage (around 12V), the LED's Vf and the desired LED current (its brightness).

But skipping all this boring technical mumbo-jumbo, using a standard 1k (or 1000 ohm) resistor with white LED powered by a decoder with DCC track voltage 12-14V is usually good safe value.  If you used a 480 ohm resistor you are over-driving that tiny pico LED. How did you arrive at the value of 480 ohms?

[Ed Kapuscinski]

I googled it.
 
I know, I should've done better homework.

[peteski]

I googled it.
 
I know, I should've done better homework.

Um, yeah. Or simply just ask here.
TBH, 1k resistor for use with LEDs is so often mentioned in online DCC installation writeups I'm surprised that Google (or its AI) would have suggested 480 ohms.

[Ed Kapuscinski]

Um, yeah. Or simply just ask here.
TBH, 1k resistor for use with LEDs is so often mentioned in online DCC installation writeups I'm surprised that Google (or its AI) would have suggested 480 ohms.

Right? I've always used 1K but I'm used to dealing with 1.5V LEDs (or so I thought). So I figured the 480 roughly made sense.

Oh well, live and learn. And the fun is in the doing, right?? Right? lol

[Maletrain]

Or, you could just buy a variable resistor and start at high ohms and turn it down until you find the brightness you like for the specific application, then measure the resistance value the variable is set to and use a non-adjustable of that value.

https://www.ebay.com/itm/333483858236?_skw=trim+potentiometer&itmmeta=01K07BHKK3F68DXTYW8B2TNC52&hash=item4da52fd93c:g:Yp0AAOSwW-Bf9Oc-

[peteski]

Right? I've always used 1K but I'm used to dealing with 1.5V LEDs (or so I thought). So I figured the 480 roughly made sense.

Oh well, live and learn. And the fun is in the doing, right?? Right? lol

Again, being pedantic, there are no "1.5V" LEDs. The forward voltage (Vf) of most IR and red LEDs is around 1.7V, yellow, standard (yellowish) green, amber and snow super bright red LEDs have Vf of around 2V, and blue tru-green, UV, and most blue-die-with-phosphor-coating white LEDs (basically all the white LEDs we use) have Vf or around 2.9-3.2V.  These variations are due to the material (chemistry) used for various color LED dies.

As long as you err on the side of higher resistance value (meaning less current passing through the LED), you are safe.  1K resistor will not cause any problems when using 12V to power any color LED.  The LEDs with the lowest Vf will just glow a bit dimmer (which sometimes is desirable for things like marker lights).

I guess this is a lesson learned (and also not to  trust online searches or more recently AI-generated technical info).

[peteski]

Or, you could just buy a variable resistor and start at high ohms and turn it down until you find the brightness you like for the specific application, then measure the resistance value the variable is set to and use a non-adjustable of that value.

https://www.ebay.com/itm/333483858236?_skw=trim+potentiometer&itmmeta=01K07BHKK3F68DXTYW8B2TNC52&hash=item4da52fd93c:g:Yp0AAOSwW-Bf9Oc-

That is a dangerous suggestion unless another "regular" series-connected resistor is connected in series with the variable resistor, so you don't accidentally turn the knob to the zero ohm position instantly blowing up the LED.

[Chris333]

But they make a cool pop sound. 

[randgust]

There has to be an Ed's Law here that says that they only fail after they are installed and painted in a finished shell.

I've been holding mine in place with what is essentially canopy glue (Krystal Kleer) as it insulates and pulls back out if and when you do screw up, and if you get sloppy it's still clear.

And I've also been very reluctant to change resistors from what comes on the pre-wired ones, I've only had epic fails when I've gotten creative with using the existing surface-mount resistors like on Atlas circuit boards; just changing the LED over to a wired one instead of one previously fixed on the board. Both 'look like' the same LED,.... maybe not though.

This is becoming a rather excellent project.   Hope you bring it to Altoona.  The first time I saw 89 (CN 911) I think I was about 10 years old and it was up at the Vermont (Bellows Falls) Steamtown, and pulled our train.  And umpteen times since at Strasburg.

[Ed Kapuscinski]

Luckily the tender light is only in with Crystal Clear.

The headlight on the other hand is gonna be interesting. I'm not really sure how to get the shell off. I've gotten this far without going it and I was hoping to avoid it.

Randy, not only am I planning on bringing it to Altoona, I'm planning on bringing somewhere for it to hang out at too.

[Maletrain]

That is a dangerous suggestion unless another "regular" series-connected resistor is connected in series with the variable resistor, so you don't accidentally turn the knob to the zero ohm position instantly blowing up the LED.

Well, not dangerous if you are using a multimeter to determine the resistance value before you connect the LED, as well as after you adjust the resistance for the desired brightness.  I always do that to be sure I have turned the resistance up all the way for the contact points I am using before I start.  With 3 contacts, the resistance between the center and one end is the full value of the resistor, while the resistance between the center and the other end is zero (or close to it). So, make sure you measure the resistance in the circuit before applying the voltage, to be sure it is the max value of the variable resistor.