Installing an LED Headlight on a Proto Heritage C&O 2-8-4

[richhotrain]

I own three Proto Heritage 2-8-4 steam locomotives, an NKP, a Pere Marquette (PM), and a C&O.

A few years back, I replaced the burned out incandescent rear lamp in the tender of the NKP with a 3mm Miniatronics Yelogo LED and installed a 3mm Miniatronics Yeloglo LED in the engine head light housing. 

A few weeks back, I noticed that the incandescent rear lamps on the other two 2-8-4s (PM and C&O) were burned out. So, I replaced those rear lamps with Miniatronics 3mm Yeloglo LEDs. At that point, I couldn't help notice that the incandescent headlights in these two steamers were very dim, especially compared to the rear lamps. So, I set about to replace them.

I had no problem with the Pere Marquette because, like the NKP, the LED fit nicely into the headlight shround. However, I ran into problems with the C&O. On the NKP and the PM, the headlight shroud has the lamp fitting directly in the center of the shroud, in line with the female fittings in the boiler that accept the two lamp wires.

But, on the C&O, the lamp fitting is at the bottom of the headlight shroud. Because the two lamp wires have to feed through the boiler weight, this made installation of the 3mm LED impossible because it prevented the headlight shroud from fitting into the boiler shell.

My solution was to install an SMD LED (Surface Mount Device). This miniature LED is slightly smaller than a grain of wheat and is powered by two #36 wires. To get such small wires to fit snugly in the female fittings, I had to solder the #36 wires to small lengths of 22 gauge wire which then fit snugly into the female fittings.

I am starting this thread in order to inform others who wish to replace this headlight how to go about doing it. Not an easy task.

Rich

 

[rrinker]

 Not easy but worth it because you only have to do it once. Replace with another incandescent bulb and you'll be taking it apart over and over to replace it every time it burns out.

                          --Randy

[richhotrain]

rrinker

 Not easy but worth it because you only have to do it once. Replace with another incandescent bulb and you'll be taking it apart over and over to replace it every time it burns out.

                          --Randy

 

Amen to that, Randy. I never want to open up those locos again.

Rich

[tstage]

Good job, Rich!   Love LED headlights.  Which reminds me that I need to get back to finishing installing SMD LEDs in my brass H20-44...

Tom

[richhotrain]

tstage

Good job, Rich!   Love LED headlights.  Which reminds me that I need to get back to finishing installing SMD LEDs in my brass H20-44...

Tom

 

Thanks, Tom. 

The LEDs really look outstanding, especially when compared to those dim incandescent bulbs.

Rich

[hon30critter]

Nice solution Rich!

SMD LEDs are what I use almost all the time now.

Dave

[richhotrain]

hon30critter

Nice solution Rich!

SMD LEDs are what I use almost all the time now.

Dave

 

Dave, as you know, they simply take up little to no space. Amazing little guys.

Rich

[hon30critter]

richhotrain

they simply take up little to no space.

That's what makes them so great! Can you imagine what the modellers of 50 years ago would say if they were presented with SMD LEDs? I don't understand Athearn's long established resistance to them.

Keep up the great modelling!

Dave

[richhotrain]

hon30critter

Can you imagine what the modellers of 50 years ago would say if they were presented with SMD LEDs? I don't understand Athearn's long established resistance to them. 

Dave, I assume no pun intended there with the word resistance. 

I agree with you that Athearn should enter the 21st Century and abandon those short lived incandescent bulbs in favor of long lived LEDs.

Rich

[BMMECNYC]

richhotrain

 

hon30critter

Can you imagine what the modellers of 50 years ago would say if they were presented with SMD LEDs? I don't understand Athearn's long established resistance to them. 

 

 

 

Dave, I assume no pun intended there with the word resistance. 

 

I agree with you that Athearn should enter the 21st Century and abandon those short lived incandescent bulbs in favor of long lived LEDs.

Rich

 

Rich,

I wish you had done this 2 years ago, or that I had thought of using SMD LEDs...I managed to stuff a 3mm led and a resistor into the smokebox of a Proto C&O Berkshire.  It was not a simple task.  Lots of filing involved.

[richhotrain]

BMMECNYC

Rich,

I wish you had done this 2 years ago, or that I had thought of using SMD LEDs...I managed to stuff a 3mm led and a resistor into the smokebox of a Proto C&O Berkshire.  It was not a simple task.  Lots of filing involved. 

I had to use an SMD LED because that smoke box weight was in the way and a normal 3mm LED kept the headlight shroud from fitting onto the boiler shell.

I got around the need for a resistor because I had a DH163LO decoder already in place and that decoder had a built-in resistor on the board.

Rich

[rrinker]

 Hmm, I guess it should be OK - the DH163L0 is set up so that it can be used directly with the P2K 3 volt incandescent bulbs. If they are 15-20ma bulbs then you kind of luck out, although the LED may be super bright, it should still be operating within limits.

                              --Randy

 

[richhotrain]

rrinker

 Hmm, I guess it should be OK - the DH163L0 is set up so that it can be used directly with the P2K 3 volt incandescent bulbs. If they are 15-20ma bulbs then you kind of luck out, although the LED may be super bright, it should still be operating within limits.

                              --Randy 

Randy, you raise a good point. The SMD LED does not appear to be super bright inside the C&O headlight housing. However, on my Proto NKP 2-8-4, the Miniatronics 3mm Yeloglow is super bright 

So, here is my question. Would it make sense to add a resistor on the board in the tender?

Rich

[rrinker]

 That probably would be a good idea. But how much? I know I have one or two of those around somewhere I could probbaly see how much resistence they already have, however, as I thought, there is an easier way. As seen in the instruction sheet

http://www.digitrax.com/static/apps/products/mobile-decoders/dh163l0/documents/dh163l0.pdf

there are two pads on the bottom of the board you cna bridge with solder which disables the on board resistors. Now you just use whatever resistors you would on any other decoder. Both resistors can be fitted in the tender, even the one for the headlight, it doesn't matter if the resistor is close to the LED or close to the decoder, and if there is limited space up by the headlight, you can just insert the resistor in the line in the tender before it gets to the loco harness. 1K is enough electrically but may still be too bright, you might have to jump to 2.2K or even 4.7K (or 3.3K, in between) to get a bright but not glaring light level. Likely different values for the Yeloglo in the tender vs the SMD LED in the headlight, too. 

Edit: the pictures on the instruction sheet were clear enough to figure out how they set it up. There aren't resistors on board, there are a pair of 317 voltage regulators configured as constant current sources. What I can't see clearly is the value of the resistor to determine what current it is set for. It's the two chips and two resistors between them between the 8 pin plug and the edge of the board. They're SMD resistors so the numbers will be something like 102 for a 1K or 101 for 100 ohm. The current is determined by the formula 1.25/R. If the resistors are 100 ohm, that makes the current 12.5 ma,  safe for the LED but brighter than the typical 1K resistor which results in around 9 ma.

                    --Randy

 

[richhotrain]

rrinker

Edit: the pictures on the instruction sheet were clear enough to figure out how they set it up. There aren't resistors on board, there are a pair of 317 voltage regulators configured as constant current sources. What I can't see clearly is the value of the resistor to determine what current it is set for. It's the two chips and two resistors between them between the 8 pin plug and the edge of the board. They're SMD resistors so the numbers will be something like 102 for a 1K or 101 for 100 ohm. The current is determined by the formula 1.25/R. If the resistors are 100 ohm, that makes the current 12.5 ma,  safe for the LED but brighter than the typical 1K resistor which results in around 9 ma.

                    --Randy

 

 

Randy, the voltage regulators are both marked LM317, whatever that means. What does LM stand for?

The resistors are both marked 270.

Rich

[rrinker]

LM is just the manufacturer prefix - LM is National Semiconductor

http://www.interfacebus.com/logic_prefix.html

270 would make them 27 ohm 1.25/27 would be 46ma - way too much for LEDs!

                       --Randy

 

[richhotrain]

rrinker

LM is just the manufacturer prefix - LM is National Semiconductor

http://www.interfacebus.com/logic_prefix.html

270 would make them 27 ohm 1.25/27 would be 46ma - way too much for LEDs!

                       --Randy 

OK, I will place a resistor on the front LED and the rear LED. If I am correct, that would mean a resistor on the white wire (front LED) and a resistor on the yellow wire (rear LED).

Randy, do you see a problem with not using a solder bridge to disable the on board resistors on the bottom of the decoder board? In other words, rather than messing with the on board resistors, I would simply leave them alone and add a resistor to each LED.

The formula to determine current confuses me. If the formula is: current=1.25/R, then the on board resistor on the DH163LO would limit current to  0.046296 (1.25/27). So, to get 46ma, wouldn't the formula be 1.25/R*1000?

One other question. What is the derivation of the number 1.25 in the formula?

Rich

[rrinker]

 You should be able to add resistors as-is, but the constant current output of the decoder makes figuring what resistor to use much more difficult.

 The 1.25 comes from the LM317 data sheet, the exact circuit used on the decoder is a standard one that's even shown in the data sheet - see my previous message.

When the units are volts (the real derivation of the 1.25 is because that this the LOWEST voltage the LM317 will regulate to, with no components on the Adjust line) and ohms, the result is amps. So 0.046 and change is 46 ma. If you add another 3 decimal places in there you are in microamps. .000046 would be 46 microamps.

 The more I think about it - I don;t think adding more resistors will work here. Your LED is being driven by a constant current source - that means it will adjust voltage as needed to insure the same current always flows. So if you add a resistor (increases the current requirements of the load), the regulator will just push more voltage to keep the current at the 46ma level, until either the current exceeds the capacity of the regulator and it fries, or the voltage limit is reached (input voltage - some loss in the regulator = max it can possibly output). So I'm afraid you will have to pop it out and solder bridge those two terminals. Or just sub in a different decoder, which means splicing the wires together and removing the circuit board.

                      --Randy

 

[richhotrain]

Doggone it, Randy, you leave me no choice. I will disable the on board regulator. 

I only have one chance to do this right, so here is my question. Looking at that photo of the underside of the DH163LO board, I assume that the solder bridge is placed into each rectangular box, one for the front light and one for the rear light. So, the two solder bridges are horizontal, not vertical. Correct?

Rich

 

[rrinker]

 Yes, horizonatally. The pair to bridge is the pair in each box.

             --Randy

[richhotrain]

rrinker

 Yes, horizonatally. The pair to bridge is the pair in each box.

             --Randy

 

OK, thanks, Randy.

I will perform the solder bridge and install resistors on the front and rear LEDs.

One last question.

 If I am correct, that would mean a resistor on the white wire (front LED) and a resistor on the yellow wire (rear LED).  Do you agree?

Rich

[hon30critter]

richhotrain

If I am correct, that would mean a resistor on the white wire (front LED) and a resistor on the yellow wire (rear LED).

If I can chime in, it doesn't matter which LED lead the resistor is attached to. However, many people, myself included, always attach the resistor to the same lead each time. Doing that makes it easier to identify the polarity once the leads are trimmed or once the LED has been installed. Again, it makes no difference whether you use the + or the - as long as you do it consistently. In your particular case, the white and yellow leads are the + leads and the blue wire is the - , often called the 'common' as well. Just to be clear, you should still use one resistor for each LED.

Another thing I do to keep track of polarity is to paint the + and - leads red and black respectively. Some SMD LEDs come with coloured wires in which case painting is not necessary, but many come with plain copper coloured leads with the positive lead usually being the longer of the two leads. Once you trim the wires that means of identification can be lost. Paint stays in place. Note that I use paint pens instead of markers because the markers are hard to see and they rub off easily.

Dave

[rrinker]

 Well, since he's installing the resistors in the tender, they sort of do have to go on the yellow and white wires so each LED gets a resistor. I suppose the blue wire splits somewhere in there and goes to the tender connector and also to the backup light and they could go there.

                         --Randy

 

[richhotrain]

Thanks, guys, I will snap a photo when I open the tender and expose the wiring.

Rich

[BMMECNYC]

richhotrain

Thanks, guys, I will snap a photo when I open the tender and expose the wiring.

Rich

 

I should crack mine (actually I think its my wifes) open so you can see how I did it.

[richhotrain]

BMMECNYC

 

 

richhotrain

Thanks, guys, I will snap a photo when I open the tender and expose the wiring.

Rich

 

 

 

 

I should crack mine (actually I think its my wifes) open so you can see how I did it.

 

Please do.

Rich

[hon30critter]

rrinker

Well, since he's installing the resistors in the tender, they sort of do have to go on the yellow and white wires so each LED gets a resistor. I suppose the blue wire splits somewhere in there and goes to the tender connector and also to the backup light and they could go there.

Randy and Rich:

If it makes more sense to put the resistors on the yellow and white wires then by all means Rich should do exactly that! Rules are made to be broken. That's what I love about them!!

Dave

[rrinker]

 I've always put mine in the function lead side, that way the blue can run uninterrupted to all lights. Electrical it makes no difference, consistency is the key, it just makes more sense to me to put the resistors on the function lead instead of common.

                               --Randy

 

[richhotrain]

rrinker

 I've always put mine in the function lead side, that way the blue can run uninterrupted to all lights. Electrical it makes no difference, consistency is the key, it just makes more sense to me to put the resistors on the function lead instead of common.

                               --Randy

 

 

I agree, and that is what I plan to do.

Rich