I’ve got 2 Atlas RS-3’s that I’ve installed 2 Digitrax DH163AO decoders in last year. I recently relized that on both locomotives, the rear light has burned out. I am in the middle of converting most of my early diesels from 14v light bulbs over to Golden Yellow LED’s. I removed all the 14v lights from both locomotives and wired in the new LED’s along with their resisters, put them back on the layout without the body’s on to check them out. Immediately I realized that with BOTH locomotives, the rear LED stays on no matter which direction the locomotive is traveling. Hmmm, maybe this is why only the rear lights burned out on both locomotives.
I then tried to reset the decoder to factory default by setting CV008 to 008. It reset and I reprogrammed only adding a 4 digit address, nothing else. Guess what…still have the rear light on no matter what direction I’m going in. The forward light turns on in FWD and goes off in reverse.
Does anyone have any idea what is happening? Seems strange that I’ve got 2 decoders doing the exact same thing.
The Cathode end would be the shorter of the two leads that come out of the LED, correct? I’ll go check that out. If I have them reversed, all I’ll need to do is reverse the leads, correct?
If you have the leads reversed, the LED won’t even come on – remember, it’s a diode, and will pass current in only one direction.
For a backup light, you should have connected the LEDs to the blue and yellow wires. Blue goes to the positive lead, and yellow to the negative. Blue will be connected to both the headlight and backup light.
A Digitrax decoder’s default is for automatic headlight reversing, so if the rear light is not turning off when you run in the forward direction, something is wired wrong or your decoder needs to be reprogrammed. CVs 49 and 50 both need a value of 0 for normal directional lighting.
What DCC system are you using? Most do not require any leading zeros on CV values; i.e., you just enter “8” instead of “008” to select the CV number and the value to program into it.
OK, I double checked my handy work and the only thing I could find was that I used the wrong resister on one of the LED’s. I am using Miniatronice Yeloglo White LED’s (3mm) These LED’s come with 2 different resistors in the package, a 270r resistor for 4-9 volts and a 470r resistor for 10-16 volts. I had used the correct resistor for the front light, but the incorrect resistor on the rear light.
So, I change out the wrong resistor on the rear LED and put it back on the track. Now Both Front and Rear LED come on bright when the locomotive is going FWD and Both LEDs dim when the locomotive is in reverse.
I’m using the MRC Prodigy Advanced here at the house.
When you programmed “8” into the decoder you set the wrong value into a CV, or you set the wrong CV. Re-read your DCC system’s iinstructions on programming CVs. A value of 8 is for Rule 17 dimmable headlight in CVs 49 and 50. Reset those two CVs to zero if you’re absolutely sure you have everything wired correctly now. I know that the Digitrax decoder’s instruction sheet says to program a value of “008” but that is for a Digitrax DCC system. I never use leading zeros for any values when using NCE, EasyDCC, or systems other than Digitrax.
The following information is from the Digitrax Mobile Decoder User Manual, and may also help:
If you can’t control the operation of the lights in your locomotive with your throttle be sure that the decoder is programmed for advanced 28 speed step mode. Do this by programming CV29 with a value of “6”. Your Digitrax decoder was shipped programmed for 128 speed step mode. You may have changed your decoder’s programming when performing the decoder test procedure. In any case, if you are not able to turn the locomotive lights on and off, you will need to change CV 29 to “6” to have proper light operation.
Note that the above value of 6 in CV29 is for a short 2-digit address. If you want to use a long address, the value in CV29 would be 38 if you want to run on both DC and DCC, or 34 if you intend to run DCC only.
I would like to suggest that you go to the Digitrax web site and download their Mobile Decoder User’s Manual if you don’t already have it, and use the chart on page 29 to determine the value for CV29.
I’ll try your advice. I reset the decoder per the instruction manual that came with the decoder. It seemed to work because as soon as I did that, the locomotive would only respond to address 003 and not the long address that I had before (1539).
I just finished with my second RS3 and it seems to work as advertised. Lights also work correctly, this tells me that the problem that I’m having is most likely a CV issue and not a wiring issue.
Cacole gave you some great advice about the CV’s. As I was reading through the thread, the first thing I thought of was setting CV29 to 6, but he’s already covered that, too.
He may be on to something with the leading zeros. Digitrax manuals refer to the values in that manner because the DT-series of throttles show them on their displays when they’re in programming mode. So even though folks complain about Digitrax doc being “user-unfriendly”, in this case they’re describing exactly what you’d see in the display. However, other DCC systems may interpret those leading zero’s differently.
As a side note, this is one of the reasons I really advocate getting a DCC system that has both CV readback and a computer interface. Using software such as JMRI’s DecoderPro makes all this CV stuff really easy. I find that plain English drop-down menus and check boxes to select options and turn things off or on much easier than “add this number to those numbers if you want this function, but add another number if some exception applies”, etc. Plus, the readback shows you, again, in plain English, what you have the CV’s programmed for right now.
Programming 8 into CV8 on a Digitrax decoder is the factory reset, and perfectly valid. When reset, the front and rear lights will perform as simple directional lighting, no effect, no dimming.
My opinion is that the 470 ohm resistor is ALSO too small. With a nominal 14 volts on the track this is nearly 30ma to the LED which is near the limit. I use 1K resistors with my LEDs. This is more like 10-12ma to the LED and they arestill plenty bright.
That said, the REAL problem is likely that the LED blowing out has ruined the function output. That would explain the output being love no matter what you program. All is not lost since those decoders have 6 functions so you could wire the rear light to a different function instead of tossing the decoders.
That’s why I just use a 1K, probably the most common resistor value there is. 1K makes Yelo-Glo and other golden-white LEDs plenty bright with my Zephyr, which puts about 12.5 volts on the rails. Thus it should be fine with a DB150 or DCS100 on the N scale setting, or even the HO setting which is around 14.5 volts. Other systems put out anywhere from 12 to 18 volts, again the 1K will keep the LED within limits no matter what the system.
With regards to LEDs and current ratings, each LED type can have a different voltage rating and maximum current rating.
When buying LEDs make a note of the forward voltage (Vf) and the forward current (If) of the LED. to find the correct resistor (R) to protect the LED do the following calculation:
R = Vs - Vf divided by If
Vs is the supply voltage.
The typical rating of If is anywhere between 20-30mA (for a 2mm or 3mm 12V LED)
While LEDs are available in just about any rating imagineable, unless you order the more oddball ones from an electroncis supplier, or buy a bag full of unknown surplus, you pretty much get one of two types. The ordinary solid color (red, green, yellow) LEDS have a forward voltage of 1.7-2.1 volts, and the whaite variations are usually 3.5 volts. Current ratings are in the 20-30ma range, but this is the MAXIMUM current. Good design practices usually call for leaving some head room. If you use a 20ma LED, and your DCC system is set for 12 volts, and you plan it out to exactly 20ma, and then take your loco to a friend’s layout whose DCC system is putting out 16 volts - you will be exceeding the maximum current rating of the LED.
Sizing resistors for colored LEDs is a bit trickier, simply because various colors tend to put out more or less light than other colors at a given current rating. Reds are almost always brighter than yellow, so if you are doign signals you will likely need a different resistor for the red, green, and yellow LEDs, not allt he same. The white types used for headlights are usually VERY bright at their rated current - sometimes TOO bright, that’s why I calculate based on 10-12ma, even though the LED can handle up to 25-30ma. Even with a 1K resistor, the locos I have used LEDs in have far brighter lights than those I’ve left the bulbs in.