I have been completely through Digitrax website with no luck. I am wanting to install some extra lighting on a few of my N scale Digitrax decoders. I have all my equipment and parts, now I can’t find info on the voltage that is supplied from the FX3 function outputs. I need to determine which resistors to use to protect my led’s but, I can’t find the voltage supply rating for the decoder FX output pads, I’ve tried reading the voltage with my meter but I just keeps faulting my system and not giving me the info. could someone please fill me in on the voltage supply? thank you for any replies.
1kohm or there abouts
Standard NMRA compliant function output should be 12 volts. As David mentioned, a 1K resistor will work fine. What Digitrax decoders are you working with?
Jim
No. Some decoder outputs are regulated but the vast majority of them are powered straight off the bridge rectifier which will give track voltage minus ~1.5 volts.
Thanx guys, now I guess I have to order some smd 1k ohm resistors, I just have 470 ohm. I am going to use 603 smd golden whites. I’m going to cut the factory light pipes, add the smd led’s to the inside end of each pipe and secure with tiny shrink tubing, it really pipes the led light out great. I have looked all over the net for a good tutorial to add operating ditch lights to N scale locos, but all I find is people advertising to install them for a price. I want to find a good way to do this and post a tutorial after I simplify it, a lot of people are like me, they like to learn how to do things for themselves instead of always hire someone else, it’s a learning thing and an accomplishment thing.
What type of decoder(s)?
What kind of LEDs?
Rich
Digitrax dn163k2
0603 smd led
Those are very bright LEDs. 1K resistors would be OK, but I have used as much as 3K resistors to tone down the brightness.
The Digitrax mobile decoders, including the DN163K2, have 500 ma. function outputs, so that decoder will support a good number of SMD LEDs.
Rich
should I use smd resister or axial carbon films, what’s your opinion?
I use 1/4 watt carbon film resistors with my surface mount LEDs.
Rich
Depends on what you have room for. I’m in HO so I just use axial lead carbon film resistors. In toght spaces for smaller scales you might want to use SMD resistors just so it all fits.
–Randy
I wish there were open printed circuits between the functions outputs and the actual function output solder pads, for easy on board installation of smd resistors, and if you added a function that didn’t require voltage drop you could simply bridge the pre printed resistor traces.
See if TCS has a decoder for that loco, many of theirs have the resistors built in. Works the other way though - if you DON’T need the drop, you bridge two pads with solder to bypass it.
–Randy
Thanks Randy, I’m still fairly new to DCC operation and I’m trying to crash course everything, nice site and layout by the way.
That is the ‘unloaded’ voltage - Under load my test DH163 drops to 12.2 volts. I suspect most decoder function outputs are non-regulated…
Jim
The regulator on the decoder is 5V,or maybe 3.3V, to power the microcontroller. Functions just get rectified DC from the bridge. Need proof? Look where you get the positive source for a keep alive, the blue + common wire. If this were regulated, it would be after the regulator, but it actually goes right tot he + side of the bridge. ANd for those decoders that do not have a connection, you tap in to the - side of the bridge for the - terminal of the cap.
–Randy
No, I am talking about the ‘loaded’ voltage, although the difference in voltage drop will not be significant between a loaded output and an unloaded output. If your decoder output is 12.2 volts, it’s not because an NMRA compliant decoder necessarily has a 12 volt output, it’s because your track voltage minus the voltage drop through the decoder equals 12.2 volts.
Most DCC systems setup for N or HO scale have a track voltage in the 14-16 volt range because that does get the maximum motor voltage and function outputs into the 12 volt range, which is what most N and HO scale locomotives are designed for. The allowed range for DCC track voltage, however, is 7 to 22 volts(depending on scale), so you can have an NMRA compliant decoder running on an NMRA compliant DCC system with an unregulated function output of anywhere from ~5.5 volts to ~20.5 volts.
Thanx everyone for all these posts and this help, I have another question. In order to wire one set of ditch lights, would I have to use two function pads, say F1 and F2, not including the blue common +. Or could I wire common + (blue) and the two ditch lights in series into F1, would I still be able to alternate flash or would they flash in unison at the same?
For alternating flash, each LED has to have its own function. If you connected both to F1, then they would only be on or off, or flashing in unison. The way it works, the ‘flashing light generator’ part of the decoder obviously has an on and off position - well, you can assign the ‘on’ side (some call this Phase A) to one function output, and the other (Phase B) to a second function. So when one is on, the other is off, and vice-versa.
–Randy
Ok, finally got my first N scale ditch light project done, what a huge headache to be such a tiny job. I learned a lot that will make the next one much easier. The one part I struggle with so much is, soldering magnet wires. No matter what process I use to prep the magnet wire, it never holds the solder, I’ve tried using seperate flux, I’ve tried stripping the enamel with hot solder and with a lighter, I can’t find anything that works good.