Polarity on PS2 headlight pads?

Are you checking the voltage with your multimeter set to DC Voltage or AC Voltage?

 I'm not sure what they will read on your meter so maybe others can tell you on the DCS forum. On the chassis, the purple should be the positive wire for all the functions. There are two sources so follow the headlight pad to the purple. It usually goes to a wire nut because of all the lights that need the source.

 I would use about a 300 ohm resistor. U can fine tune it for how bright U want the LED. About 180 would be the minimum I think? I don't know what LED U have.

As Joe stated the purple is positive and the return to PCB Ground (negative) is the other colored.  Normally Light Blue for headlight, and Green for Reverse Light.  G

I am checking for DC. I just thought it odd that I don't get a reading between pads but the lights light when set the block on the pads. I can use CL2N3 chips if I can't determine voltage. Knowing that purple is positive helps a lot. There aren't any wire nuts that I can see. I have a PS2 chassis wiring diagram, but that shows wire nuts. There is a plug on the board with 3 purple into one prong. The other pad wire is light blue. Thanks, Joe. I grew up 2 miles east of Olcott. You're probably the only guy on the forum that knows where that is.

          John

I've put tons of LED's in PS/2 locomotives, I use a 220 ohm resistor for each LED.  If I have dual headlights, I wire them in parallel and use a 150 ohm resistor. 

Yeap!

The PS2 board sends track-level high-frequency DC pulses to the headlight pads.  The pulses are actually OFF most of the time.   A typical hobby-grade meter in DC mode will indicate a couple of volts (rather than, say, 6V).  It would be interesting to confirm your "zero" DC reading if you measure the voltage with the bulb connected and operating but that's just for amusement...

Insert the resistor minding the polarity as the guys suggest and you'll see the light!

The CL2N3 chip might work but will probably be too dim.  Since the voltage is pulsed, the CL2 can only "work" when the pulse is present.  So it will be off most of the time - unless you add a capacitor or whatever which just makes things too complicated...

Since the average voltage is 6V, the CL2 is overkill, a simple resistor works great in all the LED lighting installs I've done, that's probably close to 50 now.  I no longer use the stock headlights for upgrades, I go right to LEDs.

It's actually the RMS voltage that's 6V.  That's why a typical meter in DC Volts mode (which measures average DC voltage) reads much less than 6V for a PS2 lamp output.   For a steady, "flat" DC voltage, average voltage = RMS voltage.  But for the PS2 pulsed DC lamp voltages, the RMS voltage is much higher than the average voltage.

The Marker lights which John H measured to be 5V DC uses a different circuit altogether so that's why he got the higher reading there.

I was talking about the incandescent light outputs.  I treat them like 6V DC as far as LED's are concerned, seems to work out. 

Thanks for the additional comments. I could only get one led to light with the two chips, so I wired them in series with one. Now they work, but they are dim like you say. I just got some 150 ohm resistors today and will redo, hopefully with better results. The 3mm ultra brights that I put in a PS1 are much brighter than this project. Next question: I would like to put a 5mm in a Railking PS2 Hudson. Any specific advice on that? It looks like I would have to leave the bulb in to light the markers and stick the led into the shell. Have you done these, John?

          John

Are you powering the markers from the headlight connection?  If so, I typically put the two markers in series with a resistor from 220 or larger to adjust the brightness to what I feel looks good.  For markers, I usually end up with around 1K resistance as they look way too bright as a rule with smaller resistor values.

If you have two identical white LED's, I have not had any problem simply wiring them in parallel.  If you do run into issues, put a separate 220 ohm resistor for each and wire them in parallel, then they'll work for sure. 

If you're talking something like the Evan's stuff, they have current limiting already, they're a totally different deal.

On this steam engine there is a single incandescent bulb on the chassis mounted vertically that shines through a lens for the headlight and through a translucent block that lights the front green markers. My leds are 20ma, 3v from led-switch.com, so I need to use resistors or a chip. That's why I was trying to determine voltage on the diesel. The steamer voltage should be easier to read because I can do it with the bulb on.

      John

All the headlight bulb power from the PS/2 boards are the same, so the same LED resistor suggestions should apply to any PS/2 LED upgrade.  As I said previously, the marker outputs are unique, but you won't have them available in the locomotive for the RK steamers.

I've upgraded those steamers.  You can either push out the plastic piece and use 3mm LED's, or light it from behind.

Just finished the diesel headlights with a resistor instead of the chip. They are brighter; just not as bright as the white leds I put in my PS1. Thanks for all the help.

          John

You can cut down the resistor to as low as 150 ohms for a bit of additional intensity, that's as low as I'd go for one LED.

There are 2 3mm leds that are wired in parallel with a 150 ohm resistor as you suggested earlier. It may just be the difference between the ultra warm white and the ultra white leds. They are working, thanks to everyone.

          John

Occasionally, you'll see different brands of LED's that won't play well together paralleled, but I rarely encounter the issue with LED's from the same batch.  However, for different types, I just use separate resistors, that does the trick.

The issue with parallel LED's is usually one is brighter than the other if they're mismatched. both being dim is something else, usually not enough current.