Walthers Mainline railpro install - question about LEDs

[hotrodf1]

Hey all,

Having trouble getting the LEDs to turn on.  I have 4 outputs wired to front and rear lights, and the two ditch lights.   I can verify I have voltage from the common to the output pins at about 13.8V or so, track voltage.  Ditch lights output is on/off as it should be I guess.  Verified that voltage gets to the front LED at the pins.  Also checked the LED with the diode setting on my multimeter, and it does light that way (somewhat dim).

I used a resistor on the output side, value of I believe 450 ohms.  The electronics store recommended that after doing the math for 14.4V forward voltage on a 3.2V LED.

However, I don't really know what LEDs the Walthers mainline stuff comes with.  So maybe that isn't the right resistor?  I'm getting no light at all (that I can see anyway).  What to try next?

[G8B4Life]

Presuming this is the the loco from your introduction post, it's been a long while since I looked in a Walthers Mainline loco but a search of the 'net shows the SD70Ace (Walthers didn't make an SD70Mac so again I'm going to presume the SD70Ace is your loco) has a 21pin DCC ready board so how did you wire the LM up to the model? Did you rip out the factory motherboard board and hardwire everything or use some sort of adapter?

Without knowing a lot about what wires from the LM you've hooked up to what all I can really say at the moment is to double check you've hooked the LED's up correctly; It's very easy to hook the LED's up to the wrong polarity - Positive of the LED to the blue wire, negative to the output wires. On that, also make sure the buttons are controlling the correct outputs, another easy thing to miss.

If you've kept the factory motherboard it may have resistors or other voltage control for the LED's built in, so by adding more resistors there just isn't enough current available to light the LED so check that out also if you've kept the factory motherboard. The value of the resistor you mentioned is ok if by itself. It'd give you about 25mA. Personally I'd keep it lower than that but that's just personal preference.

- Tim

[hotrodf1]

Hi Tim,

It is, and you're right it's a SD70Ace.  I couldn't fit the module in there with the factory DCC ready board, so made the decision to take that out and hardwire, along with shaving the weight down a bit for space and it fits under the shell now.  So, I did have to hardwire the LEDs direct to the LM3s.  So the resistors were added to keep from burning the LEDs up.  I presumed that the Walthers factory red and black wires to the LEDs were + and - respectively, and it appears that the red wire does go to the smaller internal section of the LED, which according to a guy on youtube, should be the + side.  Double checked again with the multimeter and the red wire on the meter to the red wire side of the LED does power it up to maybe half brightness.

I believe I used the white and yellow outputs for the ditch lights, and the green and violet for front and rear.  I do see track voltage at each output when turning the lights on, so that seems to be working. 

Just checked the voltage at the LED legs, and found that according to the meter, the polarity is in fact backwards.  I retraced the wiring again, and the blue does go to the common black wires for all 4 LED, and the 4 outputs to the red side.  Somehow the polarity seems to be flipped on the LM3s.  Is that a setting somewhere I don't know about?

[William Brillinger]

Positive leads on the LEDs need to go to the BLUE COMMON wire, resistors go on Negative leads then to the LM output wires, per the LM-3S wiring diagram.

https://ringengineering.com/RailPro/Documents/LM-3Instructions.pdf

[hotrodf1]

Wrong assumption on my part somehow.  Just thought the "common" would be the (-) side.

That would be the problem then. Thanks!

[JRad]

That's a very 'common' mistake (pun intended).  That is usually the issue when LED's won't light up. Glad you got it sorted out.

[hotrodf1]

Yep thanks guys!   They are a bit too bright, so happy that it's easy to adjust!  Railpro is so cool . . . .