Atlas C40-8/8W decoder questions

[daniel_leavitt2000]

I have several C40-8Ws that need to be upgraded to DCC. I know Atlas uses NCE boards for these engines are they standard N12A1 decoders with additional wires soldered on for ditch lights? Where would these be attached?

[crencs]

They use N12A0 boards. On the bottom side on the front end you'll find the outputs for 3 & 4, the common for each are right next them and all are pre-soder.

[daniel_leavitt2000]

Wow that helps a lot!

So C would be the - and 3 or 4 are + right? Are these already rated for 3v or do I need a drop resistor?

[John]

Wow that helps a lot!

So C would be the - and 3 or 4 are + right? Are these already rated for 3v or do I need a drop resistor?

Yes .. you need a resistor ..  https://ncedcc.zendesk.com/hc/en-us/article_attachments/200500149/N12A0v35.pdf

[daniel_leavitt2000]

It's too bad you can't just change a CV to adjust output voltage instead of a resistor.

[jdcolombo]

It's too bad you can't just change a CV to adjust output voltage instead of a resistor.

Except that then if you ever needed to reset the decoder to factory defaults, you'd reset that CV and blow the LED to kingdom come unless you remembered to enter a new value in that CV before turning on a light.  Which most people wouldn't.

Sometimes, physical solutions are better than software ones . . .

John C.

[peteski]

Hmmm . . . not familiar with this specific decoder, but in DCC in general the positive side is usually the common (blue wire).

[peteski]

Except that then if you ever needed to reset the decoder to factory defaults, you'd reset that CV and blow the LED to kingdom come unless you remembered to enter a new value in that CV before turning on a light.  Which most people wouldn't.

Sometimes, physical solutions are better than software ones . . .

John C.

And in the world of DCC the function output brightness (like motor speed) is done using PWM method which always uses full voltage pulses. Motors and 12V incandescent bulbs can absorb and average the full voltage pulses, but LEDs are very fast-acting devices, and would be very unhappy having full 10V across it (without a current limiting resistor).

[crencs]

I would say no to adding resistors because there are already 3 SMD 102's which are 1k resistors already on the common side of the LED in the lighting circuits. (unless you are using a smaller led)
Pic has bottom on leftside lined up to top on the rightside. 


Then follow manual instructions about changing value of cv output on page 5
1 - Functions are designed to use 12-16 volt 30-40ma incandescent lamps. If you are using a white LED (with 1K limiting resistor) add 128 to the CV value.

[peteski]

I would say no to adding resistors because there are already 3 SMD 102's which are 1k resistors already on the common side of the LED in the circuit. (unless you are using a smaller led)
Pic has bottom on leftside lined up to top on the rightside. 

So there are resistors on-board. Good. 1K will be safe even for the smallest LED.