Another Atlas GP30 Question

[Ngineer]

I actually have a problem with these new Atlas locos.

When running forward, the front LED is bright, but the LED on the back flickers.

The same happens if I run the loco backwards: The back LED is lit (just as it should), but the front LED flickers. It's a DC model.

Weird.

   Javier

[Steveruger45]

IIRC those old Kato Gp38-2s had a diode in line with the bulb to stop that.  Maybe that’s what is needed too for the leds on yours.  To me it seems that for a light to flicker like you say (when it should be off when going the opposite way) that some intermittent correctly polarized current flow to light the led is occurring when none should be. @peteski will know what’s causing it, I’m sure.

[peteski]

I actually have a problem with these new Atlas locos.

When running forward, the front LED is bright, but the LED on the back flickers.

The same happens if I run the loco backwards: The back LED is lit (just as it should), but the front LED flickers. It's a DC model.

Weird.

   Javier

A running DC motor , when momentarily disconnected from the power source (due to dirty track), will generate BEMF that is in opposite polarity to the voltage that was powering it.  Since LEDs are very fast-acting, that reverse polarity voltage will make the "rear" LED flicker.
Adding a small value capacitor in parallel with the LEDs will shunt those short voltage spikes.  Small SMD ceramic capacitor like 0.01uF or 0.1uF (rated 50V) will do the trick.  Kato DC locos usually have such capacitor installed.

[CBQ Fan]

I had a group of Atlas U25’s that did the same thing on my old layout.  I will have to see what happens when I get some track laid and wired up on the new one.