Hi all, I've noticed some major differences in the ways the headlights in my various analog locos work on DCC. In most of my locos, both headlights come on at full brightness the moment the loco is placed on the track, and stay on regardless of direction. In my Kato SD70M, neither light comes on when the loco is idling, and the lights come on in the direction of travel, exactly as on regular DC. short out the system, and consequently don't actually do anything. My question is, what causes these differences? Why does the Katos work normally, while the others work oddly or not at all? And just what makes the IM loco short? I dimly recall it having something to do with the capacitor that prevents flickering. Eventually they'll all get DCCed, but for now it's late, and I've been thinking (always dangerous :embarassed: ) about headlights
All my analog lamps come on in both directions at all times. Does the Kato have a "board" in there already? In other words, DCC Ready? If so, it's possible it's making the headlight do the things it does.
DCC is an AC waveform. Most locos implement directional lighting using diodes so that only voltage of the proper polarity makes it to the lamps/leds. Thus both lights are on when on DCC powered track (and brightly, as DCC is full voltage). When you mentioned the anti-flicker capacitor, it rung a bell. A capacitor will serve to average out the voltage going into it (sort of an electronic version of a flywheel). This prevents flicker when operating DC on dirty track, but it also averags the DCC +/- to zero (assuming DCC address 00 is zero). As you increase DCC address 00 speed, zero pulse stretching makes the DCC waveform have a non-zero average voltage, causing your DC loco to move and one of the lights to light. JFM! Doug
