I have converted a couple of engines to LED head and reverse lights by wiring them directly (no DCC or decoders) to track power points on the locos and simply wiring the reverse light to the opposite polarity. I get intermittent flashes of the lights running in the opposite directions. What do I need to wire in the circuits to prevent this? Some kind of diode? Please be specific as to model number of what I need and who might have it. I am still running plain old DC and have resistors wired in the light circuits.
That’s a tough one. The intermittant flashes of the ‘wrong’ LED are when the loco is losing track pickup and flywheel keeps the motor turning, generating back-emf. LEDs are efficient enough that they don;t take much - and some motors are increbily efficient as well. Before adding DCC to my Stewart Baldwin DS4-4-1000, I tested it on DC, and runnign fullt hrottle (it wasn’t all that fast, as a switcher should be) and then cutting power, it would coast a good 10 feet, the LED remaining lit the whole time. And that’s WITH extra circuitry to make it directional and constant, not just hooking LEDs right to track power like you have done. Anything you’d add in series with the LEDs would just mean they won;t light up until the track voltage is higher. Anything in series with the motor wouldn;t block the BEMF, they’d just make it so you could have the lights come on before the loco started to move (and reduce the top speed). A capacitor across the motor brushes can filter RF interference and it will alter the BEMF signal (which is why they interfere with DCC decoders) but it’s not going to stop the BEMF.
The 1N34 was the original point contact Germanium diode used in crystal radio set kits in the early 50s. I had some laying around so I gave them a shot and they worked. I have also used 1N914 diodes and they also work to stop the flickering.
Mel
Modeling the early to mid 1950s SP in HO scale since 1951
The 1N34A does reduce the flickering in the backup light about 90% when going forward, but the backup light is now very dim when I reverse the loco. Haven’t done the front headlight yet, just wanted to test out the diode. Is the resistor cutting he voltage too much when used with the diode?
The 1N914 doesn’t seem to make any difference - still lots of flickering.
It might be a dirty commutator, when the brushes arc badly that will effect the LEDs. You might try cleaning the commutator with a very fine sandpaper, 500 grit or finer. The diode has a about .7 volt drop and that shouldn’t make much of a difference.
With my older motors (Pittman DC-60/70/80 series motors) I use a pair of Zener diodes for arc suppression (1N5355 18 volt 5 watt Zener diodes) paralleled back to back across the motor to reduce the voltage spikes.
Mel
Modeling the early to mid 1950s SP in HO scale since 1951
