Dimming pass car lights with diodes

1N4001 can certainly handle 18-20 volts, since they are rated at 50 volts.

What symptoms are you experiencing and how are they wired?

If the lights are drawing more than an amp, you need to fix that!

Personally, I think you might consider LED lighting.

I thought the same thing too Royboy.  They go up in smoke around 12 volts.  Ground wired on the grey band end and the other end to hot.  John, I'd considered the LED route but the entire cost of the cars is just a few bucks more than the conversion itself.  It would seem odd that the 4 lights would draw more than 1 amp.  Unfortunately electronics is not one of my strong points so I can't say for sure.   Can you recommend a diode or something else I can try to cut the voltage down?

The one problem with sticking a diode in there is end up putting a DC offset on the tracks unless you balance the polarity of multiple cars.  Four light can't really be drawing an amp, so I suspect you may have a different issue, and I'd figure that out first!

<snip> Ground wired on the grey band end and the other end to hot.  <snip>

Well that's the problem. The diode does not go from ground to hot. That makes a direct half wave short across the power. That will surely smoke the diodes and drive the transformer crazy.

Try disconnecting the hot lead of the light. Connect the diode from the third rail rollers to the bulb and then the other side of the bulb goes to the frame.

In other words, disconnect the wire to the bulb and insert the diode in series, bridging the gap you just made by disconnecting the hot lead wire.

Thanks John and Royboy for answering.  These must have been the last cars produced without command in mind.  Worst case I'll run them conventionally if necessary.  Nice looking cars though.

Royboy I apologize I missed your last post.  I'll try wiring  it that way tomorrow and report back.  Thanks.  RICH

You can get 18V replacement bulbs for the older cars, I take tons of them out for LED upgrades.

As GRJ suggests, if you're going to go with the diode approach, install the diodes in one direction (the gray band) in 2 of the cars , and the other direction in the other 2 cars.  Since you'll more than likely always run all 4 cars together, this balances the loading on your transformer minimizing spurious bell/whistle triggering in conventional.  Even if you only run command, it costs you nothing to do this. 

Just like I have done to all my passenger cars...Change them to LEDs and install the correct resistors for the brightness you want.

Bruk, you're killing me!   Why not use this.   Flicker free, adjustable intensity, and DCS compatible as well.

rich64 posted:

 

..., I'd considered the LED route but the entire cost of the cars is just a few bucks more than the conversion itself.  

If you're willing/able to work with (e.g., solder, splice wiring, etc.) small electronic components (e.g., diodes) you can cobble together a command-mode LED solution using the ubiquitous LED strips for, say, $1 per car.  There have been dozens of OGR posts on how to do this.  From what I can tell, most guys appreciate the ease-of-installation and one-stop-shopping convenience of the Hennings LED lighting kits. 

One thing is for certain though.  No matter which way you choose to go, I can't imagine a better resource than OGR to get answers to how-to or how-come questions on passenger car lighting questions.

Well, this is what I ended up doing.  One car is done so far.  Following Royboy's directions I rewired and corrected my mistakes.  The diodes work as they should and I'm guessing the lights have dimmed by a 30%.  Perfect.  I'll do another car tomorrow then reverse diode direction in the last two cars to be done as suggested.  Can't thank you guys enough for the help.  This will be a productive weekend especially if the Pats win Sunday.  Thanks again.  RICH

Pats are going to get creamed.