LED passenger train lighting using one converter voltage regulator for the whole passenger set and plugs between cars???

This can certainly work, but I think you're doing things the hard way.  Unless you're pulling a REALLY LONG passenger train, I can't imagine the roller drag is a big issue.  Screwing around with the tethers every time you connect up sounds like a real PITA.  I can't see how this reduces the wiring, you'll have to explain that to me...

I agree with John, this sounds like a lot more trouble than it's worth, especially when you look at the low cost of the components to do the lighting boards. You are going to spend more time taking out the rollers and rewiring, plus if you ever go to sell the cars, they are no longer self-contained units, and the next person will probably have to search for the parts you took out.

You have bigger problems if you're worried about roller drag. Just do your lighting the normal way and oil the rollers very lightly. You'll be happier in the long run.

Well, this being a discussion forum I'll present a contrarian view.

I'd guess removing the center-rollers and the outer-rail wheel axle wipers/contacts cuts drag by a factor of 2x or 3x allowing you to pull double or triple the # of cars for the same # of transformer Watts.  Historically the excessive power problem with passenger cars was a bulb issue.  Going to LEDs peels the layer of the onion exposing the roller drag issue.

It is probably just me, but I find the roller noise on a long passenger car consist somewhat annoying.  Yes, trains are noisy gadgets to begin with but eliminate the rollers and it becomes easier to hear dining car sounds and the like.

I don't know if you're running conventional/command/both or DCS but when it comes to lighting I figure if going thru the hassle of re-wiring cars anyway then why not make it as universal a solution as possible.  To that end here's one approach using a low-cost buck-boost eBay module (less than $2 shipped).

A detailed write-up with plenty of pictures is on the JCS O-gauge archive here.

This is a DC-DC module so you need to convert track AC to DC first with a 20 cent bridge-rectifier.  A 20 cent capacitor is good measure for additional flicker reduction.   The 10 cent DCS inductor is self-explanatory.  This approach allows operation for conventional and command, for DC or AC track voltage, and with DCS, TMCC/Legacy, or even DCC.

In the out-of-left-field category, the tether approach is perfectly suited to battery operation since you would likely have centralized lighting power and tethers would be the only practical way to distribute it to the cars.

Additionally one of the most annoying chores with running lighted passenger cars is how to turn the $%@# lights OFF when on a siding or when parked in the yard!  With centralized power it becomes practical to control power via remote control or whatever - even if it be to reach under the chassis for the on/off slide switch.  And it's not just on/off.  I've written about how to dim passenger car lights after the train leaves the station and brighten lights when at the station.  This is less expensive if you only have to put the electronics to do so in one car.

Anyway, if you go the tether approach consider placing female connectors on the end/bottom of each car chassis.  Then make tethers with male connectors on each end.  This allows you to swap directions of cars and still have it work.  Yes, you'll need a stash of tethers but this means you don't have dangling wires.

As with others, I think that each car having it's own supply is likely the most hassle free way to do things.  

That said, If I was going for simple and low part count, I think I would just use a NiMH rechargeable battery in each car with a simple barrel jack or similar plug to charge it.  I think a pair of off the shelf AA's would do OK, but myself would use a very common 18650 battery, which is a 3.6 volt type ranging from 2000 to 3500 mAh depending how much you want to spend.  In any case, with this battery you could string a diode in to drop the voltage to about the 3 volts many white LEDs want.  

If you figure on maybe 6 LEDs per car, that's around 120mAh.  Lets say 200mAh in case you want 10 LEDs.  That's at least 10 hours run time on a charge, which isn't too bad.  

If you don't mind taking some longevity out of your batteries, you can even charge them on 20 minute fast chargers if you're in a pinch.  

JGL

Interesting suggestions.

I need to pull the cars apart and a simple wire connection is cheap and easy to use between cars. On other cars that I do not need the center rail rollers I have just wire tied them in the up position so they do not touch the rails works well. The passenger sets I have (several) are always connected together and sit in yards on my ceiling passenger loops so hard to access to do anything and for the life of them can just leave them connected.

So to pull apart some older cars just leave the light sets in them peel and stick LED strips along the roof with simple plug connections between cars I think would be easier then purchasing additional power supplies for each car and wiring them in. 

Over time the center rail rollers need oiling and can wear out with use. 

Isn't there a method with a few diodes, a choke and a cap for powering leds?

Liked your schematic!  However, remember LED's don't work on 12 volts.  Each color of LED has its unique voltage operating characteristics.  So, you will need a resistor for each LED.  I say each, because the LED's are not exactly matched to each other.  There are subtle differences that might showcase themselves in a train environment.  Arguably, you CAN run all the LED's off one supply, say for white, about 3.2 to 3.6 volts ROUGHLY, without individual resistors, but from an engineering viewpoint, I would use individual resistors.  Just check the Led spec sheet carefully for typical operating voltage and maximum "normal" forward current.  The current and applied voltage determine the resistor value, but I suspect you already know that.  However, this information may help others who read this response.  There are many very good electronic guys on the forum who can help with any electronic and electrical questions.

I understand you logic, still agree with others it is a bit of work.  One plus, is you can use a wire with heavy insulation (silicone comes to mind) put a dap of silver paint in the middle and the wires will look like air hoses.  Silicone insulated wires are typically high strand count and the MOST flexible wire available anywhere. Hide your 2 wire connector very near the end of the car (underneath) towards the center, but far enough away from the couplers not to interfere with their proper operation.

I guess if you have 10 21 inch passenger cars roller drag and noise could be an issue.

It's doubtful that he'd go the route of using discrete LED's, the 12V LED reels are so much more convenient, they also remove the issue of tons of resistors.

One other point.  You can get away with removing half the rollers and still power the cars individually, just use a supply with a large enough capacitor and it'll solve the problem of any flicker with the single roller.  Gone is half the rolling resistance of the rollers and you still don't have to deal with the issue of connecting tethers for every time you put the cars on the track.

I don't spend too much time worrying about turning off the lights on a siding or in a yard, that's what the power switch for the sidings and/or yard tracks is for.