# 3-rail AC — O Gauge Model Train Wiring

#### JimAspin2

Joined Feb 4, 2020
1
The track runs at 18VAC. I’d like to place an LED on a box car that runs on 5VDC. Can anyone share a circuit that would do the job?

#### crutschow

Joined Mar 14, 2008
25,428
A diode with a filter capacitor to common (or a diode bridge), and a resistor in series with the LED should work.
What's the type of LED and how much current?

#### Dodgydave

Joined Jun 22, 2012
9,457
If the box car runs on 5VDC, how does it get power.?

Just put a 470 ohm resistor in series with the led for DC.

#### AlbertHall

Joined Jun 4, 2014
10,397
A diode with a filter capacitor to common (or a diode bridge), and a resistor in series with the LED should work.
What's the type of LED and how much current?
You wouldn't need the capacitor if it is just feeding an LED.

#### crutschow

Joined Mar 14, 2008
25,428
You wouldn't need the capacitor if it is just feeding an LED.
I was assuming it would be powered from the AC, and the cap was to eliminate any flicker from the half-wave signal.
Obviously the cap is not needed if powered from the 5Vdc.

Joined Jan 15, 2015
5,646
The track runs at 18VAC. I’d like to place an LED on a box car that runs on 5VDC. Can anyone share a circuit that would do the job?
Most O Gauge trains locomotives run between 8 ~ 10 volts slow and 18 volts is maximum from the transformer. The track voltage is variable. I would just grab the track voltage, rectify and then maybe toss in a 5 Volt regulator so any changes in track voltage would not change how bright your LED is. Either a 5 volt regulator or a 5 volt out buck converter. Both are inexpensive on Amazon or other hobby outlets. This only if the track voltage varies when varying locomotive speed.

Ron

#### shortbus

Joined Sep 30, 2009
7,940

Joined Jan 15, 2015
5,646
The only DC train sets I recall were the HO Gauge and back then I recall the power supply being called a power pack. They were about 0 to maybe 15 or 16 VDC since there was no PWM at the time. All of my O gauge stuff was AC powered and I think somewhere in the basement is an old O gauge American Flyer transformer. Anyway when the thread starter returns I would be curious if the rail voltage changes as the train speeds up or slows down?

Ron

#### djsfantasi

Joined Apr 11, 2010
6,816
The only DC train sets I recall were the HO Gauge and back then I recall the power supply being called a power pack. They were about 0 to maybe 15 or 16 VDC since there was no PWM at the time. All of my O gauge stuff was AC powered and I think somewhere in the basement is an old O gauge American Flyer transformer. Anyway when the thread starter returns I would be curious if the rail voltage changes as the train speeds up or slows down?

Ron
The rail voltage does change. The old Lionel power packs were an 120VAC to 0-18VAC variac. Besides the variable AC, there usually was a fixed AC tap for accessories.

Joined Jan 15, 2015
5,646
The rail voltage does change. The old Lionel power packs were an 120VAC to 0-18VAC variac. Besides the variable AC, there usually was a fixed AC tap for accessories.
That's right. Wow been a few years since my model train days, I wish I still had those trains. Things like switches had a fixed voltage.

Ron

#### ronsimpson

Joined Oct 7, 2019
933
LED on a box car
My boxcar only runs on the outside two rails. It does not touch the center rail. How are you going to get power to it?

Joined Jan 15, 2015
5,646
My boxcar only runs on the outside two rails. It does not touch the center rail. How are you going to get power to it?
Oh yeah, good point.

Ron

#### djsfantasi

Joined Apr 11, 2010
6,816
Oh yeah, good point.

Ron
you simply make a center rail wiper out of some brass spring stock. Or get a replacement part catalog and purchase a center rail wiper. Several Lionel cars use one, such as the searchlight car.

Joined Jan 15, 2015
5,646
you simply make a center rail wiper out of some brass spring stock. Or get a replacement part catalog and purchase a center rail wiper. Several Lionel cars use one, such as the searchlight car.
That would work. Could likely fabricate something from a wall anchor & bolt with some creativity.

Reverse it and put some contacts in the wings.

Ron

#### shortbus

Joined Sep 30, 2009
7,940
Reverse it and put some contacts in the wings.
I don't understand that. If you reverse the wings they are solid, so why not just use the head of a screw? I would think you would want the spring loaded wing to allow so give to go over the track joints, reversing the wings doesn't allow that. Or am I missing something?

#### AlbertHall

Joined Jun 4, 2014
10,397
I don't understand that. If you reverse the wings they are solid, so why not just use the head of a screw? I would think you would want the spring loaded wing to allow so give to go over the track joints, reversing the wings doesn't allow that. Or am I missing something?
You would probably also need to round off the ends of the wings so it doesn't catch on the joints of the centre rail when travelling backwards.

Joined Jan 15, 2015
5,646
I don't understand that. If you reverse the wings they are solid, so why not just use the head of a screw? I would think you would want the spring loaded wing to allow so give to go over the track joints, reversing the wings doesn't allow that. Or am I missing something?
I seem to remember little rollers so I thought about making small brass rollers. This all short of hacking a part off another part of the train(s). I really don't know but getting creative can be amusing.

Ron

#### AlbertHall

Joined Jun 4, 2014
10,397
These are a good source of nice contact springs

#### Tonyr1084

Joined Sep 24, 2015
5,070
I was but a child when I had an O Gauge train. I hated that when you started moving sometimes it would go forward and other times it would go backward. There was an interrupt button you could interrupt the power momentarily and take a 50/50 shot at making the train go forward.

As for a center contactor - I think back to the days with slot cars that had braided wire brushes to contact the track. They had a habit of wearing out, and finding replacement brushes was not easy. I discovered that shielding from an old coax cable could be used as a brush. Strip a bit and stick it into the holder and off you went. So for a center wiper - perhaps a braided shield stripped and removed from a coax cable might be a consideration as an alternative for a center contact.

I don't remember if the trains I had were powered from both outside rails or if the center rail provided a common point and either outside rail completed the circuit. Gosh, that's been such a long time ago. Then I went with HO scale. I now have an N scale train down in the basement with dreams of one day setting it up on a board. However, simply setting it up on the kitchen floor to play with the grand children often proved difficult because the track contacts were not very good. The wife had (I have it now) a sponge with sand paper on three sides for sanding and polishing nails, three different grades and I use that to brush up PCB's before soldering to brighten up the soldering surface. I've used it to brush the tracks as well, but still find it difficult to get good contact with the N Gauge trains.

Also, I've never liked the "Power Packs" they provide, the cheap ones anyway. The more expensive ones that have realistic start off and slow down features were pretty interesting but I never bothered to spend the money to get such a power pack. I think if I ever go back into the hobby I'd probably build my own power supply, using (likely) a transformer and an autotransformer. The transformer to drop mains to a usable power level and the autotransformer to control speed. A switch to control direction.

Back in 2017 I was in Milwaukee during a train festival. I saw trains that were (I think) computer chip controlled with bluetooth to receive commands from the operator. Saw a DC HO scale train that had a center rail. It could go forward on the same track, meaning you could have a single length of track between two loop backs. Regular HO scale trains - that would result in a dead short.

#### crutschow

Joined Mar 14, 2008
25,428
When I was a kid, I had a Marx 027 train set.
It bugged me that the train would significantly slow down on the opposite side of my (simple) layout due to track resistance.
After some thought I had the idea of making one connection from the controller to the near side, and then run a single wire to the opposite side for the other connection.
That meant the track resistance to the train was fairly equal no matter where the train was, and it then ran at essentially the same speed everywhere on the track.