2 trains, 1 track, independent rheostat control

[daan]

Bob, since I have a biiiiiig transformer, I don't really mind wasting a bit too.. But it's not such an elegant solution. Couldn't find any burned up frequency controller yet. May be I'll just make the cooling plate myself. Can't wait to get it running..

[lionelsoni]

No, this is not a potentiometer, Daan. It has just two terminals and is meant to be in series between the transformer and the track. One end of the resistor coil is connected to one terminal. The wiper is connected to the rails on which it slides, which are connected to the frame.

We used potentiometers at the HO club that I belonged to in college, just to get better voltage regulation. (This was before active regulation was practical.) But we had big 3-phase transformers and rectifiers and didn't mind wasting power.

[daan]

If one of the terminals is mounted to the frame, does it have a power input and a power ground to it? If so, your rheostat is being forced to regulate between 0 and full throttle like a big pot-meter.
If you have your trains stopped with that setup, your rheostat will act as a continuous resistor between the transformer's tap points and will consume power when the trains are stopped. The pro on this setup is that every train runs from 0 to max throttle even if it uses a very low amp rate. The not used power will heat the coil and return to the earth tap point. That way your rheostats will not give a difference in the train handling, no matter if you use 4 or 2 or 1 amp to power it..
It's something I've to keep in mind if I my setup will give too much problems with handling multiple types of trains.. (i keep learning things every day..)

[lionelsoni]

The coils are in an asbestos-insulated metal box (about 25x25x100 mm). I haven't noticed any significant heat yet.

I mounted the rheostats on the wall, between two windows, and got a little surprise. One of the terminals of each rheostat is connected to the rheostat frame. My mounting screws were close enough to the corners of the drywall that they went through the metal corner bead, shorting the rheostats together and messing up the circuit. I had to put fiber washers under the mounting screws!

[daan]

Hi Bob, That's also a bright idea to use rectifiers to identify the trains. You made a very simple multy-trains control this way. I don't have a cooling plate yet for my resistors, so my setup isn't running yet. With the 4 ohms you will reach (with 4 amps) 4/0.5 = 8 => 8x2volts = 16 volts downgrade on the transformer voltage. The 5 volt one will drop 20 volts. But if you use smaller trains, using less amps, the voltage will rise on the downside of the rheostat. I'll try to get something as a cooling plate this afternoon, I want to use a defect frequency controller for it, they have a fan cooled aluminium cooling plate to cool the thyristors in it. If I can find one, that would be ideal. How do the reastats behalve? Do they heat up a lot?

[lionelsoni]

I finally got the whole scheme together. The track runs around the room, over the door and across the windows. Two trains alternate, one running while the other waits at a signal.

One train is a Lionel General set, modified from a 2- to 3-position e-unit and with a rectifier whose polarity can be selected. Although that is locked out for this setup, it allows connecting the two motor field windings in series, to slow down the motor. The coach lights are dimmed by being wired in series, the headlight by a piece of shrink tubing on the bulb. I added the ATSF baggage car to the train, which is 8701, 9553, 9541, 9551, 9552.

The other train is a little 4-wheel ETS diesel, modified from 2-rail DC to 3-rail and with an American Flyer e-unit installed (also locked out), LED headlights and running lights added, and the same selectable rectifier scheme. It pulls two ETS Czech boxcars, one of them a green and white Budvar beer car (the Czech Budweiser) and the Lionel 5704 American Budweiser in the same colors coupled to it.

The trains are powered by a fixed 16 volts from a 300-watt American Flyer 30B transformer, through two parallel Lionel model-81 rheostats, each in series with a rectifier diode so that it controls only the train with the matching rectifier polarity.

About 2 feet of track in front of the signal is the stop section, with both running rails isolated. Before that is 6 feet of normal track and, before that, about 7 feet of control track, with the isolated rail wired to the running rails of the stop section and to the common terminal of the Lionel target signal. The green lamp goes to the center rail and the red lamp to the normal running rails. The green lamp is shunted by a no. 57 lamp completely enclosed in shrink tubing, to insure that the default signal is red but not emitting any light itself.

The corners are spirals, with two 22.5-degree sections of O27-profile O54 flanking a 45-degree O27 section, screwed to half-inch plywood. The tangents are K-Line 36-inch pieces fastened to 2.5-inch corner braces every foot. Each brace is slipped under the edge of a tie insulated from the center rail (and the control rail where applicable) with black pasteboard and held by 6-32x1/4-inch screws and speed nuts. The braces are screwed to plywood or small boards fastened to the walls or stretching across the windows.

Daan, I measured the rheostat resistances. One is 4 ohms, the other 5, even though they are the same model. The trains are running with the tap about in the middle, that is, at about 2 ohms.