Running two engines at once.

[thor]

Thanks again Bob.

It hadn't occurred to me that (of course) the locos would all need their wheels insulated, so that what (on the surface) seemed like a simple change to the way power was supplied to the rails, is in fact a laborious modification that would limit my options.

Not that it couldn't be done but I decided it was a non starter in terms of what is to be gained versus simply biting the bullet and going with command control. Which I'm still not enamoured with, in fact all things considered its probably best to leave well enough alone! Thanks anyway.

[winrose46]

My last year before I went to TMCC and DCS I ran 4 trains on two loops using 2 ZW's under the Christmas tree without relays etc. I isolated 4 quadants on each loop and ran wires for each quadrant to ABCD lugs respectively. I varied the voltage on each quadrant to keep a trailing train from catching the one in front. The year before I used a single ZW and a series of toggle switches from Radio Shack to turn the voltage on or off to keep the trains separated (E units had to be set to forward only). The key is to use the number and type of cars so that the trains on a specific loop run about the same speed. This works for DCS as well to fine tune three trains on a single loop.

[lionelsoni]

I got this message from Mike Dench (thor). I am taking the liberty of posting it and my response here, so that anyone interested in this unusual way of operating can read it:

"I'm not an E.E. Bob so although I got the gist of your description about how to run two trains independently on the same track, I'd like a dumbed down explanation, if you could find the time to do so, please?

"I should have thought about the construction of 027 track but as I havent any more track at present than the oval of FastTrack my set came with, I can always go with, say, Atlas which uses plastic ties so presumably has all 3 rails isolated from each other? As may FastTrack come to think of it.

"It would be worth it to get that feature of two trains at once.

"I searched the net for an explanation of what a synchronous rectifier is but drew a blank.

"I actually have several questions but I thought I'd best keep it simple first, in case you're too busy for this.

"Thanks, Mike."

First of all, let me say that insulating the rails is by far the easiest part of using the Trix Twin system. As Bill pointed out, you also have to insulate the wheels. This could become a life's work with trains that were not designed for it.

A simple rectifier allows current to flow from the anode to the cathode whenever the anode gets a little more positive than the cathode. It can be thought of as a switch that closes in response to the difference in voltage between the source and the load. When you try to use two of these to connect two transformer taps to the load, with one intended to conduct for the positive half cycles and the other for the negative, you find that they will also conduct current from one tap to the other for half the cycle.

A synchronous rectifier is a switch that turns on in response to the difference between the source and ground--not source and load. Using two of these instead of simple rectifiers insures that only one will be turned on at a time. Each of mine is made from a silicon-controlled rectifier (SCR) and a one-transistor circuit to drive it.

Synchronous rectifiers are usually used instead of simple rectifiers because they can be built with a very low forward voltage drop across the switch, compared to the voltage drop of a simple rectifier. Therefore they waste very little power. Mine are not particularly good at that, since that is not their purpose in my application.

Using rheostats eliminates the problem of current flowing between two transformer taps, since there is only the one tap. So simple rectifiers can be used in that case.

For the remote possibility that anyone is interested in the circuit details, here they are: The SCRs are arranged in opposite directions. The one that drives on positive half cycles has its anode connected to a transformer tap and its cathode to the load. A bipolar transistor drives each SCR, with its collector and emitter connected between gate and anode. For the positive side, it is a PNP with emitter to the anode; for the negative side, an NPN with emitter to the gate. In each case the base has a resistor to ground. There is also a signal diode across each base-emitter junction and in series with each collector to protect from reverse voltage, and a small resistor in series with the collector to limit the transostor's saturation current.

I have the two synchronous rectifier circuits built onto the underside of the two "horns" of the Z transformer casting. Two of the four controls drive the rectifiers and a third drives the load directly, for when I want normal full-wave voltage, leaving one for accessories. I have added circuit breakers inside the transformer case for the separate outputs. I have two Zs modified this way. I did have an American Flyer 30B in use also, but found it hard to use despite its sexy looks.

[thor]

Once again thankyou all, there's obviously more than one way to skin a cat, I find all the various answers and approaches to the problem extremely interesting. Thanks Jake for the kind offer. I want to investigate all the options.

[Fred Bear]

There is a simple answer. Dead track and a 154C. It works out great and the trains never catch one another, The trick however, is to place the contactor at a vantage point on the oval as to trip the dead track at such a time it's IMPOSSIBLE for one train to catch the other. Feel free to write to me at [e-mail] or call 304-843-1740. I think I can describe it better that way. Jake

[lionelsoni]

Actually, Rob, I do use the whistles. I have them set up with rectifiers also. When I'm running a locomotive by itself, I can put the main motor on one polarity and the whistle motor on the other. Then I can not only blow the whistle but also play with the sound in a rather prototypical way.

Another use for the second channel with one locomotive is to keep passenger car lights on as the train stops.

[thor]

Exellent! Thankyou very much and thankyou to all who offered advice. BTW The Trix track was metal in a bakelite roadbed then fibre ties later on so the rails were all insulated.

I realised that I could get around it by using a different track system but thats just not on for now. Also the catenary system is a good idea, thanks.

[lionelsoni]

Thor, there is a way to run two trains; and I use it. It doesn't use TMCC nor DCS, nor does it require special track.

I power one train with the positive half-cycles of the AC voltage and the other with the negative half cycles. The locomotives are modified by putting a rectifier diode in series with the pickup roller, in opposite directions in the two locomotives. You also need to put about 5000 microfarads of capacitance across the circuit downstream of the rectifier.

I use what is known as a synchronous rectifier to connect two transformer outputs to the center rail alternately during the two half cycles. This is not two complicated; but an even simpler method, that I use on one overhead loop, is to use a single transformer output with two Lionel rheostats, each in series with a simple rectifier.

My locomotives actually have a more complicated rectifier arrangement than I described, which allows me to change the polarity to suit my needs or to run them on full-wave voltage if I like. But the simple scheme is what I started with and, for two locomotives, is perfectly adequate.

[ADCX Rob]

QUOTE: Originally posted by thor

Leonard, I beg to differ. I was six when I played with Trix and I certainly couldnt have handled cab control or block wiring!

According to:-
http://ttrca.co.uk/TTR.htm

'The Trix Twin Railway took its name from the fact that one could operate two trains on the same piece of track. This was achieved by having three rail track with the centre rail acting as a common return. The left-hand outer rail was then used by one locomotive to collect current and the right outer rail by another loco.'

Nothing complex about that at all. All I wondered was if I can wire Lionel the same way

There is a way, but you have to disable whistles/horns/bells/sounds. With proper placement of diodes at the power supplies & at the locos, you can run one train on half-wave -DC & the other on half-wave +DC. It's OK for just running, but you lose the benefits of the AC based flexibility built in to the Lionel AC 3 rail "system".

OR if you are running one or more electric outline locos, run one off the third rail, another off the catenary. This will preserve the AC control.

Rob

[Buckeye Riveter]

QUOTE: Originally posted by BillP1

With Lionel tubular track, the two outside rails are connected together with metal ties.

To make the system you describe work, you would have to insulate one of the outside track rails from the ties.

There is also a problem with the wheels of the locomotives and cars being connected together with metal axles which would short the two outer rails together.

By the time you got done insulating one of the outer tracks (and if you could find locmotives set up for the Trix Twin system and cars with insulated wheels), I believe you would find you would have been better off just going to command control.

---------------- Bill

[#ditto] and [#welcome] Bill

Just a hunch or a wag, but I bet that the German OO system used wood ties.[;)]

[Anonymous]

thor
My opinion based on experience, but its your railroad and you can certainlly do it your way absent any advice from me. Good luck![:)]

[BillP1]

With Lionel tubular track, the two outside rails are connected together with metal ties.

To make the system you describe work, you would have to insulate one of the outside track rails from the ties.

There is also a problem with the wheels of the locomotives and cars being connected together with metal axles which would short the two outer rails together.

By the time you got done insulating one of the outer tracks (and if you could find locmotives set up for the Trix Twin system and cars with insulated wheels), I believe you would find you would have been better off just going to command control.

---------------- Bill

[thor]

Leonard, I beg to differ. I was six when I played with Trix and I certainly couldnt have handled cab control or block wiring!

According to:-
http://ttrca.co.uk/TTR.htm

'The Trix Twin Railway took its name from the fact that one could operate two trains on the same piece of track. This was achieved by having three rail track with the centre rail acting as a common return. The left-hand outer rail was then used by one locomotive to collect current and the right outer rail by another loco.'

Nothing complex about that at all. All I wondered was if I can wire Lionel the same way

[Anonymous]

thor
With 3-rail AC you don't get "shorts" in your reversing loops.

The awkward and laborius operating procedure you are referring to is "cab control" via isolated blocks and a transformer{"cab"} for each conventional engine. Not "relatively simple" at all. However, Peter Riddle's 1993 book, "Wiring Your Lionel Layout"--Volume II,explains how to set it up.

The completely simple way to run more than one engine in /on the same power district or oval{s] is Command Control. The components for TMCC are relatively cheap, very simple and easy to wire[one wire] and make sense if you want to run multiple engines/trains.

[jimhaleyscomet]

In Lionel we usually make the outer two tracks the common (black lead) and the center the "hot" or red lead. Reversing loops are no problem. Also, to make a block just use insulated pins in the center rail at each end.

Jim H

[thor]

I've got a starter set and to make it more fun, I intend to buy more track and create two loops one inside the other connected via four turnouts so either loco can swap routes easily without needing to reverse. Then I'm going to take that outer loop and branch off a few long sidings with uncouplers so we can do a bit of shunting. That way our little girl (3) can learn to drive a train and be having fun whilst Gramps does the tricky stuff out on the yard.

FastTracks too expensive for me so I'm going to buy some convertor sections and use the old steel track instead since we're absolutely definitely stuck with a floor layout until summer when I'll try and take it outside but thats neither here nor there.

I used to own Trix Twin - a German 00 system - which allowed two locos to be independently controlled because of the way the track was wired. I assume - operating from memories of 50 years ago - it was a common centre with the two outers being fed by each controller. So as long as you dont have a reversing loop there should be no shorts.

Can one wire Lionel to pull a similar trick? I'm not interested in any of the Command Control systems, I just want to see how to get the most out of a relatively simple setup. Thanks.