Cab control wiring question

[tv_man]

I started wiring my layout with cab control to facilitate two trains running simultaneously. I have two controllers (DC) and all the track sections are supplied with dpdt switches, so I could isolate the sections on both sides and wire them with two wires running from each dpdt switch to the track but somewhere I remember reading, that it is enough to isolate only one track which would be connected to the dpdt switch while the other track (in all sections) would be connected to a common wire running back to the controllers. Apparently this would still work with two trains, but I figure it might have some problems which would make the fully separated sections preferable. Does anyone with experience with cab control have any opinions on this subject?

Hopefully this wasn't too confusing...

[Ralph]

Hi,

Right, with cab control in the "common rail" type of wiring you only need to isolate blocks on one rail. I'm including a link to the NMRA's explanation of this kind of wiring. <!-- m --><a class="postlink" href="http://www.nmra.org/beginner/wiring.html">http://www.nmra.org/beginner/wiring.html</a><!-- m --> Hope it helps!

regards,
Ralph

[Steamtrains]

As the article says, only one rail needs to be gapped, and you can use SPST/center OFF switches instead of DPDT's, and far less wiring to do. I don't know if it's still available, but see if you can find a copy of Kalmbach's basic wiring handbook (mine was published 50 years ago.....my age is showing.. :oops: ). This will explain all sorts of things which are as applicable today as they were 50 years ago. Good luck..!!

[tv_man]

I remember having seen that book you mentioned. Spent some hours soldering and the result was some nice wire spaghetti which should work according to plan. Time to go check the connections..

[Steamtrains]

Let's hope so.....

[BR60103]

I'm running my layout with common rail cab control. One feature of this (Good or bad?) is that you can run a loco from a block on cab A to a block on cab B without its stopping. This really affects those old steamers where the loco picked up from one rail while the tender picked up the other (some old diesels as well).
I have all my blocks double insulated and the common wiring is at a terminal block.
Remember that common wiring requires separate transformers for each cab. And reversing sections need fully separate wiring for both rails.

[tv_man]

Yes, they are separate transformers. Actually, there was even a warning note in the box the transformer came in against using the transformers in one electric cirquit, the dangers of the transformer working in both ways and everything.

And BR60103, although that what you mentioned is possible, wouldn't it be easier to use one cab/controller/transformer/I'm getting confused with this terminology for every engine running at the time? Would in the situation you mentioned the engine get the cumulative power from both cabs potentially overpowering it's engine? (with potentially hazardous consequences?)

[BR60103]

It's not ideal, but it doesn't seem harmful to the motors. It's something for those who want one power pack for each circle of track and another for the yard.
You'll get a similar effect with fully separated blocks and all-wheel pickup diesels; they will briefly pickup from 2 packs if you overrun.

[tv_man]

Allright, thanks. Guess model railroad stuff is generally designed to survive some abuse then.

[Ralph]

And BR60103, although that what you mentioned is possible, wouldn't it be easier to use one cab/controller/transformer/I'm getting confused with this terminology for every engine running at the time? Would in the situation you mentioned the engine get the cumulative power from both cabs potentially overpowering it's engine? (with potentially hazardous consequences?)

I'm not sure if I'm helping here, but with common rail wiring in which blocks are separated by having one rail broken into insulated sections you will not have any issues with more than one power pack's power being routed to any block at the same time. These blocks are independent of each other and you can have one run on Power Pack A while the next block is powered by Power Pack B without any interference with the other. For example you could have a stretch of mainline as one block while a siding and a couple of industrial spurs are on another block. With two power packs you can allow a train to roll by on the main while another loco works an industry on the siding and spurs at different speed and able to change direction w/o affecting the train on the mainline.

The only time you might see power pack interference is if you forget to pay attention to where your train is and accidentally allow it to run beyond the limit of a block. (Who would do that!?! ) Any way, if the next block is powered by a different pack it will take over powering the loco. I've done this with power packs running current in opposite directions. The locomotive does a little back and forth stutter move that alerts me to shut of the power. I imagine eventually you might burn something out if you allow this to go on.

You only need one power pack if you plan to run only one train at a time. Common rail wiring with isolated blocks will allow you to park other locomotives on unpowered sidings while running your train.

I you wish to run more than one locomotive at the same time then you do indeed need as many power packs as trains you wish to independently operate.

Ralph