Wiring Question

[Crow T Robot]

In wiring two transformers do you connect both common leads together and
then connect the wire to the common lead/connection on the layout? Or do
you connect them to their own connection? Would it be easier to just use a
controller or are they only to be used if you have a reversing loop? Just
trying to understand the diagrams....

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[TomDiehl]

If you're talking about HO scale DC power packs, there really isn't a common lead to tie together. The forward/reverse switch changes the polarity of the voltage to the track, and under the right circumstances can double the output of the power packs to the loco (fry the motor) or cancel each other out (possibly fry the power pack).

Insulate both rails with plastic railjoiners to prevent them doing this.

If you're talking about two cabs, the selector should be a double pole double throw switch so each pack is isolated electrically from the other.

[jecorbett]

If you are using the Atlas common rail method you run one wire from each power pack to the common rail. The other wire from each pack runs to a SPDT swtich which is what the Atlas Selector is. A Selector controls up to 4 blocks. Essentially, it is a string of 4 SPDT switches. I suppose you could connect the common leads together and run wire feeder wire to the common rail although I've never seen it done that way. Normally you run one feeder wire from each pack to the common rail. To create the blocks you simply put an insulated rail joiner between each block and run a feeder wire from each SPDT to the block it will control. Atlas Controller is used for reversing blocks. It allows you to control the polarity to the mainline and reversing section(s) separately so that one a train enters or leaves the reversing section, it's polarity will match the main line.

[fwright]

You didn't say whether this was 2 rail/3 rail AC/DC. Power pack is the term usually used for 2 rail DC and transformer used for AC powered layouts.

In either case, you don't want to ever end up with 2 transformers or power packs connected to the same section of track at the same time - whether 3 rail AC or DC. The best way to prevent this is by using "cab control" or "block" wiring. This is especially easy with just 2 power packs or transformers.

Your track is divided into "blocks", each electrically isolated form the other. You need at least 4 blocks on a continuous run for 2 train operation. Each "block" of track is fed through a double throw/center off switch. Atlas Selector is a slide switch example with 4 switches. Many also use toggle switches installed in a track diagram for this function. The two power supplies each feed terminal(s) at each end of the switch, and the track block is connected to the center terminal. This way a given block is powered by one power pack/transformer or the other, but not both simultaneously. Center position turns the block completely off.

Provided each power pack/transformer has its own internal isolation transformer - usually true except in some dual throttle units - you can use a common return and only run one of the two wires through the toggle/slide switches. Doesn't matter which terminal you as common return. However, on a 2 rail DC layout, if you ever convert to DCC you will need both rails gapped/insulated at the block junctions and both rails fed through the toggle/slide switches during the cross-over period.

If you are using AC, "phasing" the transformers is recommended to reduce the feedback voltage when a locomotive temporarilly straddles the block boundary and happens to be fed by both transformers simultaneously.

The Atlas Controller is only needed in the case of a reversing loop in 2 rail DC. 3 rail needs no special wiring for reversing sections.

Hope this helps. If you need more, please provide more specifics about your situation.

yours in transforming
Fred

[cwclark]

if you are common rail wiring the layout then yes..the two power packs wire together from one lead from both packs and then wire to the rail with the side that has all metal rail joiners (hence: the "common rail")...the other wires from the power pack go to a SP/DT switch...one wire from one power pack to the top terminal, the other wire from the other power pack to the bottom terminal, and the middle terminal is then wired to the insulated track side or block side of the rail...chuck