OK, I'll admit it, I have forgotten how to check to make sure multiple transformers are in phase. I recall something about plugging them both in and setting to the same voltage on both transformers, then touching a wire connected to one terminal to a terminal on the other transformer. little or no spark- they were in phase, big spark, not in phase, so unplug one transformer and turn the plug so it goes into different slots in the power strip. confirm little or no spark, then label the plugs. I used a white paint on one side of the plug to do this.
I also remember that if you had a mix of old and new transformers where one had a polarized plug, use that one as the constant, only change the direction of the transformer with the unpolarized plug.
Am I supposed hook the common terminals of the transformers together? Some help would be wonderful.
You are very close on this one. With the power off tie the outer rail terminals together, (the U on most of the larger transformers). Then with the power still off tie one of the center rail terminals together on each transformer, (The A on a ZW or KW for example). Now turn up the power about half-way on one transformer then SLOWLY start turning up the power on the other. If the transformer starts vibrating and feels like it's internally hemorrhaging STOP. Power down and reverse one of the power-cords. Now try again. You should be able to power up both transformers without feeling or detecting a short.
Mark the power cords so you will remember the orientation. Unless they have virgin original Lionel cords on them, replace the ends with polarized or three-prong connectors.
Good luck. Al.
Here is another great tutorial w/pics:
Marty E Tips/Tricks Phasing
Rob
I have a few problems with that website, Rob:
Fourteen AWG, not 16, is the smallest wire that is safe for a Z or ZW, which can put out 15 amperes. I don't know what a new "ZW" can put out.
Having the transformers in phase does tend to minimize the fireworks when accidentally moving between blocks; but it should not be done deliberately. In this particular case, it is impossible to set the voltages the same between the blocks. One transformer puts out a sine wave; the other puts out a phase-controlled waveform with a rather different shape. So the waveform diagrams are not correct for the two different types of "ZW"s shown.
And this statement is just wrong: "Transformers that will be used to power accessories that will share the common of the layout will also need to be phase for proper operation. These would include switches and isolated rail track sections for triggering accessories." They don't need to be in phase; and they actually work a little better when out of phase.
Something else that should be mentioned is that different Lionel transformers have their common terminals marked differently. Those that control only one train should have U connected to the center rail, not common.
("Bus" is misspelled.)
The original poster asked about connecting his transformers' commons together. If he does, the common wire from the transformers to the track should be rated for the sum of the transformers' maximum output currents. For two ZWs, this sum is 30 amperes and requires 10 AWG. It may be easier to wire the transformers' commons individually to the track through two 14 AWG wires and let the connection between them happen at the track rather than at the transformer.
Bob Nelson
Using heavy wire just moves problems down the path. I suggest installing smaller external breakers of each of the power terminals (A, B, C, and D on a ZW).
I use postwar Lionel #91 breakers, which are adjustable, electromagnetic breakers. They trip instantly, and can be set to trip just above the normal draw of the load. Note: it is possible to tighten the adjusting knob so far that they will never trip, so I would not use them where they might be tampered with. My family used them for years without issue..
Smaller breakers are fine; and individual circuit breakers, large or small, on multiple transformer outputs are very good things to have. But, whether or not you use them, you need wire heavy enough to carry whatever current the breakers in use will allow. And, in particular, if you combine the common returns at the transformers, you should use a common wire heavy enough to carry the total current, even if you protect the individual outputs with 5-ampere breakers.
If the transformer wiring is only temporary, for the purpose of the phasing experiment, having the proper wire gauge is not so important and would not have to be nearly as heavy as 16 AWG. What worried me was that readers might infer from the stress on the importance of 16 AWG that it is fine for wiring up ZWs in general.
I have the transformers in phase. I used the spark test, then found my multi meter and confirmed. Seems I got it right the first attempt.
As far as providing a common ground for the two transformers, (they are Z's by the way) can I use two lengths of 18awg wire in place of 1 length of 14awg? Is there a formula to solve for wire substitutions?
From the comments, it sounds like the U or common terminals on these transformers may not be as good a location as just connecting both transformers' common to one of the outer rails. Do I have this right?
I am still working on getting my head around using out of phase for some layout operations.....
A pretty good approximation is that the ampacity (safe-current-carrying ability) of wire doubles every 4 AWG numbers. So, in principle, you can parallel two 18 AWG wires for the same 15-ampere ampacity of one 14 AWG wire. However, there are some complications:
The NEC doesn't allow this, except in hardship situations with very large wires. The wires must be identical in length and in termination, so that both paths have the same conductivity and one wire won't wind up with the lion's share of the current. Another consideration is that wires bundled together are required to have their ampacities derated, because of the greater difficulty of heat's being able to escape the bundle. And there is also a risk that one wire will become disconnected, but that no one will notice until the other wire starts a fire. So there's no law against it for toy trains; but you might weigh the extra effort to do it safely against the simplicity and greater cost (if any) of using one large wire.
I would recommend a separate 14 AWG wire from each transformer's common terminal to the track. This is not the same thing as just described, since the wires are not in parallel; and each wire is guaranteed to carry no more than 15 amperes by its own transformer's circuit breaker.
The out-of-phase thing is just a matter of the return currents' cancelling, at least in part, where they flow back to the transformer through the outside rails that serve as the common conductor. If the currents were in phase, they would add together; and the increased current through the rail resistance would produce a greater voltage drop. To the extent that out-of-phase return currents are flowing through the rail resistance, the current is reduced, and so is the voltage drop. You don't want to do this with the track supplies, because, no matter how careful you are to avoid it, sooner or later you will slip up and run a train from a block powered by one transformer into a block powered by the other transformer. That's never a good thing; but it's less bad if the transformers are in phase.
After I posted above, I thought of the British "ring main". This is a circuit that starts at the circuit breaker, winds around the house, then comes back to the circuit breaker, which feeds it from both ends. They are very common over there, but would be anathema to American building inspectors.
The problem of course is that, if the loads are not balanced symmetrically along the circuit, most of the current can come from one end. The wire is equivalent to our 13 AWG, which we would consider good for about 12 amperes; but it is protected by a 32-ampere circuit breaker. On top of that, if anyone working on the panel ever mixes up the wires for two such circuits, by putting one end of each circuit on one breaker and the other ends on another breaker, one of the circuits may draw 64 amperes before the breakers trip.
But then, there are electrical tricks allowed in America that would "shock" the British, like light switches in bathrooms.
I want to thank each of you who have been so very helpful in getting me the information so that I can continue wiring my layout without creating a safety problem, or even starting a small electrical fire!
Your willingness to share your knowledge freely shows the kind of folks engaged with this hobby.
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