The way I see engineering is that it is the art of designing something, whether a cathedral or a train layout, by being able to predict what will work and what will not, before it is built. The engineer knows he has done his job right when it is built and doesn't fall down or burn up, respectively. Thanks for giving us the vicarious experience that is the engineer's reward for getting it right.
Bob Nelson
Fun and interesting, I did a little testing and playing with this last night. I have a panel with voltmeters and ammeters for each track output and an overall ammeter on the return line. With the 1034's in phase with the ZW250, the overall ammeter shows about 2-3 amps for just accessories (mainly lighting, buildings and switches) and then as I raise the output to a track with a load the overall amps are additive (track plus accessories). But, with the 1034's having their wall plugs reversed, I got the difference. Good stuff.
Thanks,
Scott
Bob,
I have several 1034's providing power to accessories (some which return through isolated track sections) and a ZW for my track power though all have the commons connected and phased. Should this be done differently? Should the 1034's be connected but not with the ZW? I think I understand what you are saying but am unclear on how to accomplish that in the actual wiring.
The reason for having transformers in phase with each other is to reduce or eliminate the voltage difference between track blocks when running from one block to another powered by a different transformer or transformer output. To avoid a possible dangerous fault current, not only must the phase be the same, but also the voltage and the waveform. This is risky business and why you should use electrical switches to assign blocks to transformers so that you don't have to do it. But accidents will happen; so having track-power transformers in phase is a reasonable precaution against heavy fault currents.
This consideration does not apply to accessories nor to the combination of track and accessories which might share a common return. In that case, having the voltage out of phase causes the return currents to cancel rather than add. For example, suppose that you have an 11-ampere current on one accessory circuit and a 13-ampere current on another. If they are in phase, their return current will be 24 amperes, enough to require 10 AWG wire for safety. But, if they are out of phase, the return current will be only 2 amperes. Again, suppose that a track and a number of accessories share a common (outside-rail) return. If the train is drawing 5 amperes and the accessories are drawing 10 amperes, the return current is 15 amperes with track and accessory transformers in phase. Out of phase, it is only 5 amperes; and any voltage drop due to the resistance of the outside rails is reduced by a factor of three.
This is the same principle that the wiring of your (North American) house uses. Your house receives two phases of 120 volts (red and black wires) relative to a grounded common (white). The white wire only has to carry the difference between the currents that you draw from the red and black wires. If it had to carry the sum, you would need a much bigger wire. In any scheme like this, that shared return conductor is called a "neutral". You often hear this word used as if it means "ground" or "common"; but you can see now that it is something else entirely. The confusion comes from the fact that the neutral in your house's power happens also to be grounded and to be a common return.
Bob said:
"By the way, if you have a common return for your lights and accessories, you can reduce any voltage drop on the common by operating the transformers out of phase with each other, so that the common becomes a neutral."
Bob, any chance you could elaborate on that?? I've always been so careful to run everything in phase so your comment just jumped out for me.
thanks - walt
"Each when in use draws about 11 amps." Surely not--that would be 1320 watts! I suspect you mean that each puts out 11 amperes. But then you say, "Three different 15amp circuits." Do you mean that they are plugged into three different 120-volt circuits? That doesn't hurt anything; but it should not be necessary. Each transformer would actually be drawing only around 1 ampere (more or less, depending on the output voltage you have them set for); so all three together would hardly be noticed on a 15-ampere 120-volt circuit. Are you sure they are all on different circuits, as opposed to just different outlets on a single circuit? In any case, I would say you are hardly straining either the transformers or your house wiring.
By the way, if you have a common return for your lights and accessories, you can reduce any voltage drop on the common by operating the transformers out of phase with each other, so that the common becomes a neutral.
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