Z 250 transformer

[Anonymous]

Hello to all. I was hoping to get a little input. I have 3 Z250 transformers under my layout. I use the for lights and accessories. Each when in use draws about 11 amps. Three different 15amp circuits. The old service manual says they are good for 14 amps. I'm a little over the 75% mark which is recommended. They run for about and hour and are a little warm but there out put dose not drop. I think I'm good. I rebuilt each one. I have 3 ZW's for running my trains. The Z's are just for accessories. Any input on these old transformer would help. Thanks Steve

[lionel2]

Hello, I have 2 Z's and 1 ZW and a KW that I use for my trains, My Z's put out like 25 volts and are very nice to use.  I never used my Z's for accessories.  So I am not sure how it works.  I use my KW for my accessories and my ZW for switches and running the trains.  The Z's seem to be most powerful when running trains.

[lionelsoni]

"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.

[waltrapp]

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

 

[Anonymous]

Hello you are correct. Each pulling between 11 and 11.5 amp when in full use. With a voltage setting of between 11v and 13volts on each transformer. They all share a common ground, They are all in phase. Every thing works good and the lights are at just the right glow. I was also told in the past all transformers sharing a common ground must be it phase. What do you think. You input is greatly appreciated. Thanks Steven

[lionelsoni]

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.

[Anonymous]

Thanks for the good info. I'm off to the basement to do some testing. Thanks Steven

[Anonymous]

Wow Bob thanks again. I fired up all my lights and accessories. I put 1 f3, 1 GG1 and a 46-2020. Each on its own loop of course. All six transformer humming along. Total amps measured at ground 5.2. Sweet. I think I got it. Thanks Steven

[scrager]

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.

Thanks,

Scott 

[lionelsoni]

The way you've got it seems just fine.  If you want to use the out-of-phase accessory trick, you can do it by reversing the plug(s) on the 1034s or by swapping their output connections, since you are not using the whistle control.  The idea is to balance the load currents on the two phases that you use so that you get the greatest possible cancellation of the return currents, thus minimizing the voltage drop on the return.

[scrager]

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 

[lionelsoni]

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.