Are you hooking the transformers directly to the track, and running only TMCC engines? If you were to use a TPC 400 and then hook up a Y cable set to it, you could use both Zs without having to add blocks. You would also gain a fast acting circuit breaker and the ability to run conventional engines (one at a time though) with your TMCC remote.
I am afraid I can't answer your question about bridging the blocks and the potential damage to the coils if you do make the blocks you are describing.
Hope this helps,
J White
First I'm going to ask do yo have power hook-ups about every 4 - 6 feet. also the size of you layout would help now on adding blocks and transformers is out of my league there are a couple in here that could answer your question real easy 1 loses me in his statements but I'm sure he's correct other give it in more of laymen terms which I can understand ( when it comes to electricity even thou I can do most of it for trains I still need it replied in the lowest level of understanding lol )
Reason I mentioned every 4 - 6 feet is because I run a tmcc loop that is 14' by 16' with 2 dual motor engines 2 dummy B units and 7 lighted passenger cars off of a LW transformer ( about 1/2 of a zw) and it does fine.
Life's hard, even harder if your stupid John Wayne
http://rtssite.shutterfly.com/
If everything is TMCC you are going to have 18v on the track at all times. I personally would stay away from a Z if for any reason due to it's age. A ZW can power 2 normal sized trains and have a few watts left over for accessories. But 30 cars? that breaks my record of around 20. Usually the couplers cannot withstand the load and start opening up when there are that many cars.
With that many cars it comes down to wattage. I've personally never run long heavy trains like that but zone powering from multiple transformers is not a bad idea. Do you know how to properly phase transformers? That is going to be crucial. Are both of these trains running on the same track?
Just as important as zones is to run 14 gauge bus wires around the layout for power and return. I run 18 gauge feeders to the track every 6 feet or so to minimize power loss. You should also install a 7 amp circuit breaker for every block or zone.
As for trains straddling blocks with different voltages there is a myth going around that could be hazardous. Absolutely not true. Current flow is always from power to neutral return. When an engine or car with two pickup rollers sits with one roller on 18v and the other on zero the current flow is from the 18v roller to return via the outside rails.
The only thing I would worry about in using multiple Z transformers for TMCC power is that the voltage settings might get disturbed accidentally. Aside from that, the arrangement should work as well with Zs as it would with the fixed 18-volt transformers sold for TMCC.
I'm pretty sure that if one has a transformer that can maintain one roller of a pickup assembly at 18 volts and the other at 0 volts, a very, very large current will flow through the pickup (or through a wire connecting two single-roller pickups). So the following paragraph doesn't make a whole lot of sense to me, no matter how large the typeface:
"As for trains straddling blocks with different voltages there is a myth going around that could be hazardous. Absolutely not true. Current flow is always from power to neutral return. When an engine or car with two pickup rollers sits with one roller on 18v and the other on zero the current flow is from the 18v roller to return via the outside rails."
Bob Nelson
Bob, You have made many analyses of what happens when a dual pickup loco or passenger car crosses a gap separating two blocks. You analyses are accurate and should be heeded. It is possible to burn the wire that connects two single pickups. I ran a layout with two separate transformers a few years ago. One part of the layout was in one bedroom, and the rest of it was in a second bedroom. Then the train crossed the gap separating the two blocks, it sped up as the impedance driving the train was cut in half due to the two transformers being in parallel.
Bruce, your observation touches on an important difference between TMCC-type operation and tradtional block control. I avoided mentioning it in my post from fear of muddying the water with this detail; but it is what I was alluding to when I wrote that a TMCC setup "...should work as well with Zs as it would with the fixed 18-volt transformers sold for TMCC."
The difference between block control and TMCC in this regard is just what you observed, that going between two transformers, even if matched in voltage, results in a voltage boost due to paralleling of the output impedances of the two transformers. With block control, one stays with the same transformer. A voltage boost is still possible when the separate wiring paths to the two blocks become paralleled; but that can be minimized to any desired extent by heavier wiring. But the only thing that will reduce the impedance-paralleling effect of separate transformers is bigger transformers; and there's a practical limit to that.
One last time, current flow is from the center power rail through the pickup roller through the load to return. assuming the transformers are properly phased, if two pickup rollers are connected to two different blocks with a common outer rail current will flow from the higher voltage center rail through the load to return. The motor will operate at a speed dictated by the higher voltage but not the sum of the voltages.
Don't believe me, try this. Take a ZW. Tie the A and D Leads together. Now connect the tied wires and the U connection to a test track. Crank up the A throttle all the way and the D about 1/4. Measure the AC voltage at the track, it will be around 18-20 volts. Measure it at the transformer from A-D to U. Surprise? It will be 18-20 volts. Now measure the voltage from A to D, it will be zero volts. Finally put a train on the test track and observe how the speed is controlled by wichever control is set the highest.
I think I see what you did there, Al. I'll guess that you used a modern "ZW" and not a real transformer, like the Zs that the original poster was asking about.
Try it with a Z, ZW, KW, or any two phased PW transformers. The results will be the same.
No. The result was a loud hum and a voltage intermediate between the two settings for a few seconds. Then one of the Zs' circuit breakers tripped.
Maybe this will explain it: Model the two transformer secondary windings as voltage sources e1 and e2 and their output impedances as z1 and z2:
e3 o z1 | z2 --/\/\-----/\/\-- | --> | |e1 i |e2 --- --- | | | || ~ | | ~ | --- --- |0 |0 | | -----------------
The current flowing between them is the voltage difference divided by the sum of the impedances:
i = (e1 - e2) / (z1 + z2)
The current flows from e1 to e2, in the direction of the arrow if e1 > e2 and opposite the arrow if e2 > e1. The intermediate voltage is e2 plus the product of the current with z2:
e3 = e2 + i * z2
Substituting the expression for i into this equation gives
e3 = e2 + (e1 - e2) / (z1 + z2) * z2
After some algebra,
e3 = e1 * z2 / (z1 + z2) + e2 * z1 / (z1 + z2)
Which can be rewritten as
e3 + e1 * k1 + e2 * k2
where 0 <= k1 <= 1, 0 <= k2 <= 1, and k1 + k2 = 1. That is, e3 is between e1 and e2.
I feel I have to say this:
Current flows in both directions in AC powered systems, which way depends on which half of the waveform is active. To say say it flows from the center rail to outside rail is WRONG!. Current always flows from the more negative side to the positive side. So when you have +18 volts on the center rail the current flows From the outside rail TO the middle rail. The second half of the wave would then be -18 volts and current would then flow from the center rail to the outside rail. This is why Transformers need to be "in phase" to work together, you don't want one at + 18 while the other is at - 18.
All that math gives people headaches
Current by convention flows from positive to negative. But electrons in wires and vacuum tubes flow from negative to positive, because they have negative charge. Positive charge carriers, like ions and holes in semiconductors flow from positive to negative. The US Navy did electronics a disservice years ago by trying to reverse this positive-to-negative convention. They provided training materials for electronics technicians for all the services; and they thought that it would be easier to understand vacuum tubes if they switched the current direction. In my career, I have often encountered misunderstanding and confusion between engineers and military-trained technicians as a result. Ironically, vacuum tubes are extinct now and semiconductors (which do have positive charge carriers) rule.
The sense of a current can be defined either way before solving for its value in a circuit. If the defined direction does not match the actual current direction, the solution will simply be negative. For example, I defined the current in my circuit above as positive from left to right. But, if you look at the equation for the current, you see that it can be either positive or negative, depending on the polarities and the relative magnitudes plugged into the two voltage variables. A negative current from left to right is the same as a positive current from right to left.
Since my circuit models a pair of transformers all the voltages and currents are alternating, at the same frequency. The signs of the unknown current i and of the unknown voltage v3 reflect whether those variables instantaneously match the known transformer voltages or have the opposite polarity. They imply nothing about any average voltage polarity or current direction.
I just tried my test on a KW and confirmed most of what I said. My mistake was in saying the higher voltage throttle rules. It's actually the lower voltage that rules. I tied A&B together on my KW and measured the voltage between AB-U. (note, it's not necessary to tie all Us together they are tied together internally inside the transformer.) With one control at 20V the other at 10 the measured voltage was always the lower.
I took another look on paper and realized the lower voltage control shorts out the path tho the higher so current flow will be from the lower winding tap to U.
Since we are talking AC it's a valid point that the flow is reversing directions 60 times per second. However that over complicates things. So just pretend this is DC and current flows from + to -.
If you are doing this with multiple transformers and getting a hum and breaker pop I suspect the transformers are not properly phased. Try this with you Z transformers. Tie one of the U's and A together. Slowly increase the A controls. If you hear a hum and feel the transformer about to explode shut them down. Reverse one of the Zs wall plug 180 degrees and try the test again. You should be able to turn up both A knobs with out the transformer going into overload.
Once you get your Zs properly phased you should be able to use them across multiple blocks As long as you tie one of the U connections on each transformer together and connect to the outer rail.
The transformers are in phase.
BigAl 956 I just tried my test on a KW and confirmed most of what I said. My mistake was in saying the higher voltage throttle rules. It's actually the lower voltage that rules. I tied A&B together on my KW and measured the voltage between AB-U. (note, it's not necessary to tie all Us together they are tied together internally inside the transformer.) With one control at 20V the other at 10 the measured voltage was always the lower.
I'm sorry, but I can't resist.
Where do you think the missing 10 volts went, and at what current?
Rob
no one ZW is about 250 watts so you would be putting in 500 watts into a 300 watts controller.
Just because 500 watts is available, doesn't mean that the load will draw that. However, if the "controller", whatever is in it, is not able to protect itself if the trains cause it to draw the 30 amperes or so that the paralleled transformers can supply, then there is a problem. Another consideration is that you will need 10 AWG wire for the 30-ampere feeders to the track. Not knowing what all is in the TMCC components, I would stay with separate feeds to separate blocks, imitating the normal TMCC setup as much as possible.
rtraincollectorno one ZW is about 250 watts ...
~210 watts cold, 180-182 watts continuous when warm, is the output of a postwar ZW.
rtraincollector...you would be putting in 500 watts into a 300 watts controller.
It could be 2,000,000 watts, the TPC will only draw enough to deliver 300 watts at the output.
BigAl 956I just tried my test on a KW and confirmed most of what I said. My mistake was in saying the higher voltage throttle rules. It's actually the lower voltage that rules. I tied A&B together on my KW and measured the voltage between AB-U. (note, it's not necessary to tie all Us together they are tied together internally inside the transformer.) With one control at 20V the other at 10 the measured voltage was always the lower.
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