When looking at a few of the old postwar dealer display layout diagrams put out by lionel, I came accross something that confused me. The wiring diagrams on the D-265 and the 1957 super O layout (14 x 9) both say to hook up the upgrade section of a loop to terminal A on the ZW and the downgrade section of the same loop to terminal B of the same ZW. The reason for this is so the train can get more juice for the upgrade and less juice on the downgrade so it doesn't fly off the track.
I thought that if you cross two different circuits with an engine and the voltages aren't set the same, the coils inside the ZW will burn up. Am I missing something or was the just a diabolical plan by AC Gilbert to get lionel customers to switch over to American Flyer
You're not missing anything, John. You can damage most Lionel multiple-output transformers that way. Lionel seems to have been oblivious to the problem. The only transformer with a warning against it was the KW.
Many electrically naive persons think that there is no problem with doing that, and especially if the outputs are from the same transformer. In fact, doing it with the same transformer is the most dangerous way, since the resulting fault current does not flow through the circuit breaker and will therefore not trip it.
I have often encountered the fallacious "we've always done it that way" argument, that no harm has ever come from it. This belief probably arises from the fact that small voltage differences and brief cross-connections from running from block to block do not draw enough current for long enough to burn anything up. That doesn't make it safe, since it is inevitible that sooner or later, some train will stall over the gap and not be noticed. Anyone who, unlike you, does not recognize the problem, will probably never know why his transformer burned up "for no good reason".
Neil Besougloff wrote an article in the July CTT recommending this very way of operating. I wrote a letter to CTT warning of the danger. I received a reply from Carl Swanson, the new editor, expressing skepticism and asking for more information, which I sent to him. He said that he would have a frequent contributor who is an electrical engineer "run some tests".
I had heard no more, when the next, September, issue appeared with an article by Ray Plummer showing the same problematic scheme. I wrote Carl again and attached a photograph of a damaged transformer showing a distinct burned section in the middle of the secondary winding, which I believe could have resulted only from the kind of fault I was warning against.
I also described my own tests: I measured a fault current of 11 amperes between the outputs of type-Z transformer set to a 5-volt difference; and 30 amperes with a 10-volt difference.
Carl replied that his engineer "hooked up an old-style Lionel transformer and measured the power flow through the device in every wiring combination he could think of." His conclusion was "that a fault condition will uniformly raise voltage across the windings, but at no time did the voltage approach the safe working limit of the windings." I can make no sense of this and can only imagine that there was a communication failure.
He went on to claim that Lionel transformers cannot be damaged by wiring faults. I know that this is not so.
He then invoked the "we've always done it that way" dogma and cited the experience of someone with eight transformers and block signals as evidence.
Finally, he asserted that in new transformers "[t]he waveform is always the same from the output of each 'handle'. There is no potential difference (voltage) between multiple controls regardless of their respective settings." I mention this irrelevant item only to show the extent of his electrical knowledge.
Carl was unfailingly cordial through all of this. I believe that he is completely sincere in thinking that there is no problem. I suspect that he thinks that I am a crackpot, although he would never be so impolite as to say so. However, he is an editor, not an engineer. I am posting this in the hope that other engineers and those with other electrical credentials will back me up by writing to Carl. From his point of view, it is his engineer's opinion against mine; and he knows the other guy.
I don't think it's a typo, Keith.
I might mention here that there's a safe way to do what Lionel and Neil were trying to do: You just use a single transformer output and put a passive voltage-dropping element between the transformer and the center rail of the sections where you want the train to slow down. That element can be, for example, a traditional Lionel rheostat, or, for better voltage regulation with varying load current, a diode network. Both of these have been discussed extensively on the forum.
I hope Bob Keller and Carl are reading this thread....Anyway, it would seem that if someone of Bob Nelson's obvious credentials has a caution regarding something as hazardous or potentially so as this topic, that at minimum, CTT would print Bob's caution so that the reader could make the decision to go the way Neil mentioned, or play it safe and use Bob's advice. Regardless of Carl's "engineer", I put that in quotes as we are not aware of what his credentials are, whatever his experiments results were, to have even one credible person show a potential problem warrants a warning. The "we've always done it that way" arguments doesn't stand in a court of law. As curteous as Carl was in his response to Bob, I think the more prudent thing would have been to have his "expert" call Bob Nelson and discuss the problem. If Bob was able to tell him exactly how to set up the experiment as he has done, perhaps the advise of this expert would have been different.
I will side with Bob in this one and wire my layout accordingly.
Thanks, Dennis. I don't want to disparage Carl's engineer, not knowing anything about him. As I suggested, I think it likely that Carl was unable to frame the question correctly or misunderstood the conclusion. So I agree that it would have been much better to have been able to talk to him directly.
I used a type-Z transformer. I set the difference between the A and B outputs to 5 volts. Then I shut off the line voltage input. I put a 14 AWG wire several inches long between the A and B terminals and clamped an AC ammeter over that wire. Then I switched the line voltage on only long enough to read the current, which was 11 amperes. I repeated the test with a 10-volt difference, and then later with 15 volts. In both latter cases, I measured 30 amperes.
For the voltage test, I set up my oscilloscope to trigger DC coupled at 150 volts, connected it to one of the transformer A or B outputs, set those outputs 10 volts apart, turned the transformer on, then briefly shorted the A and B terminals together with a clip lead (which doesn't look nearly as good now as it did before). Every few trials caused the oscilloscope to trigger. I would have tried a higher trigger threshold; but, lacking a times-10 probe, 150 volts was as high as I could go.
FWIW, I agree with you. My credentials are an MSEE from Purdue (1984). A quick study of the circuits shows that this fault current is going to exist, and it's going to be quite high.
What frightens me more about this "tried and true" method of wiring is that this fault current is going through the center roller assembly every time the two rollers span the insulating pin between the 2 electrical sections in the track. If it were just individual wheels spanning gaps as in the DC counterpart, the damage would be less. But with 2 rollers spaced a couple of inches and linked by a metal assembly, the spanning of the gap is not so momentary, and neither is the fault current. I suspect the postwar transformers, because of their relatively rugged construction stand up better to the abuse than the rollers.
I am willing to bet that a couple of CW-80 transformers coupled in this way would see foldbacks on a regular basis.
It is really hard to convince folks, even in the DC world, what a poor system section control is. And that block control was invented specifically to solve these problems.
After reading the postings above, I vote with Bob. Can anyone show it mathematically? graphically? TIME vs ??? graphs.
Buckeye; a BSCE Purdue 1974, and I know enough to put fresh batteries in the flashlight to walk through the railroad tunnel so maybe my vote should only be counted as 1/2. BTW, "tried and true" built the Minneapolis Bridge, too.
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I have read all the theoretical doom and gloom about all this, but does anyone have any practical experience to share in all this? Has anyone burned out a transformer or overheated anything? I'd like to hear from them.
For myself, I have been using 2 transformers to control the speed upgrade for quite some time now and I haven't had a problem so far.
dsmith wrote:... For myself, I have been using 2 transformers to control the speed upgrade for quite some time now and I haven't had a problem so far.
This will pose little if any problem. The big problem is using different taps off the same transformer transitioning from one block to another when the voltage settings are different.
Which is what I've been doing on my current layout since about 1971 w/o any problems. 4 lines, all interconnected, on 1 ZW. BUT, don't do this at home... I'm a professional.
"I wrote Carl again and attached a photograph of a damaged transformer showing a distinct burned section in the middle of the secondary winding, which I believe could have resulted only from the kind of fault I was warning against."
"Anyone who...does not recognize the problem, will probably never know why his transformer burned up 'for no good reason'."
Thanks to everyone for such a great discussion. I just got home from Long Beach Island, NJ and am very surprized by the responses from the last few days. Bob, I agree with what you have said. Unlike CTT, you are very clear on what you found. The thing that scares me the most is this: "In both latter cases, I measured 30 amperes." From what I know on ZWs, they should trip at 15 amps (correct me if this is wrong) and they are not UL listed. The fact that the circuit breaker wont break when you connect two circuits from the same transformer may be why the UL wouldn't list the ZW as a safe product. (Maybe the UL guys were reading the same diagrams I was and said WAIT THATS NOT RIGHT) This problem is also why I will not be linking circuits EVER. I love ZW transformers. They are reliable and powerful, BUT I dont trust these things as far as I can throw em'....