Didnt know they were heat activated breakers. I like that because if the transformer gets too hot it also will trip.
I have another question thats a bit off topic but wanted to bring it up before I forget. If I remember correctly, when a train crosses two unphased circuits and the rollers connect the two there is a serge of power equal to the two combined voltages. When two phased circuits are joined and not at the same voltages there also can be damage done to the coil and new electronics.
Is there anyway of putting a “resistor” inbetween the track and tranformers so that no more than 20 volts can go in or out?
What I said is if the breaker in the transformer is old, it can be slow at opening. And they do. In the worst case, they don’t open at all. I have seen torched transformer windings as a result. This one of the big reasons it is advised that old transformers be rebuilt before use on train layouts.
Are you talking coils and electronics in the new transformers? The damage would be no different than a direct short (if the transformers are phased). The thing to do is have digital voltmeters on your power supplies and make sure you get the same reading when the rollers cross the gap.
I was talking about the coils in postwar ZWs and any new electronics on the track. I figured that was the best method but wanted to see if there was some secret to solving that issue.
Well, actually what you said was, “the breakers in old transformers are slow at opening”, which is a little stronger than “if the breaker…is old, it can be slow at opening”. I can agree with the latter possibility; and I hope you would admit that an old transformer might well have a completely functional breaker. (Mine seem to!) If it doesn’t, I would be the first to advise replacing it. But I would do so with a good one of the same type, whether an exact replacement or a modern functional equivalent.
I would say (and have often said!) that “the thing to do” is not to run between blocks powered from different transformer outputs.
“Is there anyway of putting a ‘resistor’ inbetween the track and tranformers so that no more than 20 volts can go in or out?” Yes! but not a resistor. Rather, put a transient-voltage suppressor (TVS) in parallel with the transformer and track. There should be numerous posts that you can search for that will give all the details.
Didnt know they were heat activated breakers. I like that because if the transformer gets too hot it also will trip.
My usual source of information is “down” tonight so I can’t check it, but I seem to recall that in some versions and/or certain production runs of the ZW, Lionel actually wrapped a “resistor wire” around the circuit breaker in order to provide a little additional heat, so that the circuit breaker would open faster than otherwise. To put it another way, it seems that Lionel recognized that their thermal circuit breakers were often slower to pop than was desirable.
From the service manual: “Because circuit breakers of correct value could not be obtained for the ‘VW’ transformers built in 1948, a length of resistance wire in insulating sleeving was wound around the circuit breaker and served as a heater to decrease its breaking time in case of short circuits.”
So what they were doing was effectively altering a higher-current breaker to trip at a lower current suitable for the VW. I have no opinion on whether they got it right.
I realize this isn’t really front page news. However, I’d have sworn I saw something similar for ZW’s. I have never owned nor even seen a VW; but curiously enough I have seen at least one ZW or perhaps KW circuit breaker with several turns of a white wire wrapped around it.* My concern is simply that an amateur like me someone doing home repair on his large transformer might not understand what this rather odd-looking wire was for, and unwrap it, or remove it altogether, or whatever – assuming that it actually did function – a fact not in evidence.
*Seein’ as how I haven’t done much repair work on other folks’ transformers, it almost had to be either a ZW or a KW of mine – unless some dealer has sold me the old rubber peach and called it a ZW…
I no longer have a KW with which I can check, however I’m pretty sure I also remember seeing a length of asbestos-insulated wire around the circuit breaker in the KW.
I’ll dig up the inside photo I took when I sold it on Ebay, and see if I can confirm whether or not I’m remembering correctly.
Yes this wire is present in the KW also, but it is not wrapped (the wrapped one you are remembering may be the rectifier resistor). It is between the breaker and the lamp. It can be seen on pages 2 and 3 of the KW’s explosion diagrams.
One end is soldered to the lamp housing/holder metal outside. When you replace a lamp housing you need to unsolder and resolder this wire.
If I remember correctly, replacement wires can be purchased through various parts dealers.
If you are running modern electronics on the track with older style transformers, than fast blow breakers have been recomended by many because even if good, the older thrermal style breakers do not open fast enough. Surge protection is also recomended. A derailment short can cause a surge.
I would not worry about the difference in voltage when crossing tracks on older style transformers that are phased. The short is so intermediate, it shouldn’t harm the coils (heat is what does the damage). If you are using new ZW’s with electronics, then I would worry.
I didn’t word myself very well I guess. I meant it both ways really. I also said if his track feeders (off the buss wires) are not sized to the breaker, he could melt the insulation with a direct short. But now that he’s posted he’s running electronics on the track with older style transformers, fast blow breakers are a wise decision. Because like you say, the older style breakers are thermal. They don’t open fast enough to protect electronics.
I really dont have anything with new electronics except the whistle for my 1996 scout engine. Were going to get the MTH subways cars but they wont be crossing circuits, only in their own loop. I guess I should still put in a fast acting breaker for that loop.
Im a postwar guy and dont intend on getting any modern era stuff for the most part except for a few things my dad would be interested in.
Bob, Im going to take a look at the info on those TVS when I have some free time later on tonight.
So its the heat from a short that damages the coil, not the change in voltage (like 20 volts where 15 volts is on the coil)? I wonder how the wires/coils could get so hot to damage them if the breaker opens before damage can be done. Is this because when you phase transformers they become like one tranformer and when a short is caused between two circuits of the same transformer the breaker wont open?
Thanks for everyones input. This has been one of the more informative threads Ive read in a while.
Let’s say that I have TVSs connected across each of my transformer outputs, as you’ve advised doing. Would placing a lamp in series with the TVS cause any harm?
If I’m thinking correctly, the lamp should flash every time the TVS activates. It doesn’t seem to me as though it would do any harm to have any additional resistance between them, however I thought that I’d better ask someone who actually knows what they’re doing.
In addition, what about, rather than connecting the TVS across the transformer leads, connecting it from the “hot” terminals to earth ground? Would this work, it would it cause problems?
A short circuit reduces the track voltage to zero, which is not harmful to old or new locomotives. What is harmful is the inductive voltage spike which is likely to happen when the short circuit is cleared. It can easily be hundreds of volts. Short circuits are rarely clean on-off events. Instead, the short circuit may come and go dozens of times before things stop moving, generating many spikes.
A fast circuit breaker or a fuse can help by opening the circuit before all the spikes have had a chance to occur; but it is very likely that it will let a few by anyway. The TVS is a much more certain fix, since it simply doesn’t allow excessive voltage to exist on the track.
Putting a lamp in series with the TVS would prevent it from doing its job. Most of the excessive voltage would appear across the lamp; and all of it would appear across the track. Connecting the TVS to ground would be okay if the layout common is also grounded. But that is the same as connecting it directly across the transformer or directly across the track.
Apart from the voltage danger to electronics from running between separately powered blocks, there is a fire danger when the blocks involved are powered from the same transformer. In that case, the transformer’s circuit breaker will not trip. So, if the train happens to stop in the wrong place, wiring and transformer can burn up. With separate transformers, we can hope that one of the two transformers’ circuit breakers will trip.
John, I would suggest pricing 12ga stranded wire vice solid copper. In the electronic industry you will always find the use of stranded connecting wires and even in shielded cables. Stranded wire eliminates EMI (Electro Magnetic Interference). Tests have not been done but I believe it would help if someone is runing DCC or TMCC.
I’m afraid that stranded wire is electrically indistinguishable from solid wire. The only reason for using it is its flexibility.
There is a very special kind of stranded wire, called litz wire, that is electrically different but not anything you’re going to find at Home Depot, or anywhere for anything like the price of ordinary wire; and there is no particular advantage in using it for toy trains.