I have always phased my pw transformers. I understand the new transformers have different sine waves and they cannot be exactly phased but does it matter ? IS it still best to phase them when using common ground wiring? Any issues when the old and new are phased?
Thanks
dogdoc
Don’t do it with the intention of running between blocks powered by different transformer outputs, whether from different transformers or, worse, the same transformer. In order for this to work without creating a fault current between the transformers (and through your train’s pickups), not only must the phase and voltage be the same on both sides of the gap, but also the entire waveform, which, in a newer “transformer”, as you observed, can be quite different from a sine wave.
However, even if you are using a good block-control system, mistakes will happen. This is the only good reason for having the transformers in phase, not to eliminate the danger of fire and damaged wiring, but to minimize it when the inevitable mishap occurs.
All of this applies to running the trains. For accessories that share a common with the track, having the accessory’s supply out of phase with the track supply is beneficial in that it reduces voltage drop in the common return, that is, the outside rails. It’s not a big deal, however.
To protect the transformers and trains I have installed 6 amp resetable circuit breakers in series with each track output on my ZW (post war). They will trip quickly with a fault current (or any short) before anything can heat up (as with a stall crossing the blocks). The old post war trains do not even trip an eunit with a momentary fault current. They are not on it long enough for anything to be damaged. The newer circuit board trains may be a different story. I certainly do not try to have a fault current of course. I have measured it with my ammeter and if voltages are close it is not very high below the breaker levels on the old transformers(Iknow that circuit is unprotected) but the circuit breakers give me piece of mind to prevent a burned or damaged secondary coil. Do the newer transformers have fast breakers or protected circuits that the post war transformers lack?? I recently reconfigured so I can run the whole layout with either zw control or run each loop separately. When I cross, a fault current is a nonissue since I usually do it with just one output but I can do the old way if desired. dogdoc
I mostly worry about fire safety when I hear about running between differently powered blocks, and it seems that you have taken care of that with your extra circuit breakers on the ZW. But your concern about newer train’s being damaged is well founded. What happens is that, when a fault, however brief, clears, the stray inductance in the secondary winding of the transformer can put out spikes of hundreds of volts, which can do in modern electronics easily. Besides avoiding operation that may create such spikes, I often urge use of transient-voltage suppressors to take care of this problem.
Some folks believe that fast circuit breakers or fuses are sufficient protection from voltage transients. In a derailment, they will open the circuit earlier than a thermal circuit breaker and therefore reduce the exposure; but they still allow some to get through. I prefer to let the circuit breaker take care of overcurrent problems, for which thermal breakers are well suited, since they more or less model the temperature rise of the wiring, and handle the overvoltage problem with TVSs, which are well suited to that job.
What’s inside modern “transformers” is hard to say. Only the manufacturers really know; and they aren’t talking.
Thank you for your responses. Where Can I get the tvs devices and what specs do I need to look for? How are they wired in place? Thanks
dogdoc
Here is a link to a recent topic: http://cs.trains.com/trccs/forums/p/147890/1639452.aspx#1639452
You wire them in parallel with the track. It doesn’t much matter whether they are upstream or downstream of your circuit breakers.