10 1/2 Easy Electrical Tips in September CTT

[webenda]

Don't be discouraged Bob, many of us understand it is bad practice to parallel two different value voltage sources together (as occurs when the pick up rollers or slider "make" the gap in this case.)

Our three rail transformers are robust enough we generally get away with the Arc'n and a Spark'n at the transition between blocks. Your tests indicate a maximum of 14 amps (5 volt differential.) Not enough current to smoke a ZW. As you point out, current would be even less with layout wiring and rail resistance added to the fault circuit.

Without Smoke'n wires to go with the Arc'n and a Spark'n, I am afraid the "try it and see what happens" crowd wins this argument.

Your transformer with the burnt section seems to be an exception.

[Buckeye Riveter]

webenda

Don't be discouraged Bob, many of us understand it is bad practice to parallel two different value voltage sources together (as occurs when the wheels "make" the gap in this case.)

DITTO 

[lionelsoni]

It's not because I haven't preached cab control, Dennis; I'm sure of that.

Wayne, as I see it, the (barely) tolerable fault current of 14 amperes at 5 volts is not itself the danger; but it encourages the attitude, as Big Al wrote earlier, "that this never happens".  Yet it can happen.  One probably wouldn't deliberately run across a block gap with an 18-volt potential difference; but my little experiment indicates that you can easily burn something up if you do that by mistake.  The temperature rise in the wiring goes as the square of the current; so much less than the 30-ampere fault current that I measured would do the job.

The last paragraph of the column that I mentioned warned, "It is possible that an electrical short on an unattended layout may heat the foam to its ignition point."  That consideration should apply to anything that can start a fire and motivate us to avoid overheating wiring as well as keeping it away from foam and other fuels.

As for my burned transformer, it is an exception, but only in the sense that a car obliterated at a grade crossing is an exception as compared to all the other cars that beat the train.

[8ntruck]

Interesting thread.  I am currently working on a display layout that will have a long upgrade and a steeper downgrade.  In previous incarnations of this layout, I manually manipulated the throttle to keep things under control.  This year, when I build the display, I won't be able to pay as much attention to it while it is running.  I plan to use the opposing diode method that Bob suggests for speed control o the grades.

I will set the layout up with three blocks - low voltage for down hill, full voltage for up hill, and a medium voltage for the level sections.

If I were going to run  post war locomotive with an electro-mechanical e-unit pulling unpowered freight cars, I'd be tempted to use three outputs on a ZW to set the voltages for each block and take my chances that the over current would be of a short enough duration that nothing would get seriously cooked.

 

HOWEVER, I will be running a modern locomotive with sound and an electronic e-unit pulling a consist of lighted passenger cars.  In this case, the addition of the lighted cars will cause the over current to be of several seconds duration.  Long enough to worry about heating things up, not to mention the probability of zapping the electronics in the locomotive. 

Why take chances?

I am a mechanical engineer who knows enough about electricity to be dangerous.  There is good advice here.  I am going to follow it.

Yes, I will include a TVS on each block. 

[webenda]

No argument from me Bob, I concur.

[overall]

I wonder if anyone has ever actually tried using different outputs of a ZW on the same loop but with amp meters in the "hot" leads going to the middle rail. You could actually observe what it is really doing that way. As mentioned above, you should not try this with modern electronic equipped trains.

George