When I was a teenager, I built a SCR-based electronic throttle that used a lamp just as you described. I didn't understand the lamp's purpose or principle when I built it until I had a short. The protection worked perfectly and that lamp aglow was hard to miss.
My apologies for correcting your statement, but it is incorrect. The application of Ohm's law is misplaced here. In this scenario we have a DC series voltage divider circuit. There are (2) resistances at play. The first is the resistance of the wire(feeder/bus/rails). The second resistance is essentially that of the loco's motor windings. The voltage drop occurs according to the ratio of the individual resistance in question divided by the total resistance (wire+motor). The amount of voltage drop is independent of the amount of current through the circuit. This may seem counter-intuitive but it is fact. The motor winding resistance is essentially constant. But if the resistance of the current path increases, the total resistance also increases and the voltage dropped across the current path (wire) also increases. This results in a lower voltage being available to the motor. The lower voltage will reduce the motor RPM. Whether the change is apparent depends on the amount of the resistance change. Naturally if the resistance of the current path decreases, the motor RPM will increase.
Well, you are still missing the point and misleading those readers who don't understand Ohm's Law very well. A power circuit to a model railroad track may have a variable voltage (DC) where the voltage is used to control motor speed, or it may have an alternating +/- voltage with constant peak values, which is used by a power-controlling minicomputer in the loco itself to control speed. Either way, the current in the track feeder wires increases when the locomotive uses more power. With a fixed resistance in the feeder wires, the voltage drop from one end of the feeder wire to the other is going to be given by Ohm's Law as V(drop) = I(through wire) x R(of wire). So, for a DC case, when the voltage is increased to increase speed, the current increases and the voltage at the end of the wire at the track will be slightly lower than it would be if the current had not increased. But, in a DC case, you will not notice that because you just keep turning up the voltage until you get the speed you want - until you have turned it up all the way, at which point the loco is going as fast as it can go with the load and grade it has to deal with. Because most locos run way too fast at full voltage on DC, that may never be noticed. On DCC, things are different. The voltage at the loco needs to power a computer and power management electronics. Those electronic circuits are not simple, passive devices that obey Ohm's Law. As they go around the track with the locomotive, encountering changes in track voltage, they may (or may not) be able to compensate for the reduction in peak feed voltage as they control the peak voltage and pulse width of the power they feed to the loco motor. So, you may or may not see loco speed vary with track voltage. But, there is a more important consideration: during a short circuit condition, if the increased current causes the voltage drop in the wires to become high enough to limit the current to a value below the trip point of the protecting circuit breaker, then the current will persist for a long enough period to melt something, somewhere. What usually melts is some part of the locomotive, usually near wherever the short circuit is occurring. That is why it is important to check you trackwork for adequate over-current protection with the "quarter test" (or equivalent), which puts a short circuit across the track to see if the breaker will trip. All points on the trackwork need to pass that test. You cannot do this test by simply putting a volt meter on the track and reading full voltage without some sort of load, because, with (nearly) zero current being drawn by the volt meter, the voltage drop through the wires is nearly zero, no matter how much resistance is in the feed wires, they will show full track voltage when there is no load on the track. That is why it is important to realize that the voltage drop in the feeder circuits is directly proportional to the current through those wires,
Getting back to the issue that originally started the lectures on Ohm's Law: Running heavy "bus" wire along the paths of the trackwork and connecting the 24 gauge track feeders to the bus does help reduce voltage drop to the track when there is a substantial current draw, because voltage drop in the wires is related to both their resistance and the current passing through them. And, the resistance of a piece of wire is related to both its cross section (gauge) and its length. So, for long runs of wire, using thick (lower resistance) wire for most of the distance and a thin (higher resistance) wire just near the end (to get to the track) will produce a path that has overall lower resistance than using thin wire for the entire length.
I find that Kato has an all new DC power pack, a 22-018 with improvements over the older 22-014, including Pulse Width Modulation for improved slow speed control and for brighter LED lighting at slow speeds. Does the new pack have the same footprint as the old pack? My control panel is dimensioned to fit the old pack, but I want the new one instead if it will fit the same. Thank you.
Thanks MK. Unless that's the package dimension, the new pack is larger than the old. Hmmm. I might be able to run my control panel through my table saw to bisect it, add in extra width and length to the power pack area and add another layer of laminate to cover it up.
comparing the size of the two knobs, which I doubt they changed, I would expect the two to be the same dimensions.
I phoned Kato this morning to ask. They didn't offer exact dimensions, but they confirmed your thought -- both old and new packs are the same size. Good news for my railroad!
On previous layouts, I have always tended to add way more track feeders for power than I really needed too. Now, I am looking at building a smaller size (maybe 3ft x 6ft approx.) layout using UniTrack. What do you all recommend on adding additional power feeder tracks?
And stranded wire carries more current at lower resistance than solid core. Without getting into physics, most electrons travel essentially on the surface of the wire, stranded wire has more surface area than solid core...
On THERR I put feeders at the end of every 3rd piece of UniTrack. Overkill is too much work Thats a feeder every 29.25 inches on straight track. I put feeders before and after every turnout...never on the turnout itself. Mine was done in 2012 and has been working great ever since.
... And stranded wire carries more current at lower resistance than solid core. Without getting into physics, most electrons travel essentially on the surface of the wire, stranded wire has more surface area than solid core... This is not exactly true, electrons do not really flow, they just move to higher energy valence bands and then drop back to their original valence band and move the energy to the next atom. It is energy that flows from one atom to the next. But the energy does like to move along the surface......
Thanks for that feedback. I was kind of hoping I could cut back a little but that is about the same as what I did with flex track. Everywhere I had a joint in the rails, I had a feeder. I realize I'll have more joints with the UniTrack but the distance sounds like it still needs to be about the same, every 30 inches or so and before and after every switch?
My last Unitrack layout I had six feeders for each 42' loop, so about one every 7 feet. Never noticed any voltage drops. I think some folks are still trapped in the mindset that rail joiners are poor electrical connections. Certainly that was true back in the days of brass when oxidation was a certainty. Not so much with today's joiners.
It is not that they are poor conductors, unijoiners are great...BUT! You can, and probably will, be just fine, but if you are fully scenicing a layout and ballasting the Unitrack, there is always a possibility of failure at some point. Dropping feeders from each piece (where practical) is a good safe guard against future problems. For DCC, every 6 or so feet ensures a clean signal at all points.
Yuppers My first layout had flextrack that was 30 inches per stick. One feeder per stick. So I figured I would do the same with Unitrack 3 pieces=29.25 inches...close enough. In 7 years I have had only one Unijoiner that gave me grief. I'll take the easy way out every time. A quick pass with solder on the metal part of the Unijoiner and rail...and that piece has behaved great ever since.
Lots of discussion throughout this tread on the #4 and #6 turnouts. I'm planning on using the #6 for the most part. For those of you that have used the #6 to create a passing siding, I'm curious what curve section you used to come off the switch to make the siding track line up parallel to the main?
You can use any 15 degree curved section and it will line up parallel. The difference is in how much space you want between the tracks and how sharp you want the radius.
