layout question, voltage question, and I'll probably have more later

[Anonymous]

Layout
I am trying to design an n-scale layout using atlas code 55. When choosing turnouts, is there some guide as to which turnouts correspond to certain radiuses (sp?)? For example, use a # 7 turnout with 18.75 radius track, use a #5 with 15.00 radius track, etc. I am simply trying to have a turnout come out from the main line, then have a corresponding opposite turn "straighten" it out to make the new line parallel to the original line.
Voltage
I have a kato japanese bullet train (10-354 "grand hikari" 100 series). It says no more than 12 volts. Most of the transformers (MRC 200 and the like) pump out 16, 18, or more volts. Will that be too much for the train?

thanks for the help

[selector]

While I can't directly address your first question, (although I'm pretty sure it doesn't matter a great deal, ..unless space is really tight. If so, then get the tighter radii, assuming your locos can deal with it), but you should avoid what will result in an "S" curve if you can. Trains, real and model, hate s-curves, and you will place one before them if you ask them to diverge out of a turnout, and immediately swing back the other way. Strangely, this flies in the face of my first bit of advice...to get tight radii if space is an issue. Welcome to building track!

As for your voltage question, yes, that will be too much voltage, but I am going mostly on what the manufacturer is telling you. Not sure why you would second-guess that warning. Get another transformer, or maybe rrinker, our electronics wizard, will introduce you to the idea of in-line resistors, or some arcane thing. He lurks here late into the night, and may offer some advice. By the way, take his before mine...fair warning.

[IRONROOSTER]

The NMRA Recommended Practice 11 has turnout/curve recommendations for different types/lengths of rolling stock and engines.

One way to do what you are trying to do is to use a second turnout of the same size as a template for the curve.

Enjoy
Paul

[dknelson]

Seem to me the main thing is that your turnouts should not be tighter radius than your curves, but broader. There is no need to match them exactly. A turnout as the start of a curve can be effective and sometimes is needed to save space but tangent into a curve is the most pressure on the flange and a frog and points do add an element of vulnerability. If the turnout is a large number at the start of a curve it can even function as a sort of informal easement curve
Dave Nelson

[Leon Silverman]

The sixteen or eighteen volt you see on a transformer is likely to be for the AC side, not the variable Dc terminals of the powerpack. A good investment would be a multimeter, available from any place that sells tools or Radio Shack.
The stated voltage is the voltage seen when applied to the bare terminals of the power pack. As soon as the power pack is hooked up to any kind of circuit, the voltage will drop because the current supplied by the power pack has go through internal resistances which effectively lower the terminal voltages. Add to this is the resistance in the circuit itself which further drops the voltage. Consequently, the 14.5 volts available across the unconnected terminals of the power pack may actually drop below 12 volts by the time your engine sees that power on the tracks.
This is why you need the multimeter to measure the track voltage and why you see in other entries of this forum the recommendation to apply feeder wires to every three feet of track. The feeder wires mimize the effective resistance of the track and maintain a constant value regardless of the distance between the power source and the locomotive. This enables the engine to maintain a constant speed instead of slowing down at the farthest point from the power pack.

[rrinker]

On no, you'll se 16v easily from the "0-12v variable DC" side of most typical power packs. Of course, this is with no load. But, a single N scale loco is going to be pretty close to "no load" unless it's a very poor quality one (which Kato isn't).

Solution #1: Just never turn the speed control to full power. A brief hit of full power will not liely damage anything, but will shrtent he life of the headlight bulb. Continued operation with a coupleof volts too much could heat th ebulb enough to melt the shell, and possibly overheat the motor. But as most N scale tends to run 300 mph at full throttle, you probably won't run more than half speed anyway, which means you will be below the 12v at all times.

Solution #2, use a bridge rectifier to provide some voltage dropping. With each bridge you'll get 2 diode's worth of voltage drop, about 1.2 volts. A bridge rectifier has 4 terminals. Two are labelled AC, or with little waves. The other two have a + and - by them. To use a bridge rectifier for voltage dropping, you connect he two + and - terminals together. One line from the power pack connects to one of the AC terminals, and the other AC terminal goes out to the layout. You will need a bridge of suitable current capacity, 2 Amp or better should be fine for N scale.
A bridge is easier than wiring up a bunch of individual diodes - you need two sets, otherwise it will only work in one direction.
Do NOT use resistors for voltae droppign liek this. They are very inefficient plus the voltage drop varies directly with the current load - Volts = Current x Resistence (Ohm's Law). So the more current being drawn, the greater the voltage drop. A silicon diode has a fixed forward voltage drop that is not current dependent (until you exceed the diode's capacity and blow it out).

--Randy

[selector]

See? I told you it would be arcane. [:D] So, despite what I said, no resistors, but a bridge rectifier. I'll try to file that for my own benefit, too. Thanks for the response, Randy.

[Anonymous]

Thanks to all for the advice.
As for the voltage, I'm probably going to stick to solution #1, keeping the throttle down.
thanks again,
Robb