Trying to understand lektrissity!

[jacon12]

I've been building benchwork in sections for an around the wall style layout. As I completed a section I temporarily put it next to another, lay track directly down on it without fixing it permanently with nails or glue. The rail joiners are not even squeezed together. While running a locomotive around the track I noticed that it would hit areas where it slightly slowed down or picked up speed and that brought up questions about just how do you know what size power pack yu need for a given size layout. Being new to all this I'm assuming that feeder wires running from the main electrical wire (under the layout) will keep the voltage or amps (I really don't understand those two and never did!) fairly constant. I'm using Digitrax's Zephyr.
So, how do you determine how much power you need? Is it determined by the size of the layout or how many locomotives you're running or what?
Thanks for any help!
Jacon

[dwRavenstar]

Hi Jacon,

Your slowing down and increasing speed might be caused by differences in the way your track has been cleaned thus effecting the flow of electricity through the loco's motor.

With a constant source of voltage (measured in volts and akin to pressure) a change in resistance (measured in ohms) will effect the flow of current (measured in amperes, or amps) Less resistance will allow greater current flow through the circuit and greater speed from your loco for a given voltage setting.

It's like a bucket of water has pressure applied to it's sides by the water inside. Poke a hole in the bottom and water will flow out. A bigger hole offers less resistance and a greater flow of water escapes.

Film on your tracks or a loose electrical connection appears to the voltage supply as greater resistance and less current is permitted to flow through the circuit. (Positive rail to Negative rail through the motor of your loco.)

You can measure all three values; voltage, current and resistance with a multimeter.

Knowing two values allows you to calculate the third using Ohm's Law:
Voltage = Current X resistance
Current = Voltage / Resistance
Resistance = Voltage / Current

To calculate Power (measured in watts) you multiply your voltage X current

If your loco behaves the same way at the same point on the track on every circuit the problem might lie in that area of the track. If it occurrs sporadically in different places at different times it may be that there's a loose connection in the pickup mechanism inside the loco. My understanding of that is limited but to my understanding there are sprung metal connections that you can replace with a hard wired setup that should cure the ailment.

It's been my experience that a RR layout is like a day care center; you get the loudest kids quieted down and a couple of others start acting up. You gotta wanna do it to keep the frustration level at a minimum.

Hope I've been some help. Good luck in your quest. [banghead]

Dave (dwRavenstar)

[rrinker]

How much power you need is mostly determined by how many powered units (locomotives, lighted cars, and anything else that gets power from the track) you intend to run. For the most part, this works out, because the people that want to run lots of locomotives have bigger layouts, so they get additional boosters for more power.
Where this can break down is if you run by yourself most of the time yet have a HUGE layout. Both the tracks and the heavy wire which you should use for a bus under the tracks has resistance. This causes the voltage at one end to be different from the voltage at the other end. This is called "voltage drop". Say you're one of the lucky ones with a HUGE basement, and the length of your bus wires under the layout stretches 200 feet around he walls and various peninsulas in this grand layout. If you put the power source at one end, to reach a train at the opposite end, the power must flow through 400 feet of wire! (Out and back - nothing running on electricity will work without a complete circuit!) Even with very heavy gauge wire, there will be a noticeable voltage drop in 400 feet. This will lead to locomotives slowing down. In a situation like this, you may need additional boosters spread out along the layout, even if you don't really need to run that many trains.
Two things to keep in mind when planning the wiring. First, you should try to keep the wiring as short as possible. Say you have a 2x10 switching layout. The best practice is to put the power source in the middle - then you have maximum wire run of only 5 feet (10 total feet of wire). Second, use heavy enough wire, to minimize the loss. There are tables around to help you calculate the loss per foot of various wire sizes. In HO or N, I wouldn't use anything less than #14 for a 4x8 size layout, #12 for anything bigger. Remember that in American Wire Gauge, the SMALLER number is THICKER wire. Likely your problem is caused by temporarily hooking up the track sections with the loose joiners - loose joiners do not carry electricity very well, this is why you put in a bus wire and drop feeders from the rails at periodic intervals. You need A RELIABLE source of power to the rails to keep the locos from slowing down.
For the case of the large layout where you need additional power - each booster should be as centered as possible in the section it powers. Between sections you should gap both rails, and of course the bus wire also has to stop at the boundary between sections.
Because everything in electricity is related - the Volts, the Amps, and the Resistance, by Ohm's Law: Volts = Amps x Resistance, you can see that for a set resistance, like how much resistance a length of wire has, as you increase Amps, the Voltage will also increase - the more power you try to pull through a long wire run, the greater the voltage drop will be.
That's probably enough to digest at one time. If you have any more questions, ask away.

--Randy

[snowey]

get a copy of the Kalmbach book "Easy Model Railroad Wiring" by Andy Sperandeo for answers to all your wiring and electricity questions.

This book is great, he explains all about wiring and electricity, in easy to understand text, drawings and photographs. He assumes that you know nothing about it, then goes on from there.

[jacon12]

Randy, Dave... thanks for the information. A lot of it went right over my head, but some of it sank in. I used to think that fstops and shutterspeeds in photography was complicated to understand, but they're nothing like trying to fathom electricity.
Snowey, the book sounds like a good investment. Thanks!
Jacon

[snowey]

it IS a good investment; you'll never go wrong if you follow the advice in it! It's helped me TREMENDOUSLY!!![:)]

[jacon12]

"He assumes that you know nothing about it, then goes on from there."
He's got that right![%-)]
Jacon

[jacon12]

By the way, I bought the book on building benchwork, but I really could have figure all that out. A friend once told me there's nothin' to carpentry... just draw a line and saw to it, bore a hole and peep thru it. But I shoulda bought the book on wiring. Now there's something I know NOTHING about![:D]
Jaacon

[dwRavenstar]

Good luck Jacon

The madness of wiring and electricity keeps many folks out of this hobby (the Amish for instance) [}:)]

Dave (dwRavenstar)

[johncolley]

Lectric are simpul...wun wire hook-im-up too wire screw-im-up!

[jacon12]

QUOTE: Originally posted by dwRavenstar

Good luck Jacon

The madness of wiring and electricity keeps many folks out of this hobby (the Amish for instance) [}:)]

Dave (dwRavenstar)

Lol... I'll bet it does![:D]
Jarrell

[rrinker]

OK I held off but two replies and it's time to put it in. There is a VERY funny guy arnd here called Raymond the Amish Comic. You really have to be froma round here, or know somethign about the Ami***o find him funny, but boy we sure do.. anyway, he was on a local radio station promoting an upcomign show and did a little skit:

<knock knock knock>
Amish Vice! Open up! We know you got 'lectricity in there!



--Randy

[dwRavenstar]

Clip, clop, clip, clop
BANG BANG BANG
clip, clop, clip, clop

Amish drive-by