Wattage overkill?

Classic Toy Trains Forum
1

In Sept03 CTT, page 41 is an ad from Williams. A warning is given that Williams locomotives should be run with a tranformer that is at least 90 watts.

I happen to use a Z-750; and have been running trains on about 50 feet of reverse-looped track on my carpet (while my current layout is under construction). I have double-headed locomotives and have never experienced any overheating or deliterious effects from lack of wattage. As a matter of fact, the Williams locos draw less juice than my MTH PS-2s. I’m a bit puzzled by the warning in the Williams ad.

Incidentally, I will continue using the Z-750 (and a second one) that I got in 2 starter sets. As long as things don’t heat up. When they do, that’s when I’ll look into a Z-4000.

Do you think that for some of our medium-sized layouts, there is a wattage overkill? I know the dictim that you can never have enough watts. However, watts is money.

dave vergun

2

btw, a Z750 is 75 watts. For a medium-sized layout without a lot of power requirements, I don’t think that a smaller pak is any problem. I would like to get a meter for checking amps, however, since I only have a voltmeter. I always wonder why amp meters are so much more expensive that voltmeters.

3

Williams is probably playing it safe and simplifying things. Some of their engines may need 90 watts (say, two motors, etc.) but it is too confusing to rate each one.

Ampmeters need to go inline with the current being measured, and to pass all the current being measured. This is tricky. (There are also “clamp on” ampmeters, but they are, typically, more expensive.)

If you have a voltmeter, then you also have an ampmeter. Here’s how to use your voltmeter to measure amps.

Obtain some 0.1 Ohm, 10 Watt resistors. (That’s 1/10 Ohm). Place these inline with each transformer circuit you want to measure. (Permanently)

When you want to monitor current in a transformer circuit, measure the volts across the resistor (some test points or banana plugs make this easier). The current through the resistor is 10 times the voltage across it. (I = V / R, I = V / .1).

So if the meter reads .5 volts, there is 5 amps going through the resistor.

John Kerklo
TCA 94-38455
www.Three-Rail.com

4

David, what the Williams ad may be referring to is that they are adding the wattage consumed by accessories to the wattage needed by the engines. It could also be that they are referencing PW Lionel transformers, which are rated by input watts, not output watts. A 1033 (90W input) will actually have maybe 65-70 watts out. Your Z750’s are rated by output watts.
If you are running passenger trains of 8 or more cars, than 75 W is pushing it. As long as you run freight, all you have is a 2 motor engine that draws maybe 2+ amps at warp speed and pulling 30+ cars. Williams engines don’t have all the extra stuff PS2 do, so they draw less current.
As to ammeters, they are available from the major electronics suppliers, but they can be expensive. my favorite surplus supplier Allelectronics.com has a 5A ac and a 15A ac meter for 12$ each.
hope this helps, Dave!

5

Will & John,

Thanks for the info. Esp. liked how to use the voltmeter to find amps.

dav

6

One other thing that you have to take into consideration is that you
will suffer a certain amount of “line loss” due to the length of the
layout route. The transformer needs to have a certain amont of re-
serve capacity to overcome this. For instance if your locos, cars,
and accessories draw a total of 75W then a 90W transformer will
have the reserve capacity (about 15-20%) to make up for the line
loss that will be incurred at the outer reaches of the layout. This is
the reason for needing/using “feeder” lines to the layout in different
locations (usually about every 3 feet or so) and using the heaviest
wire practical. All this helps to prevent line loss. If you were to try to
run a train over a 50 foot route with only one power connection, you
would notice that the loco will run noticeable slower at the far end
of the route. This is due to “line loss”. For the transformer to over-
come this it must be able to deliver more POWER. Since the voltage
should be the same, you must increase the amperage (which is
POWER), since volts x amps = watts, it goes that if the voltage stays
constant, then more amperage is needed to deliver it to the end of
the route, therefore if amperage is increased then WATTAGE will be
increased. Hey John Kerklo…hope I explained this correctly.

Hope this helps a little.

7

The train slows down at a distance because of voltage drop along the track, which must be overcome by reducing the circuit resistance (with feeders) or by increasing the voltage at the transformer. The power lost in the resistance is small and not important in choosing the transformer size.

8

WATT ever do you mean?[:D]

Wattage overkill![8D] ME![^] Never.[:P][8D]


That’s two 1kva transformers!

That’s 2000 watts [:O] if your counting.

You can buy new ones for under $100 ea.
That’s .10 cents a watt. Not cheap…Frugal!

9

Speaking of voltage [I did over kill], on my old layout [60 foot long, dual main line was about 135 foot circle] I ran number 12 stranded feeder lines. The wire was free so I used it. Now on my new design [thanks Elliot], complete circle will be about 50+ feet. What size wire should I run for feeders? On the old layout, I spaced them about every 5 feet [depending on the blocks]. How far apart. I used an old Bell telephone key system board to “punch down the wires” [which I still plan on using]. That way I could label the blocks and etc. Remove and change them very easily. This does require all wiring to be run to a central location. Will make the farther end of the circle a long run. Comments please.

10

chief,

I too am using free wiring; leftover 12 and 14 V Romex from work I’ve done in the basement. It’s single strand.

It is my understanding that feeder wires can be smaller gauge. For instance, if you are running 14 Ga bus, then you can feed every 3 feet with 18 ga; but correct me if I’m wrong. Five feet should be OK. I’d solder the rail joints w/wire just to be safe.

I’m using DCS and I too have a problem because I have to wire every section independently and not use a bus wire like on a traditional layout. That is the special wiring case for DCS; so I’ll end up w/lots of wire too since my layout is elongated (very long but less than 3 feet wide).

I’ve got another Q. Should the drop wires just be for the center rail or also for the outside rails as well? My guess is that if you are using one of the outside rails as a control rail, then yes; but if you are using both rails as a “common” then the duplication of 2 rails performiing the same function should enable you to use very few or no feeders within each block.

dav

11

The center rail bus(es) carry current for the engine/train that is in a given block.
The outside rail bus, “track common,” carries the sum of the current for all the blocks. Thus, the track common should be a larger wire size than the center rail bus(es).

I use BARE #10 solid wire for the track common bus. Being bare, a feeder wire can be soldered to it anywhere, without the need for stripping the insulation off.

An outside track rails needs just as many drops as center rail. I use #16 stranded (fine stranded “hook up” wire) for drops; it is easier to route. These feeders are usually only a few feet long.

How many drops depends on quality of track connections. A forum topic asked the question a while back and got a broad range of answers. I use “around three track connections between drop connections” guideline.
I don’t solder track connections.

John Kerklo
TCA 94-38455
www.Three-Rail.com

12

The feeder wires should be sized not for voltage drop but for safety. They should be heavy enough not to overheat when a short circuit occurs on the track. AWG14 is generally good for 15 amperes, which is about the most that you will get from a large transformer like a ZW or a Z before the circuit breaker opens. AWG14 is bigger than you likely need to keep the voltage drop low, but you should use it for safety.

There is no need to use multiple feeders with a “home run” from each one. A single feeder with occasional taps works just as well.

With both outside rails powered, their resistance is still about one-third of the total. However, if you have multiple remote tracks, you can advantageously connect the outside rails together among tracks (even though the center rails may be separate) to reduce their combined resistance to a negligible value. My experience however is that soldering the joints of tubular rail on a moderately-sized layout takes care of the problem without feeders.

13

John & Bob,

Much thanks; good stuff.

Bob mentions soldering without feeders for moderate size layout. If you think of each rail as a wire and if you do, in fact, make a good, solid solder connection, then why are drop wires even necessary? One would think that a reliable soldered connection between sections of track would preclude the need for drop lines.

My guess as to the need to have drop wires would be resistance encountered from dirty track.

dav

14

Dav, my point is that feeders are in fact not necessary with rails soldered together. Most of the track resistance is in the joints, not the rails themselves. You are right in observing that the rails are a lot like wires. While not as good conductors as copper, they are large enough to do the job.

Dirty track will stop your trains, but plays no role in the slowdown that can occur at the far end of the layout due to the stackup of joint resistance.

In addition to soldering, I use the 36-inch K-Line straight sections extensively to reduce the number of joints greatly.

15

Bob,

I too use 36" straights (027 tubes) I remove the metal ties and bend the rails to the desired radius then mount on wood ties. Agree less joints to worry about. thx

16

Thanks guys. Some good pointers there. Since I do my own wiring, I’m running 240 to the layout with small breaker box. Got specail 30 AMP feed going to that upsatirs room. Will have separte circuits [120 15 AMP] for transformers and run #12 romex under tables with several outlets all along the layout. Then you can plug in power transformers, tools and etc without running drop cords.

17

Thought I would mention this.

In a previous post, Bob notes that #14 wire is good for 15 amps. This is a house wiring convention, mostly related to the ability of #14 wire of reasonable (house) length to trip a 15 amp breaker without heating up enough to melt the insulation. It is a safety parameter.

Now, the #14 wire and 15 amp guideline is ok for trains, but the important parameter is the voltage drop across the buss wires and its effect on train performance. The voltage drop from the wire is only related to amps through the wire, and not to the voltage being employed.

Operating trains use about 1/10 the voltage of house wiring. The same voltage drop across the buss wire will have a greater effect on train performance than on a light bulb in a table lamp. The voltage drop is the sum of the drops in the center rail wire and the track common bus wire.

#14 wire for center rail power is fine, since current draw for one train will be 2 to 5 amps, or so.

Larger wire is needed for “track common” since a bus wire will carry the sum of all the power for all trains running. If you are running six trains, each 4 amps, then the track common buss wire is carrying 24 amps.

John Kerklo
TCA 94-38455
www.Three-Rail.com

18

Seems in my past [way past] history in electronics and my father-in-law’s [worked as a big electrical systems engineer] conversations, that stranded wire would give less resistance than soild and also, the same size wire would carry a heavier load than soild. Correct me if I’m wrong.

19

Not really, however …

The resistance of wire depends on the material (electrical grade copper) and the cross sectional area of the conductor. For house wire, stranded wire is constructed so the sum of the cross sectional area of the strands is the same as the cross sectional area for the solid wire of the same size designation. No difference in resistance.

The however …
Stranded wire used in electronics service (“hook up” wire versus house wiring) is very finely stranded and, often, tin plated. Hook up wire is commonly constructed from a number of strands of AWG size wire. For example, some #16 stranded hook up wire I happen to have on the workbench is made of 26 strands of #30 wire.

Since the strands are an AWG wire size, the sum of the cross sectional area is likely a little larger than the same solid wire size. Thus, a little less resistance.

Tin plating also reduces the resistance a little. Stranded wire has more tin than solid wire.

Tin plating makes soldering easier and connections, like to transformer posts, are less likely to corode.

Stranded house wire is a larger diameter than solid. Carrying capacity is effected by the ability of the wire to dissipate heat, which is slightly better for a larger diameter stranded wire.

Also, professional wire strippers for house wire come in stranded and solid tools. The same effect can be had by stripping stranded with the next size larger wire on a solid wire stripper. Less true for hook up wire.

Hook up wire is more expensive than house wire. For economy, if physical size doesn’t matter and wiring room is not restricted, using house wire, even though overkill for the current requirements, will be less expensive.

Stranded hook up wire is more flexible and a lot easier to route.

John Kerklo
TCA 94-38455
www.Three-Rail.com

20

Thanks John. I was talking about stranded hookup wire or automotive and marine wire. It can be expensive unless you have a source. I like its flexibility. Personal preferance. I use to use the old MA BELL gray telephone wire. Would use the red and green as + and the yellow and black as -. Got it free. Doubling it made good wire to run up and solder to the track. Free was free. Now I have to purchase my wire.