Calculating transformer size for layout size

[FJ and G]

So far, I haven't seen any way to do this except to take amp measurements or just wing it and see how hot your transformer gets.

It would be interesting to have a standardized metric of X number of accessories times Y number of locomotives for Z number of feet of track.

But the ohms in each track are different, and trains and accessories (not to mention rolling stock), draw different currents. Also, power blocks or districts can be divided up to remove some of the load.

Can you think of any ways to state what transformer is good for what layout? Most of you will probably say bigger is better, meaning ZW or Z-4000, but there are plenty of guys using smaller paks like me.

For my own needs, I've found that two Z-750s, operating 2 trains over about 150 feet of mainline suffice, with HO paks used for accessories.

[eZAK]

A rule of thumb from the elders, (I had to go to the mountain top for this one),

is approx. 2 watts per sq. ft. of actual layout space.

L x W = sq.ft. x 2 = total watts

[FJ and G]

Add 2 more watts for Spankybird's fun-filled layout! :-)

(subtract nearly 2 for my desolate desert scene!)

Somewhere between the 2 extremes lies the average modeler.[:D]

[lionelsoni]

Length of track or type of track doesn't (or shouldn't) matter. If the voltage drop in the track is more than a small fraction of the transformer voltage, that is, a volt or two, you are going to have trouble running the trains anyway. The fraction of your transformer's power lost in the track will therefore be well under 10 percent, since it is proportional to the voltage drop.

[Anonymous]

You have pretty much pointed up the major problem, everything is different. That it not to say that there are not engineering formulae to calculate the current draw and thus the wattage, but far and away the easiest method is to measure it. I run an MTH 4-6-2 PS-1 pulling five Madisons on about fifty feet of track and the transformer I am using (Z-4000) has a digital amp readout. At fifteen volts which is about as much as I can put to it without jumping the track, it pulls an average of 2.5 amps, or 37.5 watts--less than one tenth of the transformer capacity of 400. Stop it with your hand to full stall, and it goes up to four amps--sixty watts--trying to pull.

Track alone dissipates very little power, enough so that you can disregard it in the calculations. Where it may affect the layout is in voltage drop, but even that is relatively negligible. You may notice the train moving in a "spurt" of speed as it passes a certain point in the layout--nine times out of ten that signals a single break in the continuity where the power is coming "the long way around" and the voltage jumps up as the locomotive passes the break.

Transformer capacity is very much a function of cooling capacity (heat dissipation). They run better in a cold room than a hot one. The whole time I have been writing this post I have been trying to remember just what it was that I had several years ago that worked just fine if I put a couple of pieces of ice on the case, and it would shut itself off if I didn't. They say the memory is the ssecond thing to go, but I can't remember what the first one is.

[wrmcclellan]

Although I am an electrical engineer, I just add stuff until the transformer gets too warm and then I branch off and add another. [:)]

Roy

[FJ and G]

Roy,

That's the best advice yet--and from an electrical engineer too!

Has anyone here ever blown a transformer from hauling a double-headed Allegheny coal drag up a 2 percent grade? :-)

Your stories please!

[wrmcclellan]

Dave, the nice thing about Lionel transformers is you can run them until the bimetallic breaker pops and then you let it cool and you are back in action (after shutting a few things down)!

BTW - I did a quick calculation and eZAK's rule of thumb works. I have two loops and a yard on an 8X12 (96 sq ft). Using the 2 watts per sq ft yields 192 watts. I use two ZWs (about 175 watts effective under load). If I use one it gets pretty hot.

The layout has accessories (6 - most with lights), Lionel 022 and 072 switches (13 - 2 lights on per switch), lights in all buildings (7), signals and crossing gates (5), light poles and towers (5), and I can run two lighted passenger trains.

Regards,
Roy

[FJ and G]

That's good for ole eZak!

I can't see no use in going out and slamming down 400 clams for a ZW or Z4K with fancy handles and all if you really don't need the power.

I can think of better things to do w/my $$$ like get my shotup TIU back in shape and buy some bones for the hound.

[cnw1995]

This is interesting stuff. I have one R transformer from which I run everything - but only 1 train at a time and a few accessories for a layout in a space about 24 by 10 ft.

[wrmcclellan]

The thing that eats current is a lot of light bulbs on the layout. The typ miniature incandecents we use average about 100 ma of current each. I am currently running about 40 bulbs, which at 0.1 A each total 4 amps! Add a PW dual motor F3 (4 amps) with 5 lighted cars (another 10 bulbs - 1 amp) and you are cooking (9 amps). At an average 14 volts - this is 9x14 = 126 watts - the ZW is getting quite warm and I have not run an accessory or another train yet!

Roy

[spankybird]

Ok – our layout is 10 x 20 = 200 sq ft x 2 = 400 watts. We use a ZW 275 and a KW on this, so 405 watts.

QUOTE: by Dave “Has anyone here ever blown a transformer from hauling a double-headed Allegheny coal drag up a 2 percent grade?”

Nope, but have done a Hudson and a Berk on a 4% grade



and we have run both the Challenger and Allegheny at the same time.



tom

[Anonymous]

Forgot about light bulbs since I don't got some yet. I got a lot of lightweight transformers that came with starter sets over the years. I bet they would be great for running lights and unloading the main transformer.

[Anonymous]

QUOTE: Originally posted by wrmcclellan

Although I am an electrical engineer, I just add stuff until the transformer gets too warm and then I branch off and add another. [:)]

Roy

Typical engineer--you need a technician.

An engineer is someone who knows more and more about less and less until at the peak of his career he knows everything about nothing.

A technician on the other hand, knows less and less about more and more until finally he knows nothing about everything.

The Lord himself quakes at the sight of a technician with a calculator (slide rule) or an engineer with a soldering iron.

[ChiefEagles]

I use to use one KW for 70 feet of main line, sidings and switching yard entry track. Ran 6 motors [MPC's]. Never had a problem. Used 1033's for sidings and the switching yard its self. Used a 1033 for accessories and lights. Right now I am running 8 motors on one KW [the new one I found] and got the old one for reserve. Plan on using the KW's for the big layout and 1033's like I did before. Will get a Z4000 one day [this summer probably, unless I find a good deal on an older ZW] just to say I have one. Then the K's will do siding and switching yard duty.

[Anonymous]

Lest I offend, in another plane of existence I was an electronics tech. That was before all the technician assemby work was outsourced overseas and they left the poor engineers to fend for themselves. It was a symbiotic relationship, the engineer designed it and the tech built it, then they both troubleshot it. Not unlike the relationship between the locomotive engineer and the fireman. Pretty much suffered the same fate, too.

[spankybird]

QUOTE: by Skyray "Typical engineer--you need a technician.

An engineer is someone who knows more and more about less and less until at the peak of his career he knows everything about nothing."

I am one of the engineers also. I love to try things with out reading the manual. Then if I can't get it going, you will have to RFM (read the F@#$en Manual).

[laz 57]

I thought an ENGINEER was the guy driving the train?
laz57

[Dave Farquhar]

QUOTE: Originally posted by Skyray
An engineer is someone who knows more and more about less and less until at the peak of his career he knows everything about nothing.

A technician on the other hand, knows less and less about more and more until finally he knows nothing about everything.

The Lord himself quakes at the sight of a technician with a calculator (slide rule) or an engineer with a soldering iron.

Skyray, it's a very good thing I wasn't drinking anything when I read that comment, especially the last part! I am very much a technician. A few weeks ago I had to do long division for some reason, for the first time in probably 15 years, and it must have taken me 10 minutes to figure out I was going backwards!

Algebra? What's that?

Oh yeah. The equation works for me. Take my Christmas layout. 4 ft x 6 ft = 24 * 2 = 48 watts. Worked just fine on my 50W Marx transformer until I replaced the switches with Lionel 1121s. It killed that tranny in short order after that--had to break out a Lionel CW-80.

My other layout is two 4x8s, so we're looking at 128 watts. I normally power it with a Lionel 1033 and 1034 (150W total).

[Anonymous]

David, looking at your layout I notice there is a two rail and a three rail ?

[cnw1995]

Dang, this math makes my head hurt. I've had light 'arguments' with fellow hobbyists claiming most of their fellows are predominantly technically - oriented vs. what I would consider is a more liberal artsy approach - any way it's a great balance

[Dave Farquhar]

Doug, there's definitely room for the liberal arts approach to the hobby--I have a journalism degree; how I became a computer technician was pretty much an accident.

I think that's why I like this hobby. There's room in it to take things apart and fix them--I love buying dead Marx locomotives and bringing them back to life--and there's room to fire up some design software and draw myself a building, then get out the glue and the knives and saws and turn that drawing into a building for the layout.

The truly great hobbyists have/had a bit of engineer, a bit of technician, a bit of artist, and a bit of historian in them. At the very least.

[Anonymous]

Hello All: Another simple way of doing it, Only load the transformer to 75% of it's capacity, or take your total load & multiply by 125% for proper transformer sizing. This is a old school approach for sizing cables & transformers or appliances in the electrical trade, & has never let us down. (Electrical Contractor with dear old Dad for 30 years) Regards Steve

[lionelsoni]

Steve's rule of thumb for derating is very close to and in the same spirit as the NEC rule that an appliance may not draw more than 80 percent of the current rating of the outlet. Thus an appliance with a 15-ampere plug (the usual kind with parallel blades) must draw no more than 12 amperes.

[cnw1995]

Dave, you're so eloquent and inspiring - my undergraduate degree was in American Studies, now I'm in charge of among other things all our college's technology - also self-taught..

[Anonymous]

Hello All: Re: Dave Farquhar, Dave you left out sense of humor Regards Steve

[laz 57]

IF the Engineer is the guy that drives the locomotive then theTechnician must be the fireman is this correct?
laz57

[Anonymous]

QUOTE: Originally posted by laz 57

IF the Engineer is the guy that drives the locomotive then theTechnician must be the fireman is this correct?
laz57

The engineer is the guy that has the ideas, steers the train, and rings the bell. The technician/fireman makes sure that he has the means to make it work. Just don't give no EE no soldering iron--it's against their nature.

All electronic devices are operated by smoke. Let the smoke out, and they quit working.

[Dave Farquhar]

Thanks, Doug.

Redhawk, you're right--I forgot the sense of humor. I'm planning a gun shop with a sign disallowing weapons on its premises in the window. Next door there'll be a bookstore with a sign in the window that says "Weapons are welcome." Does that qualify?

And to bring this back on topic, I think I'll power the lights in 'em with a dinky little HO transformer someone gave me because they heard I like trains. I'm still waiting for that hypothetical neighbor with a Carlisle & Finch in the attic to hear I like trains... :)

[Anonymous]

Dave: That certainly qualifies, don't forget the anti-gun lobbyist with the picket sign's. Kind Regards Steve