Calculating transformer size for layout size

[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]

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.

[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.

[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

[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

[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.

[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.

[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]

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]

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

[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.

[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.

[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]

[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]

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.