Calculating transformer size for layout size

[FJ and G]

scratch b.

the 2 rail and 1 wire is the end result. I've still got more wire to string as it is under construction.

I'll keep you guys apprised of the progress, hopefully not too ad nauseum!

[lionelsoni]

Dave, it seems that your appointment might be close to the ideal time to visit the dentist, that is, 2:30.

(tooth-hurty)

(sorry)

[FJ and G]

thanks for your great advice guys,

I've gotta run to the dentist in 10 minutes so may have to read the other posts when I get home tonight after running the hound.

[3railguy]

I came up with 4 watts per square foot for an average outfitted layout with modern era trains and lighted accessorys which are more energy efficient than postwar. On the other extreme, for a densely outfitted postwar layout, I came up with 7 watts per square foot.

[lionelsoni]

There are two simple ways to get (unregulated) dc:

Use a transformer with a center-tapped secondary. The center tap is one of the output terminals. Connect the anodes of two rectifier diodes to the ends of the secondary and connect the cathodes together. The cathodes are the positive terminal. (Reverse the diodes to reverse the polarity of the output.) The average voltage will be about 90 percent of the rms voltage of the half-winding, minus about .7 volts. The rms voltage will equal the rms voltage of the half-winding, minus about .7 volts.

Use a simple secondary into the ~ terminals of a bridge rectifier. The + and - terminals are the output. The average voltage will be about 90 percent of the rms voltage of the winding, minus about 1.5 volts. The rms voltage will equal the rms voltage of the total winding, minus about 1.5 volts.

If you want filtered dc, put an electrolytic capacitor across the output. The peak-to-peak ripple voltage will be approximately 8333 times the current drawn, in amperes, divided by the capacitance in microfarads. The output voltage will be about 141 percent of the half-winding or winding, respectively, minus about .7 or 1.5 volts, respectively. The capacitor's working-voltage rating should be at least as high as the filtered output voltage.

Notice that the dc output of the center-tapped transformer and its unrectified ac can share a common terminal, which is not possible with the bridge rectifier.

[FJ and G]

Thanks, Pat,

Another reason to stay away from the pricey bricks!

Besides running the trains, how would you step it down for low voltage DC for some of the accessories?

[lionelsoni]

In any situation where you would use a traditional train transformer to supply the fixed track voltage for a modern control scheme, you can perfectly well use a simple "industrial" transformer.

The reason for putting the circuit breaker after the secondary on a traditional train transformer is that, at low voltage settings, an excessively high secondary current does not necessarily cause an unusually high primary current. This is not the case for a fixed transformer. So it would be slightly safer to put the fuse or circuit breaker for a fixed transformer before the primary. If you were also to connect one side of the secondary to the equipment ground, the fuse would then protect you from any insulation failure that would put a dangerous voltage on the secondary.

[eZAK]

Doug J.,

That probaly did not get UL approved for a toy trans.

[eZAK]

Yes they can.

You just have to match one with your needs.

They come in various sizes stated in kva, i.e. 0.1kva(aprox.100 watts) or 1.0 kva(1000w)
You would also want to make sure you have a 120v pri, & a 18v or 20v sec.(there are also multi tap sec. which will give more freedom)

They come enclosed in a metal case and require wiring a 3 prong male cord end to it (H-N & case Ground) Simple!

Now hook up your sec. to your TIU or TPC. It is also advisable to add a $0.49 Transient Voltage Suppressor accross all sec. outputs.(hot to common)

[Anonymous]

Whatever happened to the "Max?" This morning I was looking through the only CTT I own, February '99, and in the product reviews on page 118, they reviewed a 600 watt train transformer that even had a program function for MTH. MSRP $799, but they used it to run ten trains, and the breaker finally popped at 15 v. and 16 a.

[FJ and G]

Pat,

Can "industrial transformers" be used in place of transformers? In my example, could they substitute for Z750s under DCS control?

(I bet the toy train companies don't like to hear your suggestion!)

[eZAK]

Steve,
That is why I said to use a TIU or TPC for track control.
You would also need a AIU or APC for acc. control.

Many older transformers are still widely used today, all without electronics.[:)]

[Anonymous]

Hello All: Pat is right about purchasing at supply houses, but I would only use them for light's & accessories, also make sure they are grounded(use a three prong cord on the 110 volt side & install a fuse or breaker on the secondary side (low Volt side). I would not use them for track power because of the electronics in the engine's & Loco's of today. The manufacture's power supply are regulated with a lot of diode's & resistor's to keep the voltage clean for today's technology. Also remember the KISS rule, Keep It Simple Stupid. Kind Regard's to All Steve

[eZAK]

QUOTE: Originally posted by 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.

Dave, You can get industrial transformers at electrical supply houses for alot less.
They come in various sizes.
I picked up a 1.5 kva for 80 clams[;)] for my cousins layout.
If you have a TIU or TPC's your in .

[Anonymous]

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

[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]

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.

[laz 57]

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

[Anonymous]

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

[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..

[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.

[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

[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.

[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

[Anonymous]

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

[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).

[laz 57]

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

[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).

[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.