Maximum number of MTH passenger cars on one tiu circuit

Not too many,..... not too many!

You have to leave room for the engines and if you want to run with the smoke turned on?

Do you have an amp meter on your power? 10 amps max per channel.

I really wonder how/why it took so long to switch to LEDs inside the cars???

Our grandsons layout fried many components trying to run several pass cars with lights. 

If you convert them to LED, more than you can likely fit on the track.

I can't speak for MTH passenger cars as I only have K-Line and GGD cars in 3 rail.  However at my club layout, with the GGD cars with LED illumination, I can run two powered MTH engines and around 18-20 cars at 7-8 amps on a 2% max grade under command.  That includes 4 K-line incandescent lit club cars.  With all K-Line cars my limit is about 10-12.  I plan on relighting them all with LEDS as my Daylight set is 16 cars long.

Currently I am experimenting on my home layout and I have 4 powered 3rd Rail locomotives pulling 15 scale cars with two being K-Line.  It runs right at about 9 amps.  Yes, the number of locos is overkill, the but sound of four units at once is awesome! 

I should point out that I don't run smoke.  That may help my energy budget.

There are many variants on passenger cars but I think of traditional incandescent passenger cars as 5-10 Watts per car.  If you convert to LED, this gets you to, say, 1 Watt or less... about 5-10x less power than incandescent.

As Joe points out you need to think about the engine.  An engine sitting at idle might draw only 5-10 Watts...but pull a load, go around a curve, up a grade, etc. and the power can easily run 50 Watts or more.  Turn on smoke and that's another 5 Watts or so.  Curiously, sound is not that much of a load - typically just a few Watts.

You can attempt to instrument your setup with voltage/current meters and "do the math" to ballpark whether your 50 Watt, 100 Watt, 180 Watt, whatever Watt transformer is suitable for what you're running.  I say 180 Watts since the typical 18V command voltage at 10 Amps is 180 Watts (Voltage x Amps = Watts).

I am not aware of any manufacturer that provides comprehensive power requirement specifications for engines, passenger cars, etc..  From what I can tell, most guys just run whatever they have...and if the breaker trips, they buy a bigger transformer.  And if it still trips, they bite-the-bullet and convert their passenger cars to LEDs using GRJ's LED lighting kit.

And if you want to stay with incandescent lighting but need to pull a few more cars, you could run the TIU in passive mode.  There are considerations, so do an OGR search if interested but it essentially allows you to skirt the 10 Amp "limit".

Thanks. I use zw's and have the power, but I have 10 amp fuses on the output and plan to stay with them. I opened most of my cars to add people and that's when I should have changed the lighting. Before I open these new cars, I'll check out John's lights for cost and installation ease. Then I have to decide how many I want to run. MTH trucks don't roll near as freely as Lionel's and can be quite a load to pull.

I hear you. Of course LEDs do not help with truck friction/drag (and noise) primarily from the spring-loaded center-rail rollers or sliders. Perhaps an indication of having too much time on your hands, but one can measure the power in Watts it takes to pull a car with powered trucks vs. un-powered trucks.  If I recall correctly, when you switch to LEDs, the transformer burden in Watts of pulling power (drawbar pull x speed) imposed upon the engine exceeds the lighting power in Watts to illuminate the car.

Stan perhaps I should start another thread for this subject, but MTH cars have a lot more drag than the Lionel cars. My engines can haul many more Lionel cars than MTH cars. My son got into this with MTH and they did admit to going to the needle bearing design for their HO line. I 'm waiting for John to respond here with some information on the led lights. Maybe I'll have to go to the website. I believe you can adjust the brightness of his lights, which I want.

Yep, you can set the intensity of the lighting modules to your liking.  As for drag on the cars, make sure you lube the axles on the MTH cars, it makes a big difference in rolling resistance.

 The MTH 2 rail pass trucks I bought roll better than many others?

I stuck a pair under a GGD car because it was easy!

If you have a properly sized fuse or breaker on the circuit, seems to me you can run as many as you want until the fuse/breaker pops.  This assumes that you have large enough gauge wire to carry the current to the tracks without excessive voltage drop, that causes locos to malfunction.

I changed by non-MTH cars to LEDs.  Haven't tackled the MTH cars, yest, because of the small bulbs & higher priority tasks.

Standard MTH 18" passenger cars are among the easiest to convert to LED, I can knock one of those out in about fifteen minutes.  You can use all the existing wiring and just add the lighting module and LED strip.  Solder a couple of connections and you're done.  It takes me longer to add the passengers than it does to light them.

GRJ, I tackled all the Lionel & MTH stuff that had those big hot bulbs.  Then priority conditions took over, since the MTH units didn't seem to be power hogs.

My 18" MTH Premier coaches with the single strip of incandescent bulbs pull .3 amps at 18 volts, when I finish the LED upgrade, they have much better looking and more even lighting and draw 1/10 of that.  While probably not a "power hog", when I put twelve of them on the rails, they still consume 36 watts, that's more than the locomotive pulling them with smoke on pulls!.

What's ironic, curious, amusing (you choose) is how all this has nothing to do with the real-world where you choose the prime-mover horsepower based on the load.  AFAIK there's no serious attempt by model train manufacturers to match the pulling horsepower to the prototype other than a loose correlation between the size of the DC-can motor(s) than fits into the shell.  Conversely, the various pulling "contests" with 100+ coal cars with plastic "loads" is a cake-walk compared to the rollers on a lighted passenger with similar prototypical weight.  Just saying...

So 10 cars = 3 amps.  Not earth shaking.  Lionel rated its dual motor diesels at 55 watts when they first came out over a half-century ago.

Any modern diesel that pulls more than a couple amps gets a quick trip to my workbench to see what's wrong.  With four motors, I might allow up to 3 amps.  Obviously, smoke adds to the total if you have it.

The old Pullmor open frame motors sucked a lot more power than the modern can motors.

If you're running one passenger train on a power district, it's normally not a problem.  However, if you have two, and sometimes during an overlap, even three, all those amps equal a circuit breaker tripping.

Besides, the LED lights look better, they have zero chance of melting the shell (I've seen it), and the erosion of the rollers is vastly reduced with the minimal power draw.

Totally agree with all you say there, GRJ.