AC track voltage regulation options

What you've found here is commonly known as a Variac, which is usually used to adjust or trim line voltage.  That means that you can adjust it's output voltage to dial in your supply from the wall (the mains) to precisely 110 VAC, or 120 VAC, or whatever you choose.  Normally they will also provide output voltage in excess of line voltage (up to 135 VAC) if you so need it, just by cranking up the knob farther.

The one you've identified appears to go a step beyond a simple Variac and includes the ability to hold its output voltage constant, i.e. regulating it, with changing loads.  I believe, although I may be wrong on this, that this is called an autotransformer.

Now here's what's interesting.  A common, old-fashioned toy train transformer is also essentially a Variac.  It operates the same way as a Variac, with a wiper, mechanically connected to its adjustment knob, that travels along the secondary coil of a fixed power transformer to provide a variable AC output voltage.

The problem with the Variac you found is that it's output voltage is roughly 7.5 times larger than we would use for powering toy trains.  So one solution might be plugging a 7.5:1 (135 VAC in equals 18 VAC out) power transformer into your Variac's output, connecting the output of that transformer to your track, and then just using the Variac's knob as your throttle.

Mike

You can buy a couple of Legacy F3's with dual can motors and cruise control for the price of that expensive variac, that's sure not where I'd put my money.

@gunrunnerjohn posted:

You can buy a couple of Legacy F3's with dual can motors and cruise control for the price of that expensive variac, that's sure not where I'd put my money.

You could also by a new ZW-L and get little regulation.  Would you put your money there?  Many people do.

Mike

@Mellow Hudson Mike posted:

You could also by a new ZW-L and get little regulation.  Would you put your money there?  Many people do.

No, I didn't put my money there.  My layout runs on four 180W bricks that I bought used at prices between $40 and $75.  Since virtually everything I run has cruise control, the minor variations in track power are a moot point for me.

CNWDON

Do you have wires from the transformer to the track every 8 ft of so of track and have those wires at least 14 gauge?

Can you measure the amperage going to the tracks?  I have an inexpensive Amprobe Clamp on 0 to 25 amp Ammeter and added 5 turn coils to made it 0 to 5 amps.  It is moved to my three LW transformers as needed.  It may help you determine if one of your engines motors is drawing too many amps and maybe find dead spots in your track

Charlie

What is the cause of the voltage drop at various spots along the track?  Curves, hills ? Are the areas in question easily divided into blocks? Are they consistent?

Do you prefer to sit back and watch them run, or are you a hands-on operator?

If you are running conventional trains, and if you prefer to let them run without your hands on, why not try an old traditional method, which is to feed the main parts of the ROW through one output of multi-output transformer, such as a ZW (or two or more phased single-output ones) and the areas that require more voltage though a separate output, with a slightly higher setting.

This is much cheaper, is easily fine-tuned for different consists at the beginning of an operating session and doesn't require fancy circuitry. Two ZW's will give you 4 big handles if your layout is that big. Add a few Voltmeters and you've got a nice solution.

The drop he's measuring is not at the track.  It's at the transformer posts.

Mike

So what you're saying is voltage drop at the transformer is not the same as the voltage drop at the track?  How does that work?

If there's a voltage drop at the transformer, odds are good it exists on the track!

Now, there can be additional voltage drops between sections of the track in addition to any drops from the transformer, so that's a factor as well.

Exactly my point, unless the track feeders are of insufficient gauge, or some other resistance is presenting along those feeders.

I think we are derailing this topic. I read it and understand because I did extensive loaded and unloaded testing of the Z4000 and several transformers including the new CW80.

Unfortunately, as much as I like Z4000s and recommend them still to this day, testing did show the power control section has some internal resistance. In a power source, what this means is when you set a handle position and get a resulting unloaded or lightly loaded voltage and adjust that to say exactly 18V, and then slam a larger load onto the transformer -example, engine is stopped when adjusting the voltage to read exactly 18v, and then you have a Williams dual motor diesel pulling a heavy consist, or a Pulmor- and it's drawing heavy load, then the resulting voltage out of the transformer sags. The problem is, when you THEN adjust the voltage to be exactly 18V under that heavy load condition and then suddenly the load is reduced or goes down the voltage rises to this new handle setpoint.

In other words- the handle is NOT a direct voltage control. It approximates a power setting. As you load the transformer, the voltage sags. The user then adjusts the handle under this new heavier load to bring the resulting voltage back to 18V and then when the load is stopped and removed- now the new setting exposes this voltage rise higher than 18V.

All transformers and control systems have some level of internal resistance. Batteries too. This is why you can use a CR2032 coin cell for testing LEDs without a resistor- because the internal resistance of the source limits the current. Again, ALL power supplies have some internal resistance thus sag as you increase the load. The Z4000 can be up to 4V sag in extreme cases. It's hard to say exactly where the resistance is, could it be reactive from the large inductors in the Z4000, or maybe the FETs, maybe even the resistance of the current shunt for the ammeters?

If you demand some super stiff power supply- go ahead buy that big L 620 Watt ZW-L and part with your hard earned cash.

Or- go the fixed voltage route of just using the common Power House 180 Watt bricks.

Or maybe you want to stay big L and still want variable power, so you go GW180

Personally, I'm still sticking with my Z4000 and its displays and meters along with remote control. The voltage sag is not an issue in my typical usage, I don't adjust the voltage under heavy load to compensate and it runs all my trains just fine.

@Arthur P. Bloom posted:

So what you're saying is voltage drop at the transformer is not the same as the voltage drop at the track?  How does that work?

Star wiring.  Voltages around the layout are different depending on feeder wire gauge and length of track segments.  Connection points on segments should match the posts, but may not under big load depending on wire gauge for the feeders.  End points on segments probably won't match at all under big load.

Mike

@Vernon Barry posted:

I think we are derailing this topic.

I don't think we're derailing anything.  Your comments, for instance and very good ones at that, are exactly on point based on the OP's post.  Most comments in between have also referenced the OP's observations.

Mike

A warning on Variacs connected directly to the track: Don't do it!  These are typically an autotransformer design where one of the variable ouput wires is connected directly to the input 125V house power.  A huge electrocution hazard.  You have to use an isolation transformer to provide the necessary safety.

A solution using a Variac is placing an 18V isolation transformer between the Variac and the track.  A 3 amp Variac (less than $100) and an 18V, drop down isolation transformer with 15A output (less than $100) can accomplish what you want.  (Postwar transformers are variable isolation transformers.)  You'll have to build a case, provide short circuit protection, direction control, whistle buttons, etc.  The end result will not be UL certified.

The effort to do this makes the off the shelf solutions (mentioned above) attractive.

The wire gauge, number of drops, and wiring topology is the first place to start correcting the speed control problem.  Ohms law applies and you can Google tables that show voltage loss over distance for low voltage A/C.

The old Right-Of-Way power supply used a pair of Variacs (autotransformers) taking 110V on the input and running the outputs through a pair of 120-to-24VAC step-down transformers. The original price on that unit was around $400 as I recall, which was less than I could build it for.

MRC makes a "Pure Sine Wave" AC transformer. We have a couple at P&P powering the visitor-operated loops. In all probability, they're using variacs to feed step-down transformers.

All that said, it sounds like you might have a current-draw/leak problem. One of the things you want to check with the Pullmor motors is for carbon build-up between the armature plates. This is from the carbon brushes and dust building up. Because it's conductive actually shorts the brushes with a resistive load and will cause a voltage drop. You can clean that out with a toothpick. You should also spray them with contact cleaner. Also make sure your track connections are solid and you have sufficient feed drops.

Hope this helps.

Thanks for the considerable energy expended here.  To correct any assumptions: From transformers to TIU and TIU on (buss wires) all is 12 gauge copper stranded, there is some 10 gauge as well for a few segments.  Drops are frequent and all 16 or 18 gauge to inner and outer rails, with outer rails tied together equally often at drops.  I use no isolated outside rail trigger circuits, so all track has both rails contributing to the circuit.  Track (GarGraves) has double soldered pins, the usual ones plus 12 ga bare copper inserted in the bottom opening of the rail ends and soldered, as well.  TIU to track drop is less than 2 volts at the farthest stretches from origin.  The problem is the power supply internal resistance mentioned in Vernon's post above.   It seems to drop those motors right into their critical narrow speed variation range.

Like it or not (I'm fine with it), I have a number of "sow's ears" from this standpoint that are silk purses for operations to the railroad's CEO.  The CP-now-C&NW custom F3 set with 4 Pullmors, the Pride Lines City of Denver with 3 open frame prewar-style motors and 2 ERRCo command board sets running them, 3 K-Line TMCC Trainmaster chassis with C&NW renumbered Lionel shells (can motors but no cruise control), and I'm sure other locos I'm forgetting in the inventory that will be brought into action as operations increase.  To fix each of those locos with remotoring and Cruise Commander boards, or just Cruise Commander M boards for DC motors, involves much cost and labor and no little aggravation, from considerable experience doing it.  Even if it penciled out slightly less costly than the low-drop Variac model I mentioned, the hassle would still make the Variac a better bargain.  I already know from tweaking the voltage while running that bringing it up within 1-2 volts of baseline solves the problem of extremes of race and crawl speeds to an acceptable level.  Getting rid of the 3-4 volt drop at the power supply posts will substantially solve the problem.  If I haven't made the point clear why I'm chasing more stable source voltage, it should be now.

I am interested in the isolation transformer safety point above, as long as that transformer doesn't have its own internal resistance problem, however, I suspect it may and it wouldn't take much to defeat this strategy with the 0.8 volts already expected as load-related drop for this model of Variac.  Otherwise, I will make the Variac safe by limiting the travel of its dial internal to the cabinet to a few volts above the 19v desired.  A second-level redundant safety in the form of a voltage-triggered breaker is the Zener diodes already across my TIU inputs for spike protection, which will fail in dead short (they have 37v ratings as I recall) with overvoltage, then tripping the transformer's own breaker (12 or 15 amp placed in the cabinet where the two Variacs would live) and preventing unsafe voltage from reaching outside the cabinet.  I have plenty on hand, so will probably add Zeners at the cabinet outputs right outside the rapid breakers so high voltage can't escape even for a moment.  No, this will not be UL listed, but input as to the safety of the strategy is welcome here.  I have grandchildren, too.

I'm also curious whether Vernon can say for "that big L 620 Watt ZW-L" that my 6+ amp 4-motored train loads won't pull its output down the same 3-4 volts.  I'm not aware of the technical differences.  My large "The MAX" is unlikely to have lesser transformer windings or greater internal resistance than whatever is in the ZW-L, but I'm speculating based on how cool it runs regardless of load.  So if actual measured volts/amps say differently, please advise.

I realize most of you wouldn't be in the same situation, so advice in hindsight that would have altered loco decisions decades ago will not help now.  Advice about how to do this and do it safely will be helpful and appreciated!

I'm not a fan of the small Timko motors, even if you can find them for your diesel.  So I'm going to offer you an out-of-the-box solution that should cost less than $100:

First: make sure your track is level at the problem spot(s).  NO sagging plywood, mismatched board thickness, etc.  An AC-motored loco will find these every time!  After the train has been running a while, feel around for hot track joints.  If you have a high resistance joint, it will be warm or hot to the touch.  Tighten the track pins or replace the faulty section(s) of track.  Double-check your lockons, if you're using them instead of a soldered connection.

If the above doesn't solve your problem: make the section(s) on your layout where the power drop is the worst an insulated block.  Feed it directly from the transformer with heavy-gauge wire.  Then, get yourself a couple of Lionel No. 95 variable rheostats from a popular auction site.  Wire the rheostats in series with the center rail feed to your other blocks.  Experiment.  Adjust the resistance in the other blocks so that your train runs at a fairly constant speed all the way around.

Some trains will slow more than others, but you should be able to obtain enough improvement so that it will run all the way around without racing or crawling.  You also may need to use multiple rheostats and a double pole-double throw switch to obtain consistent operation in both directions.  My $.02.

I cannot comment on the ZW-L fully because I do not own one and had not been able to perform the same level of testing.

Lionel's design of both the GW180 and recent CW80 utilize only 2 FETs per channel, no inductors, and thus a lower through control path resistance. Also, then the source transformer is a 18-19V rather than a higher voltage.

Also, the Legacy powermaster circuit (which in theory is similar to the ZW-L) is also 2 FET based.

Thus, both in testing and design details, less internal resistance. How much, I cannot say, but again less than what you have now.

FWIW, again, I have repaired GW180s, I bought the new CW80 for testing and comparison and broke it down, and the Legacy powermaster. They all are using 2 FET circuits for power control.

Inside a the Legacy powermaster (2 each FDP047N08)

Inside the CW80 (newest fanless version) (2 each FDP047N08)

Sorry, I don't have pictures of the GW 180 but suffice to say very similar. The difference is they are heatsinked in the G180- but it's also handling 180 Watts same like a Powermaster.

VS the much higher component count and resulting path of the Z4000

@cnwdon posted:

Thanks for the considerable energy expended here.  To correct any assumptions: From transformers to TIU and TIU on (buss wires) all is 12 gauge copper stranded, there is some 10 gauge as well for a few segments.  Drops are frequent and all 16 or 18 gauge to inner and outer rails, with outer rails tied together equally often at drops.  I use no isolated outside rail trigger circuits, so all track has both rails contributing to the circuit.  Track (GarGraves) has double soldered pins, the usual ones plus 12 ga bare copper inserted in the bottom opening of the rail ends and soldered, as well.  TIU to track drop is less than 2 volts at the farthest stretches from origin.  The problem is the power supply internal resistance mentioned in Vernon's post above.   It seems to drop those motors right into their critical narrow speed variation range.

Like it or not (I'm fine with it), I have a number of "sow's ears" from this standpoint that are silk purses for operations to the railroad's CEO.  The CP-now-C&NW custom F3 set with 4 Pullmors, the Pride Lines City of Denver with 3 open frame prewar-style motors and 2 ERRCo command board sets running them, 3 K-Line TMCC Trainmaster chassis with C&NW renumbered Lionel shells (can motors but no cruise control), and I'm sure other locos I'm forgetting in the inventory that will be brought into action as operations increase.  To fix each of those locos with remotoring and Cruise Commander boards, or just Cruise Commander M boards for DC motors, involves much cost and labor and no little aggravation, from considerable experience doing it.  Even if it penciled out slightly less costly than the low-drop Variac model I mentioned, the hassle would still make the Variac a better bargain.  I already know from tweaking the voltage while running that bringing it up within 1-2 volts of baseline solves the problem of extremes of race and crawl speeds to an acceptable level.  Getting rid of the 3-4 volt drop at the power supply posts will substantially solve the problem.  If I haven't made the point clear why I'm chasing more stable source voltage, it should be now.

I am interested in the isolation transformer safety point above, as long as that transformer doesn't have its own internal resistance problem, however, I suspect it may and it wouldn't take much to defeat this strategy with the 0.8 volts already expected as load-related drop for this model of Variac.  Otherwise, I will make the Variac safe by limiting the travel of its dial internal to the cabinet to a few volts above the 19v desired.  A second-level redundant safety in the form of a voltage-triggered breaker is the Zener diodes already across my TIU inputs for spike protection, which will fail in dead short (they have 37v ratings as I recall) with overvoltage, then tripping the transformer's own breaker (12 or 15 amp placed in the cabinet where the two Variacs would live) and preventing unsafe voltage from reaching outside the cabinet.  I have plenty on hand, so will probably add Zeners at the cabinet outputs right outside the rapid breakers so high voltage can't escape even for a moment.  No, this will not be UL listed, but input as to the safety of the strategy is welcome here.  I have grandchildren, too.

I'm also curious whether Vernon can say for "that big L 620 Watt ZW-L" that my 6+ amp 4-motored train loads won't pull its output down the same 3-4 volts.  I'm not aware of the technical differences.  My large "The MAX" is unlikely to have lesser transformer windings or greater internal resistance than whatever is in the ZW-L, but I'm speculating based on how cool it runs regardless of load.  So if actual measured volts/amps say differently, please advise.

I realize most of you wouldn't be in the same situation, so advice in hindsight that would have altered loco decisions decades ago will not help now.  Advice about how to do this and do it safely will be helpful and appreciated!

Again, I feel like- why not just use direct 180 watt bricks if running command locos anyway?

You don't need variable circuity.

Another factor- I would not be running that current THROUGH the TIU. I would run passive mode. Again, knowing that people and even my club cooked TIU jacks running Williams and higher currents and all it takes is one to heat up, melt the plastic, get looser and hotter in thermal runaway.

Thanks once again for all the thinking.  Thanks, Vernon, for the pics and discussion of the internals of the Z4000 and other recent power supplies.  Unless using 180W bricks (I have them on hand) will bring the source drop to 1v or less, I don’t see a solution above.  Will try and report.

Ted: My layout mainlines are dead level and dead flat (as in laser level used across basement and leveling legs/good framing/half-inch plywood make sure of that).  All connections to track are soldered, no lockons, no unsoldered pins except at switches where drops and bus wires bridge those places.  I’ve thought of the variable resistance idea many times, but it’s not compatible with other command locos that need stable voltage at lower loads so they run at a stable speed around mains.  If I had purely a conventional layout and trains, yours would be a handy solution.  Some folks use their four ZW  handles to do such tricks on a single main, I know.

I’ll try a brick and report the voltage drop, but I’m not over hopeful.  Building a safe box with that Variac from ISE remains my interest, excursion of Variac limited to 19v output, and with rapid breakers and Zener diodes and external horn-bell buttons for rare conventional running and a direction momentary normally-on power interrupter button to be included.  Old AC volt and ammeters on shelf have been waiting for this job, too.

I understand pros and cons of passive TIU mode, and my choice is to stick with active TIU carrying load.

Again, thanks to all, and if someone with the electrical knowledge needed has other recommendations for my safe DIY power supply, please chime in.  This morning I am recalling my old Walthers catalogs, Marn-o-Stats (I have one), and the home built power supplies of the 1930s-50s with a smile.  Never thought I’d be making one in this era.

Have some experience with auto-transformers, Variacs. First thing, if you try to stop the Variac at 19V you are going to get less than ideal resolution. Second thing is, you are tying the white wire to the track. Not good. A Variac is not isolating. It is copper wire wrapped around an iron core with a moving slider tap. It has no second winding; this is how you keep size and cost down, and get more output power for the same amount of magnet steel.

A better choice would be to have a Variac followed by an isolating step down transformer. I would like to recommend a Lionel 180W brick, but I don't know how it operates at very low input AC voltages; as in, if it has an internal circuit needs say 5VDC, at some point that circuit is not going to work. UL has limits on how much above and below 120Vac something has to work AND be safe, can't remember if its 10% or 6%, NAFTA or European union.

Another problem with Variac directly to track is if the plug was put on backwards somehow, you would have 120Vac (black wire) directly to the track. Very much not good.

If you go with an off-the-shelf isolation step down transformer, you will need fuses and/or circuit breakers.

@illinoiscentral posted:

Have some experience with auto-transformers, Variacs. First thing, if you try to stop the Variac at 19V you are going to get less than ideal resolution. Second thing is, you are tying the white wire to the track. Not good. A Variac is not isolating. It is copper wire wrapped around an iron core with a moving slider tap. It has no second winding; this is how you keep size and cost down, and get more output power for the same amount of magnet steel.

A better choice would be to have a Variac followed by an isolating step down transformer. I would like to recommend a Lionel 180W brick, but I don't know how it operates at very low input AC voltages; as in, if it has an internal circuit needs say 5VDC, at some point that circuit is not going to work. UL has limits on how much above and below 120Vac something has to work AND be safe, can't remember if its 10% or 6%, NAFTA or European union.

Another problem with Variac directly to track is if the plug was put on backwards somehow, you would have 120Vac (black wire) directly to the track. Very much not good.

If you go with an off-the-shelf isolation step down transformer, you will need fuses and/or circuit breakers.

You forgot to mention that since the neutral is tied to earth ground at the panel, without an isolating transformer, forget about running TMCC/Legacy, it won't work!  My last word on the topic...

@cnwdon get yourself a small bubble level that's only 5"-6" long and move it along the track in the problem area.  It will tell you if the track itself is bowed.  That's something the loco will react to, which is independent of a level platform, level basement floor, etc.

if you incorporate double-pole, double-throw switches to bypass the rheostats (or to selectively incorporate them for a specific direction of travel), you can easily take them out of the circuit when you're running a low current draw, speed-controlled loco.  When the rheostats are in the circuit, you can judiciously pump more than 19V into the rails, because taking into account the added resistance AND the voltage sag you observed due to load, the loco and the electronics inside of it won't be seeing more than 19V.

And as illinoiscentral said above, the way to incorporate a Variac is to put it BEFORE the industrial transformers, varying the voltage to their primaries.  That's how the Right Of Way transformer is built.  It's NEVER safe to connect the output of a variac directly to the rails!

GRJ, you provided one clear deal killer, Legacy/TMCC nonfunction.
Wonder how Right of Way unit performs re: internal V drop under load? Anyone know?

Next step is checking 180W brick on that score.

Then: Would a simple 1:1 isolation transformer used with said Variac solve concerns and not add significant V drop given absence of internal complexity of Z4000 and others? If brick idea fails, that would be next consideration.

Re: “get yourself a small bubble level that's only 5"-6" long and move it along the track in the problem area.  It will tell you if the track itself is bowed.” If you visited you’d understand that doesn’t apply. These are long,perfectly flat and level sections of slowing where only voltage can explain the behavior. Please let’s not belabor that any more.

The switchable sections are a last resort. Not what I would choose to complicate an operating session. But thanks for the thought. Won’t forget it until something else works.

Thanks for the continuing help, guys.

Here is the response I got from ISE about the 1510 Variac.  Apparently they were reading some of your minds.

“1510 Variable Transformer, $770.00 each, 120VAC Single Phase 50/60 Hz Input;

0-120VAC or 0-140VAC Output (depending on wiring);15 Amps Maximum;

With this model, you will need to add a step-up transformer to its output to reach 0-24V.”

The question then is, will I find a step-up transformer (seems backwards; aren’t we talking about a voltage “step-down” from 120v to 24v max, or 1:5 ?) that has extremely low internal resistance that won’t contribute any significant added V drop at the power supply posts?  I get that I’m recreating the Right of Way design in some measure. An advantage is that the 1510 only has 0.2v internal drop at 120v output. If the step transformer were about 1:6, that would place 19v at the sweet spot for the Variac feeding it. Or, a 1:1 isolation transformer with 15A capacity would put the Variac at its low end with low V drop as well.  Looks like such are available, though haven’t found just the thing with limited online  shopping this morning.  None give voltage drop information in their online data.  Recommendations welcome!

.

Thought: higher amp capacity isolation trans=heavier windings=lower V drop under load. So, what amp/watt rating is desirable (and available)?

It’s taken about a week to have more to report, as will become clear.  It turned out I did have a 25 foot or so length of one mainline with unusually bad voltage drop, finally realized that when I ran the same train on the other main parallel to it.  We used some inappropriately “a bit too aggressive” flux that required cleaning (not possible inside a rail) soldering track pins, that caused corrosion at the joints, for the most part just a little unsightly but in that one stretch the electrical continuity through the GarGraves rail joints appears to be nearly zilch.  The voltage drop reflected nothing conducting much except for the 12 ga bus wires with their few connections along the way adding slight resistance in that stretch, causing a maximum of 4 volts drop for those 4 Pullmor motors in the F3 set.  No wonder the stalling.  Spent a few days as time and neck and back permitted making and installing a wire harness under the layout to add a second pair of 12 ga bus wires tied to the existing ones every 6 ft or so to prevent any DCS signal reflectance problems, and adding a few more drops to the rails as well.  Now less than half a volt drop at farthest point from feed to the bus wires.  That helped tremendously with the behavior of the locos.

However still some issue with speed variation and inability to run a slow freight at constant track voltage without stalling.  So proceeded with promised comparison of Mainline Industries The MAX, Lionel PH 180 and a pair of PH 180’s set up in parallel feeding input to TIU, with PSX1-AC downstream (for now) set at ~10 amps.

Results, running with 5 to 5.5 amp load, here are the voltage drops at transformer outputs from baseline at no load to running at 5 amp load:  The MAX 1.6-1.8 volts; single PH 180 0.8 volt; parallel pair of PH 180’s just 0.4 volt.  Besides generally steady running, the parallel setup seems to make for unusually constant voltage and I could run the ore drag almost down to the prototype CNW’s operating rule of 30 mph for loaded ore trains: average 35 mph over 130 ft mainline, with two blocks each fed near center.  Curious whether anyone else has had similar benefit from using an “overpowered” setup like this to minimize V drop?  I’m inclined to change over to the parallel PH 180’s with PSX1-AC’s place in front of each TIU channel, and any necessary additions like chokes advised in other threads.

The Legacy 360 PowerMaster sounds like I should be considering it for each of the four track circuits as a safe method designed to deal with parallel bricks.  Does it deliver the full smooth sine wave when it’s set for maximum output?  I gather it chops the wave to produce lower voltage for conventional running, but would that only apply when not delivering the full 18 volts?

I appreciate the patience of each of you who is far ahead of me in these areas.  I’m hoping to need only the one TIU, avoiding Super TIU mode, using large power supplies and the PSX circuits set for 15 amps so that multiple trains (2 or 3 including passenger trains) can operate on each channel without overloading it.  Passive TIU mode is part of that plan to protect the TIU.

Glad you found what seems like the bulk of the problem Don!

With a constant voltage set, does the train slow down and/or stall in the same place every time?  What happens when you run on the same loop in the opposite direction (i.e., clockwise instead of counter-clockwise)?  If you connect an ammeter in series with the power feed from the transformer, what does it show as the train begins to slow down and stall?

I like the starting torque of the old AC motors when I run my trains hands-on.  But series-wound universal motors are inherently sensitive to changes in load.  If you're really determined to "set it and forget it" at 30 mph or less, you would probably be happier with modern, can-motored loco(s) that have speed control.  Keep us posted!

Good to hear that you have identified the power feed problem that was dropping the voltage on sections of track.

Regarding the "over powering" approach, I have noted that voltage drops  on transformer output as the load (amps) goes up on non-regulated power output (i.e. isolation transformers).  Before I migrated to PowerHouses, I was using  Hammond "filament" transformers to provide 18 VAC to my TPCs.  Hammond part numbers  165S18 (10A output), 165U18 (15A), and 165V18 (20A) are appropriate.  These are step-down isolation transformers and I used a 360 watt Variac upstream of the Variac to trim output voltage to 18v.  I noted as loads were added to the loop(s), the voltage needed to be trimmed up.   During sessions using a single 20A transformer driving two 10A outputs to two TPCs, I noted reduced voltage during conventional operations.  I ended up using discrete 15A or 20A transformers for each TPC/loop.   Airpax 10A instant trip breakers limit track current, but the over-capacity of the power supplies kept voltage close to the desired 18v on loads up to 10A.

Because I'm not running high amp Pullmor locos these days, the PowerHouses suffice for power.  They are 1/3 the weight and size of my Hammond boat anchors in their steel enclosures and include overcurrent protection.

I have no issue running dual AC motored trains, but I don't combine them as a rule.  For me, the PH180 has been more than sufficient, so my pike runs on four of them.

Thanks for the replies and information.  

Re: Pullmor F3 pair and speed variation, Ted: yes, there is some slowing near block ends, but acceptable: doesn’t crawl too much nor look unrealistically fast, so it’s OK.  I have a high percentage of hidden track, so the places where speed changes gradually don’t attract attention.  This is like the favorite fishing lure (like my ancient Pikie Minnow that caught northern pike but not much else in my youth, but still fished with it anyway…), these custom CNW F3s look perfect with the undersize Lionel ore drag, and they were what the CNW used back in the late 40s and 50s in northern Michigan to move ore, along with ten wheelers and mikados and in mid 50s baby Trainmasters.  So they are one option for those trains.  The amperage varies little, just rises a tiny bit as you would expect near block center where voltage is 1v higher or so and motors draw more power.  All appears as expected.

Re: choice of power for command operation: I already own the Mainline Industries The MAX as well as a couple of Z4000’s.  One power district: Running my 8 track passenger terminal and its district including switching postal tracks and North Western Express Terminal means that I could have a couple of trains powered and moving plus a switcher working simultaneously at times, plus lights on trains sitting waiting to depart.  Two more districts: The two Galena Division E-W mainlines each have tracks where a second train may be drawing power while one train runs on the mainline; one of those will include the multi-deck staging yard and its 2% grade approach track, the other the center third track at West Chicago where a train may be running while a switcher or other loco is active around the engine terminal.  Fourth district: Wisconsin Division on the upper level is the only “low current” area, but may add the West Chicago freight and commuter holding yard to its load to spread the amperage optimally.  Track is powered with 12 ga bus wires, and all smaller branches are at least 14 ga except for individual track section drops of 16-18 ga.

So: my preference would be to have a simple pair of PH180’s in parallel and a PSX1-AC set for 15.4 amps connected to the track buses for each of the four districts, and switch between that power supply and one of the existing transformer outputs for conventional in the occasional case of using it, using a SPST 20A capacity switch for the hot conductor only leaving the common ground alone, upstream of the PSX1-AC.  I don’t think I need to use the PowerMaster 360’s given what I already own.  I plan to buy four of Zacharia’s latest passive TIU mode boards and place the TIU in the optimum location for signal getting to all the places it must reach, including the complex passenger terminal.  With Rev L TIU, and a number of PS3.0 locos and later PS2.0 locos, I’m hopeful this will be relatively trouble free.  My collection of early PS2 locos may be a challenge.  Good thing the stacker boards are becoming available for those!  Lots of work already in place including Susan Deats’s filters at all useful places, etc, and so far good control having not yet started terminal operations. TMCC and Legacy signal problems were solved several years ago, don’t think that will cause problems.

Comments about the merits and any safety issue I’m missing, with the above description? Thanks

I should have added that I'll use one of the remote control 110v outlet products to have an emergency shutoff in my pocket for running in passive  TIU mode.