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