Changing power on postwar layout with second transformer for up and down grades

4931 views
20 replies
1 rating 2 rating 3 rating 4 rating 5 rating
  • Member since
    April, 2016
  • 2 posts
Changing power on postwar layout with second transformer for up and down grades
Posted by Reyburn on Friday, April 08, 2016 8:04 PM

Postwar lionel instructions say to insulate the down slope and up slope and to use  a different transformer to slow and speed up engine.  I have read that crossing two seperate circuits with different voltage can damage the tranformer. I am using a Z4000 instead of the postwar ZW.  I know this has been addressed before so can someone tell me how to resolve this issue without damaging my Z4000?

  • Member since
    December, 2005
  • From: Hopewell, NY
  • 2,813 posts
Posted by ADCX Rob on Tuesday, April 12, 2016 6:28 AM

I'm not familiar with the Z-4000 architecture, so you could use anti-parallel diode strings to lower the voltage on down-hills, or rheostats(adjustable - 81, 88, 95, eg.) to limit the current on those sections.

If this was a ZW-C with PowerMaster bricks powering it, there would be no problem in setting adjacent blocks to different throttle settings.

Rob

  • Member since
    January, 2009
  • 1,813 posts
Posted by 8ntruck on Tuesday, April 12, 2016 10:36 PM

I've built a Polar express themed modular layout that has a really steep downhill spiral.  I used the opposed diode methodo on the downhill block of track to control the speed.  Works well.

The only oddity is that the lighted passenger cars jumper the block to the higher voltage in the previous block of track.  This results in the train 'surging' until all of it is on the downhill block.

Good luck.q

  • Member since
    December, 2005
  • From: Hopewell, NY
  • 2,813 posts
Posted by ADCX Rob on Tuesday, April 12, 2016 10:50 PM

8ntruck

The only oddity is that the lighted passenger cars jumper the block to the higher voltage in the previous block of track.

If you power the bulbs in the cars through a 3 phase bridge rectifier or a pair of two small full wave bridge rectifiers(each powered by one truck) with the DC wired in parallel, it will eliminate this effect.

Rob

  • Member since
    December, 2001
  • From: Austin, TX
  • 9,847 posts
Posted by lionelsoni on Wednesday, April 13, 2016 12:46 PM

Another rectifier configuration, the one that I use, is a single small (1.4 ampere) bridge-rectifier with two added (1N4001) diodes.  A simple further refinement that all of the rectifier configurations make possible is an electrolytic capacitor across the lamp(s) to virtually eliminate flicker.

You could also go with the combination of a simple bridge and the capacitor, leaving one pickup unconnected.  This however increases the chance that the lights in a car will be out when the train stops.  I did this on one train that was proving too much of a load for the locomotive and had rather stiff pickups, by removing one pickup from each car.

Bob Nelson

  • Member since
    January, 2009
  • 1,813 posts
Posted by 8ntruck on Friday, April 15, 2016 8:10 PM

Just so I don't hijack this thread, Bob, Rob, could you send me a personal message with wiring diagrams?  Humor this mechanical engineer with pictures about the electrical engineering, please Big Smile.

  • Member since
    December, 2005
  • From: Hopewell, NY
  • 2,813 posts
Posted by ADCX Rob on Saturday, April 16, 2016 10:24 AM

It's all relevant, so here it is:

The two connections on the right go to the bulbs.

The three connections on the left are simple too...
-one to both ground wipers
-each of the other two to one roller.

Rob

  • Member since
    December, 2001
  • From: Austin, TX
  • 9,847 posts
Posted by lionelsoni on Sunday, April 17, 2016 4:39 PM

For those who might be interested in how it works, here's how:

Notice that each of the three input terminals in Rob's excellent diagram connects (inside the bridge-rectifier module) to two diodes.  One diode connects the input terminal to the + output terminal whenever the input terminal tries to be more positive than the + terminal, supplying current in the direction of the arrow symbol and raising the voltage at the + terminal to the voltage of the input terminal.  Thus the + terminal is at the same voltage as the most-positive of all three input terminals.

The other diode connects the input terminal to the - output terminal whenever the input terminal tries to be more negative than the - terminal, pulling current in the direction of the arrow symbol and lowering the voltage at the - terminal to the voltage of the input terminal.  Thus the - terminal is at the same voltage as the most-negative of all three input terminals.

Note that only two of the diodes in the entire circuit are conducting current at the same time, one between the most-positive input terminal and the + output terminal, and the other between the most-negative input terminal and the - output terminal.  All the other diodes are not conducting.  So, whichever two input terminals are connected to the rails of the higher-voltage block are the ones connected to the lamp.  The other input terminal, connected to the center rail of the lower-voltage block, is not connected.  That's why this circuit keeps the higher-voltage block from supplying current to the lower-voltage block.

Notice that you can build the circuit as Rob showed; or you can use individual diodes to make up the same circuit with a few more connections; or you can mix the two as I usually do, using one bridge-rectifier module and two separate diodes.  Rob shows the extra pair of diodes as not connected; you can also connect them redundantly to any one of the other three inputs, that is, assuming you don't have a third pickup that needs to be hooked up!

Bob Nelson

  • Member since
    March, 2013
  • 428 posts
Posted by BigAl 956 on Tuesday, April 26, 2016 2:07 PM

Reyburn
Postwar lionel instructions say to insulate the down slope and up slope and to use  a different transformer to slow and speed up engine. 

 

This is a traditional way to handle up and down slopes. You can use different transformers however they must be in phase with each other. A better idea is to use a multi control transformer like the ZW. With U common to the outside rail you can connect the B and C controls set for higher and lower voltage to the center rails of the up/down slopes.

It makes no difference if an engine or car momentarily shorts a center rail running at 20 volts to a center rail running at 10 volts. All that happens is the voltage of both center rails momentarily drops to the lower voltage. There is a myth going around that +10 shorted to +20 results in a 10v short circuit however that is not true on an outside rail common wired layout.

  • Member since
    December, 2005
  • From: Hopewell, NY
  • 2,813 posts
Posted by ADCX Rob on Tuesday, April 26, 2016 4:19 PM

BigAl 956
It makes no difference if an engine or car momentarily shorts a center rail running at 20 volts to a center rail running at 10 volts. All that happens is the voltage of both center rails momentarily drops to the lower voltage. There is a myth going around that +10 shorted to +20 results in a 10v short circuit however that is not true on an outside rail common wired layout.

Have you measured that fault curent? I have. with just a 5-6 volt difference on a ZW the current is over 15 amps, way over. And there is no breaker to protect the transformer.

And this is a good way to generate significant voltage spikes too.

Also, I would re-do your voltage test with a good VOM and see if the voltage drops to the lower setting, goes up to the higher setting, or meets somewhere in between(hint - this is a trick question) during these momentary block bridgings.

Rob

  • Member since
    December, 2001
  • From: Austin, TX
  • 9,847 posts
Posted by lionelsoni on Tuesday, April 26, 2016 8:43 PM

The important thing is not what voltage exists on the connected transformer taps when the fault occurs, but rather how much current is flowing between them.

I actually think that the voltage will drop, as Al says, but not to the lower of the two open-circuit voltages except by coincidence, by an amount proportional to the voltage developed across the primary winding's resistance in response to the heavy current drawn by the primary to supply the even heavier current drawn by the shorted section of the secondary.  It occurs to me that Al may have noticed such a drop, to a voltage approximating the lower open-circuit voltage, and constructed his unconventional theory to explain it.

Bob Nelson

  • Member since
    December, 2005
  • From: Hopewell, NY
  • 2,813 posts
Posted by ADCX Rob on Tuesday, April 26, 2016 9:10 PM

Yes, the voltage drops on the higher throttle track, relative to the resistance of the bridging element, and the block with the lower voltage may go up or down depending on how big the fault current has an effect on the output of the entire core.

The small wiring in a PE passenger car or a N5c modern caboose will not cause as much of a drop in observed track voltage as a two roller loco pickup assembly.

Rob

  • Member since
    December, 2001
  • From: Austin, TX
  • 9,847 posts
Posted by lionelsoni on Wednesday, April 27, 2016 10:07 AM

A thought experiment:

The secondary winding of a transformer supplies your house with electricity.  If you live in the US or Canada, the transformer's primary winding is connected to a "distribution voltage", something like 7200 volts; and it puts out 240 volts between black and red wires connected to the ends of the secondary winding.  There is also a white wire that is connected to a tap at the center of the secondary.  The black and red wires are at 120 volts relative to the white wire.  There are circuit breakers in series with the black and red wires, between the transformer and all of the loads in your house.

Now for the thought experiment:  Imagine that you have a 3-rail toy train whose motor, lights, and whatever are designed for ten times the usual voltage.  If you connect the red wire to the outside rails, the white wire to the center rail going down a hill, and the black wire to the center rail going up the hill, the train will get 240 volts going uphill and 120 volts going down.

This situation is like a setup that you might have with a real, low-voltage, toy train, except that you have 240 volts instead of 24 going up and 120 volts instead of 12 going down.  The distribution transformer is like a type Z on steroids, with the U terminal being the red wire, the A terminal being the white wire, set to half the full voltage available (12 or 120), and the B terminal being the black wire, set to the full voltage (24 or 240).  But the type Z has only one circuit breaker, in series with the U terminal, and none in series with the A or B terminals.  So imagine that the black-wire circuit breaker between the transformer and the center rail is bypassed.

Now imagine what happens when the train crosses the gap from 240 volts to 120 volts:  It connects the black wire to the white wire.  When I accidentally do that in my house, there are some fireworks, and the circuit breaker on the black wire quickly trips, demonstrating that there was a fault current flowing that was greater than the rated trip current of the breaker.  Is there any doubt that, but for the breaker, a current greater than the wire can safely carry would continue to flow as long as the black and white wires are connected together? 

Bob Nelson

  • Member since
    December, 2005
  • From: Hopewell, NY
  • 2,813 posts
Posted by ADCX Rob on Wednesday, April 27, 2016 12:46 PM

Great analogy.

Rob

  • Member since
    March, 2013
  • 428 posts
Posted by BigAl 956 on Thursday, April 28, 2016 5:16 PM

No, a very bad analogy. First of all the two 110v lines coming into your house are 180 degrees out of phase. In other words in relation to earth, (the white wire in your example), when the black hits +110v the red is at -110v. So yea you whould get a nasty surge if you connect the two together. Also in your example you would not connect white to the center, white is common and goes to the outer rail.

But thats not the point. A ZW transformer operates in a single phase. You would never have +- voltages, all voltages are +. Also the U terminal is common like the white in your home.

So here is an experiment. Set the A control of a ZW for 20v and the D control for 10v as measured to U. Now measure the voltage between A and D and you will see it's 0v. Now short A and D together and wait for fireworks. You will be waiting a long time because with 0v differential between them there can be no current flow and no fireworks. Why is there no current or voltage differential. Because A and D are both positive and in phase with each other.

To the electrons flowing through the transformer A and D are the same wire just a few ohms apart. Electrons need to flow from + to - that  means they want to travel to U. Even though A is set at 20 and D at 10v that potential is only in relation to U. 

Try this experiment and prove me wrong if you dare. I already have and proven I am corect. I have operated my layout this way for 50 years and apparently so has Lionel for 100 years.

  • Member since
    December, 2005
  • From: Hopewell, NY
  • 2,813 posts
Posted by ADCX Rob on Thursday, April 28, 2016 7:37 PM

Sorry Big Al, you're patently wrong on the ZW issue.

I get a 10 volt differential and a ~30+ amp short.

If you were right, center tap or multiple tap transformers would not exist.

Rob

  • Member since
    December, 2001
  • From: Austin, TX
  • 9,847 posts
Posted by lionelsoni on Friday, April 29, 2016 9:50 AM

Al, there's so much wrong with that, that I hardly know where to start.  I'll go through it from the beginning.

o  The residential utilization voltages have been 120 and 240 for many years now.

o  Although the voltages on the black and red wires are 180 degrees out-of-phase with each other relative to the white wire, the voltages on the black and white wires are in-phase with each other relative to the red wire.

o  In my example, I will connect the wires to whichever rails I please.  I choose to connect them to the rails which create the analogy that I am demonstrating.
 
o  The voltages out of any single-phase transformer, like your ZW, my Z, or both of our distribution transformers, are in-phase or out-of-phase depending on which wire they are measured relative to.  It is customary to describe the voltages of toy-train transformers relative to one end of the winding, labeled U on the ZW and Z.  It is customary to describe the voltages of distribution transformers relative to the white center-tap wire.  But the transformers don't know which wire we pick; and so we can pick whichever one we want that suits our purposes.  When I pick the distribution transformer's red end-of-winding wire as my reference, the white and black voltages are in-phase relative to the red wire, just as the A and B terminals are in-phase when I pick the Z transformer's end-of-winding U terminal as my reference.

o  All the voltages out of a transformer, whatever reference is chosen, are alternately positive and negative.  Statements like, "all voltages are +", and, "A and D are both positive", make no sense.

o  I find it impossible to believe that you have tried your own experiment.  I have often measured substantial voltages between the various variable output terminals of transformers.  Rob seems to have too.

o  Electrons, having negative charge, are attracted to positive voltage, not negative voltage.

o  It's the same wire, but it's wound around the magnetic core of the transformer, which contains the same varying magnetic flux that induces voltage indiscriminately in all the windings that encircle the flux.  That makes the voltages at A and D different.  There's a voltage source in series with those "few ohms".

Bob Nelson

  • Member since
    March, 2013
  • 428 posts
Posted by BigAl 956 on Friday, April 29, 2016 11:45 AM

Am I the only one on this forum that understands + and - ?

 

  • Member since
    December, 2001
  • From: Austin, TX
  • 9,847 posts
Posted by lionelsoni on Friday, April 29, 2016 12:57 PM

Just how is it that "a single winding with multiple tap points" that has one tap in the middle of that single winding and another tap at the end of that winding is not electrically exactly the same thing as a center-tapped transformer?

If I had a ZW with its A tap set at 10 volts and its D tap at 20 volts and then painted the U terminal red, the A terminal white, and the D terminal black, how would the electrons magically know that they were supposed to flow only between U and A, or between U and B, but not between A and B, while the distribution transformer, with the same winding configuration and the same colors on its terminals, allows lots of current between any two of its terminals?

Bob Nelson

  • Member since
    January, 2006
  • From: Florida
  • 2,137 posts
Posted by traindaddy1 on Friday, April 29, 2016 6:56 PM

Wow!

"Rectifier Configuration"... "Diodes"... "Residential Utilization"...

 "Varying Magnetic Voltage"

Learn more everyday. Gotta luv this hobby!

 

  • Member since
    April, 2016
  • 2 posts
Posted by Reyburn on Friday, April 29, 2016 7:35 PM

Sorry I asked the question in the first place so I will continue to use my Z4000 which has four circuit brakers, one for each circuit.  I decided to go with my No. 95 prewar rheostat to slow the down grade speed after increaseing the overall voltage for inclines.  Works fine and a simple fix to a complex problem.  Thanks for everyones imput. 

Join our Community!

Our community is FREE to join. To participate you must either login or register for an account.

Search the Community

FREE EMAIL NEWSLETTER

Get the Classic Toy Trains newsletter delivered to your inbox twice a month