Lionel Postwar Magne-Traction™ Questions

Magnetraction's main "attraction" was the ability to keep an engine on the track in tight curves.  If you like to run trains at warp speed magnetraction would keep the engine and most of the cars following it on the track.  Without magnetraction mean old Mr. Inertia will roll the train as it rounds the corner. 

If you really need additional pulling power for grades rubber traction tires do a much better job than magnetraction.  One warning note, tractions tires can get thrown, magnetraction is "built in".

IMHO, either MagneTraction or traction tires would be very desirable, almost mandatory,  based on experience on my last layout.  It had, like yours, a 4-1/2% grade.  MagneTraction engines had no trouble with it, but plain steel wheels were as good as helpless, except with a very short train.  Had to get a running start (like dad did in the '36 Ford approaching a hill) and spun the wheels all the way up.

It will not pull as well as the 681 or 682.

I have a few of the '46 models, and the gearing & speed is good, but there is a lot of wheel slip with a big train.

On the other matter, your downgrade speed issue can be addressed by powering that section with an adjustable rheostat Like the Lionel 95 or Lionel 81/Ives 1894 powered from the same transformer lever/control.  This will let you adjust the downhill speed accounting for differences in engines and loads.

Hello, and thanks for your replies. Rob, I have two prewar rheostats just like you've pictured and I was going to incorporate them into my layout, but some of the guys on this forum said those are only safe disconnected & sitting on a shelf...

Some people just love rubber traction tires.  I don't.  I have four MT-equipped locomotives, the oldest from 1949, the newest from 1984.  All have worked as advertised, with no maintenance whatever on the MagneTraction.  Yes, it does make a difference.

I don't see why the 81 or 82 rheostats are 'unsafe'. There is only low voltage going to them. They don't really get very warm and the windings are covered. If it was me I would use them with no worries about any fire or shock danger.

There must have been some misunderstanding there - perhaps they were referring to the transformers that were used with them back in the day.  I even use them just sitting on carpeting for block control of trains on the Christmas layout.

I would like to see that thread if you can find it.

Desert Center Ca,

    I like the magna-tracion on the old Lionel engines, my 59 Northern Pacific still runs

great and has a million miles on her, don't believe the guys who tell you it does not make a difference, it does. 

PCRR/Dave

I'm glad one of those reasons isn't for safety.

The rheostat is not a voltage reducing device, which is where the confusion comes in.  It limits current.  It's much easier to adjust on the fly for different trains on downgrades, etc.

The diodes are for reducing voltage with predictable and consistent results.  There is a place for this arrangement, but for block control the rheostat is so much easier to deal with.

Magnatraction absolutely does make a difference.. My Postwar Santa Fe 2343 (Magnatraction) can run circles around my 2333 (Non) Magnatraction when it comes to climbing hills, amount of cars it can pull and staying on the track at higher speeds no question about it.. and as was said earlier there is O maintenance with Magnatraction.

There is a world of difference between the 681 and 671. Magnatraction was marketed as an improvement and increase in loco pulling power. Lionel was marketing longer trains, particularly the new passenger cars, and the standard loco's of the period just could not handle the longer trains. Unless you don't mind running shorter trains, you may want to reconsider this loco. The rheostats are 100% safe. 

Gandy

It is a variable resistor, which if placed in series with the track center rail drops voltage and reduces current.  2 resistors in series.  The resistance of the motor and now the resistance of the Rheostat.  The voltage at that section of track is reduced, as is the total current flowing to the track section with the rheostat.   G

IMHO, the issue with using a resistor, such as a #81 rheostat is that it's effect may not be consistent with different locomotives. The effect of the resistor at any given setting will depend on the resistance (impedance?) of the train being run, including lighted cars and such. Also blowing the whistle will have an effect.

Interestingly, I have that as an advantage with a rheostat. 

It is a disadvantage if using a fixed value resistor, which is why I've never recommended using one.

Close, but backwards.  Being that it is a variable resistor, which if placed in series with the track center rail, actually limits current which then reduces voltage to the train.

You can test this with a VOM and no load on the track section using the rheostat.  You can slide it around all you want, the voltage will remain the same.

quote:

IMHO, the issue with using a resistor, such as a #81 rheostat is that it's effect may not be consistent with different locomotives...

Interestingly, I have that as an advantage with a rheostat. 

A couple of my layouts had steep grades, with 031 curves included. I just used the throttle, no resistors, rheostats or diode arrays.

I did use a rheostat, mounted under my control panel, to limit the top speed when my kids were little.

Rob, What is the difference?  You originally only stated current limiting which is not a complete answer.  Do you really know which occurs first?  This is just basic electrical theory applied to analyze the circuit.

It also demonstrates why diodes also are a better alternative.  The addition of the resistor limits current and drops voltage which means less energy is available for the train motor to do work.  The diodes drop voltage without limiting current available, so while voltage drops, current can rise if needed.  Power= Voltage x Current (P=V*I).  There is also less variability because the wire resistor resistance changes as the wire heats up.  Which changes current flow and voltage drop.  G

It is, and I did not change my statement.  The result will be a lower voltage, however, depending on the load.  This is a big difference compared to voltage reduction via a diode array.

I would stick with the MT or rubber tires if your pulling long hauls, I had a few of 

the older heavy engines and for me there wasn't enough pulling power for those 

cars.

Tin  

How can it be both?  ONLY current limiting but WITH a voltage drop?  If you have 6V source and a 3 ohm motor, the motor drops 6V with 2 amps of current.  When you add a 3 ohm resistor in series the equivalent resistance is 6ohms and the current is limited to 1 amp, but one amp through the 3 ohm resistor drops the voltage to 3Vs.  So the motor only sees 3V and 1 amp for a series circuit.  It is the principle used when dual motor engines are wired in series vice parallel.  Each motor gets half the voltage (from the track) and turns slower.  Parallel wired motors both get the full track voltage and current from the source.

Diodes drop voltage but do not present a resistance to current flow.  So the equivalent circuit would only see the 3 ohms though voltage would be dropped .7V  So the motor sees 5.3V but 1.77amps.   5.3V/3ohms.   G

It's not.  A resistor is a current limiting device.  Period.

You are confusing what the device is, with what happens (the result) in a complete circuit with other variables.  Unlike a diode, the voltage drop across a resistor varies with current - no current - no drop.

The motor example is very poor, as it does not take into account back EMF, and there is no way to pin down the resistance of a motor without knowing what the load is - motors also are variable resistance(very low stalled, very high @ no load). 

I thank everyone for their train advice, and I apologize for my lack of electronics prowess. How precisely would I go about wiring one of my #81 Lionel rheostats into the system? I have two of the (Super O) plastic bus clips to isolate the steep downgrade section, but I'm not sure how to proceed. It sure would be great to not have to use two different controls to power the track, and as someone mentioned above, I'm always worried that my 2-year-old is going to bump up the voltage on the transformer and cause the trains to get launched off the track at the bottom of the downgrade. Thanks!

Very simple - isolate the desired section, connect one post of the 81 to the center rail of that section, connect the other post of the 81 to the center rail of the rest of the loop(or to the same transformer binding post).

Adjust as needed for different trains & equipment.

Rob, I am not confusing what a resistor is, I just explained what it is doing in the circuit more clearly.  You can't analyze the effect without looking at the whole circuit.

And using resistors as voltage dividers is a method in circuit building.  Yes a resistor is a device that opposes the flow of current as the resistance value goes up.

DC Can motor is not a poor example.  And while there are lots of different effects for a precise answer a basic analysis can be done using ohms law.  We don't have to get into power factors either for AC.  Some basic assumptions.

Use 2 12V light bulbs instead of 2 motors.  Same effect when wiring in parallel versus series.  G

No reason to apologize.  Hopefully it all works out for you.  G

The #81 rheostat would be wired in series with the track.

That means: instead of having both wires going directly from the transformer to the track one wire goes from the transformer to a post on the rheostat, and a new piece of wire goes from the other post on the rheostat to the track terminal. Since you have blocks, the wire to the center rail buss is the one to get the rheostat.

There should still be one wire going directly from the transformer to the track.

IMHO, with young children at the controls, a quick acting, manual reset circuit breaker is a very good idea.