Lionel transformers

Recently we have acquired several hundred Lionel transformers. Our collection now comprises over 40 different Models that Lionel produced strictly to be used with their 3 rail track trains. This document is limited to the transformers they offered for sale before 1980.

Their original purpose of their transformers was very simple, which was,. how to control the speed of their trains on a layout. Understand the availability of outside technology was just about nonexistent in those days. What they came up with was simply done by a bunch of guys putting their heads together to create a system to accomplish their objective, which again was to control the speed of the trains on a layout. What they did with no training, no serious understanding of electrical theory was incredible! Here in brief is what they came up with.

The first train transformers was engineered and built with an internal transformer that was built to provide a way reduce the normal household voltage (in those days probably 110 Volts), to anywhere from 12 to 18 volts. The windings on the section of the transformer that was hooked to household current is called the input or primary section.
The output of the transformer or (secondary) gave them the needed 0 to 12 or  18 volts, which was correct to run the trains. What they did was have the secondary windings made of very heavy copper winding wound around a metal frame.   These windings were coated with varnish, on their sides, so they would not short each other out. The tops of the windings did not have the varnish, so the windings were pure exposed copper. So what they did was design a very simple lever that had a carbon roller, attached to the  lever on the outside of the transformer, that would move across the internal windings, which gave them the variable output voltage. The effect was a very stable method of controlling the output voltage to the center rails of the track. To protect the transformer from damaging itself from a short circuit (for example a derailment) they built in a circuit breaker.  Absolutely incredible considering the time this was engineered. This system worked very well and became the standard of design from then thru the 70’s. It was a very durable and stable system that has proven itself for over 100 years.

As Lionel added accessories (for example whistles, and rcs tracks to operate things like the milk cars) additional innovations were necessary. The most notable unit to accomplish these tasks, was one that has been, and still is the most widely used transformer ever made. That model is the Lionel ZW 250/275.

They also designed a bunch more transformers that hopefully would be less expensive and could be used for smaller layouts. Many of these would operate trains ok, but did not have direction or whistle controls, and thus were never very popular.  Finally, somewhere in the 50’s they came up with new lower priced model that had all the features and would operate 2 trains. That was the KW, which today is probably also an extremely popular transformer, shadowed only by the original ZW 250/275.

Since then, every manufacturer including Lionel has attempted to come up with a new design using modern solid-state parts to replace the original roller over the copper windings technique. Why? The original design is way too expensive to try to build today.  So far, many of their designs were prone to early failures. Why? Because they use (often unprotected) solid state parts to control the output power.  These components do not like AC. Our engines even today for O gauge still run on AC.

However, there absolutely are issues with the original transformers. To List a few:

  • The original circuit breakers were designed to protect only the transformers, nothing at the outputs to the accessories or to the center rail. The internal transformer is very durable and so the circuit breaker was designed to open only when there is a major short circuit that lasts for more than 10 or 15 seconds. Recently many engine manufacturers have added some great new audio toys to their engines and some of their accessories. These devices are made with modern solid state components that do not like ac. A derailment can send positive voltage to the outer rails, and a can damage these circuits, (usually fubar). Need to have a much faster circuit breaker and even additional protections.
  • The original rectifier that was used, was great, except it does not have the capability to turn on bells and other accessories.
  • The units were not UL approved, and therefore while very rare could conceivably develop an internal short which could be sent power to the outer metal plates.
  • In the case of the ZW units there was no output for a fixed, none adjustable output for accessories.

There is no question that the original design of rollers over exposed coils is still even today the very best  way to control engine speeds. We at TinMan’s objective is simple. Keep the original design and make improvements in other areas and upgrade the original design. Specifically, here is what we do when we recondition these units. For example, when we recondition the ZW’s and KW’s these are the things we do.

  • Change the rollers (unless they are like new) with an improved copper improved design
  •  Eliminate the original rectifier and replace with a modern bridge unit that will enable the transformer to operate the bell circuits found in newer engines.
  • Add externally mounted switches to choose between whistles or bells.
  •  Replace the original slow acting circuit breaker with a modern fast acting model.
  •  Change the power cord with a 3-prong plug, to make phasing easier, and ground the exposed metal plate on the base. Why? Because the internal transformer is resting on 2 metal plates that are bolted to the outside metal base. While we have never had an issue with a problem with the internal transformer, that we know of, it is possible and as a result send high voltage to the exposed metal plate. Grounding this plate will stop this very remote possibility and makes phasing with other transformers a breeze.
  •  Clean the exposed copper windings.
  •  Add an additional output power terminal on the back of the transformer which gives a constant 20v. Why? The transformer has two variable controls for accessories or to control speeds on trollies, bumper cars etc. Plus, other toys like the milk cars do not like wide open voltages. Switches, lights, RCS tracks etc work best with a higher voltage wh. In the pictures you can see the additional power output terminal to the left of the U terminals and the A to D terminals.
  • On the KW transformers change the 14-volt power out from requiring its own ground circuit which means it will not operate any accessories attached to the tracks. To fix that we modify the circuit, so the 14-volt output does work with the U terminals for it’s ground
  • Preform a final check for proper outputs with not just voltages, but also under 3- and 6-amp loads. This is done on a “transformer report card” that is included with your transformer.

Now to our latest innovation.  The circuit breakers originally installed in these transformers originally, as said were designed to do one thing, and that was to protect the transformer from burning up in case of a short from derailments or other things. This is a definite item that should be changed,

There is some talk in the O gauge community that even with modern circuit breakers are still not fast enough, for many of the new engines. Since we began changing the old breakers with the newer designed ones, we have not had one complaint about engines etc. being damaged due to short circuits. That is not to say that it never happened, just that we have heard of any. Our customers are not bashful, which is the way we like it.

In the O gauge community, there are suggestions that an additional fuse should be used in line with the train power that will blow almost instantly when it senses a short.

So, what we are now doing, as an option, is installing built in fuse holders on the back of the transformers. These fuses only protect the center rails, not the accessory lines. We are also supplying extra fuses with the option.

So, the question: Should you purchase this additional cost item for your transformer?  If you have some modern engines that have those new toys, might be a good idea. If you do not have any of those and do not plan on getting them, no, it is a waste of money. Also having a really fast power shut down can be a nuisance. It requires very little, short circuit to blow the fuse, way less than ½ the time of the breaker, which could be a pain.

So, next, what are we doing with all those other transformers that do not have things like whistle controls, or direction switches. (Thought you never would ask)

We have come up is a new method of adding whistle and direction controls to these transformers. We are doing these with virtually all of the older units with the exception for the little cubies. These cubies are still valuable for operating accessories that don’t like fixed higher voltages.

We modify most of the units so the accessory outputs on the transformer work with the outside rails for ground. Why? Switches, RCS tracks will not work with the way they configured the internal wiring. As a result of our mods, the original from Lionel wiring instructions will not work, so we install a sticker on each transformer outlining where to hook up the wires for example like this. The A, U, C, and B correspond to what is on the original transformer for wiring.

Here are some questions and answers you may find interesting.

Q.  You mentioned the voltage output for the ZW was originally designed for 15 to 18 volts output, My ZW does over 20.

A. The internal transformers are hooked directly to the power from the wall plugins. Early power from the electric company was 110Volts. Today they are typically 120+ volts. Higher input voltages equal higher output voltages.

Q. I’m being told that the original rectifier in the transformers to operate the whistles should be changed by a modern diode, TinMan does not do this Why not?

A. First these “modern Diodes” you are referring to design is over 50 years old and will not do one thing more than the original rectifier. Our system uses a full wave bridge system that sends out a much cleaner dc signal and allows the transformer to turn on some of those newer toys. By the way, changing out the rectifier, even though it works fine, is a total waste of money. If it ain’t broke don’t fix it. 

Q. So you said you can make most all the older transformers (which are cheaper) to work with whistles and direction, why should I spend the money on a ZW or KW?

A. Our additions of the whistle control do not have the ability to operate bells etc. And except for the original ZW and its 150 cousins, will only control one or two different trains. Depends on your needs, and your budget. With today’s inflation rates, we are trying to come up with some top-quality economical options for our customers.

Q. What are the differences between the ZW 250 and ZW 275?

I know I am going to stir the S— pot here, but after working and testing hundreds of both, in my opinion None, goose egg, not a dammed thing, except for the outside label.

Q. Is there any difference between a ZW 275 that was manufactured in 1975 vs one from the 40”s?

A. Yes, circuit breakers are different (not necessarily better) changed from resistant wire for light and whistle controls to large resistors (cheaper), Other than that, none that I am aware of, especially in terms of overall performance.

Q. Not necessarily the KW’s and ZW’s but with the other older units, any items of major concern?

A. Yes, the circuit breakers are a frequent issue. What will happen is you show output voltage but will not run a train, which is why we replace everyone we recondition. Mostly because of exposed contacts and because of mounting the breakers horizontally instead of vertically. Our modern breakers are sealed.

Q. I’ve heard that TVS diodes should be installed in the outputs of transformers. Why doesn’t TinMan install these?

A. 30 to 40 years ago it was a good idea. Today most all power companies have upgraded their power generators to accommodate increased demand for power. To accomplish this task what they have done is increase the voltage to the power lines in most cases by over 10 times. This change required changes at their substations and pole transformers to accommodate their changes. With these changes safety devices were installed with new technology equipment to eliminate power surges, or brown outs. Power surges are pretty much of a problem that has been taken care of.

Q. You mentioned fuses you are adding as an option. What values do you recommend, and how fast are they?

A. A 3-amp fuse will run most trains but blows too easily. We install 5-amp fuses in what we install. A dead short will blow the fuse in less than 1.5 seconds, which equates to less than ½ the speed of even our new breakers.

Warrantee: We guarantee all our transformers for 2 years. We will either repair or replace your unit. Physical damage is not covered.

KW Transformers

This transformer is designed to operate 2 different trains at the same time. It also has power connections on the back to use for various accessories, for example switches, remote control tracks, lights and other toys. It has plenty of power to handle any nice layout where you will want to run 2 trains at the same time. Using multiple of these transformers for larger layouts works out well.


The ZW is the undisputed king of Lionel’s transformer line. It was designed to operate 4 trains simultaneously, however if you do that, there is no provision for separate accessory power.  A popular solution to this is to add a small 50 to 90-watt transformer just to handle your accessories.

What is the difference between the 250-watt vs the 275-watt version? Frankly not much, the difference of 25 watts divided by 4 controls is like 6 watts, not terribly significant. The 250 watt will of course be more energy efficient.

Other transformers

Thru the years we have massed quite a collection of other transformers. If you need another transformer for accessories or a tree layout, email us with what your needs are and we can supply you with a good dependable unit for between $20 and $100 depending on size. There are just too many to list here, and the inventory changes frequently.