Tech Tips Transformers

Phasing Transformers

If you’re running more than one transformer on your layout, they need to be phased properly, or they will short each other out. Fortunately, this is an easy job.

Your secondary transformer should have a place to install at least  2 wires. The larger transformers like the KW’s or ZW’s will have multiple “ground, or common” terminals that connect to the outside rails of the track. It is these terminals that we are concerned about.

The simple way: First plug all your transformers into a power strip. Then put a wire on whatever number of transformers you have on the common terminal of each transformer. Touch any two wires together, no big spark you are good to go, big spark, reverse the plug that goes into the wall. The spark should disappear.  On your plugs put some kind of a mark on the plugs so you know they go in a certain direction on your power strip. What we do, is cut off the original plug and replace it with a 3 prong plug. Just don’t put any wires on the odd prong. then once you figure out which wire goes where, you will never have to worry about them again.

The truth about model train AC transformers

We go thru latterly hundreds of transformers, and anything over 20 volts is highly unusual. You also need to realize these transformers are relatively crude devices. There are no regulatory circuits built into them. The power from the wall socket is hooked directly to the primary of the transformer, which means of course the output of the transformer will be in direct proportion to what the input voltage is coming out of the wall socket. I have seen variations as low as 108 volts and as high as 124 volts. That’s a variation of 12% which will equate to up to 2+/- volts on the output side of the transformer. Also FYI we have recently built some very sophisticated test equipment to give us accurate means of determining exactly what the various transformers will produce, not only in voltage, but in watts and amps. Telling someone that their transformer is great because it does 21 or more volts, is worthless, because it does not tell you what the transformer does once you put a load on it. With the equipment we have we can actually watch the voltage drop on every single transformer we see. How much it depends on how much of a load we put on the transformer which can be varied from O to up to and including 15 amps, which is way beyond any model train transformers capability. Sorry for the soapbox, but I grow weary with folks being misled by other people who either don’t know what they are talking about, or only want to tell you what they think you may want to hear.   What to hear some facts? Warning you may be a little disappointed. Theoretically if you purchase a transformer that is rated at for example 200 watts, it should produce enough current to hold a voltage of 20 volts for example with a 10 amp draw. (amps X Volts =watts)  I guarantee you there is not a hobby transformer made that will do that.  A laboratory AC power supply will of course absolutely do that, if you don’t mind spending 5 to 10 thousand dollars on one For example a typical ZW transformer no load voltage of 20 volts will drop to 16 volts with only a 3 amp resistive load, about what a single engine diesel will draw. Now in fairness, once the engine is moving along its merry way the current will drop and therefore the voltage will increase in proportion. IN short, 75 clean watts should drive a single train just fine. If you want to drive 4 trains, than you need 300.

KW Transformer Tech Tip

This poor transformer has received more criticism than any other transformer Lionel ever made.
It really is not a bad transformer, its just the design engineers in my opinion got a little too cute, and the owner’s manual frankly sucks. So a picture is worth…….So let’s try to take the mystery out of this poor neglected step child.
First, these two terminals are shorted together inside the transformer and need to be hooked up to the outside rails on your layout.

These two terminals are used to run the trains and should be hooked up to the center rail for 2 separate trains.
This terminal should be wired for accessory power to for example switches, uncoupler tracks etc.It will give you a constant 19 volts or so no matter where your speed control is set.

These next two 14V have to be used together because they do not share anything with the outside rails. They are usefull for village lights etc. but you need to remember you will have to run 2 wires to each light. In other words for your lights one side of the bulb goes to the c terminal the other to the d terminal .
Lastly the C terminal that is supposed to wired like c and d (which gives you 14 volts) here you can use the outside rail power tap (u) and C to get 6 volts. For what have no idea, would have been a lot better if it would give 14 volts between C and U but no luck.
Other than that it really is not to bad.
So a summary:
U terminals go to the outside rails, no matter which one. they are both shorted together
A terminal is to run a train controlled from the A control lever and needs to be hooked to the center rail of your “A” train.
B terminal is to run another train and needs to be connected to the center rail for that train, again is controlled by the B lever
D can be used to operate all your switches, remote control uncouple/unloader tracks etc.
C and D hook to light bulbs

In a typical o gauge layout which transformer lead is really the ground lead?

Great question.   The answer? None of the leads coming from the transformer are a ground lead.  All post and prewar transformers operate from AC power. Some of the newest stuff out there operate on DC which really do have a ground. But in the case of all the rest there are 2 identical power sources, with the exception as they are different only in phasing.

The picture below is a graphic picture of a typical ac voltage. From the point where the power is created, there are 2 wires attached as shown here.  And here

The distance between the upper and lower peaks, determine the frequency of the signal, for example normal household voltage is 60 cycles per second or wavelength. The height of the two determine voltage. The reason they don’t short out is because they are 180 degrees out of  “phase” which also explains why when using multiple transformers they have to be “in phase”.

In other words the bottom spikes must be in alignment with the other transformers bottom lines.

Or if you prefer, and just everybody else agrees whatever lead goes to the outside rails should be considered as the ground lead, which is just peachy keen with  me.

You probably can’t make a mistake that we haven’t already made! Fortunately, we’ve learned from our mistakes, and in many cases, figured a better way to do things. Here are a few “Tech Tips” to help you in your quest to build The Perfect Layout and get those trains rolling again!