Phasing small starter set transformer question

[msacco]

Hoping someone can help here. It's numbered 4851 and is from an early 90s starter set. I'm trying to phase to my other tranformers for accessory use but it doesn't have the common or ground marked. I't also the type with the black nut on the right terminal where you can push down and interrupt current for reversing.

    I've checked all my stuff. Greenberg's postwar repair and operating book because I thought  this was an reissue of a postwar starter transformer but it's not in there.

    Want to phase properly and need to know what post is the common.

Looks like this:

thanks,

Mike S.

[lionelsoni]

First of all, the accessory transformer doesn't need to be in phase with the track transformer, although there's no harm in it.

A two-terminal transformer doesn't really have a common terminal, because there's nothing else on the transformer for it to be common with.  So you can designate either terminal as the common.

If you want to get it in phase with another transformer, just pick a terminal to use as common.  Then connect a voltmeter or lamp between the other terminal and a variable output (a terminal other than its common) from the other transformer.  Turn the other transformer on to the middle of its range.  Then turn on the accessory transformer.  If the lamp gets dimmer as you turn it up, you are through.  If the lamp gets brighter, simply swap the connections to the accessory transformer or reverse its plug in the socket.

[msacco]

Thanks Bob,

I do know how to phase but didn't know how to with these small jobs or rather if it had a common or not. So even if this accessory transformer will be using the same ground bus as my trains, I don't need to phase?

 thanks again,

Mike S.

[lionelsoni]

That's right.  Any track-activated accessory, like a crossing gate or an anti-derailing turnout, will be operated by connecting an isolated control rail to common through the train's axles.  The only interaction between train and accessory will be that the return currents for both will come back to the transformers through the same conductor, the outside rails.  Whether those return currents are in phase or not makes little difference.  If they are out of phase, there will actually be some cancellation of the currents, that is, the outside rails will act as a true neutral conductor, and the voltage drop will be reduced, although probably by an insignificant amount unless you have a very small train and a whole lot of accessories.

The accessory voltage doesn't even have to be the same frequency of AC and can even be DC, which has several useful properties.  So our European friends who have had to go to the trouble of getting 60 hertz to operate some of the modern American trains can still use their native 50 hertz for accessories without any trouble.  When the frequencies are different, the amount of the return current is neither the sum nor the difference of the train and accessory currents but the root-mean-square, that is, the square-root of the sum of the squares of the two currents.  So, if the currents were equal in value, the overall return current would be about 40 percent greater than each of them individually, instead of double.

[ChiefEagles]

Bob, you amaze me.  I learn something about everytime you answer a question.  Don't think I will remembr the forumla but will remember some of the results.