which post is + and which is -? - 7/31: new info added

It doesn't matter unless it has a whistle button. Photo? Model/catalog number? Technically, the post with the throttle arm connection should go to the center rail, but it's not critical until you use it in a multi-train common ground layout.

I’ll get a picture On Tuesday.

I bought it at a train show so I have no idea of a catalog number.

I don’t know what you mean by he pose with the throttle arm

Rob here’s a picture of the transformer. It’s just a cube

A little further back

The left post is connected to the throttle lever and goes to the center rail hot, the right post is the common/base terminal & goes to the outside rails / common connections.

Check the very modest rating of your "cube" - 7.5VA doesn't go very far.

@ADCX Rob posted:

The left post is connected to the throttle lever and goes to the center rail hot, the right post is the common/base terminal & goes to the outside rails / common connections.

Check the very modest rating of your "cube" - 7.5VA doesn't go very far.

Thanks Rob;  I've give that a try.  the lack of 'oomph' is OK for what I plan on using it for.

- walt

Is there a generic way to test WITHOUT knowing which transformer I am talking about????  I'm guessing there has to be some way to know which post is positive and which is ground by some kind of test.

as always, thanks = walt

I generally find most of the posts on the forum these days to be positive.  Much better than years past when a lot of the posts were negative.

In all seriousness, on an AC transformer, there really isn't a positive or a negative post.  It is hot and neutral.  That's why it doesn't really matter how it's connected to the track unless there is a bell or whistle button which puts a carrier wave across the outside rails.  AC current isn't directional as it oscillates between positive and negative to give it the momentum to travel longer distances.  If the horn button triggers the bell, the hot is reversed with the neutral.  Even on a home 120 receptacle you have a reversed neutral and it will still work, but it is a life safety issue if there is an overload.   

You could test the posts with a multi-meter.  The hot post will supply the current and register on the voltmeter.  The neutral post won't indicate any voltage.

Hope that helps!

Note the terminal post bases.  The one on the right is square. This one was originally marked 'Control' below it on the Model 1010 transformer that yours is a later model of.  The round base was the common.

@CALNNC posted:

...on the Model 1010 transformer that yours is a later model of.  The round base was the common.

Yes, the 1010 series of single train transformers was unique in that the wiper arm & direction control(& circuit breaker) are on different posts. In the absence of the direction control button, the left post should go to the center rail, and with the direction control right post to center rail. The breaker is on the right post in all models.

At times I get frustrated with answers on this forum.  I wanted a SIMPLE test to determine which post is power and which is ground, REGARDLESS OF THE TRANSFORMER IN QUESTION.  Thanks Rob, You did answer the one about the specific one that I showed here.

Jonathan ( @GG1 4877 ) : I read your comment "You could test the posts with a multi-meter.  The hot post will supply the current and register on the voltmeter.  The neutral post won't indicate any voltage."  I use my multi-meter set to 'AC' and put the red wire to + and the black to - and turned on trannie power.  Read 10V.  I switched the posts that the wires were connected to and still got 10V.  So I'm not at all sure what you meant.

BUT....I am working with my brother and he has a few unmarked.  They are not all like the one shown here.  I am hoping there's some universal way to determine - and + posts and ANY transformer.

BTW: I did some testing with 2 similar trannies to the one shown above.  Interesting conclusion = the results varied depending on whether I had them in phase or not (on these 2 trannies I know - and + and also have the plugs marked so I know how to plug them in to keep them in phase).  So I am now at a loss as to how to test.

any SIMPLE ways????

thanks  = walt

Walt,

I don't know what I was thinking!  You are absolutely correct.  It wouldn't matter which way you attach the multi-meter to the posts.  You will still get 10v because AC isn't directional.  A case of me typing faster than my slow brain can think it out.

In this YouTube video it talks about how to test for the hot side of an AC circuit in an old house with knob and tube wiring.  The principle is the same, you would want to have a known ground to attach to that isn't on the transformer to test for the hot side.  The Google search I did was "how to tell which side is hot on an AC circuit".  Lots of info and videos show up with people who are way more intelligent about this as I am.

Good luck!

Thanks Jonathan

I tried doing Google searches but obviously I used bad search criteria. I will try what you did and I’m looking forward to reading it

- walt

Perhaps sharing my ignorance here...

I'm thinking there are two different questions here.

1) which post is connected to the house hot wire?

2) which post is connected to the variable voltage wiper?

As you discovered, the answer to question one changes each time you reverse the plug.

To answer the second, one approach would be to use a known external whistle controller. If when downstream from the unknown transformer in question, it operates the whistle, the wire connected to the whistle controller is your proper center rail. If it operates the bell instead, the transformer wires need to be reversed.

As others have said, if you aren't operating locos with them, question two may not matter.

@Ken Wing posted:

use a known external whistle controller. If when downstream from the unknown transformer in question, it operates the whistle, the wire connected to the whistle controller is your proper center rail. If it operates the bell instead, the transformer wires need to be reversed...

No, that won't work. It's solely the orientation of the controller in relation to the track that determines whistle or bell.

@ADCX Rob I understand that. If you maintain a known orientation from one transformer that blows the whistle to an unknown transformer, the controller is now a constant, and the transformer "orientation" is what will determine whistle or bell. No?

Even though I haven't needed it for a LONG time I have an "external" whistle controller!  I will try what was suggested.

thanks for that suggestion.

as always - walt

As we are seeing, it isn't as easy as it sounds!

I had another random thought.  I am wondering if one of those inexpensive outlet testers would work.

While any brand will work, I like this image.  It would show if the hot / neutral was reversed.  My only question would be is that it's designed for 110V AC and if there is enough voltage and amperage coming off a transformer to get the lights to work.  However, I find this a very useful tool in my house as it is not a new house one and has been rewired at least once.

It's an AC transformer. There is no + or - post. They alternate 60 times a second. The main thing is to make sure you phase the transformer with any other transformers on your layout. I don't know how to attach a link but if you search Phasing Transformers on this site you'll find out how to do that.

as i mentioned earlier, when I did testing for + and - posts I got different results if the 2 trannies were in phase or not (the 2 I used I already knew each post and I already had the plugs marked).  I am testing to see how I can help my brother with his 4 unmarked trannies.

It's like a catch 22.  I can't test for 'in phase' when I don't know which post is positive and which is ground.

But on the other hand, I can't test for - and + properly unless that are in phase.

this is getting harder than I thought!

walt

You can always take them apart and see which post is connected to the wiper.

@Ken Wing posted:

You can always take them apart and see which post is connected to the wiper.

@ADCX Rob posted:

The left post is connected to the throttle lever and goes to the center rail hot, the right post is the common/base terminal & goes to the outside rails / common connections.

@walt rapp posted:

as i mentioned earlier, when I did testing for + and - posts I got different results if the 2 trannies were in phase or not (the 2 I used I already knew each post and I already had the plugs marked).  I am testing to see how I can help my brother with his 4 unmarked trannies.

It's like a catch 22.  I can't test for 'in phase' when I don't know which post is positive and which is ground.

If you can test for transformer phase, you can test for hot and neutral/ground.

If you have a transformer where you know which post is which, run your tests against that transformer. When you get your unknown transformer in phase with your known transformer, then you will know which wire is which.

Rich I appreciate you jumping in. Your comment ignores the fact that I don’t know how to get them in phase without knowing which post is which. The plugs are not polarized. They are older starter set transformers

@walt rapp posted:

... I don’t know how to get them in phase without knowing which post is which. The plugs are not polarized...

Just phase the right post with ZW/KW/VW/Z/V "U" or 1033/1044(and all other single train transformers) "A". Done.

@walt rapp posted:

Rich I appreciate you jumping in. Your comment ignores the fact that I don’t know how to get them in phase without knowing which post is which. The plugs are not polarized. They are older starter set transformers

Do what ACDXRob suggests, or, if you have a transformer that you KNOW which post is which, test the unknown ones with that one. However, you will have one more step do do. The older transformers don't have polarized plugs. That means that once you get one of the older ones tested and confirmed, you need to mark the plug in the wall in some way so that you always plug it in the same way. A dab of red paint on the top side of the plug would do it. This is only important if you are going to use multiple transformers and they all need to be in phase with one another.

I bought 3-into-polarized-2 adapters. Once I had phased the transformers, I plugged the neutral side into the adapter on the side with the large prong, and drew a white line on the original plug along the neutral side with a paint marker, in case I pull the plug out instead of the adapter. BTW, some of my transformers get plugged into extension cords--they all have polarized plugs.

as suggested, I personally have 5 transformers that I've been using on my DCS controlled layout for 20 years or more.  I learned about phasing them way back then.  I have always used a (can't think of what they are called) multi-plug "thing" (has room for 6 plugs) and once I had all 5 trannies in phase with each other I painted the same side on each plug so from that point on I always know how to plug them in.

I did not know that the right post is always positive!!  That's a huge help, so thanks for that.

I appreciate so many forumites willing to help me learn.

walt

@walt rapp posted:

..did not know that the right post is always positive!!

Just to be clear, neither post is "positive".  Both posts alternate between positive & negative, changing polarity 120 times per second at 60HZ household power.

On your particular transformer, the right post is best referenced as the base/common to be phased with other base/common posts on other transformers by virtue of the left post being powered by the throttle wiper arm. Using the variable post as common on common ground layouts can produce sometimes unexpected strange results.

I messed up. I meant to say what Rob said that the right POst is ground. I just Type the wrong word.

I still find that fascinating that the left post is always considered positive and the rates post is considered ground on these unmarked transformers

My brother told me something new about the transformer pictured above but I don't know what, if anything, it means.

He told me that the post on the RIGHT side can be depressed.  Instead of being solidly in place like every other trannie that he and I have seen, this seems odd. Any familiarity with a transformer that has a depressable post?

Here it it again as a reminder:

thank - walt

@walt rapp posted:

... fascinating that the left post is always considered positive and the rates post is considered ground on these unmarked transformers

The design and construction dictates the designation. Yours is a Lionel 4050.

@ADCX Rob -  That is not how I interpreted your previous comment. as a reminder is was:

"Just phase the right post with ZW/KW/VW/Z/V "U" or 1033/1044(and all other single train transformers) "A". Done."

The "and all other single train transformer" led me to believe my comment was correct.  Your new comment seems to contradict that statement.

Rob, you have to know that I think you are one of the best electrical people on this forum, so I am not trying to pick a fight with you.

this is getting deeper and deeper than I hoped.

@walt rapp posted:

...any familiarity with a trannie that has a depressable post?

Check out THESE. There are thousands upon thousands of them out there.

@walt rapp posted:

Your new comment seems to contradict that statement...

No, no contradiction, phase/connect all of the common terminals to each other on common ground layouts.

Common is "U" for multiple throttle transformers, "A" for single throttle transformers, to your right common post that is NOT connected to the throttle arm wiper.

Again, thanks Rob

I looked at that link that you provided - WOW, you sure were right.  There are tons of them.  I tried, UNSUCCESSFULLY, to find out why the ground post can be depressed.  I was trying to figure out what happens when it is depressed but I got nowhere in my search.  I tried a bunch of selection criteria.

Secondly, here's mine from a 1975 starter set

NEITHER post can be depressed, that's why my brother and I thought his might be broken (even though it seemed to work).  I don't remember how I determined 25 years ago or so which post was 'A' and which was 'U. 

as alwas, thanks

walt