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Hey -

I have 24 switches and power them only thru the fixed voltage posts of one 12B transformer.  I use another 12B to basically power 2 loops.  I saw an online video about AM switch repair and this person said it's not a good idea to do what I'm doing - that the fixed side of one transformer (I guess) is connected electrically (thru the track?) to the other transformer.  I did experience strange behavior and blew up a loco.  That could have been another issue - so I saw a video on phasing and that makes sense to be - connect the bases together - but the video was for Lionel O gauge. I believe on a single AM 12B the bases of the 2 track posts and the accessories base post all ohm out to zero - they are connected.  In electrical engineering it's good to have everything tied to the same ground, but how would I do this with the 2 transformers?  It is also possible to set up current loops - not good.  My thought is to connect the accessory base posts together - one is used for the switches, the other unused.  Anybody understand this topic who can advise me?  Thanks!

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I'm not completely certain I understand your question, but let me answer the question I think you are asking.  Yes, all the transformers used on your layout should be in-phase - which means essentially two things - one that all the "base posts" are connected together (in some cases, that connection may be through the track).  This sounds simple, and it is for simple layouts, but more complicated layouts its good to have some sort of circuit diagram so you can make sure all the base posts are connected together (obviously, if you had one transformer that simply supplied power to a bunch of isolated circuits, like lights, it won't matter - though I think as a matter of good practice and to avoid being confused, its still a good idea)

The other is that the 125VAC feeding the transformers is the same phase.  Most 'vintage' transformers - such as the 12B - do not have 'polarized' plugs.  Polarized means one prong is wider than the other, so it can only be plugged into the wall or a powerstrip in one orientation (the wider plug designates the neutral side of the AC circuit - the white wire in most cases inside a receptacle box).  However, with a non-polarized plug, you can plug the cord in either orientation - which is what can cause a pair of transformers to be out of phase.

Checking the phasing is fairly straightforward.  First, run a wire between the two base posts (transformers off is probably a good idea just to avoid an accidental short)  If you have a volt-ohm meter, for the 12B, which has both a variable and fixed output posts, then I'd first check that both transformers have the same voltage reading (or close) on the fixed voltage output.  Then connect the volt meter between the two fixed voltage terminals on the two transformers.  If they are in-phase, the voltage difference between the two output terminals should be about zero (suppose the output of one transformer is 16 v and the other is 15.5 v, so in this case, you'd see a difference of about 0.5 v).  If they aren't in phase, then the voltage difference will be the sum of the two output voltages - in this case 16 v + 15.5 v = 31.5 v (out of phase simply means that one transformer is at the top of the sine wave while the other is at the bottom, so you will be measuring that difference.

If you don't have a volt meter, you can do it with a light bulb, but you'll want to use the variable voltage terminals so if the transformers are out of phase, the combined voltage difference won't be larger than what the light bulb can handle.  Here's a useful link the describes this in a bit more detail:  http://www.kodiakjunction.com/...ks/TipsandTrick2.htm

Two really IMPORTANT things.  First, its worth examining the powercords to the transformers to make sure the insulation hasn't cracked or opened up - aging power cords do that - especially near the plug or where the cord goes into the transformer.  I've replaced power cords on several of my transformers, including a 12B.  Second, once you have the transformers in phase, mark which prong of the plug goes into the wide slot of the receptacle (which should be the neutral side).  I used a little stripe of white paint to remind me that that is the neutral side of the plug.

It is always a good idea to have all the transformers in use be "in phase." The Gilbert turnouts have no connection to the track. Power supplied to the yellow (sometimes white) and black wires from the turnout control boxes does not have to be in phase with track power but it is a good idea to have it be phased.

Try to avoid the reference to "ground." There is no ground point in Gilbert transformers. The base post and 15V posts are just opposite ends of the secondary winding. If you want, the Base Posts on multiple transformers can be connected together after the transformers are correctly phased. I recommend that in most cases not be done. The reason is Gilbert turnouts have a 2-Train power routing capability. Tying the base posts of multiple transformers supplying the track together can defeat the selective power routing in many track plans, forcing the use of more insulating fiber pins. The base posts of the 12B are common, they are connected together inside the transformer.

For more information visit the site traindr.com and look at their Transformer Guide. It can be very helpful.

thank both of you gentlemen.  The big issue is I have a separate 12B for switches - I have an oscilloscope and multimeter.  I ohmed out the switches/ track and didn't see zero ohms but it's nice to get that conformation. I will mark my plugs in the wall and read your docs.  On my 2 big outside ovals (50 feet each at least) I have 8 power feeds - in my mind's eye I picture the engine drawing from the nearest

one - do I need to worry about current loops?              Thanks

I always powered my 720A track switches, plus some other accessories, from a separate transformer. I used a 19B for each loop, nothing but the track was connected to the 19B's. This method of wiring a Gilbert layout will not cause any problems.

Current loop concerns, in a word, no.

Sounds like a spacious layout, I hope you enjoy operating it.

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