Common Ground & 2 Transformers

[Anonymous]

I'm sure this counts as another stupid newbie question but here goes anyway. I'm doing a two transformer two train set up with switches (turnouts) connecting the inner loop to the outer. I've got a copy of Riddle's book Wiring Your Toy Train Layout (CTT pub.) I understand everything except why Riddle tells us to use a common ground between the two transformers (p.29). I have no problem understanding how to do this it's just the "why?" that is escaping me. I have a sneaking suspicion the answer is obvious but it still remains a Riddle to me! [:D]

As usual, a great big thanks to this web site and all the old timers who help us newbies!

[Buckeye Riveter]

Good morning, Ron. If you watch this web site closely, I seem to always be up early on Saturday mornings while some of the others are snoring. [:D]

I have a 1975 Lionel Train and Accessory Manual and on page 8 they give a very simplistic explanation. I have the page scanned into the computer and will send it to you. Just send me an email and I will do a return. You are now going to learn about phasing of the alternating current and putting more power to your track [:D]

With the newer transformers, the three prong plug is supposed to take care of the phasing. [^]

[spankybird]

Also if you have a newer transformer, the AC plugs will have one prog larger than the otherone, so it will only plug in one way. This is also for phasing.

tom

[Anonymous]

Hi Guys, let's see if I have this right...does this mean that if I have all new transformers etc. that I will not have to worry about the phasing issue?

[spankybird]

Larry - correct.

[jimhaleyscomet]

As to why, I know that trains will "balk" crossing blocks if the transformers are not in phase. I believe, but am not abolutely shure, that unphased transformers create a dead short if metal touches the same rail on both sides of the block (like an engine).

Jim H

[Anonymous]

Why common ground? Because the track outside rails are connected together and this will connect one side of each transformer together. It is more efficient and better to do this at the transformer and helps prevent some other problems.
Why phasing? The other side of the transformers get connected together at the time the train crosses over the center rail insulator. So? I will try to explain simply. With DC power from a battery the + side is always the + side and the - side is always the - side. This never changes. Our trains run on AC power. This means that the + and - sides keep switching back and fourth 60 times each second. Phasing means that the same terminals of each transformer change together so that + of one is never connected to - of the other even though they are both changing, they are "In Phase". Now when they are connected together when the trains crosses from one to the other + is connected to + or - to - but never + to -.
I hope this was not more information than you wanted but I see this question asked a lot.

[ChiefEagles]

WHAT!!! Where did that come from? Someone needs to read their train manuals on tansformers. Buckeye and Tom are right.

[lionelsoni]

Where did what come from?

Running from one block to another with different transformers powering the two blocks requires that the two voltages be not only in phase but equal. Any difference in transformer voltage will be the difference at the rail gap that will be shorted by the pickups and could result in a substantial fault current. I think that a much better practice is to switch blocks between the transformers so that any particular train stays with the same transformer no matter which block it is in. (It has never occured to me to check whether my transformers are in phase.)

Polarized line-cord plugs can only guarantee that a transformer's phasing will not change from time to time when it is plugged into a particular outlet. The relationship between the phases of the primary and secondary windings may differ from transformer model to model and very possibly from example to example of the same model if the manufacturer does not make an effort to be consistent. Furthermore, the phasing of outlets varies. About half the outlets in any typical house will be out of phase with the other half. Occasionally duplex recepticles are wired, for good reasons, with the upper and lower outlets having opposite phases. So, if you choose to run between blocks, you must get the transformers into phase and keep them that way. An outlet strip with a switch is a practical way to do that.

[ChiefEagles]

Right on Bob and others about phasing. [I was refering to the repeats and repeats.]

[Anonymous]

Many thanks to everyone who took part in this discussion. Thanks specially to Buckeye who went to the trouble of scanning some helpful documents and emailing them to me! Issues of phasing aside I now understand why the two transformers should share a common ground--you have a higher liklihood of voltage consistency (no guarantees, just a higher liklihood!) If this is not correct I hope one of you will hit me over the head with the right answer!

Thanks again for everyone's help!

[eZAK]

QUOTE: About half the outlets in any typical house will be out of phase with the other half. Occasionally duplex recepticles are wired, for good reasons, with the upper and lower outlets having opposite phases.

Geeze! I hope not! For safeties sake!
All residential property is divided 'Single Phase'. 2 Hots and a neutral. 110v potential for each hot leg to ground, 220v potential between each leg.

You would Not want both hot legs at the same duplex outlet. b/c If you loose the neutral you would have a potential of 220v.

Comercial property on the other hands uses 3 phase power.

[lionelsoni]

Yet, as far as I know, it is perfectly legal to wire split recepticles from a three-wire circuit. In fact, I found a Canadian requirement that "at least two split recepticles, each supplied from a separate a three-wire circuit, must be installed for kitchen counters."

[ole1]

If your still working on phasing transformers I'd suggest you get a copy of Greenbergs "Model Railroading with Lionel Trains volume II: Advanced Layout" It has a section on this with explanation and pictures. I have a copy from our local library