# Electrical question about 2 connecting loops



## swashplate (Dec 9, 2012)

I have had an overhead RR loop in my living room for years. It has always been my intention to extend that loop into the Den as well using a set of 4 switches as a crossover. As of today the 2nd loop is in place - yay! I am using a "Starter Set" LGB transformer for the first loop and a Bachmann transformer for the second loop.


My question is....... When it comes time for me to swap the trains from one loop to another, what concerns should I have about the "positive" vs "negative" power inputs of the two separate systems?


I have "gap" rail joiners to isolate the two systems if that is the best way to go?


I have included a pic of the layout.



The Layout as of 12-2019 by swashplate1, on Flickr



Thanks,


Robert


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## Treeman (Jan 6, 2008)

I don't see any problem with wiring, no reverse loop.


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## Jim Agnew (Jan 2, 2008)

Connect an automobile bulb between the outside rails of both loops, if the bulb lights, switch the direction of one of the power packs.


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## Pete Thornton (Jan 2, 2008)

Robert, as Jim says, you need to make sure that the trains are trying to run in the same direction when the gap is crossed or you will have a short circuit.

As the loco crosses the gap in the rails it conducts from one side to the other through the wheels and pickups so you will be effectively connecting the 2 power packs for that brief period. Shouldn't be a problem, but there is a fail-safe way of isolating them. Put more air gaps either side of both pairs of switches and connect them to both power packs with a DPDT switch. Normally you would run with the switch connecting that part of the layout to the same pack as the rest of that loop. When you want to swap to the other loop, just let the loco run onto the crossing and stop, then flip the DPDT switch so that the other power pack of the destination loop is powering that track. (Make sure the other pack is set to roughly the same speed and direction.) Once the loco is across then flip the DPDT back and normalize the crossing.


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## Greg Elmassian (Jan 3, 2008)

I would say it would enough to match voltages somewhat when crossing between loops. 



Throw away the LGB starter set transformer, unless you are always going to run small LGB locos only.



Buy 2 identical transformers and set the direction and speed the same when crossing the loops might be simpler.


Greg


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## toddalin (Jan 4, 2008)

Pete Thornton said:


> Robert, as Jim says, you need to make sure that the trains are trying to run in the same direction when the gap is crossed or you will have a short circuit.


It's not a "short circuit" but rather a "crossed circuit."

If an engine passes the gap into the other transformer's block and they are set to different direction, the engine will do a "cha cha" back and forth. When the engine is in that area where both packs are providing power, the engine will go in the direction of the transformer with the higher voltage until it clear both units where it will reverse.

I've had it happen a couple times and nothing was damaged and the breakers didn't even pop. I would just notice the engine doing the cha cha and correct the problem. 

YMMV.


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## Pete Thornton (Jan 2, 2008)

> I've had it happen a couple times and nothing was damaged and the breakers didn't even pop. I would just notice the engine doing the cha cha and correct the problem.


Must have been small locos - better you than me. But I confess I have no practical experience doing this with large scale locos.


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## swashplate (Dec 9, 2012)

Greg Elmassian said:


> I would say it would enough to match voltages somewhat when crossing between loops. Throw away the LGB starter set transformer, unless you are always going to run small LGB locos only.
> Greg


Thanks Greg. Yes, the LGB loco will be the only one running on that transformer.


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## swashplate (Dec 9, 2012)

toddalin said:


> It's not a "short circuit" but rather a "crossed circuit." If an engine passes the gap into the other transformer's block and they are set to different direction, the engine will do a "cha cha" back and forth. When the engine is in that area where both packs are providing power, the engine will go in the direction of the transformer with the higher voltage until it clear both units where it will reverse. I've had it happen a couple times and nothing was damaged and the breakers didn't even pop. I would just notice the engine doing the cha cha and correct the problem.
> YMMV.



Without thinking through this AT ALL, I began testing the newly installed system. Wait a minute, both locos were running from 1 transformer! Well of course, the systems ARE connected - DUH! Easiest solution......, gap the switches for isolation of the two systems. Should I desire to swap trains, (prolly won't), then I will use both transformer and make the swap and the gaps live there for ever.

Thanks for all the input and suggestions,

Robert


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## toddalin (Jan 4, 2008)

pete thornton said:


> must have been small locos - better you than me. But i confess i have no practical experience doing this with large scale locos.


USA GP-9.

Two AristoCraft Train Engineers powered from two Meanwell 24 volt, 12.5 amp power bricks.


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## Dan Pierce (Jan 2, 2008)

I would use a DPDT switch so when crossing I am on one power source, and after crossing, go back to 2 separate power sources.
Or go DCC and there is no issue.


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