Multiple transformers on one TIU input

It's possible to parallel plain transformers, but not the CW-80, those will likely get very confused in parallel.  Electronically controlled transformers don't do well in that environment.

Now THAT'S the ticket! My main lines are powered by two MTH Z4000 transformers, but the yard & yard lead, and the engine terminal are each powered by a 180 brick. Works great!

Transformers should n ot be wired in parallel, especially if they have variable voltage outputs, because the chances are that the outputs will not be precisely equal in voltage.  This will cause an internal short circuiting among a few turns of the secondary winding.

Well, it doesn't really cause a short circuit if it's not alternate outputs of the same transformer.  I don't argue that it isn't a bad thing to do, only that there is no short circuit.

If one transformer is outputting 15.7 volts and the other 16.0, there will be a current flowing other than the current going through the tracks.

J,

   You can run 2 different Transformers in Phase on different channels, no problem.

I would not run 2 transformers in Parallel into the same TIU channel (Input), to many variables can occur.  Purchase 2 bigger better transformers, and run 2 channels (Inputs) from each Transformer to power your layout.  Get rid of the CW-80.

PCRR/Dave

There may be current flowing, but there is not a "short circuit" between "a few turns of the secondary winding".

For real transformers, very little current will flow, I actually did the experiment.  I connected a PH180 and a PH135 in parallel and measured the current flow between them.  The PH180 puts out 18.3 volts open circuit, the PH135 puts out 20.5 volts open circuit.  I got around 150ma of current between them paralleled.  Not desirable, but not exactly a huge problem either.

Lionel actually used to recommend paralleling two transformers for input to the TPC in some configurations, I'm sure they considered this issue before publishing that recommendation.  I don't necessarily agree with the practice, just noting that it's obviously not a huge risk.

Interesting.   2.2 volts into a minimal resistance should yield more than 150ma.  I wonder if the TPC was enough of a load to pull down the voltage of the PH135. What happens if you remove the external load?

For the benefit of the casual reader, I'll note that we are not talking about paralleling two outputs of the same transformer, where there would definitely be an internal short circuit between the two movable fingers on the secondary coil if not set identically.

This situation is more akin to a car or boat that has two 12-volt batteries paralleled.  What happens if one is outputting 12.6 volts and the other 12.8?

There was no external load, I just connected the two transformer secondaries together to see what currents would flow between them.

FWIW, many (most) larger sailboats parallel multiple lead-acid batteries in their battery banks.  I have two friends with boards 35' and 37', they both have four batteries, two in each bank, and the two in each bank are directly paralleled.

Your schematic shows the transformers connected to a TPC.  I assumed that there was a load there.  Which leaves me wondering why a 2.2 volt EMF would produce only 150ma????

As I think about it, I am reminded that if there is no load on the secondary of a transformer, current flow through the primary is minimal, although Ohm's Law would call for a heavy current flow, due to the reverse effect of self-induction, and that is probably why only 150ma flows.

FWIW, I also have two pairs of batteries on my boat, but use switches so only one of each pair is connected at one time, although they can be paralleled for emergency use.  Reason is to avoid having all batteries run down which would preclude engine starting or ability to communicate by marine radio.  But that's getting beyond the scope of this forum.

That's why there are two pairs of batteries on board!   One set is normally in the mix, the other set is isolated and simply charged as needed.  They can be switched in for emergency use, normally they're just there for stuff like starting the engine.  Since the one guy is currently in the Bahamas with his boat, and he goes most every year for 5-6 months, I'm assuming battery power hasn't been an issue with his setup.  He also has a wind turbine and solar array to help charge them when he's away from power.

As far as the transformers, I didn't expect much current, I was somewhat surprised with 150ma.