mixing PSXX-AR with older PSX and PSX-AR

[nickelplate759]

[originally asked in my layout thread]
I have old (7+ years) PSX-2 and PSX-AR boards, salvaged from an old (N-scale) layout.

1.  What are the advantages to going with all-new boards (PSXX and PSXX-AR)?  Better functionality, reliability, etc?
2.  Will the old boards play nice with the new ones?
3.  Should I worry about something else instead?

[nickelplate759]

well, after reading further, it seems that they can be mixed.  However, I see that the PSXX series has a fast-acting current-limiting feature that the PSX series does not.   That seems like a good reason to spend the money for new PSXX boards.

[Mark5]

had to look up what PSX etc refers too.  (DCC Specialties circuit breakers)

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Will add this to my layout build research (thanks!)

[Maletrain]

There is a potential electrical issue with mixing the older PSX with the newer PSXX versions. 

It is complicated to explain, but the basic issue is making sure that ALL breakers break the SAME phase of the DCC track circuit.  DCC circuit breakers, like most circuit breakers, only break one of the two phases. 

So, if breakers on 2 sides of a track rail gap break opposite phases, then there is still a path for a short circuit between them, through the unbroken phases in each, because one will leave unbroken Phase A and the other will leave unbroken Phase B.

This problem between the 2 versions of the PSX/PSXX breakers seems to have come about due to renumbering the 4 input terminals so that they increase in opposite directions as you view the boards from the same perspective.  That is compounded by the different instruction sheets talking about different connector terminals by numbers and drawings that swap the colors of the output phases.

Trying to unravel this mess by words is confusing.

The best approach is to just make sure that the same OUTPUT phase is broken by EVERY breaker you install.  That is easy enough to check with a multimeter.  Keep track of the INPUT wiring so that you can identify which terminal is getting Phase A (or "track 1" - or whatever terminology your command station uses), then make sure that the OUTPUT terminal that goes dead when you short the outputs is that phase.  That can be done by comparing the output terminals to the input terminals on the same breaker with the multimeter.  (Or you can specify that all breakers break Phase B / track 2 - which phase you chose doesn't matter - it is the consistency to always break the same phase that matters.)

This check is important when mixing breakers from different manufacturers, too.

The other consideration between PSX and PSXX has to do with the current limiting feature of the PSXX version that is not in the PSX version.  The newer version is designed to limit the short circuit current to the breaker trip value before the breaker actually can trip.  That feature was NOT added to the PSXX autoreverser.  So, the recommended installation configuration was CHANGED to have PSXX autoreversers fed by PSXX breakers, which is different from the recommendation for NOT feeding PSX autoreversers through PSX breakers.

Timing for breaker trip vs autoreverser reversing action is critical for getting autoreversing to work without tripping the breaker on the track section that is NOT reversing, which would stop the loco until the breaker resets.  So, mixing components from different versions or different manufacturers might necessitate timing adjustments. HOWEVER, PSXX BREAKER TIMING IS NOT ADJUSTABLE, and it is fast.  The trip timing on the older PSX breakers is somewhat adjustable by CVs.

The PSXX breakers and PSXX autoreversers are TIMED to operate together.  However, to get a PSX autoreverser to operate in conjunction with a PSXX breaker, the PSX autoreverser must be set to a lower TRIP CURRENT value.  (Not sure how well this really works, because I have not personally tested it.)

Also, the instructions say that PSXX breakers are NOT COMPATIBLE WITH Zero Bit Stretching for ANALOG LOCOs.  The PSX instructions do NOT say that, or mention it at all.  (I have never tried it with either version.)

[nickelplate759]

Thanks @Maletrain for the comprehensive writeup.  VERY helpful!

I'm going to go with PSXX breakers (retire my old PSX-2), and try them with my two existing PSX-ARs.  If it works, great, if not, I'll replace them too.   The reversing sections are way down my track-laying schedule, so that's not urgent.

Anyone want a used PSX-2 ?

[Maletrain]

Frankly, I have both and like them both. 

So long as the PSX autoreversers are not interfacing across rail gaps with the PSXX breakers, I don't think using both in different track sections will cause any problems.

And, they aren't cheap, so I would hang onto the PSXs if they were mine. 

You might find a use for them later.  Even putting one on a separate non-track circuit for accessory decoders would avoid any conflicts.

[nickelplate759]

Frankly, I have both and like them both. 

So long as the PSX autoreversers are not interfacing across rail gaps with the PSXX breakers, I don't think using both in different track sections will cause any problems.

And, they aren't cheap, so I would hang onto the PSXs if they were mine. 

You might find a use for them later.  Even putting one on a separate non-track circuit for accessory decoders would avoid any conflicts.

You meant "So long as the PSX breakers are not interfacing across rail gaps with the PSXX breakers..." correct?

[Maletrain]

I don't think that having PSX BREAKER on one side and PSXX BREAKER on the other side of a rail gap is going to be a problem.

I think the problem COULD occur with a PSXX breaker across a gap from a PSX AUTOREVERSER, because I think the breaker might open before the autoreverser could reverse, and the PSXX breakers do not have timing adjustments to delay their tripping to solve that problem. 

I am having that exact problem with OTHER types of breakers and autoreversers on a club layout right now (NCE EB1 breaker), and am working on slowing that breaker to eliminate the problem. 

But, remember, I have not actually tried it with the PSX-AR + PSXX breaker, so that concern is speculation on my part.

The effect of the problem is that the train reaches the gap where there is a phase mismatch, and the breaker opens before the autoreverser has reversed the phases.  So the train stops abruptly.  By the time the breaker autoresets, the autoreverser has made the phase swap on the rails, so the loco restarts.  If it is a sound loco with momentum, there can be a substantial delay in getting the train back up to speed.

And, because the breaker kills power to a large section of track, other trains may stop, too.

My experience with the similar problem during the club open house show yesterday was that long trains coming abruptly to a halt had a tendency to uncouple somewhere when restarting with all those car couplers, some on curves, going into buff condition due to the abrupt stop.  So, the effects of the breaker opening compounded in unexpected ways, and were very annoying.