Need Help - Connecting MTH Operational Track in Parallel to DCS AIU

mjrodg3n88 posted:

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My question is: Do I have to provide a common wire to the operational track too or can that rely on track power?  It seems that I run a common from the same power source, it will be in contact with the track common VIA that tabs that connect the Realtrax.

IIRC this was the original picture showing how to use an AIU ACC port in parallel with an OFF-(ON) switch to activate a Realtrax uncoupler.

If I understand your question, yes you must provide a "common" black wire connection from your alternate power source to the outer-rail track common.  If the alternate power source is, say, the 14V Accessory output from a Z-4000 transformer, then the common connection is already made for you inside the Z-4000 itself; that is, the black/common terminals of the Z-4000 are connected internally.

OTOH if your alternate power source is a Z-500 brick or an AC wall-wart adapter then you must make a connection from the common of the alternate power source to the outer-rail.  This connection should be using heavy-gauge wiring similar to whatever you're using to run track power.

Thank you, Stan.  I know I have a similar thread asking about using a push button for the same track, but I figured it may be better if there was a topic that was different so that if somebody was looking for the same thing later on, they could find it.

Will I or should I isolate the common rails from the rest of the loop or is it okay that they are connected?

It is OK for the common rails to be, uhh, in common....probably why it's called a common rail.   All kidding aside it would be quite the wiring mess to have 4 "islands" of outer rail for your 4 uncoupling sections wired together....only to be connected to the outer rail of the rest of the loop anyway!

But as for using the AIU Accessory port to activate an uncoupling coil, did we discuss the danger of accidentally pressing the DCS Accessory ON button which would apply continuous (instead of momentary) power to the uncoupling coil?  Your only indication of this would be a minute later when smoldering/smoke wafts up from the melting coil!  If you're all over that and assure me this would never happen, then so be it.  A 50 cent reset-able fuse or the like is cheap insurance.

Also, for the cost of a 25 cent lamp or LED you can place some indicator at the uncoupler itself that power is in fact present on the coil.  You've probably heard the buzzing of an uncoupler coil but if your control panel is some distance from the action and you have noisy trains running it can be of use to have some visible/audible indicator coming from the coil.  Just a thought seeing as you're in the construction phase...

Thank you, Stan.  That makes perfect sense, the whole common thing (apparently I wasn't really using my head).  I don't fully understand what you mean about having four islands though.

We did discuss (or at least I read on here somewhere) about the danger in using the DCS ACC On button.  On my control panel, I will have a blue LED mounted above the momentary push button for the uncoupling section that will also be in-line after the AIU, so this should light up if power is applied to the operational track.... I hope.

I guess I will find out, hopefully in the next two weeks.

Hi Mike, when you said,

Will I or should I isolate the common rails from the rest of the loop or is it okay that they are connected?

I misunderstood this to mean that each 10" long Realtrax uncoupler section would need to have its common/outer rail isolated from the common/outer rail of the main loop.  In other word, you'd have 4 10" long "islands" of common that would somehow get tied together at the alternate power source...only to then be tied to the main common at the train transformer.  I think we've leapfrogged that issue so never mind!