Wiring O22 Switches to MTH AIU

I have no idea, MAW23, but appreciate you raising this issue.

My guess, and it's only a guess, is that you want be able to have your 022 switches fully functional using the AIU as you are seeking to do.

I happen to be very content running my MTH PS 2 and 3 locomotives using the DCS remote and TIU, powering my numerous 022 switches using a ZW as you do, and using the traditional Postwar knife switches that are alongside my two Z4000 transformers. Arnold

Connect a wire from the ground terminal on your transformer to the IN terminal on the AIU switch terminals.  Connect wires from the 1 and 2 terminals on the AIU to the outside terminals of the 022.  Swap the wires around to get straight or diverging as you want them.  If you going to connect a number of switches you can connect a jumper wire between each of the AIU IN terminals, then you only need the one wire to the transformer ground.  Also if you use the fixed voltage plugs you will be able to throw the switches without having to power the track - handy when running in conventional.

Honestly, I concerned that AT the switches you are somehow losing common.

What I mean by that: You are not using the middle screw post on each switch- and that is local common at each switch.

I personally would have run 3 wires from each switch, from the normal screw post terminals for the remote controller, to the AIU. The middle one goes to "IN" on the AIU terminal.

I think what is happening is you somehow lost common at the switch, the only way it gets that now as wired is via the track pins for outer rail, and it's possible you either have loose pins or maybe some other wiring issues with your track. Again the fact you lost light and lost anti-derailing are telling and the clue as to what is going on.

Again, as I look at what is going on- OK, fine running common to the AIU from a bus. I mean that is one way to skin the cat. Common in theory is common.

But..... We have 2 major symptoms- Lights at the switch are not working, and anti-derailing is not working. Those functions completely 100% require local common at the switch- normally provided by specific outer rail track pin locations.

You could run common from that same bus, to each of the middle posts on each switch- which is frame common to the switch. Normally this would be redundant, but again for one reason or another your switches appear to be "floating" electrically not properly connected to common.

I'm more worried about how and why that happened, because in theory that also affects track power for trains trying to run on these switches.

Edit, that all said, again, a test is, connect a common wire between the middle current unused screw post of the switches not working (no light is your first obvious clue) and the light should then light up and then anti-derail should also begin working.

Hi, Vern.  If I am not mistaken, the center post is a ground.  The 022 switch control is just an SPDT switch where the ground from that center wire is looped back to either of the outside posts on the switch motor.  I would think a direct ground from the transformer to the outside post of the switch motor would be more reliable.  I use Fastrack remote switches now and haven’t used 022’s for years, so I could be wrong.

@Danr posted:

Hi, Vern.  If I am not mistaken, the center post is a ground.  The 022 switch control is just an SPDT switch where the ground from that center wire is looped back to either of the outside posts on the switch motor.  I would think a direct ground from the transformer to the outside post of the switch motor would be more reliable.  I use Fastrack remote switches now and haven’t used 022’s for years, so I could be wrong.

Trying not to use the word ground, rather common.

That said, we are saying and thinking on the same path, just not saying it the same way. Again, if you have a switch, and you supply aux power- and the light doesn't light- Bingo- that switch likely is not connected to common- that's how the light lights up. Anti-derailing is the same way, it basically is the 2 outer posts- connected to the sensing sections of track. When you "common" one of those outer posts to common, then that coil fires.

Again, the symptoms are:

• Switch light not working
• Anti-derailing not working
• AIU- I think can currently throw the switch.

This group of symptoms is also unique to the wiring- specifically that the AIU relay output ports were wired to a bus and common direct from the transformer. Right now, this is the only momentary path back to common- based on the symptoms.

The loss of both light and anti-derailing are a symptom of the switch not physically or electrically connected to common but getting a power feed, just no return path to common.

This should help, but again, the general loss of common at the switches- could be a bigger symptom of losing common to your layout track???

Also, one note- 20V fixed seems a bit high IMO. I probably would use something less in the 14-16V range for switches- especially those light bulbs....

Edit- another thought.

Given this is a ZW transformer, another known failure mode on ZWs is the U terminals inside connected via a strip- over time that might fail and one of the U terminals is either high resistance or open circuit. Because those were riveted or staked contacts and over time wiggling the posts and just usage and wear and tear, the strip sometimes literally just pops right off that is the common U bus. The fix is normally repair posts with nuts on both outside and inside the transformer.

Again, just bringing this up since somehow- we lost U common to the track....

Actually, the more I look at this, I question- how is the track connected? Or is this transformer only powering accessory power?

If that is the case- then you never connected U common to the track or your other transformers?

Worse, when you do that, you need to check phasing if you are using more than one transformer.

Gentlmen,

Thanks for your input.  The key was running another u (common) wire to the TIU.  Once I made that connection this morning everything works. So the original diagram is correct only missing connecting a U (common) to the TIU.

Tanks again for your input,

Mark

While the center terminal was only to provided a common () to the controller to be routed back to either of the outside terminals, there may be some benefit to common between the AIU and that terminal.  Considering that these switches are 50-70 years old, this connection could help get a good common on a switch that may be dirty or oxidized.

Vern is right about these switches operating at 14-16 volts.  If you need more than that, the switch needs to be cleaned, paying attention to all of the electrical connections including the metal track pins.