Seeking advice for AIU power-switched spurs.

Dave,

Have 5 spurs (single ended track sections) for parking engines. I purposely picked 5, as it's the max for my 1 TIU. I understand that if I wish to add a 6th engine, I need to give consideration to the amperage available to the single TIU channel providing power to my 5 spurs, so I must either add another TIU, or physically switch out engines as desired (my actual plan in fact).

The maximum number of engines that a TIU can handle is 99, by using all of the available DCS engine ID#s. The real limiting number of engines is related to how much power is available on the tracks for the number of engines that are powered up (started up or not) at the same time.

If you run a TIU with power passing though the TIU channels, you may safely draw only 10 amps per channel, thereby having (approx.) a maximum of 5 engines, powered up and started up, at the same time on that TIU channel.

However, if you run a TIU wired passively, i.e., power does not pass  through a TIU channel, there is no limit to how many amps you can have available to run trains on any particular TIU channel, and therefore no limit to the number of engines that may be drawing power on that TIU channel at the same time.

What do you folks do, who have spurs or sidings switched only through the AIU (mechanical switches), specifically related to putting the desired engines into DCS mode (and not in conventional)?

Regardless of whether for not you are switching siding power via the AIU or with external switches, there are only three ways to bring a DCS engine that has started up conventionally because it missed the watchdog signal, into DCS mode:

• Turn off power to the TIU channel, switch on the siding and turn TIU channel power back on
• Press either Startup to put the engine into DCS mode, ready to operate, or press Shut Down to make it dark and silent
• Select the engine in the DCS Remote's engine list, switch on siding power and immediately press the thumbwheel. This sends a "pseudo watchdog signal" to the engine.

I almost wonder if it would make more sense to:

• Wire all spurs to the normally-closed contacts of the AIU.
• This would allow ALL engines to receive the watchdog signal when the TIU & AIU are powered-up.
• All engines would stay silent, and not start up in conventional (only to be shut down).
• One could *then* shut down power to the spurs for the engines that won't be used.
• The above would add a bit of time to the Chronometer of each engine, but by very little (less than a minute I would think).

You can stop wondering - it doesn't make sense to do this.  

This and a whole lot more is all in MTH’s “The DCS O Gauge Companion 2nd Edition", available for purchase as an eBook or a printed book at MTH's web store!

May I respectfully ask why?

All 5 spurs are going through 1 TIU channel (so the limit of 5 engines is consistent with what you've stated). And no, there are no major current-drawing devices on the track (the spurs aren't long enough to support more than 1 or 2 passenger cars; engines only). Edit clarification: All 5 spurs are running off of one TIU channel (though technically can be re-wired at my panel). So while I understand that I'm not limited to 5 engines, my wiring to a single block that feeds the 5 spurs technically does limit me (by my own design). That's OK with me.

So let's say I want to run a recorded sequence of 5 trains, and don't want to deal with "pseudo watchdog", why not use the normally closed contacts?

Specifically, I don't have the manual switches (at this time) to do as you say: "Turn off power to the TIU channel, switch on the siding, and..."

NOTE: Technically I do have every switch and indicator needed to wire a manual control panel, but I'm a bit at a loss as to what material to use (Plexiglass cracks easy when drilled, and Lexan doesn't crack but scratches easily). Still working on that part...

Dave,

May I respectfully ask why?

Sure!

It's because the easiest thong by far is to just shut down the engines or start them up. Your way is a lot of work for no practical gain, particularly since you'll eventually complete your control panel and use switches instead of tiring up an AIU port.

In the mean time, just cobble together a piece of wood with 5 toggle switches on it. Place it where the control panel will be and, after the panel is built, simply move the 5 switches to the panel, reusing the wiring.

Thanks Barry!

They say "A picture is worth a thousand words", but sometimes a few of us self-described "dense" folks would argue that a few more words are the same as a thousand words. Maybe you should consider selling a 2x4 piece of pine to people like me with the instructions to: "Whack yourself upside the head until you comprehend".

Between what you've provided above plus what is in your book, I must agree with you 100%.

Without any ill intention on your part, you've inadvertently pointed out the anal side of me, that tends to ignore the fact that I have plenty of scraps of thin plywood on-hand, paint to coat it (temporary...until my final design), and mounting hardware to secure it (and as stated above, I already have the switches).

I really don't see an advantage for someone like me who WILL be planning on a "real" physical switch panel to use the AIU outputs (but instead will later "move" the switches as you've suggested above). However, I'll concede that those who never plan on mechanical switches and only plan on the AIU to perform their switching, then their direction is pretty clear. But, that's for another forum thread.

I already bought your fantastic book...where do I PayPal the great advice to?

While it sounds like you have a solution, another technique some guys use it to re-purpose a DCS Remote Commander (the one that comes with Starter Sets) as a watchdog generator.  So you would put the DCSRC on an unpowered spur track(s) and when those track(s) get initial power its sole-purpose in life is to generate the watchdog to keep any engines on the spur track(s) silent.  Then, any actual DCS commands would come from the already-powered TIU channel which long-ago had sent its watchdog. 

Again, this is for the special situation where the TIU channel is already powered.  As to whether it's "worth" going out and buying a DCSRC just for this is a question but lots of guys started the DCS journey with a Starter Set and have a DCSRC gathering dust somewhere!

Stan,

There is one caveat of which to be aware.

If the sidings to which the DCSRC is connected are in turn connected to different TIU channels or, worse, to different TIUs, turning on power to those channels will also bridge the channels and/or TIUs, with potentially undesirable consequences.

I'm not following you Barry.  If you just connect the DCSRC in passive mode to the track, how is it creating a cross connection?  You would need one for each power district I suppose.

I'll bet with a relay for each siding and a little logic delay you might be able to make one DCSRC work for all the sidings...

John,

If you just connect the DCSRC in passive mode to the track, how is it creating a cross connection?

Because I stipulated:

"If the sidings to which the DCSRC is connectedare in turn connected to different TIU channels or, worse, to different TIUs, turning on power to those channels will also bridge the channels and/or TIUs, with potentially undesirable consequences."

Put more directly, you need one DSCRC for each TIU channel that has one of these  sidings that miss the watchdog signal.  You cannot have the same DCSRC connected to multiple track sidings if the sidings are not all on the same TIU channel.

I'll bet with a relay for each siding and a little logic delay you might be able to make one DCSRC work for all the sidings.

You'd lose that bet.

If a DCSRC is connected to more than one track block, all of those track blocks are de facto connected to each other.

Stan,

The problem is that, regardless as to how it's done, the DCSRC receiver must be connected to all of the track sidings for which it is to provide watchdog signal generation.

In order to get it to talk to only one track block at a time, you need to, in effect, have a device that senses when a siding is toggled on and sends a command to some other device (a relay) to selectively connect that track block only to the DCSRC, thereby triggering the DCSRC to send the watchdog signal to that block only.

If it's desired to turn on multiple sidings at once, you have a choice to make:

• You can turn them on, one siding every few (one or two, at least) seconds or so, if you can program your $2-3 worth of parts to do so. (By the way, since you need one relay per siding, $2-3 most likely isn't going to do it.) This would then take 10-20 seconds to actually turn on 10 sidings, at 1-2 seconds each.
• You can turn on all requested sidings at once, again if you can program your inexpensive device to do so. However, this could unintentionally connect multiple sidings across, perhaps, multiple TIU channels or TIUs. This was my original concern.

While anything is possible, this one is certainly outside the skill level of anyone who is not at least an experienced electronics "enthusiast", or the equivalent.

Regardless, if you believe that there's a market for this type of device, I'd encourage you to develop and sell it. I assure you that I'd be among the first ones who would pay (a modest sum ) for guaranteed watchdog signal generation across my entire layout (some 70 or so engine sidings), by using one DCSRC receiver.

Hmm...  Right after I get the Super-Chuffer launched.

See:

https://ogrforum.ogaugerr.com/t...12#30009354134193412

Sorry for the delay in responding.

I have the problem of my PS2 and PS3 not receiving the initial watchdog signal from the TIU on unpowered spur tracks as discussed before.  When I power up the tracks, the engines start, but I can easily get them into DCS mode with a startup, shut down, or even just moving them.  However, I do not want all my PS2/PS3 to start when I switch power onto the spur every time.   Is there a reason why the TIU does not send out a watchdog signal more often.  Legacy must send out a command signal on a regular basis because my Legacy engines do not auto start when I power the spur.  Is this a feature request that can be programed into new versions of DCS.  I am using 4.2, does 4.3 correct this?

I am using 4.2, does 4.3 correct this?

There's nothing to correct. That's the way it works and there's no reason to change it that I can see.

The behavior of the watchdog signal is entirely predictable.

However, I do not want all my PS2/PS3 to start when I switch power onto the spur every time.

There's a way around this. From page 102 of The DCS O Gauge Companion 2nd Edition:

Missing the Watchdog Signal

If individual PS2 engines miss seeing the watchdog signal, they can be either brought directly into DCS active mode by pressing the Start Up key or put into DCS stealth mode by pressing the Shut Down key. However, this is not the same for lashups.

If a lashup is powered on after the watchdog signal has come and gone, perhaps if its siding was toggled on after voltage appeared at the TIU channel outputs connected to its siding, there are two ways to put the lashup into DCS mode. One way to put the engine into DCS mode is to turn off power to the inputs for the TIU channel that is connected to the track upon which the lashup resides, toggle on the siding and then re-apply power. The other way is to first highlight the engine in the remote's Active or Inactive Engine list. Then, flip the toggle switch and immediately press the thumbwheel to select the engine. It will come up in DCS stealth mode, dark and silent. This also works with individual PS2 engines.

Do you have a copy of this book? If not, you should.  

This and a whole lot more is all in MTH’s “The DCS O Gauge Companion 2nd Edition", available for purchase as an eBook or a printed book at MTH's web store!

This has been discussed a number of times before, as well as various solutions. The reason Legacy operates different is it is different in concept.  Anytime there is a TMCC signal on the tracks, Legacy assumes command mode.

Thanks John and Barry.