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(Guest)    J&C Studios O Gauge Archive    Dale H    Automating a passing siding
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Topic: Automating a passing siding
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Dale H
Joined: Sep 25, 2010
Topics: 32   Replies: 39
posted on Feb 15, 2012 06:20 PM:
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Got a few emails from people asking how to do this. This circuit seems to work at least on paper. I have not tested it. Please check my drawings and let me know if you see a mistake.

To do this we need 4, 3PDT 10 amp relays. Below is a sketch of a passing siding with 2 turnouts and shows the relay coil circuit. For simplicity only the center rail is shown for the pattern and the loop connects in whatever configuration desired. A separate transformer is used for relay power so only one bridge rectifier is needed. The minus of the bridge rectifier shares a common with the U terminal of the track transformer. If a tap is used from the track power transformer it could be done also with a bridge rectifier to each 12 or 24 VDC relay. For this hookup see my post on using relays for accessory activation. A diode is placed across each relay coil as shown for spike suppression and a capacitor 470 uf 35 volt is also across in proper polarity to eliminate relay chatter when the outside train wheels complete the coil circuit. Relays coils 1 and 2 are activated by outside insulated rail X. Relay coils 3 and 4 are activated by outside insulated rail Y and both are as long as the maximum stopping distance when power is removed or reduced to the oncoming train. A corresponding center rail is also insulated as well as Insulated center rails X and Y are the same lenght as the outside one. Following each is an additional insulated center rail (X behind) and Y behind). These are as long as the longest train to be run. The function of these will be explained later. Note that the relay power for relay 3 coil is in series with the NC (normally closed) contacts of relay 2 and relay coil power for relay 2 is in series with the NC contacts of relay 3. (left set of contacts ,relays 2 and 3) This prevents both relay coils form being activated at once. Which ever train arrives first or is left on the block will be on. When both blocks X and Y are occupied, either relays 1,2 and 4 or 1.3 and 4 will be on but 1,2,3, and 4 can not be activated together as relays 3 and 2 lock each other out.

Below is the wiring for the center rail track power.

If relays 1,2 and 4 are on Center rail X is hot and center rail Y is off. If relays 1,3 and 4 are on Center rail Y is hot and center rail X is off. This circuit is the left set of contacts,relays 1 and 4. The right set of contacts,relays 1 and 4 is used to disconnect X behind and Y behind respectively from track power and connect it to X center and Y center when blocks X or Y are occupied. This allows for shorter stopping distances and eliminates roller jumping of X and X behind. As soon as power is cut to blocks X or Y,the whole train,not just the engine will get zero or reduced power. The NO contact of relays 1 and 4 can be used to circuit reduced power to the stop block. In this drawing Tap B of the transformer is set at around 5 volts,stall power. This will allow for more gradual stops and leave enough voltage to keep the lights on the stopped train. This will increase stopping distance so if this optional circuit is used the blocks need to be sufficiently long. The right contact set of relays 1 and 4 prevent transformer taps A and B from ever being connected together. Note: The left contact set NC terminal relay 4 goes to B tap of the transformer. It can be connected to the left contact set NC of relay 1. This was not drawn in to simplify the drawing. Also note stopping voltages and characteristics can vary greatly between engines,so a median voltage must be kept to avoid collisions.

The last drawing is the circuit used to throw the turnouts in the proper direction. The center set of contacts of all 4 relays is used to do this. This drawing assumes that the turnouts can take continuous voltage without damage. Other types such as Atlas can be thrown safely with capacitor discharge.

So in the loop drawn the trains can be made to go in opposite or same direction and will alternate when they are both on the passing siding. So if blocks X and Y are occupied,the train that was there last will proceed. So if relays 1,2 and 4 are made Train at X will leave the loop and return to X. When it leaves,relay 2 will drop out and relay 3 will come on since Y is occupied and the lock from X is broken. When it returns,relays 1,3 and 4 will be energized ,the turnouts will be thrown in the proper direction and the train at Y will make the loop. (Y behind) will have track power as the train enters the block but when it reaches Y block it will disconnect from the track power and connect to whatever power Y has.

This circuit will be very mechanical in operation. As soon as one train leaves,the other one will start,so it is not so realistic. With 3 more relays and a timer a time lag can be set so there is an interval between when a train arrives and departs. I will describe this circuit later if there is any interest. With some more relays and a timer, a soft start circuit can also be added to make the automation more realistic.

Dale H


Joined: Jul 24, 2013
Topics: 0   Replies: 6
posted on Jul 25, 2013 06:10 PM:
My Archive Category  

Awesome, and just what I've been looking for! A quick question about a
possible simplification:

It seems like in your third schematic] the third (center) set of contacts
could be eliminated entirely if you have non-derailing switches; all that is
really needed is your connections of the straight to straight switch posts together,
and the curved to curved posts together. When a train starts up and reaches
the switch, that pair of wires seems to be sufficient to ensure that the two
switches always move in unison, so that the moving train will return to
the same siding. I'm worried that this proposal might cause some unwanted
circuit interactions, so I thought it best to ask for a sanity check :-)

Since 3PDT switches are problematic to put on a standard breadboard layout,
I'm hoping that this will let me get by with four DPDT switches instead. The
whole thing then can be easily wired on one standard breadboard circuit board.

ps -- I had been trying to automate a passing siding using just three relays.
I figured that if one of them was a latching relay, the latch should
be able to 'remember' whose turn it was next -- but I never was able to
get the logic quite right. So, I was really pleased to find this post
(and envious that there are people who can just reason all this out without
first going through endless experimentation :-)


Dale H
Joined: Sep 25, 2010
Topics: 32   Replies: 39
posted on Jul 25, 2013 07:29 PM:
My Archive Category  

So many kinds of switches I can not answer for sure with out though .Problem I think is setting up anti derail when the train enters the siding. However I would throw them with relays,that way we are sure they will be in the right position. 3pdt switches are readily available but 2, DPDT ones in parallel (or series such as 2, 12 vDC ones in series with a 24 volt system) could also be used. The 4th set of contacts could trigger a timer allowing for a delay between train arriving and departing. Such a system is more realistic as operation is less mechanical. A twin coiled latch relay can also be used but these are expensive with multiple contacts with adequate switching capability. You could use a cheap one, to power the relays. A lot of ways to do things. The train can run in the same or opposite direction.



Joined: Jul 24, 2013
Topics: 0   Replies: 6
posted on Jul 26, 2013 01:57 PM:
My Archive Category  

Thanks for the prompt response! I happen to have some tiny DPDT relays
and could fit all 8 on a single breadboard, but they only carry 2 amps. Might
these tolerate the current needed for a typical small Lionel O-gauge engine?

I'm starting simple, with O22 Lionel switches, but I'd eventually like to
do something similar with 1122 switches. Unlike the O22s, the 1122s don't
automatically disengage the solenoids after the switch is thrown, so it seems
like the 3PDT relays would keep the solenoids activated for long periods.
You've suggested using capacitor discharge in this case, which I assume means
that we don't run continuous power to switch posts, but instead have the
relays connect a charged capacitor. I'm not sure what is an appropriate size
of cap to use, and am also fuzzy on the mechanism for getting the capacitor
recharged for reuse. You might decide this capacitor discussion may be
better placed in your other tutorial on relays (which I likewise found to be
extremely enlightening -- thanks again for sharing your expertise).


Dale H
Joined: Sep 25, 2010
Topics: 32   Replies: 39
posted on Jul 26, 2013 06:54 PM:
My Archive Category  

You need contacts of at least 10 amps. I suggest mounting the relays separate.

Many switches can be thrown by capacitor discharge. See my post on throwing atlas switches with a toggle in my blog or the electrical section of JC studios here.. Relay contacts can also be used.

1000uf capacitors usually work,if not go to 2200 uf 35 volt. 2 machines can be thrown at one time also with a 4700 uf. This assumes no binding of the switches. In the Atlas circuit,one capacitor is charged while the other is discharged into the switch machine coil. A resistor 33 ohm slows the charging slightly to prevent arcing of the relay contacts or switch. Use the smallest cap which throws the switch reliably.



Joined: Jul 24, 2013
Topics: 0   Replies: 6
posted on Jul 27, 2013 08:12 PM:
My Archive Category  

OK, I've bought some hefty relays and am discarding the breadboard idea,
based on your advice. I've run across one concern with the wiring, though.
With the track transformer A terminal connected to the left common post on
relay 1, it seems that if relay 1 (or 4) is off, this connects directly
to the left NC terminal on relay 1, which is in turn connected to terminal B on
the transformer, and we've shorted transformer terminals A and B, regardless of
the state of the rest of the circuit. I'm wondering if transformer terminal A
was instead intended to be routed to the left NO post of relay 1? This
effectively turns the two relay posts you've labeled 'A' into 'A or B, depending
on the the state of relay 1.'

Even in this modified configuration, the two NC posts to which terminal B is
connected are isolated until either relay 1 or relay 4 turns off. That would
seem to imply that there is a brief period of time when the 'waiting' train is
not being fed stall power. I've been too chicken to conduct a 'smoke test' without
first soliciting further advice to straighten out my thinking. Thanks once again!


Dale H
Joined: Sep 25, 2010
Topics: 32   Replies: 39
posted on Jul 28, 2013 10:44 AM:
My Archive Category  



Dale H
Joined: Sep 25, 2010
Topics: 32   Replies: 39
posted on Jul 28, 2013 10:48 AM:
My Archive Category  

I will think about this and get back to you. The relays switch pretty fast. Instead of 2 transformer terminals you could use a voltage dropper made from bridge rectifiers. That would prevent any A_B shorts. Stalling trains in collision avoidance is not that reliable. I would cut power all together. However soft strat circuits can be made if the voltage dropper is used.



Joined: Jul 24, 2013
Topics: 0   Replies: 6
posted on Jul 28, 2013 07:40 PM:
My Archive Category  

OK, after staring at this for about four hours, I may have a (partial)
workaround. I think my fix leaves the X section without any power until the
engine is again given full power, so that means the engine light is off, but
it would seem to give full voltage and stall voltage to X-behind at all the
right times. (There may well be interactions I'm not anticipating, and you're
likely to find a more elegant solution, so you probably don't want to spend
much time reviewing this unless you hit a dead end -- so perhaps ignore it
until then.)

Besides moving the connection from terminal A to the rightmost NO post
on relay 1, I think the X-behind center rail can be connected directly to
the rightmost common post of relay 1. This gives full power to X-behind
whenever relay 1 is off, which is when the 'X train' is on the common
portion of the track or the engine is on X-behind, approaching the X section.
It only switches to stall voltage when the engine touches the X section.
(There may be a roller-jumping issue here.)

I think this can free up all the right-most posts of relay 1, which could then
be used for other things -- the X center rail can just be connected directly to
the rightmost normally-open post of relay 2. I believe this means that X gets
power only when R1=on, R2=on, R3=off, and R4=on, which is only when the
'Y-train' has returned to Y, and persists until the caboose of the 'X-train'
has cleared the X section. That sounds mostly like what is needed (except that
the engine has zero power rather than stall power all the while it waits).

Relay 4 would get similar rearrangements, but I haven't traced out all the
scenarios yet -- bad interactions may still be lurking. I really appreciate
all the time you've devoted to solving my problem, so please don't feel obliged
to respond or even analyze my suggestion if (as is highly probable) you are
pursuing a better strategy.


Joined: Jul 24, 2013
Topics: 0   Replies: 6
posted on Aug 11, 2013 04:22 PM:
My Archive Category  

Got it! (Only on paper; still have to actually try it.) I'm too embarrassed
to say how many diagrams I analyzed... In hindsight, if I had just taken your
diagram and tried various ways of making it symmetrical, I would have found
what you intended a lot sooner. If I can successfully figure out how to upload
the diagram, you'll see that it's basically your design for track power (your
second photo), but now symmetrical (as we should expect). The four posts I
labeled A are connected to the A terminal on the transformer, and the two
posts you labeled B should still be fed stall voltage.

The sequence the relays become active is 124 (just as X starts), then 34
(once X has moved a full train length ahead, then 134, then 12, then it
starts over. As Y arrives and stops, relays 1, 2, and 4 are on, and 3 is
off. X and X-behind get A-terminal power, Y gets 0 volts, and Y-behind
gets B voltage (so the Y-train should stop quickly). When only relays
3 and 4 are on, X is at 0 volts (which is fine, since no cars are there now),
X-behind has full power (so the X-train can return without stalling), Y and
Y-behind now have stall voltage. The symmetrical situation holds for the
combinations 134 and 12. This matches what you described, except we don't
have to worry about increased stopping distance.

In the third diagram, I think it will be possible to eliminate one set of
poles. Since 124, 34, 134, and 12 are the only combinations, instead of
testing for 124, we could test for 1-on, 3-off, 4-on. By using both the
NO and NC poles of relay 3, relay 2 can be bypassed altogether. So, it may
be possible to get by with one DPDT relay and three 3PDT relays.

I'm still many days away from having this implemented, but I'll eventually
post a followup once I have something concrete to report.


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