OK, still working on same club layout. We have a series of stop sidings, and trigger tracks. The train stops in the stop siding, until another train going in the oposite direction triggers the stop track, through the common outside rail causing the stopped train to proceed. This Works. Where we have a problem is this. We are operating 2 or more trains in opposite directions. We need to slow down the ones at 3 points going down grade into the staging area through a 1/2 turn helix. We can do that with the bridge diodes or a # 81 resistor or whatever. So far so good. But then we have a train coming out of the staging area, that needs to go up the grade. It needs the full voltage, not reduced. So short of a logic circuit what ideas do you have to have the reduction circuit in place for one direction and not for the other ? Thanks, Dave
Did you measure it under load? The diodes need a little current through them to develop their voltage drop. A voltmeter usually has a very high input impedance so that it will draw very little current from the circuit being measured.
Nevertheless, the voltage won’t be correct unless you are using a “true RMS” voltmeter. You should also not expect even with a true-RMS voltmeter that the sum of the load voltage and the rectifier-string voltage will equal the transformer voltage. You can look at the waveform on an oscilloscope; but you would have to do a lot of computation to come up with an RMS-voltage number.
The simplest way to measure the voltage with a small incandescent lamp. Hook up the lamp with an SPDT toggle switch so that you can instantly switch it between the voltage to be measured and a sine-wave source, like a train transformer. Adjust the transformer so that the lamp’s brightness doesn’t change when you throw the switch back and forth. Then measure the transformer’s voltage. That will also be the RMS voltage of the bridge-rectifier setup.
I think you only need a relay to do this. Or you can used a timed relay. Basically if you have a relay connected to the same ground track that the siding engine is sitting on, you can have the supply power of that relay connect to the same 3 slow down tracks as well, since you can “lay” higher voltages over lower voltages safely on the same track point. That way the train will come into the siding, slow down and stop by using 3 decreasing voltage points on the rectifiers, wait for the “trigger train” to complete the ground when it’s safely out of the way, and then it will trip that relay and send higher voltages to the siding train to get it up the hill and past those 3 reduced voltage tracks. You will have to find a place on the layout to put your release track for that relay so it’s ready for the next approach into the siding.
As for a timed relay, that’s what I use and a lot easier.
http://www.etrainshop.com/tek9.asp?pg=products&specific=jocnoqeph0
It only allows 15 seconds of run time before it closes, so your siding train would have to be able to get past those three slow down sections in that amount of time. Mine is infra-red, but is made to fit on MTH realtrax. I have not shopped around for other IR devices. I bet there are more generic ones that still have the timer. I’m thinking that Lionel has one that looks like a power box that you see at RR crossing gates. Anyhow, it’s really about the same as the relay above, but easier. You set it at the “trigger train” location, and run your “higher go up the hill voltage” from the bridge rectifier stip to it, and then connect the output to all 3 of
Dave, I get from your post that you don’t particularly need anything new to start the trains going back up the hill, you just need the voltage reduction on the hill to depend on the direction of the train going up or down the hill.
For this, I think you do need a DPDT relay. Return the coil to whatever voltage is suitable for it, but through a lamp which is also rated for that voltage and is large enough that there is not much voltage across it when the relay is operated. Connect the side of the relay coil that is connected to the lamp to a control rail A at one end of the hill. Connect the other side of the relay coil to a control rail B at the other end of the hill. Connect a normally-open relay contact in parallel with control rail B, to layout common (“ground” or the outside rails generally).
Now, when the train passes over control rail B, the relay will operate and will be latched on through its contact. When the train passes over control rail A, it will light the lamp, removing all voltage from the relay coil, and release the relay. Use the other relay contact to change the tap on the rectifier string to get the two track voltages you need for uphill and downhill running.
The relay can be run on AC or DC of any voltage, whatever is suitable for its coil. You don’t need to worry about “phasing” for this application.
Other possibilities: Atlas makes a mechanically latching relay that they call a “snap relay”. It has two coils and DPDT contacts (of which you need only SPDT). You can operate each of the coils from one of the two control rails. I assume it is meant for 12 volts DC.
You can also eliminate the lamp in my circuit and use a normally-closed contact of another relay, in series with the coil of the first relay, to release the first relay.
Hi, I’m trying to draw this out, and not quite getting it. Do you have the ability to draw, scan and post your idea? How I envision it is that the light builb and the Realy coil are connected at one end of the coil, and this is connected to the Relay Voltage, be it DC or AC. Then depending on the trigger either A or B, either the Coil is energized, or the bulb. The bulb having low resistance when lit would then open the relay. Not sure what is going on through the contacts. Perhaps you can word it a little different for me, am I on the right track. Thanks, Dave. Also I’m aware of Atlas relays, they are actually their switch machines with contacts. Have to look at that also.
I don’t have a way to post a picture, but I’ll try some ASCII art:
(ground)—(relay supply)—(lamp)–A–(relay coil)–B–(NO relay contact)—(ground)
A and B are the isolated control rails, which are grounded when the train wheels pass over them. If you ground B, the relay operates, the normally-open (NO) contact closes, and the relay stays operated even when B is no longer grounded. If you ground A, the lamp lights and the relay releases, since it has ground on both ends of its coil. When it releases, it opens the contact; so, even when A is no longer grounded, the relay stays unoperated.
This circuit uses one of the relay’s contact sets. The other contact set is used to move the center-rail connection from one tap to another on the rectifier string.
You can also do this with a resistor instead of a lamp; but the resistor draws a lot more current. The lamp’s resistance goes up greatly when it is lit, limiting the current to a much lower value when the train grounds A.
Thanks, I was able to draw and figure it out that way. But… in doing so I reduced the parts count. All I need is one trigger track and one SPDT relay. The trigger track will be just upgrade of where I need to slow down. Lets call it trigger “A” The downhill train completes the circuit to ground at “A” which engergizes a relay coil. This kicks in the N.O. contact connecting the Lionel Rheostat or Diode Bridge to the center rail of the slow down area. When the last car of the down hill train clears “A” it doesn’t matter, the engine is already on level grade and out of the slowdown area. Then when the uphill train leaves the stop track and heads upgrade, the relay has already return to N.C. which is full track power at the slowdown area. By the time this engine and train completes the circuit at “A” effectively lowering the voltage at the slowdown area , it just doesn’t matter, because the engine is out of the isolated slowdown area. Thanks for all your help. Till the next problem… Dave
Dave, that could work. The only problem might be that the grounding connection to the control rail through the car wheels might not be continuous, letting the relay chatter. You would improve your chance of success by making the control rail as long as possible, to get several wheelsets on it at once. In any case, if you use a DPDT relay, you can always add the second control rail and the lamp later if you need them.
If you use a single contact to slow down the train, it will have to be normally closed, not normally open. However, you might as well use the entire SPDT, wired simply to shift from one tap to another. That way, you don’t short out a section of the rectifier string, so it can be tapped for more than one slowdown situation if you have others on that transformer output.
Hi Bob, I’m building a conventional layout where I plan to use this kind of setup. My end goal is to have my trains maintain a steady speed going up and down grades and on the level sections of the layout.
Taking your rectifier idea one step further, is it possible to use a relay to “select” the right power level for a “2-way” grade? I want to have a couple reversing loops where the train will go down a grade and then level out into a reversing loop. That same train is now coming up the grade it just came down. Can I use a relay to select the right voltage for going up/down the grade? If that’s a possibility, any ideas on the best setup? Thanks.
Here’s one way to do it using two relays:
One end of the coil of each of relays K1 and K2 connects to the relay supply voltage.
K1 is the relay that selects the track voltage. The other end of K1’s coil connects to a control rail in loop 1 and also to the track common through a normally-closed contact on K2.
The other end of K2’s coil connects to a control rail in loop 2.
Since I run conventional on a three level layout I run two insulated blocks. One is on the lowest level track rising to the middle level . That block sees 16V and helps the long train climb. The other is on a downhill grade from the top level to the middle (table) level. To slow the train I use a two ohm power resistor to the insulated block middle rail power. It works well and it keeps things simple.