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Is it safe to use high-frequency power?

Ralph PlatzRalph PlatzOGR Forum Member

 

Is it safe to use high-frequency power?

Back in the 1950s, after reading Linn Westcott's article on High-Frequency Lighting in the Model Railroader, I converted an old AC/DC radio into an oscillator, using a home-built air-core transformer.  I had no oscilloscope or other measuring equipment, but I think the frequency of the oscillator was around 100 KHz.  I superimposed its RF output voltage onto the 60-Hz output of the Lionel transformer so that both frequencies went to the tracks in the same manner.  The RF voltage had no effect at all on the wire-wound items like the locomotive motor or the whistle relay, but it lit up the light bulbs nicely -- and they stayed on even when the 60-Hz transformer was turned off.

I have been thinking about trying something like this again for use with conventional transformer control for conventional locomotives — using the RF (20 Khz - 100 KHz)  either (a) for lights,  or (b) for activating a relay which alone will allow the E-unit to receive power, or (c) for actuating a relay to open a coil coupler, or (d) for actuating a relay which will cut power off from the locomotive motor but will allow power to remain on for everything else (lights, whistle, etc.).

But this question is nagging me:
If I have two separately and independently powered track loops, the one powered by Legacy-controlled 60-Hz chopped AC and the other powered by conventional 60-Hz sine-wave AC with the RF voltage superimposed on it, and if (in forgetfulness or carelessness) I allow a train to cross (by switchtrack) from one track loop to the other, momentarily bridging the center rails,  (1) will the RF voltage do damage to the Legacy control electronics (in the ZW-C, in the TPC-300, or in TMCC/Legacy locomotives),  and/or (2) will it interfere with the TMCC/Legacy 455-KHz signal?

Before I try to experiment with this idea, I would appreciate any feedback (even best-guess hypotheses) from any of you who understand the workings of Legacy/TMCC electronics.

/Ralph Platz

 

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AP Arthur P. BloomOGR Forum Member

Wow, I hadn't thought about that high F method in years.  But these days, there are easier ways to get a signal or two to a loco for extra features, like couplers, horns, toggling lights, etc.  Here's what I use in one of my radio controlled switchers (a K-Line MP15 in LIRR livery) to open the couplers.  I use these because the radio controller that controls the loco itself only has the one channel that operates the electronic motor servo.

 

 

PLEASE LEARN HOW TO POST LINKS!

Just pasting a web address into your post is NOT the way to do this. I fixed this one.

 

 

 

Last edited by Rich Melvin
Ralph PlatzRalph PlatzOGR Forum Member

Thanks, Arthur.  This sounds like a great idea.  But 2 questions:

 

1) I assume that the receiver units are put into locomotives, tenders, or rolling stock.  What are the approximate physical dimensions of the receivers?  (The website does not seem to give that info.)

 

2) Does some kind of antenna need to be connected to the receivers, or do they

work at a high enough frequency that they contain their own antenna?

 

/Ralph Platz

 

Last edited by Rich Melvin
Ralph PlatzRalph PlatzOGR Forum Member
These are great ideas from Arthur and gunrunnerjohn. They are, however, based on broadcasting a signal from an antenna on a hand-held transmitter to a receiver in a specific locomotive which could be located anywhere at any time on any of the tracks..

What I have been thinking about is somewhat different.  I would like to have a way to avoid antenna broadcasting to any and all locomotives equipped with a receiver, and instead channel the signal to specific sections of the center rail in specific isolated block sections. Any locomotive in the selected block (if equipped with the receiving electronics) would respond to the signal; no locomotive in any other block would see the signal.  This would be consistent with the general manner of simultaneously but separately controlling multiple conventional locomotives on a block-by-block isolation basis.

One possible application of this would be a signaling system that automatically prevents a locomotive from going into a block protected by a red signal (without turning off its lights, its ability to whistle, etc. — i.e. turn off only the motor). When the signal goes red, the immediately prior section of the preceding block still continues to receive the 60-Hz. AC power from the transformer, but the signaling system superimposes the RF signal on the AC fed into this isolated block.  The circuit inside the locomotive senses the RF and actuates a relay which interrupts the power feed to the locomotive motor (but not the power feed to the lights or whistle, and not causing the E-unit to cycle).   This type of selective automatic control cannot be done if the signal can come only from a hand-held human-activated remote transmitter broadcasting the signal from an antenna.

 

Last edited by Rich Melvin
S stan2004OGR Forum Member

Another approach which I've proposed several times with no takers is to use a localized infrared or optical signal to disable the engine's motor.  So called "side-glow" fiber could run along the few inches or feet of the track section under control.  The fiber would illuminate (except invisible to the eye) with modulated IR when you want the stop action.  Low cost IR sensor (50 cents) in the engine would sense this and flip a relay or solid-state switch to cut the motor.  The detector circuit could even be powered by the DC motor drive signal itself since by definition the relay would only need power when the motor is being driven.  This would make it easy to tack-into any typical modern engine.

 

This way you do not have to add a fuss with adding a signal onto the existing AC voltage.  There are problems with doing so especially given the variety of AC sources out there.  In the case of the chopped sine-wave source you mention, this is undoubtedly done with a triac so you have a wild source-impedance variation between on and off.  In the case of "pure-sine" sources, these are typically generated with pulse modulated drivers which might be switching themselves at frequencies near or close to the signaling carrier frequency range you're suggesting - so again wild impedance variations in the region of interest.

 

While you may be solving a one-off layout issue, I'd think it would be a contribution to the hobby if whatever method you work on could apply to more than AC chopped-sinewave 3-rail systems.  In other words, wouldn't it be neat if it could work with 2-rail, DCS, DCC, non-block isolated, and whatever other O-gauge systems we use.  That is why I've thought this problem needs to be solved outside of the track voltage technology and with some kind of optical, magnetic, whatever system.

 

What would really pique my interest is if someone wanted to experiment with modulating the "red" light in a signal light.  In other words modulate the red LED in a dwarf or 3-aspect signal light.  Of course, to the human eye modulated red light would just look like a solid red light.  A sensor in a cab would be looking at the signal and "see" the modulated red light and cut power to the motor.  Heck, this would actually be prototypical in how it operates!

 

Anyway, the other issue with modulating a track voltage signal that I'd consider is future "upgrades" if you want to send more than an on-off command using your high-frequency signal.  In other words what if you decide to encode additional information by modulating your signal.  When you have a 60 Hz AC signal, the signal disappears 120 times a second.  Depending on your design there are cases where this is a real disadvantage because the bridge rectifier in your engine turns off at this rate meaning your signaling voltage does not get past the bridge (unless the modulating signal itself is large enough to turn on the diodes).  This may or may not be an issue depending on how your design your detector.

 

In any event, great idea and as GRJ says, let us know how you make out!

Ralph PlatzRalph PlatzOGR Forum Member

 

Stan,

Thank you for your very informative and helpful response.

1)   You have answered my initial question regarding the superimposition of RF voltage on the newer AC-power track feeds.  The system which I had built back in the 1950s worked well with the simple transformers of that era -- just primary coils, tapped secondary coils, and no electronics (except for whistle-activation diodes).  Today, however, a superimposed RF voltage may not be so "friendly" to modern transformers that use electronic switching and pulse-width-modulation technologies.

2)   The problems of automatically stopping model trains at red signals and then automatically re-starting them at yellow/green signals has, to my knowledge, never been solved in any reasonably simple manner.
 
  • An automatic shut-off of track power at red signals will indeed stop any locomotive, but it will also shut off the lights and will disable the whistle/horn.
  • An automatic restoration of track power at the signal's return to yellow/green
    • will re-start a conventional locomotive only if its E-unit had been disabled; otherwise it will cycle the E-unit into "idle".
    • will leave a TMCC/Legacy loco standing still waiting for explicit operator action; it cannot be automatically re-started; only a human operator can re-start it.
3)   The idea of using a localized IR emission at red signals and equipping the locomotives to detect the IR signal and correspondingly interrupt power to their motors (but leave power connected to all other functions) would solve the problem elegantly — without needing to tamper at all with the supply of track power.  An IR-illuminated side-glow fiber laid between the rails and IR detectors mounted underneath the locomotives would seem to be the most practical general way of doing this.
I myself, however, do not know how to design the electronic circuits for IR emission and IR detection, nor do I perceive any universally simple way for mechanically mounting the IR detectors underneath the locomotives.

4)   The modulation of the signal's red light is an even more interesting idea, but I would not understand how to design the modulating circuit nor how to design a photo-detection circuit that responds to modulated light.

Thanks again.
/Ralph Platz
Ralph PlatzRalph PlatzOGR Forum Member
Originally Posted by Flash:
I think RFID is a better method for automated train control. Each locomotive can have a specific ID. Sensors near the track can ID the train then a computer addresses the locomotive and issues commands to that specific train.

 

I agree.  This would indeed be the ultimate automated solution, with extensive flexibility to do almost anything.   It is the ideal solution for those who understand electrical engineering and computer programming.

But for the average model railroader it also presents several difficulties:
  • Implementation complexity   it is not simple
    • to equip all locomotives of interest with RFID,
    • to set up RFID detectors at all points of interest,
    • to provide and set up a computer for this purpose,
    • to interconnect to computer interfaces all of the RFID detectors and all of the control wires from all of the signals, and
    • to write (or obtain) and parameterize the requisite computer software.

  • Cost — The cost-sum of a computer, of RFID components, and of interface circuitry is not negligible.

  • Set-up complexity   Even if everything is pre-planned and pre-designed carefully and is modularly tested, "bugs" (both in hardware implementation and in computer programming) have a way of sneaking in and remaining elusive.  It would require a good deal of time and dedicated effort to find all the bugs, to isolate them and be able to reproduce them, to fix them, and to verify that the fixes are effective.

  • Operational complexity   Once everything has been correctly implemented and set up, its operation is entirely under the control of the computer.  Programming the computer may be a simple task for a computer programmer, but it is a very complex task for those who have less background in computer programming; they would require some kind of point-&-click interface to set up parameters in the data structures on which some commerially purchased software would operate.

  • Maintenance complexity   If at some later point in time, there would be an operational break-down somewhere, it may not be so easy for a non-engineer to track down the source of the problem and to fix it.
/Ralph Platz

 

Ralph PlatzRalph PlatzOGR Forum Member

 

I am really happy with this discussion thread, because I am learning a lot.

I appreciate in particular the link to the Forum thread on "infrared sensor".

And decoupling the detection and activation schemes from dependence on some central computer control would significantly reduce the costs and complexity of everything.

Also, for making forward train motion automatically compliant to the red-vs.green signal status, communicating with the locomotive via trackside emitters (IR or electromagnetic) eliminates dependencies on block isolations and eliminates all problems that might be caused by tampering with the integrity of the center-rail track power.  I remain, however, a bit skeptical about my own mechanical ability to install detectors on the underside of locomotives, and I don't know whether I would be able successfully to design and install an electromagnic induction pick-up loop for a locomotive.

Another consideration is that the dependence on trackside emitters for holding a locomotive stopped (motor off with lights on) allows it to be so stopped only at those locations where the emitters have been trackside-embedded.  It does not allow the operator himself to stop the locomotive motor at arbitrary locations on the track; that would have to be done from an additional system such as suggested above by Arthur and gunrunnerjohn.

Again, thanks to all who have responded. It will take me some time to dig into all of this information and try to understand well what the possibilities are, but I will have fun in doing so.

/Ralph Platz
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