I can't find who recommended using Eaton FAZ-C3/1 breakers for circuit protection on my layout. I'm using an old 275 watt ZW and want to protect my trains. After installing the breakers, I tested them by laying a screwdriver across the track and the breakers didn't blow. Does anyone use these breakers and, if so, can direct me to what I'm doing wrong? Thanks!
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Maybe you are referring to this video which no longer exists (thankfully!) https://www.youtube.com/watch?v=aVeCPeeeRNk which was discussed in a few posts.
I don't think those breakers are really appropriate. The AirPax Instant Breakers are a much better choice for conventional and command operation, and don't forget the 1.5KE36CA TVS Diodes.
Thanks for the info, do you have a picture of the airpax wired in? I'm trying to figure out where to put them. Also, on the diode, do you recommend placing them directly on the ZW posts? I'm using fastrack, where do they go on the track?
In general, just about any circuit breaker is wired in series with the load on the hot side. In other words, insert it between the lettered throttle post and what is being powered.
The TVS diodes are wired in parallel and go between the lettered throttle post and the U post. It is argued that placing the TVS closer to the sensitive electronics is beneficial, but you can do it right on the transformer - that is what I do.
@texasspeciallionel posted:Thanks for the info, do you have a picture of the airpax wired in? I'm trying to figure out where to put them. Also, on the diode, do you recommend placing them directly on the ZW posts? I'm using fastrack, where do they go on the track?
If you follow this link AirPax Instant Breakers there is a diagram showing how to wire these breakers and the TVS diodes. I also use postwar 275 Watt ZW transformers with these breakers. The 10 Amp model is a good choice for these ZWs
10 Amp PP11-0-10.0A-OB-V https://www.onlinecomponents.c...00aobv-10090622.html
The TVS diodes are intended to protect the electronics in your trains and the closer these diodes are to the circuit boards, the better they protect them. The best place is inside the locomotives connected to or near the circuit board where track power goes into it.
@bmoran4 posted:..It is argued that placing the TVS closer to the sensitive electronics is beneficial, but you can do it right on the transformer - that is what I do.
Brain, as one of your followers and one who greatly respects your opinion, I want to make it clear I'm not looking to start any kind of argument, rather a discussion. I have heard from others, who like you, have placed TVS diodes across their transformer outputs and elsewhere around the layout, and this has worked for them. Until I read the explanation linked below from @Adrian! , I too was unconvinced that placing TVS diodes inside the Locomotives may be best for protecting them, and that doing so would be a PITA. After reading this, my opinion changed in favor of placing the diodes inside my locos.
Maybe you've already seen Adrian's explanation, but in case you haven't, it's interesting to ponder.
@Adrian! posted:It's not so simple actually. You want the TVS right up against whatever it's protecting:
There's a little bit of RF design principles here (sorry it's complicated)... let me try to explain it easily:
What happens when a train derails is the motor and bouncing contacts produce transient events (fast changing voltages and currents over a short time duration... like 1-10ns range). These transient events are short in time which means they are very wide-band in frequency (fourier transform describes this).
They can be up to the GHz range, which means they behave like RF waves on the wiring and track (because they have a comparable wavelength in the 10s of inches regime). Once you are into this wave propagation behavior it means that the whole wire length is not the same voltage at the same time. So just because you null out the voltage at one point along the wire with the TVS between the train and the TIU doesn't mean the transient voltage at the TIU or train is zero because of the waves bouncing up and down the wire.
If you want the basics it's here: Transmission lines
So the only way to be 100% sure the transient voltage at the protected device is safely held down by the TVS is to physically place it very close to the thing your protecting (like within 1/10th of a wavelength). That's why it has to go right on the board inside the TIU.
Hope that wasn't too poorly explained!
Here's a link to the original topic and reply
@SteveH, I am aware of the wave propagation theory discussions such as what Adrian describes and read many of the manufacturer papers on TVS products and placement guidelines. I came to the conclusion that the absolute best place for the TVS is at the source of the transient, but in our layouts that can be "unpredictable", so next best is at the entrance points to sensitive electronics (inside the locomotive), but ultimately clamping somewhere instead of nowhere may be a reasonable compromise.
@bmoran4 Thanks for your considered reply. I agree that a TVS diode or a few around the layout is certainly better than none.
Personally, I have not yet installed TVS in all of my modern electronics laden locos. I prefer to do so whenever I open them up for some other reason.
You guys seem to have the topic well covered, but in case anyone reads this and get confused let me say explicitly what everyone else is already saying implicitly.
There's two different goals to circuit protection accomplished by different devices:
1. You want to prevent short circuits from developing large currents in the layout when possible.
This is what breakers, fuses, etc are for. Large currents stress the power devices (switching FETs in an DC-DC chopper like the one in a Z4000) and stress the transformer windings in a step-down source like a PH180 brick or other coil-based source. Prolonged short circuits tend to destroy power devices and power components but generally don't damage the electronics since in a regular derailment short circuit the large current doesn't flow through locomotive electronics. One exception is if you have power coming in through an MTH TIU (in that case the current does flow through the electronics). Generally these shorts are at low frequency (60 Hz and down) and you can just treat the wire like a wire (same voltage everywhere it's connected at the same time) which is why you can place the current protection device any old place and it's fine.
2. You want to avoid kickback voltage... high voltage transients developed in the layout from normal train operation...
Motors are inductive and inductors produce voltage depending on the change in their current. VL = L di/dt. Big change in current makes big voltage. If your train bounces along the rail making and breaking contact or it has momentary disconnects going over switches and stuff, the Ldi/dt term is big since di/dt is discontinuous going from current to no current and back to current again. Those discontinuities generate voltage transients well over 100s of volts that have duration in the 1-100ns type of timeframes. These transients are not defects... these are part of normal train operations... but you need to stop them from propagating and damaging electronics which are mostly semiconductors like the ACT244 driver in the TIUs, or GRJ's buffer circuit and like PS boards in the locomotives themselves, (all have breakdown voltages in the neighborhood of 10-20V). This is what the TVSs are for. The big difference from current protection is these short 1ns voltage transients are a broadband event, (the Fourier transform of a 1 ns pulse is a sinc(w) going all the way out to a GHz.
Since these transient voltage pulses are GHz range they have wavelengths on the order of a few inches meaning they can bounce around a layout like a transmission line and the TVS you put way over here by the station won't suppress the transient over there by the train yard since the transient voltage pulse is physically only a few inches big wherever it currently is. (wavelength = c/freq). For that reason you have to put the TVS device physically near what you're protecting (well within a wavelength).
Bonus Topic: Loading
Both DCS and Legacy/TMCC are pretty high frequency signals (broadband even in DCS's case), and while @gunrunnerjohn's booster and the TIU act244 driver do a pretty good job of driving loads, it's not going to drive fractions of an ohm. If you put too many TVS diodes everywhere or TVS diodes that are too too big, that capacitance starts to add up and eat into the voltage swing of the superimposed signalling leading to signal integrity problems through both RC loading (bad time constants sloping out your waveform) and LC loading (unhappy ringing waveform).
Also, I'm not dead. Mars helicopters and model trains are competing for my time, and sadly the trains haven't been winning.
@Adrian! posted:Also, I'm not dead. Mars helicopters and model trains are competing for my time, and sadly the trains haven't been winning.
Welcome back, I wondered if you had abandoned the trains! 
I hope the part shortages aren't cutting any MARS missions short. 
@gunrunnerjohn posted:Welcome back, I wondered if you had abandoned the trains!
The future of America's space program is stuck in some containers down in Long Beach. Really.
@Adrian! posted:The future of America's space program is stuck in some containers down in Long Beach. Really.
I'm surprised they're not still out in the harbor! 
@Adrian! posted:You guys seem to have the topic well covered, but in case anyone reads this and get confused let me say explicitly what everyone else is already saying implicitly...
Also, I'm not dead. Mars helicopters and model trains are competing for my time, and sadly the trains haven't been winning.
Adrain, thank you for expanding upon these points. I appreciate the additional details you've offered here.
Thanks to all! I've ordered diodes and Airpax breakers. One more question, How do I know when to replace diodes over time?
The typical failure mode of a TVS is a direct short, so it will be obvious. You can replace them periodically to account for the less common failure modes if that gives you peace of mind.
in the case of a direct short "obvious" in that I'll see the TVS change shape, i.e. expand or that I'll have to get a meter to assess the failure?
It would be obvious in the sense that the breaker it's connected to will keep tripping until you locate the failed TVS diode and remove it. If you have more than one TVS Diode on the same power block, you'd have to disconnect one side of each diode, one at a time, and check for continuity thru the diodes until the failed one is found.
The less common failure mode is when the TVS diodes fail to clamp transients voltage spikes any longer, which is why @bmoran4 suggested you may want to periodically replace them. Testing them for this type of failure is a bit more complicated.
The case of a direct short is... well... a direct short! If the TVS is connected across track power, it'll be obvious if it turns into a direct short!
IF you're putting multiple TVS diodes across the tracks, let's hope you aren't running MTH DCS, that would seriously degrade the DCS track signal.
got the diodes and airpax breakers. hooked them up temporarily and work fine. Before installing them in my control board, I thought I'd ask yall's opinion on what gauge wire do you recommend from my ZW to the airpax breakers? Trying to clean up my wire mess. Thanks again to you all!
No reason not to use at least #14 or maybe #12 if you have it.
@Adrian! posted:2. You want to avoid kickback voltage... high voltage transients developed in the layout from normal train operation...Motors are inductive and inductors produce voltage depending on the change in their current. VL = L di/dt. Big change in current makes big voltage. If your train bounces along the rail making and breaking contact or it has momentary disconnects going over switches and stuff, the Ldi/dt term is big since di/dt is discontinuous going from current to no current and back to current again. Those discontinuities generate voltage transients well over 100s of volts that have duration in the 1-100ns type of timeframes. These transients are not defects... these are part of normal train operations... but you need to stop them from propagating and damaging electronics which are mostly semiconductors like the ACT244 driver in the TIUs, or GRJ's buffer circuit and like PS boards in the locomotives themselves, (all have breakdown voltages in the neighborhood of 10-20V). This is what the TVSs are for. The big difference from current protection is these short 1ns voltage transients are a broadband event, (the Fourier transform of a 1 ns pulse is a sinc(w) going all the way out to a GHz.
Since these transient voltage pulses are GHz range they have wavelengths on the order of a few inches meaning they can bounce around a layout like a transmission line and the TVS you put way over here by the station won't suppress the transient over there by the train yard since the transient voltage pulse is physically only a few inches big wherever it currently is. (wavelength = c/freq). For that reason you have to put the TVS device physically near what you're protecting (well within a wavelength).
Follow-up questions pertaining to a layout with Legacy, LionChief and Conventional operation only (no DCS):
1) When discussing where to install TVS diodes inside the locomotive, usually the suggestion is to install them where the pick-up and collector wires attach to the circuit board. But, since the motor coil(s) become voltage spike sources in the event of a derailment, would where the motor(s) connect to the motor driver board be better locations to install TVS diodes inside the locomotive or would TVS installation in both places (where the motors connect and where the pick-ups/collectors connect to the circuit boards) be best?
2) If a TVS diode is also installed across each transformer secondary powering the layout, would there be a good case for installing any additional TVS diodes around the layout (assuming all Locos had individual TVS protection installed)?
@SteveH posted:If a TVS diode is also installed across each transformer secondary powering the layout, would there be a good case for installing any additional TVS diodes around the layout (assuming all Locos had individual TVS protection installed)?
I sometimes see that there are those who think only to focus on the track/locomotives and completely overlook the accessory power buses.Accessories are filled with transient inducing solenoids and what not. Take a look at your track switch machines, your crossing gates etc... and that there are other accessories that have sensitive electronics in them.
I guess there are two points I am trying to make:
@bmoran4 posted:I came to the conclusion that the absolute best place for the TVS is at the source of the transient, but in our layouts that can be "unpredictable", so next best is at the entrance points to sensitive electronics (inside the locomotive), but ultimately clamping somewhere instead of nowhere may be a reasonable compromise.
Also, I see you specifically disavowing DCS, but I just want to make it clear that TVS diodes and DCS are not automatically a no-no, but it is true that they do raise the capacitance and there will be a point at which that capacitance becomes too high and interfears with the DCS signal. You could expect to have DCS issues if you put a TVS diode on even piece of sectional track ;-)
@bmoran4 posted:I sometimes see that there are those who think only to focus on the track/locomotives and completely overlook the accessory power buses.Accessories are filled with transient inducing solenoids and what not. Take a look at your track switch machines, your crossing gates etc... and that there are other accessories that have sensitive electronics in them.
I guess there are two points I am trying to make:
- Transients don't solely exist on track power buses
- When addressing your accessory buses, be sure to think about placement:
All good points with which I agree. Any inductive coil which has it's voltage source abruptly removed is a source of Transient Voltage Spikes. I was curios about asking the specific case of derailments and where the best protections would be against the energized coils associated with that scenario.
Agreed that any accessory coils (uncouplers, crossing gates, switches, etc.) which happen to be energized at the time a breaker tripped that is powering all of them and the track, each one would also become a source of spikes. Also , during their normal operation, each accessory's coil also generates voltage spikes when deactivated, so TVS diode protection at each of those sources would also seem to be ideal.
To my recent question, I'm still interested in the electrical engineering consensus about which TVS diode installation location(s) inside the locomotive would be optimal for protecting the locomotives' electronics.
As I've frequently said, the absolute best place for the TVS is inside the locomotive directly across the track power feed. Obviously, this is also the hardest place to install them, and you have to modify every locomotive. Of course, while you're in there, you can add the 22uh choke in the track power feed for any TMCC/Legacy locomotives to minimize any effect the their electronics on the DCS signals. If you choose to do that, the best way is to put the choke in the center track feed and then the TVS diode across the feed after the diode. That way the DCS signal isn't significantly affected by the bulk capacitance of the TVS diode in the locomotive.
@gunrunnerjohn posted:As I've frequently said, the absolute best place for the TVS is inside the locomotive directly across the track power feed.
Obviously, placing the TVS diodes across the track power feeds in the locomotive will help with spikes coming from the track, but I think @SteveH raises an interesting question about the motors in the locomotive themselves inducing transients back trough the driver circuitry (say an ACDR)
@gunrunnerjohn posted:As I've frequently said, the absolute best place for the TVS is inside the locomotive directly across the track power feed. Obviously, this is also the hardest place to install them, and you have to modify every locomotive. Of course, while you're in there, you can add the 22uh choke in the track power feed for any TMCC/Legacy locomotives to minimize any effect the their electronics on the DCS signals. If you choose to do that, the best way is to put the choke in the center track feed and then the TVS diode across the feed after the diode. That way the DCS signal isn't significantly affected by the bulk capacitance of the TVS diode in the locomotive.
John, Thank you for your reply. I do remember your previous assertions about the best place inside a locomotive to install TVS diodes would be across the track power feeds and your cautions about excessive TVS diodes diminishing the DCS signal. This assertion combined with thinking about @Adrian!'s recent explanation (quoted above) I'm wondering if the following may be better on a non DCS layout and if not, why?
If motor coils are one of the primary sources of voltage spikes in a derailment scenario, wouldn't clamping these spikes at the point where the motors connect to the motor driver board reduce the spikes before they pass through all the circuit boards' electronics on their way to previously suggested TVS diodes connected at the other side of all those electronics at the track pick-up connections?
As I understand it, another major source of voltage spikes in the derailment scenario would be from the transformer coils. So in addition to installing TVS diodes on the loco's motor driver side of the locomotive, also connecting TVS at the transformer outputs would seem to be optimal (non DCS), as well as accross each accessory with coils.
@bmoran4 posted:Obviously, placing the TVS diodes across the track power feeds in the locomotive will help with spikes coming from the track, but I think @SteveH raises an interesting question about the motors in the locomotive themselves inducing transients back trough the driver circuitry (say an ACDR)
I'm sure there's more circuit protection that could have been designed internally for various boards, but I think maybe that's carrying it a bit too far. I didn't think the object of the exercise is to redesign all the TMCC/Legacy/DCS boards for maximum transient protection, that would be a huge job!
Tiny note. Remember that a TVS looks like a "C" when it's not in conduction, and a 22uH choke looks like... well a 22uH choke. So when these things are placed together you're making an LC, which has issues...
The TVS suppresses voltages by very quickly going into conduction creating a giant current change. The inductor's physical nature is to reject fast current changes (V=Ldi/dt), so having the choke before the TVS would render the TVS less helpful since it can no longer respond fast in series with the choke. You'd want the TVS across the track first (so you have to suck up the capacitance hit), and then the choke in series with the electronics behind it.
@Adrian! posted:Tiny note. Remember that a TVS looks like a "C" when it's not in conduction, and a 22uH choke looks like... well a 22uH choke. So when these things are placed closely together you're making an LC, which has issues...
The TVS suppresses voltages by very quickly going into conduction creating a giant current change. The inductor's physical nature is to reject fast current changes (V=Ldi/dt), so having the choke before the TVS would render the TVS less helpful since it can no longer respond fast in series with the choke. You'd want the TVS across the track first (so you have to suck up the capacitance hit), and then the choke in series with the electronics behind it.
Well, I am trying to protect the electronics in the engine, so why is the TVS less effective? The TVS will clamp any voltage in excess of it's rating, the speed of the ramp-up doesn't seem to be a major issue. I must be missing something (and probably am).
@gunrunnerjohn posted:Well, I am trying to protect the electronics in the engine, so why is the TVS less effective? The TVS will clamp any voltage in excess of it's rating, the speed of the ramp-up doesn't seem to be a major issue. I must be missing something (and probably am).
I think I'm probably confused and not saying the right thing for the thread or didn't write it well. Back to step one...
1. You can't put a choke at the input of a DCS engine since then the PS board gets no signal.
2. You can't put a choke in series with a TVS to protect other electronics, or the TVS is no longer effective at suppressing a voltage across the series combination.
Also when you bring the TVS and choke together in parallel you're making a LC tank circuit and it can cause ringing that may or may not be an issue depending on the topology of how it's placed.
This is a sim of 22uH, and an SA5.0 TVS in parallel and excited by a DCS waveform with a 10 ohm Thevnin source.
@Adrian! posted:I think I'm probably confused and not saying the right thing for the thread or didn't write it well. Back to step one...
1. You can't put a choke at the input of a DCS engine since then the PS board gets no signal.
2. You can't put a choke in series with a TVS to protect other electronics, or the TVS is no longer effective at suppressing a voltage across the series combination.
I think John is talking about an L-C low-pass arrangement, with the TVS as the C. The supply to the electronics would be taken off across the TVS. So, the L protects the DCS track signal from the shunt capacitance of the TVS, but the TVS is directly across the electronics, affording maximum protection to the electronics, but less protection to the track.
@PLCProf posted:I think John is talking about an L-C low-pass arrangement, with the TVS as the C. The supply to the electronics would be taken off across the TVS. So, the L protects the DCS track signal from the shunt capacitance of the TVS, but the TVS is directly across the electronics, affording maximum protection to the electronics, but less protection to the track.
So L is series with the engine board meaning the DCS waveform won't enter. That means this discussion is not for a DCS engine right? (I think this is what I was missing above).
The electronics we are talking about protecting are not DCS decoders. Right?
@Adrian! posted:So L is series with the engine board meaning the DCS waveform won't enter. That means this discussion is not for a DCS engine right? (I think this is what I was missing above).
The electronics we are talking about protecting are not DCS decoders. Right?
Yes, John was specifically talking about TMCC/Legacy locomotives. Here is his exact quote-
Of course, while you're in there, you can add the 22uh choke in the track power feed for any TMCC/Legacy locomotives to minimize any effect the their electronics on the DCS signals. If you choose to do that, the best way is to put the choke in the center track feed and then the TVS diode across the feed after the diode. That way the DCS signal isn't significantly affected by the bulk capacitance of the TVS diode in the locomotive.
Easy to miss that point with all the back-and-forth.
Another missed item are the questions that revived this thread today for the electrical engineers here:
@Adrian! posted:2. You want to avoid kickback voltage... high voltage transients developed in the layout from normal train operation...Motors are inductive and inductors produce voltage depending on the change in their current. VL = L di/dt. Big change in current makes big voltage. If your train bounces along the rail making and breaking contact or it has momentary disconnects going over switches and stuff, the Ldi/dt term is big since di/dt is discontinuous going from current to no current and back to current again. Those discontinuities generate voltage transients well over 100s of volts that have duration in the 1-100ns type of timeframes. These transients are not defects... these are part of normal train operations... but you need to stop them from propagating and damaging electronics which are mostly semiconductors like the ACT244 driver in the TIUs, or GRJ's buffer circuit and like PS boards in the locomotives themselves, (all have breakdown voltages in the neighborhood of 10-20V). This is what the TVSs are for. The big difference from current protection is these short 1ns voltage transients are a broadband event, (the Fourier transform of a 1 ns pulse is a sinc(w) going all the way out to a GHz.
Since these transient voltage pulses are GHz range they have wavelengths on the order of a few inches meaning they can bounce around a layout like a transmission line and the TVS you put way over here by the station won't suppress the transient over there by the train yard since the transient voltage pulse is physically only a few inches big wherever it currently is. (wavelength = c/freq). For that reason you have to put the TVS device physically near what you're protecting (well within a wavelength).
@SteveH posted:Follow-up questions pertaining to a layout with Legacy, LionChief and Conventional operation only (no DCS):
1) When discussing where to install TVS diodes inside the locomotive, usually the suggestion is to install them where the pick-up and collector wires attach to the circuit board. But, since the motor coil(s) become voltage spike sources in the event of a derailment, would where the motor(s) connect to the motor driver board be better locations to install TVS diodes inside the locomotive or would TVS installation in both places (where the motors connect and where the pick-ups/collectors connect to the circuit boards) be best?
2) If a TVS diode is also installed across each transformer secondary powering the layout, would there be a good case for installing any additional TVS diodes around the layout (assuming all Locos had individual TVS protection installed)?
@SteveH posted:John, Thank you for your reply. I do remember your previous assertions about the best place inside a locomotive to install TVS diodes would be across the track power feeds and your cautions about excessive TVS diodes diminishing the DCS signal. This assertion combined with thinking about @Adrian!'s recent explanation (quoted above) I'm wondering if the following may be better on a non DCS layout and if not, why?
If motor coils are one of the primary sources of voltage spikes in a derailment scenario, wouldn't clamping these spikes at the point where the motors connect to the motor driver board reduce the spikes before they pass through all the circuit boards' electronics on their way to previously suggested TVS diodes connected at the other side of all those electronics at the track pick-up connections?
As I understand it, another major source of voltage spikes in the derailment scenario would be from the transformer coils. So in addition to installing TVS diodes on the loco's motor driver side of the locomotive, also connecting TVS at the transformer outputs would seem to be optimal (non DCS), as well as across each accessory with coils.
@SteveH posted:Another missed item are the questions that revived this thread today for the electrical engineers here:
1. If you put the TVS across the motor, you're guarding this train's electronics from it's own transients, but not transients from other sources on the layout (other trains, solenoids, relays, ...).
2. If you have digital signaling like DCS, adding too many TVS all over will begin to impact the signal performance, since even when not-clamped they present significant capacitance at their input terminals. If you have no digital signaling then there's no harm done.
@Adrian! posted:1. If you put the TVS across the motor, you're guarding this train's electronics from it's own transients, but not transients from other sources on the layout (other trains, solenoids, relays, ...).
2. If you have digital signaling like DCS, adding too many TVS all over will begin to impact the signal performance, since even when not-clamped they present significant capacitance at their input terminals. If you have no digital signaling then there's no harm done.
Adrain, thank you for confirming this.
Assuming strategic location of TVS diodes elsewhere around a non-DCS layout (transformer outputs, and across accessories with coils and other locomotives on the tracks:
Would there be any significant attenuation of the TMCC signal by adding TVS diodes on a locomotive's motor driver board output(s) as well as on the PCB track power inputs, thereby maximizing protection of the electronics in the locomotives?
@SteveH posted:Adrain, thank you for confirming this.
Assuming strategic location of TVS diodes elsewhere around a non-DCS layout (transformer outputs, and across accessories with coils and other locomotives on the tracks:
Would there be any significant attenuation of the TMCC signal by adding TVS diodes on a locomotive's motor driver board output(s) as well as on the PCB track power inputs, thereby maximizing protection of the electronics in the locomotives?
The short answer is no. The entire layout (trains, track, accessories, your body if you stand too close) are all one side of the legacy voltage ... the entire layout goes up and down at 455 KHz. The building ground (3rd prog of plugs, water pipes, ...) is the other side of the voltage. As long as the TVS is placed from layout thing to other layout thing, then it's capacitance is not presented to the legacy signal as a load it needs to drive.
Related side-note: Legacy/TMCC and the way it couples to antennas and the building ground is all super complicated equations because trains and layouts are usually "electrically short " - meaning it's not like traditional radiating 1/4 and 1/2 wave RF antennas, but like a dirty mix of capacitive couping and radiative coupling.
@PLCProf posted:I think John is talking about an L-C low-pass arrangement, with the TVS as the C. The supply to the electronics would be taken off across the TVS. So, the L protects the DCS track signal from the shunt capacitance of the TVS, but the TVS is directly across the electronics, affording maximum protection to the electronics, but less protection to the track.
Correct, I'm not trying to protect the track, as Adrian has already pointed out, a TVS at some distance across the track may provide minimal or no protection.
@Adrian! posted:I think I'm probably confused and not saying the right thing for the thread or didn't write it well. Back to step one...
1. You can't put a choke at the input of a DCS engine since then the PS board gets no signal.
2. You can't put a choke in series with a TVS to protect other electronics, or the TVS is no longer effective at suppressing a voltage across the series combination.
Correct, and I was specific as to the engines I recommended this combination on.
@gunrunnerjohn posted:As I've frequently said, the absolute best place for the TVS is inside the locomotive directly across the track power feed. Obviously, this is also the hardest place to install them, and you have to modify every locomotive. Of course, while you're in there, you can add the 22uh choke in the track power feed for any TMCC/Legacy locomotives to minimize any effect the their electronics on the DCS signals. If you choose to do that, the best way is to put the choke in the center track feed and then the TVS diode across the feed after the diode. That way the DCS signal isn't significantly affected by the bulk capacitance of the TVS diode in the locomotive.
This combo was what I envisioned for TMCC/Legacy locomotives. It serves a two-fold purpose. Not only does it isolate the track from the stray capacitance of the TVS, but it also addresses the issue of the TMCC/Legacy electronics attenuating the DCS signal. We know that a number of those locomotives will have a negative effect on the DCS signal, so this checks that box as well.
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