Location of TVS & clamping voltage

I have both the PSX-AC's and PH-180's. Similar to Cappilot and superwarp1, but wired a bit differently. I currently have the PH-180 feeding the PSX-AC then the TIU input. No choke yet, but no problems with the DCS signal either.

On the bench before setting up my permanent layout the PSX beat the PH-180 every time in my purely un-scientific tests. The Ph-180 never tripped. I added the Sonalert alarms to my PSX-AC's and they are now in operation on my permanent layout. I currently have 2 isolated loops, 2 PSX-AC's and 2 PH-180's (1 PSX & PH for each loop).

The real world results have been a little different from the bench tests. The PSX always trips before the PH-180 as I hear the Sonalert go off briefly, but now about half the time the PH-180 still trips just as I hear the Sonalert go off. At first I thought it was just happening on one loop, but since then both loops have turned out to operate about the same. I have also tried swapping things around with no difference noticeable.

I still believe in the PSX's, they are extremely fast and they are also electronic, but this is an interesting development. I've thought about calling the PSX dealer, but have not done so yet. I keep fiddling with things every now and then to see if anything changes, nothing has. I will get around to calling someday.

I have had several derailments and shorted the track a few times without any problems to the TIU or any of the engine electronics. Between the PSX's and PH-180's, they appear to be doing their jobs.

22 uh choke from Digi-Key

http://www.digikey.com/scripts...=4285987360367507150

Dear Willgee

Susan has a great website with the values of the PTC and other information. Here is the link. http://www.slsprr.net/technical/CircProt.htm

Electrical figures and fact get misapplied a lot on this forum.

Lets think practically.  OK install a TVS.  Two days later you have a derailment and a voltage spike.  You have know way of knowing a voltage spike occurred, but you do know you had a derailment.

Internal to your engine the TVS clamped this spike and failed open.  ONE TIME protection. 

Now what!  You no longer have protection.  You just don't know it.  So what should you do.  Change all TVS on any engine on the track after a derailment?  Change them on a frequency scale weekly, monthly, yearly?

Your buying yourself assumed protection, and risking more damage in pinched wires or shorted diodes.  Unless your willing to go in and change TVS on a routine basis your just tricking yourself into believing you have protected your engine.

The Transformer and TIU TVS on the output of the AC power is good coverage.  I use K-line track with TVS installed at lockon.

I think it makes sense to install an easily accessible TVS at your transformer.  Change them out on a monthly basis or after a derailment.

Installing them inside your engine has far more risk then benefit especially if you choose to leave them in and forget them.

Just my 2 cents, but you need to think these things through.  I replace far more board for folks with good intentions and due diligence that pinch wires putting shells back on, or soldering wires poorly on motors and speakers.

I have run my layout for over 20 years with out one electronic board failure using Power House bricks and TVS at lock ons.

There is a reason manufactures don't put them into the engine.

Protecting a complicated PCB from itself with TVS in the circuit designed to work with the parameters of the circuit board makes sense.  Using specific value TVS on the output of power source make sense.

Putting them inside an engine that you hope you don't need to go into doesn't make much sense to me.  Especially if your not going to do the preventative maintenance.

Like adding oil additive to your car and never changing the oil again.  

NVOCC5 hopefully your comment was not meant to imply no one other than John and Stan know anything about electronic and trains? 

Just remember, it is the operators who refine the products the theoretical engineers build in the lab.    G

"Internal to your engine the TVS clamped this spike and failed open.  ONE TIME protection."

Does a TVS fail each time it clamps a spike?  How often do they actually fail?

Bill

They shouldn't fail at all or very rarely, unless they were not properly sized(wattage, peak clamping volts, current, etc, etc) for the application they were installed.  I've never seen one fail in a model train environment, either the ones installed in my PSX breakers or the ones I installed at the output of my transformer. With that said, with these high wattage transformers we use now and with a short of a derailment I guess anything is possible when a spike is generated.

The only place I've seen shorted or blow open transzorbs is in Aviation due to a lightning strike or other high static discharge but you can imagine the volts involved there.

No one know, that is the fun part of this discussion.

Tail of 2 TIU.  Both have a VAR channel fail with constant output voltage.  I test and found a shorted FET.  Replaced it.  At the time I did not know the FETs are TVS protected separately.

2nd tiu same symptom, but the FETs are OK.  Why constant voltage though?  Well well, I found a TVS shorted.  Replaced it and fixed TIU.

Truthfully, I should have replaced the TVS when I fixed the FET on the first.  No way to know if it works or not without test equipment I don't have.

Now I know better.

TVS can fail either open or shorted.  When they short symptoms are obvious.  If fail open, you would never know.

For the first TIU was the FET just defective, or did the TVS fail previously.  Don't know.

But if you want TVS protection put in around your layout were accessible, not inside your engine.  Several around the layout vice dozens or hundreds inside all your locomotives.

Practical application of the device.  G

How do you know any of this?  I have replaced plenty of TVS shorted on TIU, Z-1000.

I have replaced many a FET that were protected by a TVS.  So did the TVS work, not work, work once, twice....

You know surge protector companies in the fine print state after a suspect surge replace the surge protector.  How many people do that?   G

what spec tvs are you using?

I've seen TVS parts fail in TIU's several times, all of the ones I notice are failed shorted.  If they fail open (not the common failure mode), you probably will never know unless you do a specific test, that requires removing the TVS from the circuit.

Like Gary says, the TVS should be effective for lots of transients, not just one.  If it died after one transient, they would not be very useful. 

This is all an exercise in statistics.  The TVS is just one more layer of protection for the electronics, it's not the end-all, be-all for electronic protection.  Proper specification of components and proper design of the circuit are the primary drivers in reliability.

George, the surge protector strips that talk about replacing them after a suspect surge use MOV components, they're quite different than the TVS.  The MOV is degraded every time it absorbs a surge, and eventually it fails.  If you run the TVS within it's power ratings, it should last indefinitely.  A MOV that gets a large enough surge typically fails by exploding, sometimes fairly spectacularly.  An MOV tends to be smaller for a given surge suppression rating than the TVS, but you have the tradeoff of the degradation for every surge.

Slightly OT.  I installed  a whole house surge protector.  It is required to be wired after a linked set of low amperage breakers.  If a TVS shorts to ground or across the phases, the breakers trip.  There are two LEDS on the panel.  If one is out it means that TVS has gone open and module needs replacing.  If both are off, either the breakers tripped (shorted) TVS or both TVS failed open.  So far both LEDS still shining away.

I replaced one of those for a friend.  He had one in place, it was tied to 30A breakers.  They had a floating neutral on his power and the box literally exploded, the MOV's were charred and shattered beyond recognition.  He had gone down and notice the breaker was tripped and flipped it back, that's when the box exploded!  He wouldn't go anywhere near the panel after that, so I came and installed the new one to replace that one.

BTW, if you open that box, I'm almost certain you'll find MOV's, not TVS's.

Yep John, probably MOVs.

I am using the ones the manufacture installed in the TIU, and K-Line lock on track.

As far as the failures I have seen, they are all manufacture OEM specific.

John,  Sure the TVS you know have failed are shorted.  You have no clue how many TVS are not working.  How many FETS have you changed on a TIU, since the FET is TVS protected by the factory can we assume it failed?  I don't know, but I think it may have.

I am just stating that opening every engine you own and installing TVS as a fix all does not make sense to me.

This is not a PCB circuit that may have 4 or more independent electrical circuits and hundreds of discrete components all susceptible to various independent transients.

We are talking about a 18VAC 60hz transient whose source is the voltage present on the track, even if it comes from an accessory coil or a derailment.

Since electron travel at the speed of light, I feel confident that the TVS 5 feet away can do its job, or maybe the one at the TIU or lock on 10 feet away.

I don't want a device that may short inside my engine as the fail safe.  Will do more damage then good when the track side TVS can clamp just as well.

That is why I think the technical paper talking about PCB component failure is not a good model to dictate the TVS is best place inside the engine as close to the circuit board as possible.  Sure some highly sensitive electronic maybe, our trains IMHO not necessary.

But I would love to see empirical data.  Protected and unprotected, track protected versus engine protected.  See it there really is a statistical difference.

I am just leery of recommending some one install a TVS inside a command engine when they need to ask what wires it attaches too.  Better to just let them put it on a terminal track side.   KISS principle.  G

rrman,  Question on the 2 LED lights on your house TVS surge protector.  Do you have a schematic on on how the LEDs are connected to the TVS providing a short or open condition.

Thanks 

RDA400

Slightly off topic, but I don't know how many are familiar with the No Longer Available QSI Power Guards? My club uses one on each of the three mainlines and has for years. The active component is a TVS but it also contains a couple of lamps that flash every time a spike a generated. Its not uncommon when running engines with dirty rollers or on dirty track to see the lamps constantly flashing. Handy tool for assessing your track and rolling stock.

Pete

I am sure some of you have probably seen this? Has any one tried one making one or studied the circuitry to see what it's capabilities are and if it would be a good thing to have? Full details, schematics and parts lists are posted here: Surge Protector. I would be interested in comments from any of the more knowledgeable electronics folks around here. Might be something interesting to toss around here and maybe even something some of us would all like to have? Looks like it could be an interesting evening or weekend project if it fills a need.

I haven't taken the QSI Power Guard apart but wouldn't be surprised if it was a commercial version of this device.

Pete

GGG,  This thread started off asking about TVS specs/sizing.  A 1.5KE36CA TVS which has been discussed a lot in prior threads, has different clamping Volt and peak Amp specs depending on which manufacture made it.  Curious, of the actual specs of the TVS that are used in TIU & K-line.  Are they similar to LittelFuse 1.5KE36CA which has a operating V of 30.8, break down V of 34.2, Clamping V49.9, Peak A of 30.6 & Peak A of 1500.  Sorry in getting into the fine details, but correct sizing can male a big difference.

Thanks,

Rad400 

Paraphrasing your words slightly: If you don't know what you're doing, don't warm up the soldering iron!

That's great John, it should become your new tag line.

Bill

It's certainly appropriate, especially with expensive circuit boards.

What are MOV"s?

I have TVS across my ZWC outputs.  How can I tell if they are bad.  I have had several shorts & the bricks always trip & I just reset & have never had any problems.

Ken M

The QSI devices were before my time, I was out of the hobby then until 3-4 years ago. It would be interesting to know of they were the same or similar. I was gathering parts to try one of these before we moved which sidetracked everything. Now I have the PSX-AC's instead, also with some interesting results (see my post above about those).

Anyone else have anything to add on these things? The more the merrier here!

Metal Oxide Varistors.

Gilly

Interesting reading.  I would like to ask how one can test a TVS?

John, You don't know what you don't know.  And you do not know what the predominate failure mode is.  Your starting to fabricate stuff. 

Your assuming the FET died of over current, it wasn't an overloaded TIU.  I have seen TIU with the main inductor coils melted but the FETs still worked.  They are tremendously heat sunk and rated over 20 amps.  So I assume it was a Voltage spike that got it, or it could have just been a week component.  Or maybe  the TVS just did not work, or had already failed.

I have repaired one engine with TVS installed internally and the engine board failed on a front truck derailment.

Your argument is it must be in the engine to work, yet no empirical data to support it.

My argument is that TVS have to be considered expendable at some point and why go to all the maintenance to put them in the engine.  I just believe we have taken a PCB related paper and apply it where it doesn't really have merit.  So I agree we disagree.

Guys and gals can do what they want, with their rail road.  G

This would be hard to say, unless I could identify a manufacturer on the component.  Plus, manufactures have been known to change components.

MTH used the 1.5KE33CA on the early TIU outputs.  Rev Ls I have seen have 39.  Transformers like the Z-1000 and 4000 have 51s.  The TIU FETs have a 51.

G

Don't you raise and eyebrow when a manufacture says I won't warranty my product with any transformer, unless you buy my surge protector? 

I have worked on several hundred PS-1 board.  I can count 3 top boards that where bad and I could not fix with a simple software reset.

I can count 2 bottom boards that had capacitor failures, and about 10 with signal diode failures that you might relate to voltage spikes.

Everything else has been undersized diodes (early on) and undersized traces that burn up on overloaded engines, or voltage regulator failures.  So what was the failure that required a QSI surge protector?  QSI first version boards had undersized diodes and other components.  Once they beefed them up the were pretty bullet proof to hardware failures.  Just battery software glitches.  Even the QSI rep stated that.

I have derailed my PS-1 more times than I can count, ran it dead on 3 different batteries and it still has not failed, other then one software reset. 

Lionel TMCC stuff has been pretty bullet proof, Most MTH is attributed to a pinched wire or short to chassis from a speaker or smoke unit.

There certainly are plenty of audio amp failures from derailments, but the audio amp has an AC input for bell and whistle.

The predominate failure that has totally killed a MTH PS-2 board is a pinched or grounded DC wire to AC Chassis.  Or a failure that is left powered up trying to figure out what is wrong.  This overloads the Power Supply and other components usually resulting in a trace short internal to the PS-2 board. 

The paper is a pretty interesting read, a device that shows these spikes is nice.  Is the protection working, these engineers seem to think a track device was good enough.  G 

In my opinion, the QSI PowerGuard was an interesting attempt to make a transient clipper.  The basic technology is to use a Darlington pair of transistors to short across a fullwave bridge sitting across the AC line.  The trigger to the base of the Darlington pair is supplied by a 36V Zener diode.

A modern 1500 Watt TVS probably provides much better protection.

The PowerGuard also monitored for a DC voltage component for Whistle/Horn and Bell.

I would like to add one more aspect to this discussion.  As far as FETs failing, I would like to point out that the protection circuits in the Powermaster, 180W brick and the modern ZW all sense an overcurrent on only one half of the AC sinewave.  That means that the control FETs can be subjected to totally unlimited peak currents for at least half a cycle in the other direction.  This is not a voltage spike situation.

I have repaired enough of these devices to see that the failures are more commonly on the "unprotected" direction.

I don't know if MTH also has this "convenient shortcut" in their overload sensing, but it wouldn't surprise me.

As stated above, a TVS does not degrade like a MOV when it is called upon to conduct current within its ratings.

  A tvs with a microfuse in series across your inputs...would this help in the unlikely event of a tvs short?

for example

http://www.electronicsurplus.c...amp-32v-package-of-3

Dale or John,

Do you have a method to test a tvs to see if it had blown?

You test a TVS the same way that you test a Zener diode.  First, you would probably want to remove the TVS, or at least one end, from the circuit to avoid damaging the circuit during testing.  I would put a 220 ohm resistor in series with the TVS and connect this combination across the output of a 0-40V DC power supply.  Place a DC voltmeter across the 220 ohm resistor.  Crank up the voltage.  The voltage on the meter should remain at zero volts until the total power supply voltage reaches near the breakdown voltage of the TVS +/- 5%.  At this point you should see less than .1-.2V across the resistor.  Any further increase in voltage should yield a sharp increase in current and the resulting voltmeter reading.  Do not exceed 5V across the resistor.  Reverse the TVS's leads and repeat the test.

Although our TVS's are rated at 1500 watts for a short transient burst, they are only good for 1-2 watts on a steady-state basis like in this test.

(If you had a triangle or sawtooth generator capable of plus and minus 40V peaks (80V p-p), using the same connection you could use an oscilloscope to see the voltages at which each of the peaks clipped off.  This is essentially how a curve tracer works.)

Nobody has mentioned the 1200pF of capacitance each installed TVS contributes near the zero crossing of the AC waveform.  This doesn't degrade the TMCC/Legacy track signal, but I would be wary of sprinkling too many TVSs around a DCS layout. 

Willygee, a fuse has an "I squared t" rating that determines how fast it blows.  As the current goes up, the time to blow decreases by the square of the increase.  If you were to match the "I squared t" rating of a fuse to the pulsed-power capability of a TVS, you could indeed protect the circuit from a blown TVS, but what happens then?  The circuit has no protection from transients, and you might have generated yet another transient when the fuse in series with the TVS blows.

It is better for the TVS to fail as a short, tripping the circuit's main overcurrent protection to shut down the damaged circuit.

Some day I should put my oscilloscope across the transformer to see what kind of voltage spikes are caused by dirty track and by my near and dear horizontal-motor F3's.  That would be a good application for a digital 'scope, which I don't have.  John???

  There are many of us that may have an unknown open tvs inside our TIU's especially the channels that have suffered the most incidents of "angry electrons". I am thinking at the very least  we should install a new tvs across the outside TIU terminals every 2 or 3 derailments or so? Definitely easy to do.

Originally Posted by GGG:

John, You don't know what you don't know.  And you do not know what the predominate failure mode is.  Your starting to fabricate stuff.

I do know how to read manufacturer test data.   Tell me, how many open TVS diodes have you personally found?  Perhaps you should do a search on failure modes of TVS protection diodes.  In fact, let me GOOGLE that for you.

Your assuming the FET died of over current, it wasn't an overloaded TIU.  I have seen TIU with the main inductor coils melted but the FETs still worked.  They are tremendously heat sunk and rated over 20 amps.  So I assume it was a Voltage spike that got it, or it could have just been a week component.  Or maybe  the TVS just did not work, or had already failed.

 

And you're assuming the TVS protection failed, yet you have nothing to back up your assumption.  Also, how in the world did you determine with 100% certainty that there wasn't an overload?  Just because you see some FET's that survive an overload, that really is not a guarantee that all will survive a similar experience.  It seems you're making as many, or more assumptions than I am.

 

I have repaired one engine with TVS installed internally and the engine board failed on a front truck derailment.

 

And your point is?  I never said the TVS was a guarantee against any sort of failure.  With any such protection device, it's all a game of statistics.  The statistics indicate you're less likely to have a ESD related failure with the protection than without it.

 

Your argument is it must be in the engine to work, yet no empirical data to support it.

 

Now you're putting words in my mouth that I never uttered.  I said that the most effective protection using the TVS is close to the item being protected.  I never said it must be in the engine to offer some protection, those are your words.  I do believe that the most effective protection is indeed in the engine. 

 

My argument is that TVS have to be considered expendable at some point and why go to all the maintenance to put them in the engine.  I just believe we have taken a PCB related paper and apply it where it doesn't really have merit. 

 

For some reason, you think the PCB that's inside your locomotive is unique and won't benefit from the transient protection, I don't agree.

 

So I agree we disagree.

See, there is a point of agreement after all.

 

Guys and gals can do what they want, with their rail road.  G

 

Very true, and I'll even let you have the last word.

 

 

John, I am LMAO.  You never read what you googled did you?

Let me give you a few quotes from google from the TVS papers.  Most use the exact same terminology.  First one:  Very appropriate

"Words have different meanings to different people, which is the case with the

term “Fail Safe”. A TVS device cannot assure a fail safe environment. Unfortunately,

a TVS will fail when subjected to a transient beyond its designed capability."

"In most applications, if a component is going to fail, the preferred mode would

be a short, which is the easiest to identify."

These paper say the preferred method is a short, not the most common failure.

Makes sense, when shorted you know it failed.  Open or degraded would require testing.

The failure modes are:

"There are three basic types of failure modes:

shorts, open and degraded (outside of the specification

limits)."

I don't think I am putting word in your mouth.  You have recommended they must be closer to the protected item, and you have stated you put them in the engines.

So folks take that as gospel and do it.

I really am not assuming, John.  I am post fact I have and potential issues.  I acknowledge in the FET example there may be other reasons.  You stated clearly it had to be an over current.

Like Dale, though I don't have his electrical background, I have repaired a lot of TIU and Boards.  As a previous operating engineer I understand the concepts of protection, maintenance, and not over engineering something that makes it harder to maintain, limits continuity of operations, or expends money on items with limit or no value to the overall operation of a system.

It is not easy or should I say simple to remove and re-install soldered equipment inside and engine or a TIU.

The concept of Surge suppression seems to have value.  If the Transformer, TIU or PH is not sufficient adding track side may be the ticket.

Change them out after a know issue or on a periodic basis.

I started questioning this on the merit of folks putting them in the engine.  I also started to question the reliability based on what I am seeing (small sample).  Failed engine with TVS, failed FET In TIU protected by TVS.

I will take Dales Advice and start tracking which FET failed, it very well may be a half wave issue with an unprotected side.  G

Gentlemen,

I have the utmost respect for all of you who willingly and graciously give of your time and knowledge here on the forum.  Us Navy guys have to stick together here but John, I must say that I gotta side with George on this one.  Something I learned in "Uncle Sugar's Canoe Club" many years ago - SIBKISS.

Yes, putting a TVS in a locomotive may be the ultimate protection but what a pain in the kiester to check and/or change them out as a PM task.  Taking your advise John, just three days ago I put a TVS in an MTH 4-8-4 N&W J and when I put it on the test track; NADA.  The loco just sat there in both conventional and DCS environments - did the TVS kill the signal?  Don't know but when removed, the loco once again was responsive.  Ohmed out the TVS and it is not shorted - didn't take the time to test it further.

Regarding the "unprotected side" thingy... would putting a TVS diode across both the input side AND the output side of a TIU offer the protection we're seeking?

Best,

Dave

Hi G

I was also an operating engineer in a powerhouse, I was also an electronics technician and serviced the instruments there and in a water treatment plant. I ran a side business servicing coin op games. At work and in my business I witnessed the transition in technologies. Power plant instruments from the 1950s into the 1980s (Bailey) were actually air operated (I cant remember how to spell pneumatic), 3 to 15 pounds or something like that would position a valve for example or measure air flow etc.  Actually these instruments were very accurate and easy to troubleshoot. Later these were replaced with electronic sensors and systems. 3 to 15 or 5 to 25 ma as I remember. Coin op games switched from electromechanical hybrids  with computers. I had to attend school and learn about new systems such as Allen Bradley logic controllers and the like.

I can tell you that the new systems were not optimal and some of the EEs designing them were not up to speed. In fact some of the designers were not even EEs.  One of the problems we technicians had in the new systems were voltage spikes. In many instances transient spikes were not addressed and we had to add them. Fortunately I worked with MIT and Bell Labs engineers with doctorate degrees who had the patients to explain things to me. I was told how and where to add TVS devices in various systems when we experienced problems,often intermittent and hard to diagnose. In one case for example the program settings of a computer would be erased at random intervals.  When this happened all valves would be left in their last position and the rest of the system would continue running without being metered. This resulted once in the spilling of thousands of gallons of chemicals. Yes,a very poor non redundant design the company purchased from an outside contractor. The cause we eventually found out was a flashing high or low PH alarm. Every time it flashed it generated voltage spikes. Sometimes it erased the memory of the computer controlling the system. It took the install of 3 TVS devices on the system to solve the problem.

Sometimes it made no sense to me,but me arguing with those with multi doctorate degrees in electrical engineering and physics would be like Mortimer Snerd arguing relativity with Einstein. Normally I would listen and ask questions so I could learn.

I can tell you, you try to clamp a spike as close to where the spikes is generated as possible. This can be a simple diode across a DC coil or putting multi TVS units around an operating system. They were sprinkled around like candy in an Easter egg hunt with no ill effects. This is very common practice. They are cheap and there is not much downside to doing it. It is not over engineering.  Spikes can be generated in various places not considered. I never witnessed one shorting,not that it cant happen.

The TVS is not any more prone to failure than any other system component,in fact probably much less. Forensic study of board failure is interesting but we hardly have a wide enough sample to prove cause and effect, with and without a TVS. Then you have other factors, such as people paralleling transformers with 20 amps on a loop and doing other things probably not good practice.  And how do you measure how many failures were prevented by the TVS,the engine you are not servicing because there are TVS devices installed? For 50 cents each,I put a few around each loop of my layout and on accessory lines. Modern accessories have PC chips too. If one shorts out,it will trip the fuse or breaker. If it is soldered in,I will cut it out and replace it. If I open an engine up,I might put one in an engine,depending on complexity. Not sure it is worth it.  I really don't worry about them.

I know this wont change your opinion and you are entitled to it. Hopefully this is a discussion with no hard feelings. I enjoy reading your posts and you have helped many people with problems and I appreciate it. It is also nice to have John and Dale Manquen here to answer technical questions. You can get a free education here if you want it.

Dale H