Best place to locate TVS Diode in regard to MTH TIUs.....

Junior,

Over the years on this forum there have been several specifics on TVS usage that seem to pop up a lot.  They are:

1.  The TIU already has a TVS on each channel.

2.  TVS has a failure mode that is undetectable (at least not without expensive test equipment).  So I have at least two TVSs between the engine and the transformer.

3.  The closer the TVS is to the board you want protected, the better.  Some advocate inside each engine, although I don't want to do that myself.  

Counting the TVS in the TIU as one, I put a second TVS at each track connection.  Here is a diagram I did in the past that shows my thoughts on this.  I'm sure there are other ways to use TVSs, but they are cheap and don't interfere with any signals so don't hesitate to add them.

UPDATE:  Diagram corrected for Legacy base wire connection.

CapPilot! Thanks for responding! Wow....your diagram is awesome and shows clearly what I will do.

When I ran my searches across the forums for TVS usage, I did get a lot of hits; but nothing that showed or discussed TVS placement. So, I sincerely appreciate you rehashing/reposting a topic that sounds like it's been beaten to death. 

Ron has a good plan there, easy and doubles the protection in case of a component failure.

I agree GunRunnerJohn! In fact, CapPilot's diagram would be an EXCELLENT addition to the Electrical Reference Materials & Manuals topic (which I just discovered)!

We put one on each input and output post of the TIU.

Gentlemen,

   I must be loosing it because why have a double TVS set up.  Is the TVS in the TIU not good enough, mine has never failed to safe guard my layout.  Am I missing something here?

PCRR/Dave

Pine Creek Railroad posted:

Gentlemen,

   I must be loosing it because why have a double TVS set up.  Is the TVS in the TIU not good enough, mine has never failed to safe guard my layout.  Am I missing something here?

PCRR/Dave

As I mentioned in my post above, a potential issue is that the TVS has a failure mode that is not detectable unless you have the right equipment and want to test each TVS on a regular basis (daily?).  I'd rather just have multiple TVSs since they are cheap and have no impact to operation. 

Also, per previous posts the TIU TVS is the 33 volt version not the 36 volt version I show in my diagram.  The 33 volt version is adequate if your power supplies can only put out a maximum of 18 volts, like the PH180/135 transformers.  Any transformer that can put out more than 18 volts, or has a whistle or bell button that adds voltage to the circuit when pressed, could over powered the 33 volt version so the forum standard now is the 1.5KE36Ca.   Because of this, I personally add another TVS at the input to each terminal block so I don't depend on the TIU TVS.  Maybe overkill, but as I said these are cheap.

Pine Creek Railroad posted:

I must be loosing it because why have a double TVS set up.  Is the TVS in the TIU not good enough, mine has never failed to safe guard my layout.  Am I missing something here?

Dave, one failure mode of the TVS protection diode is open.  That is undetectable unless you take the TVS out of the circuit and test it.  The bottom line is, you don't really know if it's safe guarding you, you're just assuming it is.

I replaced the diagram in my first post with this one below (both are now the same).  As I mentioned, it was an older diagram. 

While the OP did not mention anything about Legacy or TMCC, my original diagram had the Legacy base connected at the transformer, which is not a good place for this connection.  The connection from the Legacy or TMCC based should be on the OUT side of the TIU so the TMCC signal doesn't go through the TIU.  If the loops are not connected together, then the Legacy base wire needs to be connected at each TIU black/common out.

Hello Ron,

I am considering adding the TVS Diodes to my DCS layout.  I went up on the Digikey web site and downloaded the PDF document associated with the 1.5KE36Ca diode and found two diodes listed, one uni-directional and one bi-directional.  Since the transformer is supplying 20v AC, I will assume that I should order the bi-directional version.  Is this correct?

Ted

Ron,

Ignore my previous post.  The KE36Ca diode is bi-directional. 

Ted

Not sure if everyone agrees, but one way to implement Ron's TVS placement plan is to use a 2 gang terminal block at each track drop.

Screw the small terminal block to the underside of the layout; attach an 8"-10" drop from the track to the small terminal block on one side and the wires from the main terminal block from the TIU to the other side. Then solder a TVS across the + and -  wires right on the block.

Thanks to John H.

I recently had the same questioned raised by the OP in this thread, and am resurrecting it because I found the comments herein to be extremely helpful. Others contemplating where to put TVS Diodes might similarly benefit from this excellent thread.

Arnold

The easiest way to add the TIU is in passive mode.  Just run wires from the OUT side of the TIU to the track wires.  I added two additional TVSs because the TVS inside the TIU is not longer in line with the power to the track.

However, the original diagram several posts up is old.  On my test layout I got tired on changing fuses so I now use PSX-AC electronic CBs.  A choke is needed because the PSX seems to degrade the DCS signal.  So this would be an updated diagram:

Yes, probably overkill on TVSs but I bought a 100 of them (cheap) so I am using them.

On my layout, I have the TIUs in passive mode.  I need the PSX-AC CB because I use it to run 15 amps to the track as well as it having a very fast CB.  Here is my setup with at least three TVSs between the transformer and track (one in PSX)

@Richie C. posted:

Not sure if everyone agrees, but one way to implement Ron's TVS placement plan is to use a 2 gang terminal block at each track drop.

Screw the small terminal block to the underside of the layout; attach an 8"-10" drop from the track to the small terminal block on one side and the wires from the main terminal block from the TIU to the other side. Then solder a TVS across the + and -  wires right on the block.

Thanks to John H.

With updated pic of power drop to track from two-gang terminal block with TVS installed and waiting to be hooked up on the other side to main power.

Thanks to everyone who has provided information about TVS usage.  Until a year or two ago, I was unaware of the risk, and it's nice to be able to mitigate it so inexpensively.

Questions re the use of multiple TVSs since a failure is difficult to detect...

What causes a TVS to fail?  (One event, a certain number of events, defective from the factory, etc.?)

Can a TVS survive multiple occurrences?

Since it's not feasible to test a TVS, do people replace them periodically?

I cannot answer the technical questions, but I don't plan on replacing TVSs.  That is why I am using multiple ones.

The TVS has at least two failure modes; one that is not detectable and one that shorts out the circuit causes the CB to open.  Because of the short failure, I am not soldering the TVSs to the circuit, but useing connectors to allow easy replacement.

The TVS is a double-edge sword, it does good things, but in abundance, it can do bad things.  The large 1500W TVS diode that we typically suggest is 1500W 33.3V TVS at Digikey.  The capacitance across the this part is between 1000pf and 2000pf, dependent on the applied voltage.  Let's take the minimum value of around 1000pf, at 3.27mhz (DCS carrier), the capacitive reactance of one TVS is around 50 ohms.  If you sprinkle ten of them around on one loop, you have five ohms of capacitive reactance dragging down the DCS signal.

@Mallard4468 posted:

Thanks to everyone who has provided information about TVS usage.  Until a year or two ago, I was unaware of the risk, and it's nice to be able to mitigate it so inexpensively.

Questions re the use of multiple TVSs since a failure is difficult to detect...

What causes a TVS to fail?  (One event, a certain number of events, defective from the factory, etc.?)

Can a TVS survive multiple occurrences?

Since it's not feasible to test a TVS, do people replace them periodically?

A TVS is able to attenuate unlimited transients as long as it's peak and average power ratings aren't exceeded. In theory, it can withstand infinite events as long as it's ratings aren't exceeded.  Obviously, in a very small number of cases, the part may be defective and fail.

The vast majority of TVS failures are shorts, but they can fail open and also simply degrade their protection.  There is no practical way to in-circuit test a TVS, by nature of the device, any test would be hazardous to the device it was protecting!

Another form of transient protection is the MOV, however it degrades every time it suppresses a transient.

Here's one of many blurbs on each device.

The Truth about MOV's

Failure Modes and Fusing of TVS Devices - Vishay

Is a TIU recommended if I’m only using a Cab 1 and Cab2 ?

Does the diagram from CAPPilot other than eliminating the TIU ?

You do not need a TIU unless you plan to run MTH DCS command engines.  My diagrams above include DCS and the terminal strips for block wiring used for star wiring which works best for the DCS command system.  If you are running TMCC or Legacy only, you don't need to break up your tracks into blocks.  For TMCC/Legacy you can use bus wiring which greatly simplifies things.

Here are two diagrams for TMCC only that I dug up, one for using a ZW and one for using a PowerMaster.  Bus wiring may not be the best choice if you plan to add DCS in the future.

Thank you very much.

To add my two cents, there's a good article written some time ago that discusses transient voltage. Here's the link....

https://www.hirailers.org/tech...tm#Surge%20Protector

But to my knowledge, I've never found any discussions indicating model railroaders built any of these circuits in this article.

Thank for the info.  CAPPilot, what type fast acting 10 amp fuse should be used.

A long time ago, I purchased several 4-fuse holders from a company no longer around (Scott's Odds N Ends).  I used fast blow 10 amps like in the picture.  Several here on the forum use automotive fuses and holders.

I now used PSX-AC electronic circuit breakers. You can see them on Charles Ro site, where I get them.

@Stephen G posted:

Thank for the info.  CAPPilot, what type fast acting 10 amp fuse should be used.

Here’s a fast breaker discussion thread on the forum that may be helpful for an alternative to fuses.  Apologies if this is a thread jack.

Fast circuit breakers

Thank for quick response.

Thanks Ted and CAPPilot.

Would there be any reason to but a TVS diode on fastrack switches being powered from a aux transformer?

Well, it probably won't hurt, OTOH, it's probably not needed.

@Casper posted:

Would there be any reason to but a TVS diode on fastrack switches being powered from a aux transformer?

If any electromagnetic coils or motors (Uncouplers, Operating track, crossing gates, etc.) are on the same circuit as the FasTrack Switches, the coils will induce voltage spikes into that circuit, which could potentially damage the electronics in the Switches.  This may be a good enough reason to add TVS diode(s) at each switch location.  I believe that the extra capacitance introduced by these multiple TVS diodes would not affect the DCS signal, because the track power circuit with DCS on it would be separate.

Steve, so would it be a good idea to have the switches on a separate power feed than an operating track?

@Casper posted:

Steve, so would it be a good idea to have the switches on a separate power feed than an operating track?

I think so.  If switches and other larger coils are on separate circuits, the spikes they generate stay isolated from the switches.

Also, FasTrack uncouplers (including the ones in Operating Track) are recommended to be operated at 10-12 volts AC to reduce the risk of melting the housing and/or coil.  Some operating cars on operating track benefit from an independent variable voltage source to improve operation, depending on the type and era of the car.

I think the FT switches work better at around 16VAC.  These are the reasons why I like to keep them all separate, but to each their own.

@CAPPilot posted:

I replaced the diagram in my first post with this one below (both are now the same).  As I mentioned, it was an older diagram.

While the OP did not mention anything about Legacy or TMCC, my original diagram had the Legacy base connected at the transformer, which is not a good place for this connection.  The connection from the Legacy or TMCC based should be on the OUT side of the TIU so the TMCC signal doesn't go through the TIU.  If the loops are not connected together, then the Legacy base wire needs to be connected at each TIU black/common out.

@CAPPilot posted:

The easiest way to add the TIU is in passive mode.  Just run wires from the OUT side of the TIU to the track wires.  I added two additional TVSs because the TVS inside the TIU is not longer in line with the power to the track.

However, the original diagram several posts up is old.  On my test layout I got tired on changing fuses so I now use PSX-AC electronic CBs.  A choke is needed because the PSX seems to degrade the DCS signal.  So this would be an updated diagram:

Yes, probably overkill on TVSs but I bought a 100 of them (cheap) so I am using them.

On my layout, I have the TIUs in passive mode.  I need the PSX-AC CB because I use it to run 15 amps to the track as well as it having a very fast CB.  Here is my setup with at least three TVSs between the transformer and track (one in PSX)

Just getting back to this thread for a refresher.  Appreciate the clear and complete wiring diagrams - very helpful.

One question about something that I just noticed - the diagrams show fast-acting circuit breakers on the Z4000 and PowerMaster outputs.  I thought that these power supplies already contain good quality fast-acting breakers; am I mistaken on this, or are these breakers added in case the built-in ones fail?  (If they're there in case the built-in breaker fails, is such failure common?)