How do you determine when TVS diodes have lost their effectiveness?

yes the more often you get track shorts or derails the sooner it might failed shorted, if it shorts you'll know but if it opens you will have no protection and voltage transients, spikes  will damage what ever was trying to be protected. now  if a tv diode fails open in an tiu you will lose protection and the tiu will be damaged and loose signal  gradually depending how many 244 ic's fail. there is one in each channel. 4 channels total! If a tvs diode fails open in your engine it might damage the board, but if in a engine and fails shorted your engine will stop and z4000 track short light will light letting you know you have a short somewhere ! 

FlyPlanes-PlayTrains posted:

Finally getting around to adding these, and fast blow external fuses to my KW.  

   Do the TVS diodes expire from a derailment?  Do they age & need changed semi-regularly?   I’m assuming there’s a way to test them, an ohmmeter’s probe on each leg showing infinite resistance perhaps?

TVS diodes fail sorted about 80-90% of the time, and then it's obvious that they're dead.  There's no practical in-circuit test for open TVS diodes as the testing involves significant voltages to force the component into conduction.  It's actually not that common to find them open.

   Is TVS diode placement needed on a track power bus that’s fed by a PH-135?  I know the powerhouse has the fast circuit breaker, but do they also contain an internal TVS type feature?

Let's dispense with one myth.  The PH135 does NOT have a fast circuit breaker, that's the PH180.  The PH135 has an ordinary fairly slow thermal circuit breaker.  There are no TVS protection diodes in any transformer that I'm aware of, perhaps the very latest ones like the ZW-L might have them, I haven't checked.

It's a good idea to put a TVS diode on any track feed from the transformer.  It's not only the transformer that generates spikes, any inductive load that is suddenly disconnected from power can generate voltage transients of hundreds of volts.  Think about how an old-time car spark coil works.

Great stuff guys, thank you!

If I’m understanding correctly, a failed open diode will essentially act as if I have the hot & common terminals connected together.  

Also, I didn’t realize the PH135’s breaker was “slow” by comparison.  Going to add a fast external fuse there as well. 

Tom

FlyPlanes-PlayTrains posted:

If I’m understanding correctly, a failed open diode will essentially act as if I have the hot & common terminals connected together.  Tom

Tom I think it's the other way around.  A shorted TVS is like having the hot & common terminals connected together.  Guns will correct me if I'm wrong.

A TVS Diode failed open acts like it just isn't there.

Corrections are... correct!   An open TVS diode is simply AOL, the shorted one will trip your breaker or blow the fuse on the spot.

Yes, the PH135 breaker is nothing special, and certainly nothing like the electronic breaker in the PH180.

gunrunnerjohn posted:

FlyPlanes-PlayTrains posted:

   Do the TVS diodes expire from a derailment?  Do they age & need changed semi-regularly?   I’m assuming there’s a way to test them, an ohmmeter’s probe on each leg showing infinite resistance perhaps?

TVS diodes fail sorted about 80-90% of the time, and then it's obvious that they're dead.  There's no practical in-circuit test for open TVS diodes as the testing involves significant voltages to force the component into conduction.  It's actually not that common to find them open.

 

 

So if your breaker trips and there is no explanation for it (nothing on the track), start replacing your TVS diodes on that circuit until the breaker stays closed.  Right?

Well, you don't need a ton of TVS diodes, so it shouldn't be that much issue to find it.  I have recommended to folks to add a 10A fuse in series with the TVS, and if you're really anal, you can add an 18V bulb (or LED & Resistor) across the fuse.  That way if the TVS shorts, the fuse blows and the light lights to tell you.