Which tvs

Zener Transient Voltage Suppressor.  TVS.

1.5KE27CA DO-201  (1.5KE27)  1500watt.   27volt.  clamps at 37 volts.  non-directional (doesn't matter +-)

I get them on ebay.   cheap.

Conventional; mount across + -  leads to track between transformer and track.

Digital; mount between transformer brick leads + - and before control unit (DCS, etc.) 

I also put one in each of my LED lighted passenger cars, or anything that requires power.

Here’s a couple photos, but you can connect them across a lockon, or between center and outside rail at a power drop connection.  Given your comfort zone inside the engine from power pickup to chassis.  Your choice of location.

I actually recommend a higher value for the clamping voltage for O-gauge model train use, the 1500W 36V TVS at Digikey.  The 27V model can clamp at too low a voltage for O-gauge use.  Peak voltage for 18V RMS is 25.45 volts, very close to the minimum breakdown voltage of the 27V TVS.

 TVS (transient voltage suppressor) across old pw ZW terminals or, as protection on terminal strip equipped with plate jumpers for railpower distribution to multiple track locations. White marked wire from 180 powerhouse is common, green is hot, protecting 5 energized screw heads each side. On layouts with long ovals/ power districts I soldered railpower conductors to every 37" section of Gargraves flex track and between track switches in the Service yards,etc. Thus,  protected distribution strips. I agree with Gun Runner's specification on the TVS.

If you are operating modern engines from a pw ZW  a TVS is a good idea.

So how do you know when to replace them?

Failed shorted, would be easier to identify. Is that common? Do they just fail open? Could we connect a light to them?

Engineer-Joe posted:

So how do you know when to replace them?

Failed shorted, would be easier to identify. Is that common? Do they just fail open? Could we connect a light to them?

Without some pretty sophisticated test equipment, you don't know when they are worn out, and they do wear out.  However, unless you are having all kinds of voltage surges often, in normal "train" use they will last a life time.

hi the only problem you run into when you use TVS diodes around your layout is when one shorts and you have to disconnect one at a time to fi nd the shorted one other then that will SAVE you ELECTRONICS sometimes and it is well worth using them for that purpose!

IMHO

Alan 

gunrunnerjohn posted:

I actually recommend a higher value for the clamping voltage for O-gauge model train use, the 1500W 36V TVS at Digikey.  The 27V model can clamp at too low a voltage for O-gauge use.  Peak voltage for 18V RMS is 25.45 volts, very close to the minimum breakdown voltage of the 27V TVS.

 

I asked an electrical engineer friend of my son who designs electric motors for specific needs and he told me I wanted a TVS that was just above the maximum constant operating voltage of the system.  He said a TVS just begins to break down at that rated voltage and actually clamps at a higher voltage.  So 27 volts is just above 25 volts but it doesn't really clamp down until about 37 volts.  He said too high a clamping voltage is like no TVS at all.

You don't want to be in the breakdown area at all.  The spikes you're really worried about are considerably above the clamping voltage of the one that I posted.  The maximum clamping voltage of the 27V one you specified is 37 volts, that's a specification maximum.  Perhaps this reference for selecting a TVS will help.  Note that they specifically state that the peak voltage in the circuit should NOT be greater than the Reverse Standoff Voltage Specification.  For your 27V TVS, that's 23.1 volts, considerably less than the 18V RMS  peak of 25.45 volts.  Another factor is many transformers, including some Lionel transformers, actually put out 19 or 20 volts, and some MTH transformers even more.

How To Select Transient Voltage Suppressors - Microsemi

I do occasionally know what I'm talking about.

Absolutely!

gunrunnerjohn posted:

You don't want to be in the breakdown area at all.  The spikes you're really worried about are considerably above the clamping voltage of the one that I posted.  The maximum clamping voltage of the 27V one you specified is 37 volts, that's a specification maximum.  Perhaps this reference for selecting a TVS will help.  Note that they specifically state that the peak voltage in the circuit should NOT be greater than the Reverse Standoff Voltage Specification.  For your 27V TVS, that's 23.1 volts, considerably less than the 18V RMS  peak of 25.45 volts.  Another factor is many transformers, including some Lionel transformers, actually put out 19 or 20 volts, and some MTH transformers even more.

How To Select Transient Voltage Suppressors - Microsemi

 

I do occasionally know what I'm talking about.

Well, this is one we will have to agree to disagree on. 

Whatever works for you.

Exactly.

Gentlemen,

   Just upgrade to running DCS, it has built in TVS that has worked for me for years.  No need to argue.

PCRR/Dave

Pine Creek Railroad posted:

Gentlemen,

   Just upgrade to running DCS, it has built in TVS that has worked for me for years.  No need to argue.

PCRR/Dave

Sure spend $300 plus for a lil protection, when all i run is postwar and a new lionchief plus or 2, all this added protection isnt even for the postwar stuff, you cant hurt em, i simply wanted a lil protection and piece of mind for the new 726 Berkshire i purchased this year, $4-500 for an engine isnt anything im going to do regularly, much less over $1000 for the legacy steamers, not when its likely all this newer stuff will end up trashed long before postwar gives up, most of my fleet is 60- 70 years old and still running strong, oil and grease, run em hard week after week, tremendous amounts of fun and laughter,  havent seen any new stuff stand up to the way they used to make em, its all go digital and keep throwing money at it...you need this, you need that, not to mention the cost of the locos, nice ones...forget that, i gladly spend spend a few bucks on tvs for the new stuff i run, added protection, but going digital for protection is counter productive, everyone here still says add tvs to that system too, not the answer i was looking for, thanks anyways..i appreciate those that have given great information.

Happy RR

Glad MTH is putting them in their TIU's.  Would be nice if their engines came with them installed too.  I imagine it would help cut down the warranty work load.

TedW posted:

Here’s a couple photos, but you can connect them across a lockon, or between center and outside rail at a power drop connection.  Given your comfort zone inside the engine from power pickup to chassis.  Your choice of location.

 

so if I install them across my ZW terminals as pictured will that be sufficient or they need to be installed at the point of track connection too?  thank you

Dave Zucal posted:

Glad MTH is putting them in their TIU's.  Would be nice if their engines came with them installed too.  I imagine it would help cut down the warranty work load.

I would point out that MTH didn't use the 27 volt TVS for the reasons I stated previously.

Let me ask a couple of questions. 

If I were to install the exact same spec 33v TVS between the transformer and TIU as MTH installs in the TIU, which would clamp first, or would they both clamp at exactly the same time? 

In a severe voltage spike, which would fry first, or would both fry at the same time?