Voltage spikes and TVSs

Please explain what TVS means so I can learn?  Thanks

Those will work for all your trains. The TVS is for the trains & electronics, not the transformers.

Transient Voltage Suppression

Thanks for the reply Rob.  I understand they protect the electronics, but what I'm not clear on is the rating of the TVS.  It is also my understanding that different (sized) transformers can produce larger voltage spikes given their rated output.  Am I incorrect in this belief?

Is a 36-volt TVS suffiecient or can a lower rated one work in my application?  I believe the 1.5KE36CA has an operating voltage of 30.8v?  So would 1.5KE36CA TVSs be fine to use on my layout and installed on my trains?  Thanks again for your reply.

I use a voltage suppressor from Scott's and a bank of fast blow fuses - one fuse per block, siding, etc.  Here's a link for info http://www.trainelectrics.com/...age-suppression.html Mine is the predecessor to the suppressor shown, but then again I bought and installed it nearly ten years ago when we started getting electronics equipped engines from L-AF, SHS, and AM.  A short or sparks will create a spike or spikes and this suppressor detects that and stops current from flowing.  Spikes can be of 2-3X nominal voltage in value although very briefly.  The suppressor will even throw itself down (for good) if severe enough conditions persist.  Here's an example how I know it's working, when I run my Gilbert 741 hand car, the hand car runs along fine (sparking wheels and all) and soon stops.  The suppressor does not tolerate the voltage spikes from the sparking wheels of the original 741 which BTW draws more current (higher value spikes) than the modern can motor copy.  I cut power, remove the old 741, wait a minute, and everything goes to back to normal.  I use 7A fast blow fuses on my S tracks and 3A for my Sn42 (On30) DCC controlled loops.  10A is what most O gaugers use.  I have found 7 and 3 respectively serve their purpose well without being "over-reactive".  Nothing throws or blows faster than a properly spec'd fast-blow.  No resettable fuse comes close in reaction/activation time.  Sure there's the hassle and cost of replacing them when blown, but what's that compared to the potential hassles and costs of a damaged modern engine.  Where did I learn about the preventative measures of a suppressor like Scott's Odds and Ends unit and fast blow fuses?  From reading O gauge forums and adapting that to S.  O gaugers got TMCC in 1995.  We (S) got it in 2005.  They also got very expensive engines to protect that much sooner that we as well.  I have been pleased with the protection this approach provides.  Try it.  You might like it too. 

Thanks Rob and Sgaugian.  Invaluable info; it's greatly appreciated.  I got my parts on order.  Thank you again.

Check out electro-magnetic mechanical adjustable/resettable instant breakers like the Lionel #91. Very fast(faster than any fuse), and non-consumable.

Also, a TVS diode does not stop the current flow, it clamps the voltage to a specified maximum by bleeding it to a short circuit(only the over voltage, and there is no induction in a diode).

TVS diodes.......the best possible 50 cent investment you could possibly make. Dirt cheap and worth their weight in gold.

Roger

ADXRob - maybe, but take 15-18VAC and short a contact point resettable unit, then a 7A fast blow.  I predict you'll see the difference in reaction time -- without an oscilloscope.  

The 91 is not "contact point resettable", and it's not thermal. It's electro-magnetic.

It has contact points - see the diagram.  It is resettable - push the reset button (it is not, however, self or auto resetting).  It is not thermal, agreed, no one said it was.  

You are correct here - the 91 will trip much faster.

Check the other circuit breaker thread later today. I'm going to post  a video of my "new" 91s in action with all the others I used to use still connected. Very cool

Roger

Rob,

You said it all in short paragraph. So much can be written about the topic when all that's needed is a, "Advanced Search" on ,"TVS". Other than this it's all a matter of opinion. I too enjoy reading about the,"old school" techniques. Sometimes these threads lead to old time shouting contests and frustration. I assure you that the bottom line is nothing short of comical.

God Bless,

"Pappy"

Regarding the original question, it is best to actually measure the maximum output voltages from your transformers.  Some people live in areas where the line voltage is frequently or always on the high side of the tolerance for the nominal 117/120 VAC that we expect.  This will lead to a higher output voltage.

The TVS is rated for the peak of the sine waveform.  A nominal 18V output has a peak of 18 x 1.4 = about 26V.  If the line voltage is 10% high, that becomes almost 30V.

I have used 30V or 33V units on plain bricks and 36V units on older transformers that have a voltage boost circuit for when the whistle/horn is activated.

Dale, thank you for that extremely valuable information.  Very specific to my original question.