The absolute best place is, as you indicate, next to the circuit being protected. However, excellent protection is afforded at the last connection for power to the track leads. In the case of really large layouts, it may be useful to add some form of TVS at the opposite end of the layout where the power feeds the track. Having successfully used these devices only at the leads from the source (post control electronics) to the track on layouts with distances of 50' from the the transformer point has lead to zero problems. The layout referenced gets around 250 hours of use a year. Guess this comes down to how much you want to spend for a belt and suspenders solution.
gunrunnerjohn posted:Barry, the TVS is directly across the output terminals, so it's there for passive or active mode.
How can we tell when a TVS placed on the TIU is no longer functioning? Is there a way to test a TVS?
There is a failure mode of the TVS that is not detectable without some sophisticated test equipment. So unless you have this equipment and want to test each TVS on a regular basis, you will not know of this failure. Plus the TVS in the TIU is the 33 volt one, not the 36 volt one recommended on this forum. Because of this, as a minimum I put one at each track connection. This is not as good as John's recommendation to put it inside each engine, but it does put two TVSs between the engine and the transformer.
Because TVSs are cheap, I also have one across the inputs to the terminal blocks. Now that is probably overkill.
Barry Broskowitz posted:John,
the TVS is directly across the output terminals, so it's there for passive or active mode.
I learned new something today - thanks!
I must be missing something here. How does a TVS across the output terminals of a TIU in passive mode protect the engine? The TIU is not between the engine and the transformer. Thanks.
In passive mode the TIU output (with the TVS) is directly across the track. It's like it's connected to the track, but it's connected through the wire to the TIU, so it's farther away from the protected device, hence probably slightly less effective.
Both Barry and John make good points. It still comes down to what is good enough. With the added TVS across the leads to the track from each power source (regardless of what is between the transformer and the track connection) protection is provided. What is protected is any electronics on or connected to the track. Yes, there is failure mode of all electronics and some of us have the equipment to check it. The greater the complexity, the greater opportunity for failure. The TVS can and will provide protection. If someone wants multiple levels of protection, go for it.
CAPPilot posted:... Plus the TVS in the TIU is the 33 volt one, not the 36 volt one recommended on this forum.
FWIW, someone here once explained that the 33 volt TVS was for command control only and the 36 volt was needed for conventional operation due to the offset needed for the Horn/whistle and bell functions. I believe the idea was to use the 36 volt model so everything would be covered no matter what type of train running one was doing.
I have the info saved here somewhere, but I don't recall off hand who originally posted it without trying to find the saved post. If you are interested I will try to find it.
I think another place would be between the engines rollers and chassis ground. (common) Every engine would need one.
Gregg, that's what I've said many times. The absolute best place for them would be in every locomotive on the input power. For obvious reasons, some folks balk at taking a couple hundred locomotives apart to do this. 
Also note that in the practical application, the difference between the 33V and 36V TVS is minuscule as far as protection is concerned. The voltage spikes we're really worried about are a much higher amplitude than the TVS will clamp.
Gunnerrunnerjohn said, "For obvious reasons, some folks balk at taking a couple hundred locomotives apart to do this."
The bottom line really is that in real life there is more than one method to provide protection. Having used a less intrusive, practical solution for many, many years on multiple layouts, I see no reason to spend the time to do addition work. In addition, a detailed technical understanding of the pros and cons does not support the extensive work you suggest. There is no reason to get insulting just because you have a different opinion!
K4s-RRA posted:Gunnerrunnerjohn said, "For obvious reasons, some folks balk at taking a couple hundred locomotives apart to do this."
The bottom line really is that in real life there is more than one method to provide protection. Having used a less intrusive, practical solution for many, many years on multiple layouts, I see no reason to spend the time to do addition work. In addition, a detailed technical understanding of the pros and cons does not support the extensive work you suggest. There is no reason to get insulting just because you have a different opinion!
WOW! Where is that coming from? How do you figure that's insulting you? This was not addressed to you, it was a simple statement of fact. I agree that for most folks, doing all the work to put them inside the locomotive is too much to justify for the protection gained. I'm having a hard time seeing how you're offended by that statement, you seem to be in agreement with it.
Now that you bring it up, I would ask where your detailed technical understanding comes from. Have you done extensive work in high EMI environments and evaluated the pros and cons of various transient suppression solutions? Have you lead a number of products that were subjected to the RTCA DO-160 EMC Testing and got to evaluate first hand the effectiveness of transient suppression techniques?
I'm not sure who was getting insulted here, but I suggest a thicker skin if you thought what I said was an insult!
For obvious reasons
What John said was pretty obvious to me.
Professionally I have had several positions on advanced state-of-the-art satellite programs. These were mostly military programs that had to deal with EMI, ECEMP, SGEMP, and potential nuclear weapon effects. The top two positions were director of engineering and lead engineer both on multi-billion $$ programs. So yes, I have been around the block and understand technical trades to achieve a high level of mission performance while working to keep costs within budgetary bounds. Working on toy train electronics is a walk in the park in comparison.
Being curious and always trying to learn, I just took a look at the Royztrains surge protection device. What will it do for me for $12 that a $0.65 TVS Diode from Digi-Key which I have been using won't do? I may have to order one of these just to see what's inside and check out the circuit.
Also Royz website says their device is designed to limit the voltage spikes or surges to 30 Volts. Isn't that a tad low? I guess it works or they would have had to change something by now. Probably a trivial amount anyway, like the 33 vs 36 volt TVS?
K4s-RRA posted:The Royz Trains Surge protector has more than just the TVS and the cost of the TVS used (sans shipping and overhead) is 57 cents.
Thanks for the reply. I figured that it had additional parts, but I was curious to know what parts. However, I didn't word my question properly, I just re-read it. 
I guess I might just order one and take a look inside. I have a plan around here somewhere for a surge protector that I got from some train club's website. Was just curious if there were any similarities between these two items? Royz is a lot smaller than the train club's verson, but theirs had LEDs to show, I believe, normal/shorted or power/no power or something like that. It's been quite a while since I looked at it. I built one of these, but ended up using PSX-AC's instead, so I never tried it out.
From the description on their site, it sure sounds like a TVS. If you get one, I'd be interested in what is inside.
My curiosity is piqued, I'll send pictures!
Visiting the Forum after a couple of years absence I find it interesting that the same TVS thread of arguments is still being posted regarding Voltage spikes and over-current surges. However a good discussion for newbies and non-believers.
Way back in the day before two savvy, exceptionally helpful EEs , the California upside down operating train guy and the Pennsylvania Gun Runner joined the Forum, an EE from the competing CTT Magazine Forum warned about voltage spikes and their affect on fragile boards and wires in our newer engines. When many, including me, argued that my fuses/fast-acting breakers would protect my engines, he opined that a voltage spike would not trip a breaker as a current surge would. He suggested Transient Voltage Suppressors [TVS] should be installed for the former and fast-acting breakers or fuses for the latter.
I became a believer after replacing a MTH board, fried from a derailment, while my Potter-Brumfield breaker napped for 8-10 seconds before tripping. The only truly fast-acting breaker I ever had was a $90 magnetic unit but at that cost I only bought one. Fortunately Lionel soon offered the 180 watt transformers with electronic breakers which were near fast and a perfect partner for linking with my TPCs.
Now at 85 years far two many of my breakers are tripping and I would would welcome a good surge in the right places.
Happy railroading
.
Dewey Trogdon posted:Now at 85 years far two many of my breakers are tripping and I would would welcome a good surge in the right places.
I'm not 85, but I share your sentiments. 
Thanks for the information.
