ZW, Lion Chief, TVS, Fuses

You have to protect against 2 different things: Current (AKA Amps) VS Voltage (specifically peak voltage).

In terms of a water analogy, water pressure is Voltage.  Amount of flow is Current (Amps).

So here is the basis of the whole thing. Your transformer is the source of the power. It provides both Voltage and Amperage. The ZW transformer itself at best has a high amperage slow acting thermal based circuit breaker meant more to protect the transformer than any load connected to it.

Fuses and circuit breakers- again, being Current control devices- are placed in series with the load so that the current must flow through them and that's how they can sense and cut off the current flow in a fault condition. Again, internally the ZW has a breaker, but it is way too high of current rating (well over 10A for several seconds, maybe more).

A key point or rule I was taught early was put a fuse or breaker nearest the source. This way, any downstream wiring or connections are also protected. Again, like a river, the fuse or breaker should be near or right at the source of power (in this case, transformer).

You should use individual fuses or circuit breakers on each of the 4 possible outputs of the ZW in series with each load. The fuse or circuit breaker rating should be reasonable and slightly above the normal expected load with some margin, but well below the maximum of 10A typically for most scenarios. I typically stay in the 5 to 7.5A range- especially given the thinner wiring found in many modern locos like Lionchief and rolling stock.

Voltage suppression- AKA TVS:

The problem is that modern electronics have a voltage limit. In other words, the electronic components inside have a maximum (back to the water scenario- pressure) voltage before they break down. Because of capacitance and inductance of the wiring, track, motors and accessories, because we are using rolling wheels to connect electrically, we generate huge amounts of inductive voltage spikes. For the same reasons the spark coil in your car creates huge voltages to jump spark plugs gaps, we in model trains, create these votlage spikes of well over 60 to hundreds of volts.

A TVS (Transient Voltage Suppressor) is used to short (AKA clamp) these voltage spikes. It does so by being put in PARALLEL across the track and power wiring. Again, in order for the TVS to sense the voltage and be able to do something about it, it must be in parallel to the load or source.

@pajoek posted:

Hello everyone, I've read a lot of posts about this topic and I'm just looking for some clarification.

I'm using ZW transformers to power my layout. Nothing "wrong", but just a note, these are fairly heavy duty power sources and have less than great circuit protection built in- hence you concern is valid.

I'm running all post war Lionel in conventional mode- If running these post war engines and accessories at the same time, they have higher inductance, draw more current, and tend to generate a lot of voltage spike events. It doesn't harm them- but anything else electronic- bad news.

but do have a Menard's F3 and a few Lion Chief engines. Again, 2 characteristics of these engines are they have electronics so they will not tolerate a lot of excessive voltage spikes that can break down the electronics. Further, they also have thinner pickup wiring and other details, so derailment shorts where one truck is on the track, one off derailed can result in smoking this internal wiring- also applies to modern lighted or sound equipped rolling stock.

I'm also using a Lionel TMCC Direct Lockon.- This device adds short circuit- AKA current protection in the similar way that a circuit breaker or fuse does. I do not think it adds TVS protection against voltage spikes.

I've decided to follow the recommendations I've read on the posts here. I bought TVS's from Mouser.

What size fuses should I use?Again, using the TMCC Lockon- you technically have a fast acting breaker.

Should they be fast blow or slow blow or doesn't it matter?What about the other circuits or outputs of the ZW not protected by the TMCC Lockon??

Where and how in my circuit does everything connect from transformer to lockon to track?We need how your system is currently wired to give some recommendation

I'm using buss wiring. How?

If the TVS provides protection in the event of a short, does it blow and will it need replaced? TVS tends to fail shorted when they die from too many hard voltage spikes. Since this would short the transformer- we put the TVS AFTER the breaker or fuse so when they fail, they do not sit and cook.

I have no idea how it works but do want the protection it offers. Thank you in advance for reading my post and answering any of my concerns.

Joe

Hello Vernon, thank you for the information. If I understand what you are saying then with the TMCC Direct Lockon I do not need to add any fuses. Am I correct? I am running my hot and common wire around the layout with 14 gauge wire. I'll be dropping feeds every few feet with 16 gauge wire. I'll only be using 2 circuits from my ZW to operate the main layout. I have two lockons.  I have 3 other circuits but I will not be using them for the Menard's F3 or the Lion Chief engines. I do have other transformers. From your drawings are you suggesting a TVS be installed at every track connection as well as after the lockon?  Is there any way to tell if the TVS blows or goes bad?

Thank you,

Joe

I'd also like to add that I won't be mixing motive power. I'll either be running post war with conventional control or I'll use the Menard's F3 and Lion Chief instead, not both together.

@pajoek posted:

From your drawings are you suggesting a TVS be installed at every track connection as well as after the lockon? I would consider that slight overkill. Worse- don't put them in hard to reach places- you might have to reach them. The takeaway is at least one, after the lockon, then, place where easy to get to- easy to replace when needed.

Is there any way to tell if the TVS blows or goes bad? As stated, they tend to short out when failed. See this additional answer https://ogrforum.com/...tvs-protection-diode

Vernon, What if you have star wiring? Where do the TVS go?

@BradFish1 posted:

Vernon, What if you have star wiring? Where do the TVS go?

Not having this debate. TVS, in theory, goes nearest what you are trying to protect- a train, a car, an accessory, a piece of control equipment (TIU or other). Catch22- each TVS is some capacitance that degrades DCS signal if using MTH DCS. Further- again, when/if a TVS fails, they short out- requiring replacement.

So if you go nuts and put one on each feeder, and then have one fail- now you are chasing down a short, and because let's face it, you wired everything together it all looks shorted.

Generally, there is a balance. One external on each TIU output, one maybe at the hub of the star, maybe a few on feeders- but where you can get to them.

All my feeders are 12 to 18" long connected to a 2 position terminal block, fed by block wires from a 12 position MTH buss terminal block. I have a TVS on each 2 position terminal block. There is one MTH block for each fixed output of the TIU. It's been flawless for 10 years. If one goes bad or does its job, I would just disconnect each block at the MTH terminals, one at a time.