Breakers, TVS diodes and the ZW-L

The ZW-L circuit protection is more than adequate.  TVS diodes are always a good idea.

The ZW-L, like all earlier iterations(and PH 135/180 bricks), has no native protection against transient voltage spikes. If you are running equipment prior to 1972, this is a non-issue, but the newer your stuff is, the more important TVS diode protection is to have.

Thanx Marty & Robb.

I have the ZW-L and have installed TVS”s on both A and D outputs.  I don’t have any accessories so no need for the other two outputs.

Additional circuit breakers are not necessary but TVS’s are cheap protection.

This old thread is exactly my question.  I now have 3 command locomotives, 4 older locomotives along with some postwar powered units (6 trolleys, 3 gang cars, 1 fire car, and an inspection car).  I'm not really running things now, but hope to be within 6 months.  I've been considering getting a second mortgage on the house so I could afford a ZW-L () because of the circuit protection (not sure if that's the right term).  I have to ask if the TVS diodes are only needed between the posts of the ZW-L?  I've looked at threads where the recommendation is to install a TVS diode in the engine itself, along with one on the posts of the ZW.  Is installing a TVS diode in the engine not necessary with the ZW-L?

In theory installing the tvs on the engine is a further protection, since you are protecting it right at the engine, in case a spike got past the tvs upstream. To me that is overkill, and then you have the bother when the TVS has died of having to open the engine up and replace it. Regardless of whether you put a tvs on the transformer outputs, across the track feeds, or engine+upstream, you need that with any transformer. As Rob pointed out, no transformer has built in spike protection so you need a tvs with the zw-l. If you don't mind the work, having one on the engine and upstream across the power output is additional insurance. Just make sure to check the tvs in the engine, as across the output, to make sure it is still good (and again, that is true with any transformer, new or old), they wear out.

Thanks, @bigkid.  Your answer jives with my 6 month old recollection about it.  I'm glad you called it overkill.  I had a no-delay circuit breaker on my old layout, along with TVS diodes on the postwar ZW, along with having a TVS diode installed in my one and only (at the time) command engine.  The electronic whizzos on OGR can install a diode in the engine and make it look like a factory-installed part.  My installation will work, but even I say 'That looks like a second grader did it.'.  So, I'd rather not install one in the engine, just on the posts.

How does one know when the TVS diode needs to be replaced ?  Is there a regular maintenance period where you replace it annually ?

Remember- your power strips with surge protectors need to be changed about every three years; the surge protection begins to fail.  These protect the layout (and TVs., stereo equipment, and computer equipment) from line surges in the home.  Also- if a surge protector does its job as in a lightning strike, it need to be replaced.

@IC Gulf posted:

How does one know when the TVS diode needs to be replaced ?  Is there a regular maintenance period where you replace it annually ?

When they fail, typically they fail shorted.  As such, being in parallel to the track and parallel to your power source, they get very hot when shorted.

If, and this is a big if, you have a big enough surge event to blow one open circuit- then you look for the massive burn mark and crater where the TVS was and is now vaporized.

If you want to replace them yearly to every 3 years, they are cheap enough- consider it a maintenance cost.

Again, the more obvious answer is replace them when they fail, and most likely- you are going to know, because you have a dead short across your power supply.

@bigkid posted:

In theory installing the tvs on the engine is a further protection, since you are protecting it right at the engine, in case a spike got past the tvs upstream. To me that is overkill, and then you have the bother when the TVS has died of having to open the engine up and replace it. Regardless of whether you put a tvs on the transformer outputs, across the track feeds, or engine+upstream, you need that with any transformer. As Rob pointed out, no transformer has built in spike protection so you need a tvs with the zw-l. If you don't mind the work, having one on the engine and upstream across the power output is additional insurance. Just make sure to check the tvs in the engine, as across the output, to make sure it is still good (and again, that is true with any transformer, new or old), they wear out.

You miss the point about how transients act, a random placement of the TVS diode is a crap shoot as to whether it's effective.  @Adrian! explained it far better than I could and included graphics, see link below.  In point of fact, the only place that it's most likely to actually have the desired effect is right at the connection to the electronics in the locomotive.

Adrian!'s Words about TVS Placement

Hey @gunrunnerjohn....

I (like I'm sure many) have installed TVS diodes on the transformer outputs or the TIU outputs or on the power distribution blocks.

But I've always wonder now many model railroaders have actually opened up their digital engines and installed TVS diodes inside their engines.

I have not done this only because I'm fearful of adding the diode incorrectly and "toasting" the onboard electronics.

Have any forum subscribers running Command actually done this?

Thanks for the info, and I can see why putting it in the engine is really the only way to truly limit spike damage. That said, it also can be daunting for people who have never opened up one of these beasts to put one in.I would assumed that you put it across the power feed coming in from the roller and ground which is definitely upstream of the boards. I forgot about spikes upstream from where you have it and why the closer is better.

@Junior posted:

Have any forum subscribers running Command actually done this?

I've done it to locomotives I have open for some other reason.  I have not cracked them open just to install a TVS.