TVS placement in PS2 PS3

Correct, directly across the track voltage.

Why doesn't MTH do this? 

For that matter, why doesn't Lionel?

i thought somebody[ gunrunner]? was installing these closer to the board for better circuit board protection. if i am not mistaken the red wires and black wires which have wire nuts each are rail power. i have 9 locomotives..some 3 rail and some 2 rail..some ps3 some ps2 and the latest Rev L TIU.

Nope, anywhere inside the engine and directly on the pickup leads is correct.  I typically put them up where many locomotives have the wire nuts, easier to mount them there.

Willy,

Everyone has their own idea as to where to put the TVS, but since the transformer is what produces the spikes, I would install it at the transformer outputs. Installing 2 at the same place might be a good idea encase one blows apart you'll still be protected.

Having build avionics for many years, I can tell you that the most effective place for the TVS, or any transient protection, is close to the circuit you're protecting.  It's not bad to have a TVS across the transformer, but the best protection for an individual engine is right across the pickups.

I would agree with you if the engine was in danger of lightening or spikes after the transformer, but it's more likely to happen with derailments causing spikes to come from the transformer with model trains in my opinion. And it's much easier to install them across transformer terminals. I never run trains when lightening's around.

Why do you think that the transformer is the only place that spikes could be generated?  Any inductance around the layout connected to power could cause a spike on a derailment.  Also, the TVS isn't as effective when there's 50 feet of wire and/or track between me and the TVS.

Let's agree to disagree on this topic, you have your knowledge, and I have mine.  I'll trust mine on this particular point as it's been proven by years of experience.

You may be right, but where would the voltage get induced from if not the transformer?

Any current that is flowing through an inductance will generate a voltage spike if the current changes rapidly (as with a derailment.)  The quickly rising current can generate a voltage, but probably even worse is the spike generated when the current is interrupted - even if the interrupter is a fuse or circuit breaker.

So if you didn't want all the trouble of installing TVS in all your engines, where would the second best place be? I know the TIU has them already.

I'd probably just distribute a few around across the track supplies.  I am not opening up engines just to put a TVS in them, but when I have them open for other reasons, I try to stick one in as well.

I see Dale has answered the other question.

That sounds reasonable

You see I ran these trains for at least 5 to 6  years with just a transformer before getting the DCS system and never had a problem even with derailments taking out a board. I don't think it's a good idea to have everyone thinking you need this extra protection in their engines when it can be placed in plain view easily. And it's much easier to check if one goes bad. It may even void their warranty installing these in new engines.

It may also not be a good idea to take a sample of one and extrapolate the whole of all user experiences.

Electronics do fail on derailments, one only has to read the forum for a period of time to figure that out.  Would a TVS in each engine help statistically?  I believe it would, and I have years of experience in design of transient protection for critical systems to back that up.

Do you need a TVS in every locomotive?  Probably not.  Do you need Flood Insurance if your area hasn't flooded in the last 100 years?  Probably not.  However, ask the folks in Staten Island if they needed flood insurance for the 100 year flood, many will say they wished they had it.

The TVS, or any other protective measure, is like insurance.  It's not likely you'll need it, but if you do, it saves you a bunch of money and time.

Avionics probably sets the bar for required circuit protection for obvious reasons..i see no reason not to extend this to my railroad electronics. I can understand the apprehension with the electronics in your locomotives. I did automotive and marine dio and repair for years so i actually enjoy electronics. I do out of habit wear an antistatic wristband and use electronic safe [screw drivers with plastic shanks]tools.

John,

This (underlined, above) sounds like a good option.

I have a good number of MOV's left over from long ago projects, but have not heard them mentioned. [MOV - Metal Oxide Varistors]. Wouldn't the MOV's work also?

Thx!

Alex

I'd forget the MOV's and use the TVS diode.   MOV's have more capacitance than a TVS and may affect DCS signals.  Also, MOV's deteriorate as they absorb surges, where the TVS doesn't.

I think you have missed my point. I'm not saying you shouldn't use a TVS as they are also used in the TIU. It's just that they are easier to be placed on the track instead of the engine. Especially for the average operator who doesn't want to open up all his engines and install a TVS with a chance of pinching a wire.

I don't think I missed the point at all.  I'm saying the best protection is in the engine, distributed TVS protection around the track is next, and a single one on the transformer output feed is better than nothing.

Thanks

John thats what I wanted to hear.

Thank you

Clem 

Thanks, John -

I'll get some TVS.

Alex