diragram on how to put TVs in a a locomotive and steam engine..

Yes, one side to the roller and the other side to chassis (ground). I believe this is a TVS that is recommended.

Larry

I really wasn't kidding, wire it like you were trying to short out the track power coming into the locomotive.

lets see if I have it wright..heres a drawing of it..see if I have it wright..

Ok what is a TVS and what does it do?  I'm curious cause Gunrunner is usually dead on with mods.  

If you have a power surge do to derailment the TVs helps protect your circuit boards from getting fried from the surge..

TVS=transient-voltage-suppression diode.  Basically a spike protector to protect the engine's electronics.  Zener is another type of diode you might see used in a similar fashion.

Could someone clear up the TVS polarity?  Which side to ground?

the silver stripes end of it is possitive...but from what gunner.john told me it doesn't mater..its bipolar...

A Zener diode is a simple voltage regulating device that clamps an over voltage to it's breakdown (Zener) voltage. It does no clamping if the applied voltage is under it's breakdown voltage. Use a true TVS for protection.

Larry

Polarity does not matter with a TVS

i usually put one right across the two posts of each transformer output.

The Z-4000 makes this really easy since it has small holes drilled right through each binding post already. It doesn't get easier than that.

Arguably the transformer is the best location to install a TVS because it is generally the source of back EMF spikes resulting from making or breaking a circuit.

I also put them at each main terminal strip and junction block.

They cost under 50 cents a piece.

Rod

Please note that there are two types of TVS diodes, so make sure you have the bipolar models for AC use.  Here is a suitable TVS for model train voltages, and it is the proper bipolar version.

1.5KE36CA at Digikey

Additional reading for those that are curious what the TVS diode does.

What's a TVS Diode

Yep those are the ones I got...john is my drawing wright on how I should put my TVs at?

josey;

If I may jump in here; from what I can see your connections are correct.

But the hots will tie together at some point, either at the plug on the steam engine, or the board on the diesel.

So you don't need two TVS in each engine. One will do, connected between the common hot point and the chassis (outside wheel) ground.

I think that is what folks have been trying to convey to you all along.

Rod

Rod has it, only one TVS is required, the two won't hurt anything, but they're overkill.

OK then why does mth got two wires comming out  of the hot and ground plug from the board for..can tie the ground together at the plug and do the same with the hot positive side too?

If you could post a picture of what you are referring to, we may be able to comment intelligently.

Rod

Regardless of how it is wired, if you hook up one TVS the way you have it drawn, that will effectively kill any transient voltage spike that arrives at the engine.

The easiest place to wire it would likely be where the red wire screw connects to the insulated pass-through that is directly above the pickup roller. The other end to any convenient chassis ground screw.

Many MTH's have both the hot roller screw and ground screw adjacent to one another.

Rod

I usually find the spot where the roller connections come together and connect it there.  Many times it's a wire nut that you can just add another wire to.  Put some short jumpers on the TVS and wire it in.

Once again, you only need one.  I have never seen a locomotive that didn't connect the rollers together at some point, so electrically they're all one circuit.

I think we've beat this to death, so this will be my last post on the topic!

My Goodness! John, What happened to all of your stored up patience?

"Pappy"

well its done..thought to do it this way..get it closed to the source..does run great too..

Is there a disadvantage to just mounting the TVS to the track?

wouldnt hurt to do both..or do the transformer instead of the track..but would be best to add tvs to the loco because of the electronics in there that can use the protection..

IMO the transformer is the easiest and best place to put a TVS. 

But some folks like to do each engine as well. No problem with that. 

Rod

The reason I was asking is that the transformer is basically an inductor. If you think about the circuit you have Ltransformer + Lwiring + Ltrack where L=Inductance. When you have a derailment you would think the inductive voltage spike would occur at the derailment as the train wheels are intermittently shorting out the transformer. Without knowing the inductance of the track and wiring, I would think the transformers inductance dominates the inductance of the track + the wiring. Given that the transformer would be the majority of the inductance, the majority of the voltage spike should occur across the transformers output terminals. I would assume its ok to place the TVS diode at the transformer. This is what I do. I was just looking for the input of the more senior members. I'm just a young EE.

If you always run on your own layout then not really. If you run your engine on a club layout then there is an advantage to putting the TVS in the engine too.