mth z-1000

William,

To answer your question, yes you need additional protection for your modern engines.  Here is one potential way to protect them assuming you run conventional only.

I am a little confused on the engines you have.  It sounds like you have engines with both of Lionel's command control systems, TMCC and Legacy, as well as MTH's command control systems PS2 and PS3.  It also looks like you have some MTH PS1 conventional engines.

Do you run conventional only?  Or do you use a command control system to run your trains, like Lionel's Cab1 or Cab2, or MTH's DCS TIU?  Might help better answer your question.

MTH Z1000 brick has a relatively slow acting thermal breaker. IMO, it is not fast enough to protect some of this modern equipment from overcurrent during derailment shorts. Highly recommend something faster or lower amperage rated between your track and the power source.

The MTH Z Controller that is between your track and brick has at least one TVS in it, but that is more to protect the FETs inside the Z controller than the output and thus track from a voltage spike. So yes, I also in the big picture given the cost of repairs, lack of parts (boards) reccomend adding TVS in parallel to the output.

TVS protects against voltage spike generated whenever something draws high current (like a short) and then goes open circuit. This creates hundred of volt if not higher spikes and yes, they can kill modern equipment.

Breakers protect against over current (Amps) that melts and burns up wires, contacts, and so forth.

The only difference I recommend in @CAPPilot's drawing is put the breaker first before the TVS.

Here's the why: The brick and the Z controller are the power source. The TVS can and will short in extreme failure. The idea is the current protection breaker should be between the current source and the load- any load, including the TVS.

Again, very minor change physically, but changes what happens when a TVS fails.

thanks for the replies.what is TVS?i run a mix of legacy and TMCC.I have no DCS system.All MTH engines are run conventionally by way of powermaster lionel 6-12867.lionel says it has  a cuircut breaker.Is this useful?where do I get TVS breakers

Circuit breakers and fuses protect against excess current flow in a circuit.

TVS (Transient Voltage Suppression) Diodes protect against Voltage Spikes within a circuit.  They are a type of Zener Diode.  Ones for use in Alternating Current circuits are bi-directional.  They will become conductive when the voltage across them reaches the TVS's breakdown point.  This selective conductivity appears as a brief partial short (by varying their resistance) across the voltage source(s), thereby limiting the voltage to other components in the circuit.

The ones recommended here on the forum for use with O Gauge Trains are the 1.5KE39CA

Here's a link to where they can be found in stock at present:

https://www.mouser.com/Product...4E6o59DLOItJEQ%3D%3D

The other notable thing about Voltage spikes on a model railroad layout is that they can be generated at very high frequencies (up to 1GHz) with very short wavelengths, approaching 1 inch.  The best place to install TVS diodes to provide protection against these high frequency spikes is as close to the sensitive electronics as possible.  I like to install them inside my locomotives where the track power wires connect to the motor control circuit board input.

Here's a link to a Post by Adrian! with a very good explanation about why the best place to install TVS diodes is as close as possible to the electronics you want to protect.:

https://ogrforum.ogaugerr.com/...-about-tvs-placement

@Adrian! posted:

This comes up on many threads over and over so here's a simple explanation all consolidated into a single thread.

A TVS goes in the system to prevent over-voltage stress from damaging electronics. This is different than a fuse or circuit breaker that protects from over-current stress. Unlike current at low frequency (60 Hz for most layouts) the transient voltage events that result from derailments, collisions, and general sparking are very broadband transient events, usually in the range of 1ns to 100ns.

That means they are a wave function, like a pulse of voltage bouncing up and down the wiring that has a fixed length, not like a continuous current flowing through it. At 1ns (so 1 GHz bandwidth) the wavelength in air is 11.8 inches and in RF we usually say 1/4 wave is where the wave effects start to matter.... so about 3 inches in air. However cables are not air and have a slower wave velocity depending on their dielectric constant (a property of the insulator) and their physical geometry (diameter, and how far apart the + and - are). All in all ... you can think of transient pulses as about a 1 inch wide event.

So if you put a TVS into a circuit and that TVS is more than an inch away from the thing you're trying to protect, chances are you're not actually protecting it because of the wave effects.

See the handy diagram below that explains what's going on. The bird is your electronics and the guy waving the rope is the train, making angry waves. If you pinch the cable in the wrong place (that's what a TVS does, clamp the cable voltage) the bird still gets bounced. The only way to avoid this is to do the pinching near the bird, in this case within the 1 inch.

and that's why the TVS needs to go in the locomotive right by the board, or in the TIU right by the drivers.

If you want a much more academic understanding.... Take a look at the telegrapher's equation.

steve how do I install them.I apologive for my ignorance.are the soldered?I would not know where to intall them on a legacy engine,nor do I have the knowledge to work on sensitive electronics.thanks for the info you have given me

@William Kolina 122419 posted:

steve how do I install them.I apologive for my ignorance.are the soldered?I would not know where to intall them on a legacy engine,nor do I have the knowledge to work on sensitive electronics.thanks for the info you have given me

William, no need to apologize.  We all learn new stuff at different times.

You are correct, solder is the best way, in my opinion, to splice a TVS diode onto the two wires (hot and common) that feed track power into the motor control circuit board.  I prefer to shorten the diode leads as much as possible and cover the bare leads and solder connections with heat shrink tubing to prevent shorting.

If you feel comfortable soldering, it's relatively easy to do.

Here is an example:

On this locomotive, the Black wire is Common and Red is Hot.  To verify that I had the correct connections, I traced the wires visually and used an Ohm-meter from the frame and center rail pick-up rollers, respectively.