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The answer depends on what you're using to power your layout.  Please post the model numbers for your transformer(s) and any other power control devices you're using such as the Legacy Powermaster or TPC and which models.  If you're also using MTH DCS, which units?

Other needed information would include how many independently wired track loops you have and how many locomotives you plan to run on each loop at the same time.

This information will provide a good starting point to answer your question.

Last edited by SteveH

Thanks for taking the time to identify what info is important for your response.

here is my input:

1. I run a home layout with 5 grandsons ,ages 5-15.  They are careful but make mistakes.

2. I have 5 circuits I wish to protect

3.I use two Lionel ZWs and 1034 to power my layout.

4.I run MTH DCS with 1 TIU and 2 AIUs, using handheld MTH remotes or an iPad.

5. At maximum, we run 2 engines (post war Lionel)and/or MTH ps-2 (on an inner and outer loop) , and one post war trolley circuit.  These are used most of the time.  But I also have two circuits and two separate tracks that run off  Momentary push buttons for fire car and a gang car.

Hope this helps and thanks for your thoughts.

Jack

I can say that agree with wanting to protect your trains from the potential damage that a stock ZW can do especially during derailments.  In addition to breakers installed external to the PW ZW, also adding TVS diode protection would help.

275W PW ZW x 75% efficiency = 206 Watts output typical

206W/20V = 10.6 Amps nominal out



Since I don't have any experience with DCS, someone else would be better suited to making recommendations for that.  To make the answer easier for that person, I'm including links to some possible so called "Instant Trip" options.  Choosing the correct current rating and trip delay time are also important factors to consider.

Links to where to buy Airpax Snapac "Instant" trip Series Breakers

5 Amp
PP11-0-5.00A-OB-V
https://www.onlinecomponents.c...00aobv-10090638.html

7.5 Amp
PP11-0-7.50A-OC-V
https://www.onlinecomponents.c...50aocv-10090644.html

10 Amp
PP11-0-10.0A-OB-V
https://www.onlinecomponents.c...0aobv-10090622.html#

@IRON HORSE posted:

So if you went with a 10 amp and that overstated your power requirements, it wouldn't really protect your stuff from overload because the circuit wouldn't break until it reached past that point, right?  Am I understanding this post correctly?  I am asking because I'm wondering if I may need circuit breakers for my twin Z4000s as I run 5 PS3 engines at a time on a TIU using DCS.

Breaker sizing is to protect the secondary winding in the transformer, and that is all.  Getting a good magnetic "instant" trip breaker is to remove current as quickly as possible after a short.  This can help to reduce the chances something gets damaged by wild voltage swings when a derailed loco is shorting, then not, then shorting again during a derailment.

There is no silver bullet, but a TVS diode combined with a breaker like above or one of the PSX1 devices is your best bet to protect engines with sensitive electronics (and your TIU).

For the Z4000, I'm not positive, but I thought it had pretty good circuit breakers, someone else can comment on that part as I do not own one.

Last edited by rplst8
@rplst8 posted:

Breaker sizing is to protect the secondary winding in the transformer, and that is all.  Getting a good magnetic "instant" trip breaker is to remove current as quickly as possible after a short.  This can help to reduce the chances something gets damaged by wild voltage swings when a derailed loco is shorting, then not, then shorting again during a derailment.

There is no silver bullet, but a TVS diode combined with a breaker like above or one of the PSX1 devices is your best bet to protect engines with sensitive electronics (and your TIU).

For the Z4000, I'm not positive, but I thought it had pretty good circuit breakers, someone else can comment on that part as I do not own one.

The only fast-acting breakers on the Z4K are 5he fixed voltage outputs. They trip instantly. The breakers for the track power outputs are very slow and I wouldn't rely on them to break an overloaded circuit. I was very surprised to learn this after I bought 2 brand new Z4Ks.

I "eavesdropped" on this conversation, since I need circuit breaker protection for track power provided by a MTH Z1000 to my modest size L-shaped layout. As I understand it, the circuit breaker built-in to the Z1000 isn't fast enough to protect the circuit boards in my MTH Aerotrain (with PS3) in event of a derailment. So I ordered the 10 amp circuit breaker cited in the thread.

Then I read that this circuit breaker is intended to protect the TRANSFORMER, not the circuitry in a locomotive. Maybe I wasted money on a 10 amp circuit breaker?

Mike Mottler    LCCA 12394
mottlermike10@gmail.com

Mike, the breaker needs to be sized to be less than or equal to output of the transformer.  As I understand it. the max rated output of the Z1000 is 100Watts.  That would be a 5 Amp max breaker.  A 10Amp breaker shouldn't ever trip on this transformer and would not offer additional protection.  If you recently, placed your order you may still be able to call Online Components and cancel or change your order.

TVS diodes in combination with a very fast breaker will help protect the other electronics in a derailment.

Last edited by SteveH

I "eavesdropped" on this conversation, since I need circuit breaker protection for track power provided by a MTH Z1000 to my modest size L-shaped layout. As I understand it, the circuit breaker built-in to the Z1000 isn't fast enough to protect the circuit boards in my MTH Aerotrain (with PS3) in event of a derailment. So I ordered the 10 amp circuit breaker cited in the thread.

Then I read that this circuit breaker is intended to protect the TRANSFORMER, not the circuitry in a locomotive. Maybe I wasted money on a 10 amp circuit breaker?

In addition to what SteveH said, let me explain in a little more detail.  There are really two overcurrent failure modes that we’re looking to solve here. One is protection of the transformer windings.  This is a slow, time vs. heat dissipation problem.  

The transformer is made from copper wire and all wire has a current carrying capacity.  When the rated current of a piece of wire is exceeded, it doesn’t instantaneously explode, or even melt.  It begins to heat up on a sliding scale.  Eventually, yes it could melt, or catch fire, but pulling 7.1A through a wire rated for 7A does not spell doom.  However, in a transformer the wire does not have any insulation, just a coating of varnish.  If that melts, it will short the winding and then a LOT of current can flow totally destroying the transformer.

Ideally we want a breaker that will allow us to pull the rated output power of the transformer without nuisance trips, yet save us when we try to put one too many lighted cars on the tracks.

Generally speaking many, if not most, manufacturers “cheat” by using thermal breakers and downsizing them so protect the transformer.  This works because thermal breakers have a natural trip curve where at 1x rated capacity it might take 2 hours to trip.  At 2x capacity it might trip in 1 min.  Who runs their transformers near max capacity for 2 hours straight?  Not many I’d wager.

The second overcurrent failure mode is a short circuit.  Here, because the resistance is near zero, A LOT of current will flow quickly.  This will typically heat up a thermal breaker very fast and cause it to trip in seconds.  However during a derailment, contact is often on again off again on again possibly not long enough to heat a thermal breaker or trip a “slow” magnetic one.  While this is going on, each short, open, short, spark, etc. is causing wild voltage swings.  It’s these high voltages that can damage electronics.  

It is for this reason many of us have become interested in “instant” magnetic breakers.  They trip so fast that once the first short happens, the circuit is disconnected, reducing the time, and therefore probability of damage.  Combined with TVS diodes, this is a layered protection strategy to help prevent damage from accidents on the rails.

Last edited by rplst8

@rplst8 Ryan, thank you for taking the time to write an excellent explanation of the issues we're trying to address with the instant breakers and TVS diodes working in combination to prevent damage to our train's electronics.  My hasty reply just before dinner was in the hope that @Mike H Mottler might still be able call to change or cancel his order before Online Components in Arizona closed today.

To anyone considering the purchase of one of these "instant" trip breakers, if you are unsure of which particular model to choose, I'm sure someone here in the Electrical Forum would be happy to offer guidance on the right one(s) based on your individual circumstances (transformer and number and types of locomotives and cars you typically run on your layout).

Last edited by SteveH

Steve H.

Thanks for your follow-up comment.  With a good intention, I placed the order for the circuit breaker. But I cancelled it with the hope that I'm not too late to avoid a misguided purchase.

Meanwhile, I'm considering a second Lionel "trackside cabinet" accessory that is a fast-acting circuit breaker for my layout. I already have one in the track power circuit fed by a Lionel Powerhouse "brick."  I need another one for the track power circuit fed by a MTH Z1000.

Mike Mottler     LCCA 12394
mottlermike10@gmail.com

I believe the The Lionel TMCC Direct Lockon SKU: 6-34120 (135W setting) breaker's trip current would a bit too high to provide adequate protection with the Z-1000.

There are a few electrical fundamentals in addition to the trip delay time one should understand when choosing a breaker. The transformer Output ratings are a good place to start.  Here's what they mean:

Volts - (electrical energy potential) in Conventional operation this sets the train speed.
Amps (current flow) - More Locos, cars and such (and shorts) pull more current through the circuit from the transformer.  The transformer only delivers as much current as required by the load, up to a point.  This point is it's Output rating.

AC Transformer Output ratings are usually given in either Watts or VoltAmps, both of which have essentially the same meaning when choosing breaker size.

Watts = Volts x Amps = VA   or    Watts/Volts = Amps


From the MTH website: Z-1000 Owner's Manual

It shows a 6Amp breaker inside the transformer housing.  This is presumably a thermal (slower) breaker designed to protect the transformer from overload.
Output: 14VAC 80W
             18VAC 100W

Current at 18V = 5.56 Amps, or at 14V = 5.7 Amps

Given all this information, if you are interested in providing faster protection than the Z-1000 internal 6A thermal breaker, I believe the 5A Airpax Instant might be a good choice for you, especially if you also add TVS protection are recommended.

PP11-0-5.00A-OB-V   https://www.onlinecomponents.c...00aobv-10090638.html

I hope this helps.

Last edited by SteveH

Steve H.
Thanks for the add'l info. I was too late to cancel my initial order for a 10 amp circuit breaker, so I place another order for the 5 amp version.  What is a TVS and where can I order one? I'll add that to the circuit.

GRJ:
I'll rely on the 5A circuit breaker and TVS for circuit protection; not the Lionel direct lock-on based on your comment.

With appreciation,

Mike Mottler   LCCA 12394
mottlermike10@gmail.com

mott

@Casper I'm not very familiar with the Z4000 and before you buy breakers, maybe someone who is could confirm.  According to a quick look at the Z4000 Manual, it's track outputs are 180W each.

I think one 10Amp Airpax Snapac "instant" breaker on each variable track output may be a good match with the Z4000, but not on it's Aux outputs.  I believe the Aux outputs may be rated for less wattage.

Steve H.

Today I placed an order online for 10 TVS devices. More than I need, but they're cheap; I'll have extras in event of burn-outs.  I intend to place them on my L-shaped layout in the track power circuit between the MTH Z1000 transformer output and the MTH Remote Commander receiver.

OR ... should the TVS be installed after the MTH Remote Commander and the track lock-on?  I'm a novice at this device ...

With appreciation,

Mike Mottler     LCCA 12394
mottlermike10@gmail.com

Edit:  I see GRJ beat me to this, but maybe this is still helpful.

Mike, I'm also somewhat of a novice with TVS diodes, but I've been studying it and reading the advice of others with more experience and an in depth understanding of Transient Voltage propagation. I'm especially a novice when it comes to working with DCS control and wiring.

What I think I understand correctly from what others more knowledgeable than me have written (and makes sense) is that the closer the TVS diodes are to what they're intended to protect the better they protect it.  The ideal place would be in the trains right next to their sensitive electronics, wired directly across the incoming power wires at the circuit board end.  Additional places throughout the track circuits improve this protection.

Personally, I'm not sure I want to install TVS diodes in every locomotive, because of what would be involved.  I'm considering installing my TVS diodes at every power drop at the track end, adjacent to the track and maybe (or maybe not) in certain locos.  There is some risk by not installing the TVS diodes in the locos because of the way the high frequency transient electrical waves created by derailments "bounce" back and forth along all conductors attached to the track.

Put another way, as I understand the principle, even though a TVS diode may be clamping the voltage to a safe level at the exact spot where it's connected, inches away the voltage can oscillate substantially higher for brief periods of time until after the "instant" breaker removes the current driving this wave and the TVS diodes working in concert can sufficiently attenuate this "bouncing" voltage wave.  Maybe this isn't a 100% technically correct way of explaining the transient wave propagation, but I hope it at least gives you a better idea of what we're trying to deal with.

If I've made a misstatement, or if application of TVS diodes in a DCS environment would differ, someone else please enlighten us.

Last edited by SteveH

Steve H.
Thanks for the add'l info. I was too late to cancel my initial order for a 10 amp circuit breaker, so I place another order for the 5 amp version.

Your extra 10A breaker may not be a waste.  Combined in series with a typical thermal breaker, it should still provide fast acting short circuit protection.  I haven’t measured to see, but I’d wager the Snapac would beat any thermal breaker during a short on transformers that can normally supply 5 or more amps.

GRJ:
Steve H:
Thanks for the electro-psycho-emotional support as I wander into (for me) new territory with a circuit breaker and a TVS!

GRJ:
Also, on Saturday my layout helper and I will tackle the geometry problem that limits my MTH Aerotrain from getting around an O42 curve because the Elevated Trestle supports for the upper level (located right above this curve) are set too close to the rails of the lower level where the Aerotrain is running. Meanwhile, there are two other locations on my L-shaped layout where similar geometry problems lurk.

We'll remove as many supports that block the path of the loco at the curves. I may have to re-install supports (with a smaller profile) to provide adequate support to the upper level -- where three trolley lines and 35 DEPT 56 lighted porcelain buildings are placed.

I feel like the guy who built a boat in the basement and when finished discovered the craft wouldn't fit through the cellar door to the outside.

Mike Mottler     LCCA 12394
Obviously, not an honor student in HS Geometry Class
mottlermike10@gmail.com

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