Thank you, Bob.
That was the only way I could figure it, nice to know I figured right for a change.
Pete
"You can’t study the darkness by flooding it with light." - Edward Abbey -
The three input terminals go to the frame, one pickup, and the other pickup. The + and - terminals go to the lamp(s) and, optionally, an electrolytic capacitor. The lamp then gets the greatest difference in voltage among the three input terminals, but there is no direct connection between the pickups and therefore no possibility of their shorting out the track.
Bob Nelson
How is a three phase bridge rectifier wired in a passenger car?
Thanks.
While a short circuit outside the locomotive may damage under-protected layout wiring, it poses no danger to electronics inside the locomotive, because the voltage across a short circuit is zero. I can imagine only a couple of electrical hazards to the insides of rolling stock in a derailment:
o A locomotive or car with separate pickups connected internally, as opposed to a two-roller pickup assembly, if they come in contact, one with an outside rail, one with the center rail, may have the wire connecting the pickups damaged if it cannot carry the rated overcurrent protection. However, other electronic innards should be safe. (This is why I have been wiring my passenger-car lights with 3-phase bridge rectifiers in recent years.)
o A coupler knuckle spring or the thin metal strip in the drawbar of 2500-type trucks can be burned out if the frames of two coupled units contact center and outside rails.
BigAl 956 Having experienced derailments and shorts that have melted trucks and an entire cable harnes I can tell you that a breaker in series with the block power does indead protect the train and/or layout from high heat damage that occurs during a derailment or similar short.
Having experienced derailments and shorts that have melted trucks and an entire cable harnes I can tell you that a breaker in series with the block power does indead protect the train and/or layout from high heat damage that occurs during a derailment or similar short.
In this case, a 6 amp short at 12 volts will still cause damage due to heat on par with a very large soldering iron, your breakers won't help any. If this kind of damaged is evidenced, it's not due to an equipment issue.
Rob
The TVS will protect the electronics from transients but is not intended to be a fuse or breaker.
Having experienced derailments and shorts that have melted trucks and an entire cable harnes I can tell you that a breaker in series with the block power does indead protect the train and/or layout from high heat damage that occurs during a derailment or similar short. The wires used inside modern engines are quite small in guage with easily melted insulation. In the event of a short with a postwar transformer you deffinately want some type of breaker.
A TVS will prevent the electronics from being fried by power spikes however I have never deployed them and never lost electronics. Not saying it can't happen but a short with heat realted failure and even fire has happened on my layouts and can happen often when running with PW transformers.
As mentioned earlier the internal transformer breaker is for the transformer and not the trains.
BigAl 956... I use 7amp breakers to protect the trains...
Big Al, those breakers aren't protecting the trains. See above for details.
I power my layout with 4 ZW transformers. I operate mostly PW or modern PullMore motors. I use 7amp breakers to protect the trains.
Here is a vew of my layout control showing how I wire the breakers in. I use house wiring components as they handle the curent loads easily.
Rob is right, except that it should be 1 per circuit. I wouldn't trust multiple transformer outputs to share all their stray inductance. And a TVS connected to a circuit that is turned off, and therefore disconnected from the transformer secondary, surely won't protect another circuit that is turned on.
I doubt that the exact location matters otherwise. Putting one in a locomotive has the interesting benefit of taking its protection with the locomotive when visiting another's layout.
TCO RailwayWhen using a ZW, fuses and breakers do not provide additional protection for modern engines. However, adding a sufficient quantity of TVS diodes at appropriate locations is essential.
You really only NEED 1 TVS, placed in the right location. The problem is guessing the location, as the trains move around. Ideally, you could install 1 inside each loco where the power comes in to the chassis. One per power district would be ideal.
Otherwise, placement is a compromise, as with many things in life. Better to have a few rather than none.
Equipment that could benefit from TVS protection is really anything with semiconductors - starting with the Sound of Steam, Electronic Whistle, & Electronic Horn of the early 1970's.
While these are just sound systems, it's a starting point, leading to protection of electronic reverse units in the early 80's, and then more sophisticated sound & control systems in later years.
So just to be sure I'm understanding...
When using a ZW, fuses and breakers do not provide additional protection for modern engines. However, adding a sufficient quantity of TVS diodes at appropriate locations is essential.
As an aside, is 1987 generally accepted as the start of the "modern" era? Is there any way to know which engines require the extra TVS protection? I'm looking into GG-1s built in the late 1980s and early 1990s and I don't think there are boards on these trains, but I can't get a look under the hood.
There are some reasons to use supplementary fuses or circuit breakers with postwar transformers, but they have nothing to do with protecting modern locomotives in particular:
o The circuit breaker in these transformers is in series with the common terminal; so it does not protect against faults between non-common terminals, whether accidental or deliberate. The fine print on the KW schematic warns of this; but Lionel otherwise ignored the problem.
o Lower-rated supplementary circuit breakers used with a large transformer allow you to wire your layout safely with smaller wire. For example, the 15-ampere breaker in a ZW or Z calls for 14 AWG wire; but 16 AWG would be okay downstream of 10-ampere breakers, or 18 AWG with 7-ampere breakers or 20 AWG with 5-ampere breakers. However, the heavier wire is often advisable anyway to reduce voltage drop in the wires.
Often, fast-acting fuses or breakers are advised. But these serve no particular purpose. Once the fuse blows or the breaker trips, however quickly, the damage to the electronics is already done. They will also blow or trip on harmless momentary overloads--"nuisance tripping"--and may have to be replaced or reset frequently.
TCO Railway...And, which if any of the modern power supplies come with these fuses already embedded in the supply as manufactured? MTH z1000? MTH z750? Lionel CW-80? (I have one of these from the Polar Express set.)
MTH z1000?
MTH z750?
Lionel CW-80? (I have one of these from the Polar Express set.)
None. They all have internal breakers(MTH) or current limiting circuits(CW) to protect the transformer and wiring.
TCO Railway... However, I've also seen recommendations for using in-line automotive fuses of varying ratings, and the rationale and implementation of these fuses with a ZW has been more elusive to me. Why are these fuses necessary? How are they best implemented?
Why are these fuses necessary? How are they best implemented?
Your confusion is valid. The use of those extra fuses is completely non-nonsensical. The idea is, to many, that a fuse will protect the trains. It's simply not true. The application for a fuse is for current limiting, not voltage/high voltage protection, which damages the electronics of newer trains, and you have that covered in your TVS points. The fuses are to protect the wiring and transformer. Once you accept that, now you have to move on to the question... why fuses? Well, if you enjoy stocking consumable parts and spending the money to do so, then fuses are your game. Otherwise, what you want is appropriately sized circuit breakers for the power districts they protect. You may want, for example, to limit a district to 5-6 amps nominally from an output on a ZW or KW, both of which are capable of putting out much more current. A breaker on each district/loop will trip on its own w/o shutting down the entire layout or relying on the 10-14 amp internal thermal breaker of the larger transformers to take the time to heat up. It really is a convenience issue more than anything. I've never used an external breaker or fuse in 50+ years of running O trains and building at least two seasonal layouts per year. My current O-27 layout has been running fine since 1971 with three postwar transformers, no extra fuses or breakers.
In researching newer engines and power supplies, I have found myself directed to the ctt community forums more and more frequently. So I have decided to join the discussions directly. The depth of knowledge of many posters here is considerable, and far beyond my understanding in most cases. I look forward to learning from you.
My first question concerns powering modern engines. Aside from a Polar Express Berkshire 1225 2-8-4 engine, all my engines are postwar except for an early-MPC 8206 Hudson 4-6-4. I've used postwar ZW transformers to power all my engines.
I'm intrigued by a few modern engines, and so I'm trying to learn what to do to power them properly. I've seen discussions that suggest I can use a ZW, but protect the electronics in modern engines by placing TVS diodes (1.5KE36CA, available at Mouser) across each lock-on. That one makes sense to me. However, I've also seen recommendations for using in-line automotive fuses of varying ratings, and the rationale and implementation of these fuses with a ZW has been more elusive to me.
And, which if any of the modern power supplies come with these fuses already embedded in the supply as manufactured?
Other recommendations?
I'll sit back and get ready to learn. Thanks!
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