@Bruce Brown posted:Exactly! These are the same breakers I've used for 20+ years at $5 each. I give the stock numbers in my post above. It's all you need!!!!!
I use those 5 amp thermal breakers in line with 10 amp Airpax magnetic breakers. If I short a 24 awg wire across the track with only the 5 amp in line, the wire burns up before it trips. With the Airpax in line, the Airpax instantly trips. That is closer to what I need.
Gary,
While I agree and support the use of the PSX-AC (an excellent CB IMHO), I don't see anything in the literature about TVS protection nor on the board that resembles a TVS. I would put one across the output terminals. If it fails shut, the board will not reset until you remove/replace the failed TVS. I'm not sure how to tell if it fails open.
Chris
LVHR
Sorry to beat a dead horse but have two buddies getting their Rev L repaired now. I understand adding the breakers between my Z4000 and the TIU to protect from that end (I may get the PSX AC) but on the output of the TIU between the track drop down terminal blocks, I see various recommendations that I could use a little clarifications from you experts:
Thanks guys.
You'll get the normal million opinions on this...but IMHO you just need to protect the TIU outputs with the thermal circuit breaker. I believe the TIU already has the TVS built-in. The TVS that several people use on their layouts or internal to their engines is the 36V Littlefuse 1.5KE36CA.
Yes, MikeH built that nice tutorial on making a box with Eaton thermal breakers AND TVS diodes for the side between the TIU and the track. But again, has both breakers and TVS so you would somehow have to know when to replace the TVS if it were to absorb a spike and fry?
@SteveMa posted:Sorry to beat a dead horse but have two buddies getting their Rev L repaired now. I understand adding the breakers between my Z4000 and the TIU to protect from that end (I may get the PSX AC) but on the output of the TIU between the track drop down terminal blocks, I see various recommendations that I could use a little clarifications from you experts:
- With the breakers before the TIU, is there a need for additional breakers after the TIU?
- NO
- With the breakers before the TIU, I understand the idea of adding another TVS after the TIU, between it and the track drop down terminal block but is there such a thing as a resettable TVS diode?
- NO
- If it blows, you have to diagnose somehow and put a new one there?
- If you want the same protection.
- What size TVS would be recommended?
- depends on supply voltage
- I hate to wrap a TVS around the inputs to each terminal block around the table since you are crawling around under there to find a problem but is that the way to install them versus just four on the output of the TIU posts? see comment below
Thanks guys.
IMO, you can have too many TVS. They can diminish the DCS signal.
@Oman posted:IMO, you can have too many TVS. They can diminish the DCS signal.
HOW? Technically the last TVSS you add should be on the output of the transformer.
As for circuit breakers, if you are trying to protect DCS hardware you are wasting your time adding thermal breakers. WAY too slow. Not cheap, but between the TIU and the track install a DCC Specialties PSX1-AC Powershield Intelligent Circuit Breaker.
@Gilly@N&W posted:HOW?
TVS diodes have a capacitive element. Capacitors short circuit high frequency signals. DCS is a high frequency signal.
YMMV
OK, I just ordered 2 of the PSX-AC's from Tony's. Some people are saying to put them in between the Z-4000 and the TIU. Some people say they should go after the TIU. Can someone please clarify this for me before I get them wired in and find out I did it wrong. I have one Z-4000 going to one TIU and I use all four outputs on the TIU. What about signal degradation if I do put them after the TIU? I'm looking to protect my TIU and locomotives more than the Z-4000.
Don
If I recall correctly if put after the TIU it will kill or at least degrade the DCS signal. So either put before the TIU or run it in passive mode.
while I’m not using the PSX-AC I have a PCB that I made nor the TIU in passive mode. It simply adds a 22uh choke that help bring the DCS signal back on par if not better than when in active mode. I also added a TVS diode 
@Oman posted:TVS diodes have a capacitive element. Capacitors short circuit high frequency signals. DCS is a high frequency signal.
YMMV
Good discussion. So, placing a TVSS before the TIU, would diminish the DCS signal coming out of the TIU? Interesting.
As for the DCC Specialties breakers, we installed them between the TIU and the track feeders on our club layout(s). We see DCS signal "10's" everywhere, If there is degradation, we're not seeing it.
Gilly,
It sounds like you put the PSX1-AC between the TIU and track. Did you have any signal degradation?
Gilly, sorry I didn't see your most recent post. Don
@Trestleman1 posted:Gilly, sorry I didn't see your most recent post. Don
No prob
@Gilly@N&W posted:Good discussion. So, placing a TVSS before the TIU, would diminish the DCS signal coming out of the TIU? Interesting.
The opposite; placing a TVSS after the TIU, could diminish the DCS signal coming out of the TIU? One or 2 on each TIU output, probably isn't going to cause a problem, but some people want to put them everywhere possible, like on every pair of screw terminals.
Like I said, your mileage may vary.
so with the PSX between the track and TIU you are still seeing '10' DCS signals but will those will protect the TIU from the (I believe called transient?) voltage spikes coming from the engines back? But then the shorts coming from the z4000 to the TIU aren't? UGH! I believe Keith you said breakers on both sides of the TIU aren't needed for protection.
Is the only plug and play solution for protection the PSX on all four TIU inputs and all four outputs, or that is overkill or crazy or what?
If all four TIU outputs have PSX between track terminal blocks then does that cover it all? Or only for the fixed ones?........so baffling
@SteveMa posted:Sorry to beat a dead horse but have two buddies getting their Rev L repaired now. I understand adding the breakers between my Z4000 and the TIU to protect from that end (I may get the PSX AC) but on the output of the TIU between the track drop down terminal blocks, I see various recommendations that I could use a little clarifications from you experts:
- With the breakers before the TIU, is there a need for additional breakers after the TIU?
- With the breakers before the TIU, I understand the idea of adding another TVS after the TIU, between it and the track drop down terminal block but is there such a thing as a resettable TVS diode? If it blows, you have to diagnose somehow and put a new one there?
- What size TVS would be recommended?
- I hate to wrap a TVS around the inputs to each terminal block around the table since you are crawling around under there to find a problem but is that the way to install them versus just four on the output of the TIU posts?
Thanks guys.
I have used this method (only half-wired in pic) for each power drop to my Legacy/DCS layout (about 20 in all) and have not experienced an issue with degradation of the DCS signal anywhere. If you solder the TVS to the terminal block before installation, it's a snap.
I've always understood it like this.
A TVS suppressor (actually, redundant since the "S" stands for suppressor), is a "transient voltage" suppressor, which protects against over-voltage conditions. When the TVS senses such a condition, it tries to send the excess voltage back to its source in order to protect the device in front of it. When that happens it's likely the TVS is no longer effective and should be replaced.
A fuse or circuit breaker protects against over-current loads and when it senses an overload condition, shuts down the circuit (either by breaking the metal strip in a fuse or tripping the circuit breaker closed) so you don't end up frying your electronics or welding the wheels of your Big Boy to the track.
So, basically, the two kinds of devices (TVS vs. fuse/circuit breaker) are protecting against different kinds of faults/failures.
The speed and ratings at which these devices operate is variable.
If I'm wrong, well it wouldn't be the first .............
@Oman posted:The opposite; placing a TVSS after the TIU, could diminish the DCS signal
When you consider TVSS is Transient Voltage Surge Suppressor any/all transients are on the Line side not the load side. There is no source for transient voltage surges on the load side. So, I concur with you (from a different tangent) that TVSS has no place on the Output side of a TIU.
If you are wanting to protect from shorts (derailments) and overloads, the DCC Specialties boards as already discussed are IMHO the best way to go.
@SteveMa posted:I believe Keith you said breakers on both sides of the TIU aren't needed for protection.
Correct, but I'm referring to the overcurrent function, not transient protection. I don't know the PSX, but it sounds like it has both overcurrent protection and transient protection. Maybe that's causing some confusion.
@Oman posted:I don't know the PSX, but it sounds like it has both overcurrent protection and transient protection.
The PSX does squat for Transient Voltage issues. The TVSS still has it's place.
For your TIU:
Before In TVSS (transformer output, and breaker panel if you can)
After Out PSX (before the track)
Any and all circuit breakers, be it thermal, magnetic or PSX protect everything downstream for overcurrent. If the PSX doesn't have any transient voltage protection, there's no benefit of placing it between the TIU and the track. Best to place it on the power supply output.
I've explained this the best that I can, so I'll bow out of this discussion. Maybe GRJ can chime in and correct me. 
John 
@Gilly@N&W posted:When you consider TVSS is Transient Voltage Surge Suppressor any/all transients are on the Line side not the load side. There is no source for transient voltage surges on the load side. So, I concur with you (from a different tangent) that TVSS has no place on the Output side of a TIU
That’s not quite true but how much it effects you may depend on your transformer. Let’s just say for example sake it’s a old ZW with a basic iron core transformer. If the input primary voltage is raised then so will the output secondary voltage. So if your house experience a voltage spike and now instead of 115VAC going in you get 150vac then your output will also raise. I’m just a service tech not an engineer so I don’t know the exact math to say what the secondary voltage would be.
the same would happen with a new electronic transformer then the question is would a Z-4000 or ZW-L be quick enough to compensate for that spike. I wouldn’t bet money on it. So while our main cause of Transients is from derailments, they can still come from that dirty power that gets fed into your house
The fact that you see sparks does not mean that, as far as TIU, transformer, and wiring are concerned there is an overload. The presence of sparks indicates that the circuit is making and breaking, so the actual amperage may remain below the rating of a breaker. Note that 5 amps can give a great spark, but won't affect a 10-amp fuse or breaker.
This is a very interesting topic and I have a question. I run conventional on a small layout with two transformers, a KW and a 1044. Several of my newer engines have circuit boards and I would like to add some protection. In line fuses (5amp or 10amp) are simple to install on the output of each power feed. I've seen photos on the forum where people have installed TVS components at each lockon location or on the transformer terminals. Would that be sufficient for my layout? I don't see myself going to DCS or another Command Control system but I've learned to "never say never".
John
This is a good thread and discusses key points for all of us. A picture tells a thousand words so I took a few minutes to see if this graphic distills the key points which most agree with.
Nice graphic. Other comments above still give me pause as they have stated that the circuit breaker placed after the transformer will protect everything beyond that from over current events (so the TIU and wiring and trains).
The second circuit breaker after TIU is then not needed as all over current events (which only come from the transformer side) would be already protected by the first breaker? Please confirm electrical gurus.
If this is true, then the transient voltage events that could come from the train/track side back toward the TIU would be shielded by adding TVS at the voltage drops. This protects the newest Rev. L TIU that has TVS protections built in but they’re not strong enough apparently?
Steve, the first breaker or fuse is for the transformer, it may have other stuff too connected. The second is needed too based on more sensitive, less rugged components it protects.
Food for thought no matter where the breaker is high current must pass though it. 99.9% of the time where the current is going is going to be a short on the track or derail. Power is always coming for the transformer and it's always going to take the path of least resistance so no matter if your breaker/fuse is before or after the TIU there always going to be the current before the tip that's going to go through it. Again I am by NO means engineer, IMO the best way to avoid high current through you TIU is by not putting it there in the first place I like my solution with running the TIU in passive mode you can see father up in the thread. We currently have a layout with 2 150ft mainlines and have no DCS signal issues. Granted it's also a brand new TIU.
Let me throw a fly into the appointment. Say you have a postwar ZW. It has a single secondary winding. 10 amps is about the most it can/should carry for an extended period. You place a 10 amp fuse or breaker on each handle controlled terminal, ABC&D. The transformer is not protected by those fuses / breakers, because they will allow up to 40 amps through the secondary. (Actually, internal resistance will probably hold this to a lower level.) The existing internal breaker, if functioning, is the protector because it is on the U terminals.
RJR,
You have a good point, but just to counter it would take quite a short circuit, electro-mechanically speaking, to short all 4 outputs downstream of the added breakers at the same time. I can't think of many reasonable scenarios where any more than one would short at any one time. That's 10 amps max if the breakers are in each leg.
Maybe two at once -- if a derailment across adjoining power districts.
Mike
True, Mike. But consider if you're only drawing 5 amps on each leg, which is a reasonable draw of you're running pulmor motors, multiple trains, passenger cars, etc. No leg is overloaded, but if the internal thermal breaker doesn't cut off......
If you have accessories and incandescent lighting on the accessory terminals and a few trains on each throttle, easy to get over 10 amps.
Solution is to also have a single ground going to the U terminals through a single 10-amp breaker.
Zachariah, on may layout I use semi-passive. The hot leads go through the TIUs. The common bypasses the TIUs altogether, but all TIU black outputs are connected together and into the single common circuit buss. My layout is wired a bit unusual, in that a heavy common buss runs all around the layout, and all outside rails and accessories are tied into it.
Wow. Well, now after reading all the responses I know exactly what I'm going to do. I'm going to make sure I never have another derailment or leave anything metal on my tracks.
Ok, I guess I will get some TVSs for the side the TIU to the track. Best source is?
I'm no expert and I am running conventional. I use TVS diodes if someone brings over a more modern loco.
But is there any reason you can't just use an auto resetting Polyswitch? They are installed in line (series) with the variable voltage feed.
John
PTC's are very slow devices, they're probably not as fast as a thermal breaker, much less a magnetic breaker. They do have their uses, I replace the fuses in Legacy power bricks with them, never have to open it again. 
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