Bryan
I would install the TVS downstream of the breaker of fuse. That way if it trips during a short or overload,a spike still has a path to common. The way I mount it is shown here for a PW type transformer. The TVS requires no protection from a short or overload.
www.jcstudiosinc.com/BlogShowT...=486&categoryId=
Dale H
Thanks Dale,I appreciate the info.
Can someone tell us all reading these post, what a TVS is and how does it work?
Can someone tell us all reading these post, what a TVS is and how does it work?
A TVS conducts AC voltage over a certain threshold. A 36 volt one for example conducts voltages over that but not under that. Voltage spikes can occur in the loop by anything that has induction,such as the motor in the engine. 18VAC is a sine wave shape going from 0 to about + or - 25 volts peak, 60 times per second. However if a spike is generated it could be as high as 80 volts. This is a brief occurrence,a fraction of a second and is not breaker protected. These spikes can be damaging to IC chips,commonly contained in electronics in modern engines. Over time the chips can be damaged.
The TVS (transient voltage suppressor) is placed across the track power,just as if you are shorting it out. However since it only conducts over 36 volts no short happens. However when a spike is generated,say 80 volts, 44 volts of it is clipped or sent harmlessly to common so only 36 volts goes to the track. Most IC boards can handle this. This is such a brief happening that the breaker on the transformer is not tripped. This device therefore is used to protect modern electronics from voltage spikes. 36 volt value was selected as it is can handle the peak voltage of a PWZW with the whistle button depressed (about 34 volts). A 33 volt TVS can be used on some modern transformers. If the TVS value was too low it would short the track and quickly burn out the TVS device.
The TVS, (one common style) is cylindrical,about a half inch long with 2 wire leads.
Dale H
Can someone tell us all reading these post, what a TVS is and how does it work?
If you have an engine open for other maintenance, I recommend connecting a TVS directly across the track pickup to frame for the best protection of individual engines. I do that whenever I open one for something else.
Thanks so much ,John. I will surely start using TVS protection. I run all MTH engines with a TIU and their 100 watt bricks. Would you recommend 33volt and can these be purchased at radio shack? Shouldn't TVS protection be installed by the manufacturers. Hope they look into it.
Well, I've always been of the opinion that manufacturers should install TVS protection, but they're not listening. 
I use the 36 volt TVS diodes, they rate the breakdown at 34 volts, which is about right. I get mine at Digikey, much cheaper than you could possibly get them at Radio Shack.
At those prices, and very cheap shipping, I just buy a quantity so I have them when I need them.
Well, I've always been of the opinion that manufacturers should install TVS protection, but they're not listening.
I'd be curious to know Jon Z's thoughts on TSV's.
Me too, I have to believe it would be a nice reliability improvement.
Dave Zucal
Dave
The MTH TIU is already equipped with TVS.
Dave Zucal
Dave
The MTH TIU is already equipped with TVS.
On the inputs?
I've worked with large 3 phase motors in the sawmill industry and understand the nature of the beast, on how a motor not only uses electricity, but can also creat electricity when held back and then sprung loose, causing a spike. Even when the power is cut, but the motor is coasting to a stop, it can still kill you if you touch a connection.I'm sure the same happens even with small train motors. this is a great topic, and we can only hope that the manufactures realize the are only as smart as the people they employ.
I put an LED with a 1K resistor across the TVS (parallel circuit). The LED lights when the TVS opens.
Gary,
Are you sure you don't mean in series with the TVS? When you say open, do you mean when voltage would spike the LED would light up, or is it to indicate the TVS has burned out and no longer working properly?I may not understand what you mean by"in parallel". I'm thinking one lead of the TVS is connected to the center rail, the other connected to the resistor's one lead and the other resistor lead connected to the LED and then the other LED lead to the ground rail. Please correct me if I'm wrong.
I put an LED with a 1K resistor across the TVS (parallel circuit). The LED lights when the TVS opens.
The TVS should always be open, it only presents a low impedance circuit when you exceed it's trigger threshold. I'm not sure what you're doing, but the TVS is invisible to your LED circuit I would imagine.
I think there may be some confusion as to what open means. I'm thinking it means current won't flow through it, like a light switch that is shut off. Is this correct?
Correct, the TVS appears as an open circuit unless you exceed the trigger threshold.
John
Your question regarding the TVS at the TIU inputs? I don't know where on the TIU the TVS is located. Just the issuers report that it is installed.
Perhaps I have reached obsolescence but it seems to me that the old school EE advice to install TVS at the transformer output still applies since Voltage Spikes emerge from the power source and the varmits can be arrested there. Installation in downstream wire runs, including in the engine, is certainly good advice for spike snuffing backup. However, the problem for many O-gaugers, likely a majority, is having the skill to open engines and satisfactorily deal with the fragile circuit board components.
I put an LED with a 1K resistor across the TVS (parallel circuit). The LED lights when the TVS opens.
The TVS should always be open, it only presents a low impedance circuit when you exceed it's trigger threshold. I'm not sure what you're doing, but the TVS is invisible to your LED circuit I would imagine.
Well it's been working for over 10 years! When there's a short I know which TVS protected circuit to remove the power from so that it resets.
I put an LED with a 1K resistor across the TVS (parallel circuit). The LED lights when the TVS opens.
The TVS should always be open, it only presents a low impedance circuit when you exceed it's trigger threshold. I'm not sure what you're doing, but the TVS is invisible to your LED circuit I would imagine.
Well it's been working for over 10 years! When there's a short I know which TVS protected circuit to remove the power from so that it resets.
Well, I have no idea how you really have it wired, but if it works for you, that's all that's important. 
I'm just telling you how a TVS works...
John
Your question regarding the TVS at the TIU inputs? I don't know where on the TIU the TVS is located. Just the issuers report that it is installed.
Perhaps I have reached obsolescence but it seems to me that the old school EE advice to install TVS at the transformer output still applies since Voltage Spikes emerge from the power source and the varmits can be arrested there. Installation in downstream wire runs, including in the engine, is certainly good advice for spike snuffing backup. However, the problem for many O-gaugers, likely a majority, is having the skill to open engines and satisfactorily deal with the fragile circuit board components.
I suspect the TVS is on the outputs, but I don't know for sure. While the voltage spike can certainly come from the transformer, they can also be generated by incidents on the rails like derailments. That's why I like the TVS in the engine. I agree with your point that many people would be reluctant to rip their stuff apart to install them, that's a whole separate issue.
Perhaps Gary is mistakenly referring to a circuit breaker as a TVS. In that case, the LED would indicate an open breaker if the short is still present.
Perhaps Gary is mistakenly referring to a circuit breaker as a TVS. In that case, the LED would indicate an open breaker if the short is still present.
Not sure Dale, I only know for sure that a TVS wired in that fashion won't yield the described result.
I have a basic dumb question...
If there is a short, The voltage goes down and the current goes
up. Then the breaker trips.
Where does the spike come from ? Am I barking up the wrong tree ?
Does the damage to the electronics come from the low voltage/high current
situation ?
Bruce..
All of our train circuits contain some amount of inductance, which is simply some energy stored in magnetic fields created by wires that are carrying current. When the current is abruptly changed, the magnetic energy stored in the inductance tries to resist the change by generating a voltage. If the current change is large and quick, the inductive voltage can be a very large voltage spike. (This same voltage spike can create an arc across switch contacts when the switch is opened.)
One source of a damaging spike is the actual abrupt opening of the circuit breaker. The voltage across the circuit breaker's contact gap will spike, and this same voltage spike is seen by other devices in the circuit, such as the electronic power controllers and the locomotive electronics.
An even more serious situation is a dragging derailed set of wheels. The current may spike and fall numerous times before a circuit breaker will operate. The falling current is the hazard since it is not shunted away by the short circuit.
As an example, a common 12 volt DC relay's coil can easily generate a voltage spike of over -100 volts when the current to the coil is abruptly interrupted. We normally add a protection diode in parallel across the coil (connected in reverse polarity to the normal 12V drive) to the circuit to "catch" this spike.
Just hold a 12V relay with each hand on the two coil contacts. Power the relay with 12VDC, then switch off the power. That shock you feel is the voltage spike generated by removing the power.
Even easier, looks at your car's spark plugs, that voltage is also generated by removing the voltage from a coil. The collapsing magnetic field is what generates the voltage spike in any kind of coil when the voltage is interrupted.
Thanks Dale and John...
Now that being said. Is running a TMCC engine in conventional mode
and using the direction button a real bad idea ? It's creating that
power interruption right ? Maybe the newer transformers do something to shunt
the voltage, but if you had an old ZW. would you use it ?
Well, with a conventional locomotive, how else would you reverse? You can take the throttle to zero and then bring it back up. However, the roller or wiper on the transformer is generating transients transitioning the individual coil windings, so that's not really a solution either. 
If you go to this web site and look at the technical report on surge protection it has a diagram and instructions on how to construct a surge protection unit with indicator lights.
I have the correct TVS install on every input and output on any device that is carrying electrical current. This includes Powerhouse, TPC's, ASC's, and any other control module.
It is my understanding that MTH incorporated transient voltage suppression of some type in all of the DCS devices from the initial production up until the present versions.
During the initial design stage MTH asked me to provide them with information related to surge protection which I did and I was assured that they would make sure that the devices incorporated surge protection. I would guess you would have to open them up to make sure.
QSI did a report that was published in the February 1999 edition of OGR magazine about damage caused by voltage surges. In some ways it was an effort to promote the QSI PowerGuard product. The reason for the study by QSI was in response to so many failures of their PS1 and similar boards.
According to the article PS1 and similar boards were severely damaged by any voltage spike above 35 volts and Lionel boards were damaged by spiked above 50 volts.
The higrailers site does an extensive study on the subject and I would highly recommend that you read it. It is not however the last word on the subject but should be considered with other information from qualified, and I stress, qualified sources.
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