life of TMCC circuit boards

[overall]

Is there any reason why short circuits due to track derailments should shorten the life of a TMCC circuit board? The board itself should not see any fault current since it is not in the circuit during a derailment. It should only see the voltage fall suddenly. Is there something I am missing? What are some things to avoid that might shorten the life of those boards?

Thanks

George

[Big_Boy_4005]

George, are you sure that you are seeing an actual degenerative condition? I suppose it's possible that a particular component is weakening, ultimately leading to failure. What you may be seeing is, once in a while, you are just getting too much current through to the elecrtonics. Remember, electricity always wants to take the path of least resistance, even if that goes through the board.

We walk a fine line, because we need to send enough current through the rails to power motors and lights, but any single device doesn't need the full amount.

I'm not sure what kind of protection is built into the actual boards. Most of the protection is supposed to be supplied between the power source and the rails, but clearly that is not enough. The circuit breakers commonly used simply aren't fast enough to prevent this damage.

I haven't even started to run trains yet, but this problem worries me. Maybe the answer is a suplimental surge supressor / citcuit breaker that could be installed in the loco between the board and the pickups. It could be tailored to the current draw of the motor, and set to about 110% of that value.

[lionelsoni]

George, I agree that a simple short circuit should not cause any harm. The only mechanism that I can imagine that could do that is an inductive spike from the transformer when the short circuit is cleared. This could happen within milliseconds if the short circuit involves rapid making and breaking of the circuit, which seems likely during a derailment. If the boards can't handle that, they shouldn't be in toy trains.

This sort of thing brings out the luddite in me. I don't use TMCC et al.--and I drive very old, computer-free cars.

[wrmcclellan]

George,

Part of the problem comes from surge currents and voltage spikes that can be associated with short circuits. Current (amperage) does not like to stop instantaneously and when confronted with a short can produce very short (shorter than many protection circuits can react to) surges that can cause all sorts of problems for delicate circuitry such as that in the TMCC and DCS circuits. From what I have seen on the TMCC and DCS boards, protection devices such as Tranzorbs and Metal Oxide Varistors (MOVs) do not appear to be present. The problem Lionel likely faces is that these devices take up significant circuit board real estate and there is not enough room. Some of these protection devices do not react fast enough to be effective and some devices only work on DC lines as they are essentially fast clamping diodes (and thus would attempt to rectify the AC input).

Luckily for us, most of the components used by Lionel and MTH are proven devices with a good history of reliability (no "bleeding" edge stuff in our trains thank goodness). This is why on the whole, we see good (I did not say excellent) reliability in these circuits on our trains. However, as someone posted quite some time back - all electronic circuits will eventually fail. Integrated circuits typically fail naturally because the deposited metals (aluminum, silver, etc.) on the semiconductor substrates are "noble" metals and thus the metal migrates, eventually shorting out a transistor junction (takes only one bad one out of 40,000 to kill the device). Sort of like the lead dendrites that form between the "+" and "-" plates in your car battery with age - eventually shorting out the cell.

Do short circuits shorten the useful circuit life? Probably the answer is yes. How long? Very difficult to predict. ESD (ElectroStatic Discharge) into electronic components has been studied extensively for many years to produce a set of guidelines for electronic design. What is not known is whether the lifetime is 50, 20, 10, or 2 years after a non-fatal ESD event (of which a short circuit can cause similar distress to a circuit).

Things to avoid? Obviously no shorts and derailments would be nice, but that is not practical. Never handle exposed TMCC boards without appopriate ESD grounding systems (wrist or heel straps). You may wi***o consider a surge protection device that a few vendors sell for your transformer-to-track connections. Be aware that these devices are not foolproof (but the $30-40 investment is not a bad one particularly if it saves just one TMCC or DCS board).

What will be interesting to watch is that MTH has gone to 3.5 volt (from typ 5 volt) circuitry in DCS and thus the ability to survive certain ESD events is proportionally reduced.

Unfortunately there is no clear cut answer for you on this. Enjoy the trains!

Regards,
Roy

[overall]

Thanks to evryone for the replies. I have a frieght yard on my layout that I cansort cars with. It is hard to get through an operating session w/o a minor derailment, usually from shoving cars into a classification track. This happens even though I take it as slow as I can and leave the track voltage on about 6 volts. I had to send one of my engines back to the manufacturer to have it's TMCC board replaced as I am not that up on the new locomotives. I just wondered If I was grandually destroying the boards w/o even knowing it. If I am then I may need to go back to analog for yard operations.

Thanks,


George

[jkerklo]

You mentioned that the problem may be related to derailments in your "yard," that is, around track switches. If these are soleniod-type switches (e.g. O-22, etc.) then you might want to check the voltage phase of the power on the switch CV plug.

The AC power for the switch appears on the non-derailing rail (through the coil). Just the right derailment can put the sum of track voltage and switch constant voltage across the engine pickups.

John Kerklo
TCA 94-38455
www.Three-Rail.com

[SPFan]

George, Are you running your TMCC locos with conventional transformers? I would believe the source of any spikes would be mainly the power source and secondarily, any accessories which are connected to the track. TMCC and DCS power sources should have protection built in to minimize the spikes sent to the track. The TMCC locos themselves should not be able to generate destructive spike voltages. If you are using post war conventional transformers you should put some sort of protection between it and the track. Also all your accessories should be run back to that transformer, possibly through its own isolating device. I believe these circuits are commercially available and also Jim Barrett has a video on how to build a 4 channel fast acting circuit breaker. I have built similar circuits that can react in microseconds which is considerably faster than the fastest thermal breaker.

Pete

[wrmcclellan]

George,

Pete and John make good points. Your last mail clarifies that you are running TMCC locos in conventional mode and that derailments may be typically cars in the yard.

I do not think cars derailing and causing shorts are very harmful to the TMCC circuits.

You may have just had a random failure. Regardless, a surge device for your layout would be a good idea.

Regards,
Roy

[Anonymous]

The boards should last a very, very long time, if treated properly.

I think Elliot got it right immediately-proper spike protection is very important, whether the boards in question are command boards or simple electronic reversing units. Several manufacturers make surge/spike protection devices.

We always operate both PS-2 and TMCC through a TIU-it has built-in spike suppression.

Both the Lionel (TMCC) boards and the MTH (PS-2) boards are pretty stout.

[overall]

I am going to show my ignorance and ask, does Lionel make the TIU and what does "TIU" stand for.

Thanks,
George

[Big_Boy_4005]

QUOTE: Originally posted by RAK402

The boards should last a very, very long time, if treated properly.

I think Elliot got it right immediately-proper spike protection is very important, whether the boards in question are command boards or simple electronic reversing units. Several manufacturers make surge/spike protection devices.

We always operate both PS-2 and TMCC through a TIU-it has built-in spike suppression.

Both the Lionel (TMCC) boards and the MTH (PS-2) boards are pretty stout.

Thanks, I wish I was more of an electronics wiz. I have actually been thinking about this problem for almost a year now, but from a different perspective, up until this conversation.

I have a TMCC lock-on, the early version that clips directly to the track. I have opened it up, and tried to figure out what the circuit does. As best I can tell, it senses the current, and drops a relay if there is too much trying to pass. The actual track power goes through the relay contact.

I have some very large power supplies that I will be using. They can put out 20 amps, which is way more than a post war ZW. My problem is how to limit the current going to any section of the layout. My theory thus far has been to try to create a simplified version of the TMCC lock-on.

The problem is that the device is too expensive, and has features that I don't need, such as the pretty housing, and the fault indicator LED's. The one feature that wood be handy is an extra set of contacts on the relay, that could be used to trigger a master fault indicator.

Lionel's theory is that most people only need one of these lock-ons for an entire layout. A larger layout might require a few more. The issue is what is the threshold of this device, how much current is allowed to pass?

Take for example a modern, dual motored set of F3's, pulling a lighted pasenger train. This combination of equipment could easily draw 5 amps. Circuit breakers whether in the power supply, or trackside have to be rated higher than that, or we wouldn't be able to run the train at all, the breaker would just keep popping.

This is where the trouble starts, because there is a legitimate reason for allowing that much power to go to the rails. The thing is how do we keep it from reaching the sensitive parts of the circuit boards, in the event of a derailment? An onboard circuit may provide the best protection against fried boards.

[wrmcclellan]

George,

TIU = Track Interface Unit and is manufactured by MTH. The TIU can feed 4 track circuits (2 variable, 2 fixed) and is placed between one's transformers and the track. MTH's TIU is used to inject the DCS (Digital Control System) signal for MTH PS2 equipped trains for remote control operation. The TIU can be fed by 1 to 4 transformers depending upon your layout's requirements. Each TIU output handles about 10 amps and are fuse protected at 20 amps. The TIU, since it connects to your track also contains surge protection devices.

Unfortunately MTH does not use their web site to provide much info about the TIU and how to hook it up and utilize it. They do have some interactive stuff for the operation of the DCS remote.

Here is one useful link with a PDF file for operation: http://jerseycentral.home.att.net/dcs_how_to.pdf

Another source is the O-Guage RR forum for MTH and DCS: http://ogaugerr.infopop.cc/eve/ubb.x?a=frm&s=63160042&f=93360682

Unfortunately not a lot of pictures.

Elliot,

The TMCC lock-on is setable for the power available from the 135 or 180 watt Powerhouses. Although this does not directly answer your question, one can assume this means protection for 7.5 or 10 amp circuits (assuming 18 volts from the PH)

Regards,
Roy

[Anonymous]

Elliot,

I think the Lionel TMCC Lock-on is just like a very sensitive breaker. I do not believe that it includes spike protection. I think QSI or Scott's Odds and Ends make devices for Spike protection, but I am not sure.

I think Roy's description of the TIU is pretty concise. We have very few problems with electronics with one of these devices in the circuit.

To add a little to what Roy said: two of the channels of the TIU are fixed (i.e. whatever voltage you put into the input, comes out of the output), two are variable (working like a Powermaster to vary the voltage from the DCS Handheld). The two variable channnels can also be optioned to operate in the same way as the fixed channels, if desired.

We have the TMCC and the DCS signals on all four channels, all the time. If we run non-command electronic locomotives (PS-1's for example) from the variable channels, even they can benefit from the spike protection.

[Big_Boy_4005]

Thanks guys. Roy, I said I had an early version of the TMCC lock-on, and I wasn't kidding. The citcuit board is clearly marked version 1.2. There is no switch, Lionel must have thought of that later. Either way, the lock-on will still permit a level of current to reach the train that could be damaging under the perfect conditions.

Ultimately, we aren't just looking for surge protection between the supply and the rails, we really want to prevent deadly spikes from reaching the board. Successfully do that, and no more fried boards. This device would need to go on the engine, inline between the roller and the board.

Maybe something along the lines of a power transistor, which would allow current to pass up to a certain level, above which it would block it.

I'll check Scott's. Jim Barrett's magic box is more supply to rail protection. Unfortunately, it is impractical for my application, since it requires a manual reset.

[wrmcclellan]

Elliot,

That means the lock-on you have is the 135 watt version.

In my opinion, Scott's is offering the best device currently available to provide protection.

Here is a link: http://www.scottsodds-n-ends.com/p8-surge_arrestors.htm

The DTK-Z is the latest - optimized for TMCC and DCS.

Regards,
Roy