TVS and Lionel/MTH

There can be catastrophic failure in anything manufactured by man, depending on the circumstances and considering numerous variables. The actual likelyhood of certain failures may be unknown.

 

I have run 2 180w Lionel bricks parallel through a tpc unit at 18v to the track for several  years. I've had numerous derailments many of which tried welding the wheels to the track. No damage to any loco electronics of any kind, the breakers on the bricks pop in an instant.

 

Yes there are exceptions to all rules, you must ask yourself, what types of transformers were being used during the failures? Many folks are proud of their postwar power supplies but they are designed with 1950's electronic protection.

Secondly, what  is the track voltage used by those having the failures. Some have posted running 20+ volts so they can get better smoke. Varibles could go on and on.

 

Just because a loco derails does not automatically mean there will be damage to the electronics. What other factors could contribute to this?

 

Having said all that I'll have a derailment tommorrow and fry one of my legacy steamers, but I still think that folks cutting corners on wiring or using outdated or not necessarily compatible transformers raise the risk even higher.

I don't doubt there are a lot of factors in play when damage does occur.  I know that a TVS close to the bone is just one element in protection for my electronics.  I don't delude myself into thinking that nothing could possibly happen because I've installed them.

Adding tvs is a waste of time IMO. I have been running command engines since 1995 and have never had a problem. 

 

What RickO said has allot of truth to it. If you run your modern electronics with 60 year old transformers then you are just asking for trouble. Good wiring, a modern transformer and running your trains at around 16-17 volts, there should never be a problem. 

David1 I could say the same thing you're saying until last week. I didn't even have a derailment. The engine I was running didn't have long enough pickups to span my Atlas #7.5 switches. It could make it at medium and high speed but not low. It stopped twice at the switch and on the second time it fried the radio board. By then I'd figured out what was happening but it was to late. Did the board die on its own, Maybe/ maybe not. For the cost of a few tvs diodes I can be sure I didn't fry something. Cheap Insurance if you ask me.

Ron

The 7.5 switches have been problems since they were released and you found one of the reasons. 

 

A board can blow at anytime for any reason. There is no proof the the tvs would have prevented what happened to your radio board. I blame the switch and the fact that your transformer breakers did not shut it down. Also a inline fuse between the transformer and your tack could have helped.

 

I do not think it is worthwhile for me to use the tvs in dozens of steam locos For the rare chance of a blown board. 

 

But to each it's own. 

David no transformers breakers would have shut down. There was no short circuit. The engine didn't derail it just stopped for lack of power. My power setup is very sensitive to shorts and works very well BUT a circuit breaker doesn't protect against a spike in current it only protects against a short. I studied all the problems with the Atlas switches and took care of everything except the long length of center rail missing. All my switches are extremely reliable with all my Steam and Diesels until this one. The pickups need to be about an inch longer to span the missing center rail. I have a fix for this but I haven't had time to make it yet. It will make the #7.5s bullet proof.

Ron

 

P.S. By the way besides the fast acting breakers there is also fast acting 7.5 amp fuses in the lines to the track for double protection.

Fred...you post a very good question.  Voltage spikes are a problem and if the ideal place to install a TVS is in the locomotive, then why don't manufacturers do this.  I'll bet we would be more than willing to pay much more than the real extra cost per unit in order to have a more reliable product.  Inquiring minds would like to know!!!

 

Alan

proubley so they can make more money off our poor sorry butts..thought I read some where that MTH is now putting those TVS in the trains?

Good post Dale H.

Thanks

There's also no proof that a TVS would not have helped.  All you're doing it trying to prove a negative here, a difficult task.

 

A fuse is much too slow to affect transients, they are nanoseconds to at most a few microseconds in duration.  No fuse is going to act that fast before the damage is done.

MTH puts TVS's on the TIU outputs, so they must think there worth installing.

A TIU is a far more sensative component than a TMCC/legacy base.  Generally speaking there "seems" to be more posts concerning MTH board or TIU failure. I'm not sure how this relates to the "hot" being the signal delivery as well.

 

Just to make make myself clear I don't disagree with those above who recommend the use of TSV's.

 

 

It just seems as though that there was a recent post of a board failure and now everyone thinks their locomotives are going to go up in smoke.

 

 Mind you that post had some of the "varibles" I mentioned above. I think some folks are missing the other benifit of the post outside of the "scare" that the solution to the problem was located and the loco will run again.

 

Should any of us experince the same misfortune with or without a TVS, we will know what actions to take regarding the repair.

 

 

 

 

I will toss this in.

I design boards for an Industrial Control company. We have a 5 year warranty on everything in Industrial use.

I put a TVS on everything a user can contact. Every connector pin, every jumper, every pot, every switch.

Adding a TVS (Which in SMT parts at relatively low quantity cost only one cent each) is a very cost effective life extension for electronics.

Now, the TVS must have a good connection to ground to be effective, perhaps MTH does not have a good ground and therefore does not put them in the engines.

Lets think about that. The Ground (Common) comes in through the drive wheels, these must rotate and need lubrication. Many engines have a copper finger rubbing on the axle of a wheel pair to add to this connection. This is a thin line contact, it offers a high resistance to transient spikes and is a poor ground for a TVS. There is no Hard connection to ground through a non moving part.

 This means they are not the best ground but are satisfactory for power flow.

Power is DC or 60 Hx AC, Transients are in the Mhz at minimum. They have a totally different reaction to a connection VS low Freq or DC power.

All that said, I have not seen a PS3 board, it may have a TVS, it may not.

On a side note, A TVS is rather large for common SMT or Through hole parts. It may be a space availability issue.

As long as the TVS is between the outside common and center rail connections in the locomotive, it's providing the protection to that locomotive.  At that point, the connection to the rails, however tenuous, is not an issue, as the spike we're worried about is differential voltage to the circuit common.

 

However, the potentially poor connection from the track to the locomotive IS the reason that TVS protection on track feeds is not as effective as TVS protection right at the circuit being protected within the locomotive.

 

As I said before, in order to pass many of the lightning tests for aerospace equipment, we had to use a generous quantity of TVS protection on avionics, as Russell says, on virtually every line that left the instrument or box in question.

Russell & gunrunnerjohn,

   Thanks for the education, I knew a lot of this engineering because our computer driven Tig welding machines at NASA had all kind of guards on them also.  I can see

that space would be a big determining factor as to using a TVS that could actually safe guard the engines.  But if the engine has a TVS and the TIU had a TVS it might be a combination big enough to actually safe guard everything from these spikes.

The TVS in my TIU has never let me down so far as it is.

PCRR/Dave

 

There is no question that a TVS will limit the voltage spike to its rated voltage and power rating.

  Try this experiment sometime; Take an old engine and an old transformer and while running monitor the track voltage with a modern meter. My meter bounced all over and read as high as 80 volts. With out the train on the track; steady 16 vac.

  Poor contact with an inductive load (the motor) resulted in voltage spikes. 80 volts may not have been the correct reading but it was obvious that something bad was going on.

  I'm not saying you need a TVS. If you run all older with old transformers you are probably fine. If you run with new transformers you may be ok with newer loco's but if your going to spend $250 to $750 and up for a loco with a bunch of electronics built in the TVS is a good idea. You can put them at the Transformer, the lock ons or direct in the loco.  The loco is the best place.   All IMO; Don

It's not like the locomotives die every day from voltage spikes, there has to be some thought to transients when they design them.  However, I've had a couple of bad boards come to me as a result of derailments, so I know it's possible.  It may be that there was no TVS protection anywhere, and that was a factor.  OTOH, it may be that I'm right and the best place for it is in the locomotive.  I've never personally lost one to a derailment, and I've certainly had some.  I just figure it's cheap insurance.

 

I adhere to the principle that it's my RR and I get to run it my way.  I also get to equip it my way.

I do not fully understand the science but I am always on the look out for the K-line illuminated lockons. Someone on the forum dismantled one and confirmed that it has built in TVS. If it even extends the life of the boards just a little, It is worth it and if not, then the placebo effect is good for a little bit of piece of mind. FMH

Fred, I have two of those K-line lockons with the TVS inside that I am not using. If you want to buy them send me an email. My email is in my profile. Dave

Will do.

heres a interesting video to protect power surge ..from mike reagan lionel..

I have several K-Line lited lockons.  How do I know if they have a TVS in them or not - I'm thinking that there might be different kinds of K-Line lighted lockons.

 

thanks  -walt

That's what wire cutters are for.   You can splice in anywhere, and I think it actually goes into a connector.

 

Walt

I haven't opened an engine in a good many years and can't now. But as I recall the wire to the roller pickup on my K-Line Mikado was tied together between the PC board and pickup by a small white or grey wire nut. You might get lucky or as John said, cut it, and then use a wire nut[s].

Embarrassingly I never thought of that option!  Thanks for stating what to you is probably obvious.  Now I am WAY more serious about trying!

 

Thanks Dewey - I'll look to see.

 

- walt

 

If the tender doesn't have power pickups, no real reason to add one there.  The one on the engine pickups will do the job.