MTH TIU Fire During Open House

You must of been doing more than six amps for that to happen or you had a bad connection with some resistance that heated up.

My understanding is the newer TIU have fuses.

Also you might be better to have Rich move this thread to the DCS section of the forum for the DCS experts to chime in.

I had one melt down a year ago. The case and contents were destroyed. I replaced it and have had no problems.

From the looks of it the binding post had a poor connection internally.  This is all speculation based on the photos.  I have heard of others having similar issue with this type of connection on other devices.  Glad it wasn't more serious.

What type of connector was used? Banana plug style or crimp terminal style? Connector loosed internally? Thinking this was a bad connection with arcing rather than amperage overload.

If the wire attached to the output was loose, or if the internal wire is loose, that creates a resistance and a hot spot.  So your effectively heating that area and it was hot enough to melt the plastic.

That banana jack can be replaced, and then that channel needs to be tested to ensure the DCS signal is still present.  Many times that excess heat can damage an internal component that kills the DCS signal.  Should be repairable, but you need to make sure all your connections are tight.  G

Marty and George nailed it.

It looks like the wire that was connected to that terminal was not connected tightly. This results in a "high-resistance" connection.

Passing 6 amps of current through a high-resistance connection would generate enough heat to do this.

I believe the original G version had the internal wires soldered, but was changed late on . Don't know why..... Anyway scary!! as G mentioned  Keep your connections tight.

 This post is a good reminder of what can happen.  Fortunately the outcome wasn't that bad. Not good but could have been really bad.

What is the best way to redundantly  fuse this setup? 

Please name placement, brand, source and specs.

Thanks,tt

PS what is the safe use range of banana plugs?  Early on I was advised not to use them for model RR type of application.

I don't know how you would protect a loose connection? Tighten it but should we check the internal connection?

it was crimp on forks and they where tight with some locktight blue to stop them from vibrating loose. 

our ZWL where catching a lot of the shorts and over voltages the past two days i did open up the TIU this morning and did see fuses but they are 20AMP mini spade car fuses crimped on to some pins on the board i am surprised they did not heat up as well I don't know if i mentioned what type of TIU we have it is a rev L.

For what it's worth, I have 10amp fast-blow automotive fuses on each output terminal of my TIUs. I have blown many a 10amp fuse, and have never had any issues with either the TIUs nor the transformers. Those 10amp auto fuses tend to protect the electronics inside all the model locomotives too.

Interesting. Does the thread locking compound increase the resistance at all?

We've thread locked electrical connections by a drop at the end of a nut on a threaded stud, never by applying it to the threads the nut will go down.

Tom Tee, Overheating a connection can occur on loads that are far below capacity, and therefore cannot be protected by fuses or breakers.  Feed 5 amps or even less through a poor connection, or through an undersized conductor such as in-car wiring, and you can get serious overheating.

Fuse/breaker  sizing in model railroad circuits should follow the rule to use the smallest size that will operate to-be-expected loads.

Products that catch fire need to be returned to the manufacturer for failure analysis and root cause determination.  I would recommend returning the TIU to MTH for root cause failure analysis and appropriate corrective action as warranted.

The G&O Garden Railroad had this problem with its single TIU.  The TIU started to smoke and burn.  We took it out of the circuit.  The G&O's problem was caused by a short on the track that happened when the lead truck of an engine derailed.

A local MTH repair person opened the TIU and found that a part had burned out.  I believe he said it was diode but I am not sure.  He repaired the TIU by replacing the part.

I was at the CTTOM show when this happened.  There were several derailments and stoppages  on the layout in the half hour prior to this event.  Multiple overload instances may have weakened a part and then caused it to fail and the fire.  This is scary.  

The ironic thing about this failure is that I didn't see anyone running any DCS engines during the time I was at the show (Saturday morning).  All the trains that I saw were either Lionel of conventional.  As best as I can recall, the following trains were running when this happened:  1.  A long Santa Fe passenger train pulled by a single diesel.  All cars were lighted.  2.  A long WP freight pulled by two powered diesels.  3.  A long freight pulled by a Lionel Big Boy.  4.  A long TCA passenger train with lighted cars pulled by a Lionel N&W Class A.  5.  A long freight pulled by a Lionel SP Cab Forward.

The CTTOM club is well worth the visit if you are ever in the San Francisco Bay Area.

NH Joe

Our Gulf Coast Chapter TCA portable layout had this problem and it was loose terminals. We never had a fire but the case was deformed from the heat. I have found that most TIU terminals will get loose over the years from normal attaching and detaching wires unless care is taken to keep them tight.   

I've seen a number of TIU's with loose binding post connections, it's a problem that will create exactly what you see.  I had one here that had some melting, just not to the extent you had.

GRJ, I expect that you've seen the inside of all TIU versions.  Can this be a problem with all versions?

first off glad you enjoyed the show. and your right we did not run any mth engines on Saturday but DCS TIU are still looped in our wiring on the layout in case some one did come and want to run a DCS engine the Santa fe and Big boy passenger car trans have been converted to LED lighting boards so they draw little to no amps the tca passenger cars i believe still runs the incandescent light bulbs but we where still under 5-6 amps on that out put. As for the shorts the ZWL that powers the tracks is quick on detecting a short and will turn off the faster then a person turning the handle now Lionel did a demo on this here is the youtube link https://www.youtube.com/watch?v=pN5S7X6y9sM skip to the 14 min marker to see the safety features when it come time for a short. That was the biggest reason on buying that transformers. i will post a time laps of sunday show here for people to look at

After reading this I am forming the opinion it would be prudent if everyone opened their TIUs and checked the connections? There's no other way to tell if one is loose, is there?

Robert, you need to realize this is not a short.  This is just high current with a resistive load based on the loose connection.  Any transformer just sees a load and will provide the necessary current.  Any limit on over current probably was not met. 

I have seen several TIU like this, with internal fuse cases even melted, let alone what happens to the power inductors.   G

Nope, other then feeling for excess heat at the connections.   G

Loose connections will bite you anywhere, not just in the TIU.  I did take one apart that had the wires soldered to the ends of the binding posts and not the classic way with the nut holding the connection.  I don't know if someone did this or MTH did some that way.

Robert, you need to realize this is not a short.  This is just high current with a resistive load based on the loose connection.  Any transformer just sees a load and will provide the necessary current.  Any limit on over current probably was not met.

George, I assume you're talking to me.  That is precisely what I said.

 I just finished operating the trains with my two grandchildren, for about 90 minutes. I check each post and could not feel any heat issues at the posts.

     I have each wire connected to the posts on the TIU , with a Ideal® Brand Terminal Connector. These connectors are tightly crimp to the wire with a crimping tool.

     I got out the MTH Operator's Manual and read over page 135 in the Trouble-Shooting Chapter. See page 135 above. MTH does talk about the 20AMP automotive type fuse. All my connection points are tight at the TIU.

     I am a end user and will need some help with this issue.

Gary • Cheers from The Detroit and Mackinac Railway

My gut feeling is not to use loctite, as it may serve to insulate.  Note that when speaking of loose terminals, one may be speaking of the external black or red knobs, or the screw terminal itself, which pass through the case,  If loose, the wire inside may have a poor contact.  External knobs should be checked periodically.

I believe the carrying capacity of banana plugs is a matter for discussion.  The fit inside the tube will determine the contact area.  Most banana plugs I've seen have split ends or spring centers, so the actual contact area could be quite small.  I prefer crimp connectors for a certain large contact area.  But, in speaking to a marine air conditioning manufacturer, I was advised that a major cause of problems is inadequate crimping, which causes overheating and failure.

This also brings into consideration where you locate the TIU's. I just made a modification to the location of my two! 

     Just my own advice take it or leave it. If some is good more is better! When working with (crimp connectors ) I have always taken off the red, blue or yellow insulators and put them on the wire that is going in the crimp connector. I would put the striped wire in the crimp connector and solder it in place. When the crimp connecter would cool I would put the insulator back on the crimp connecter. All the car radios, speakers and automotive wires I have worked on I have never had any crimp connectors come loose or pull apart. I also prefer to use stranded wire vs. solid copper. If possible use the round (loop) crimp connectors instead of the (U) crimp connectors because you have more contact surface with the (loop) vs. the (U) crimp connectors. Unless you can not get the nut to come all the way off the threaded stud then you have to use the (u) crimp connector. Just my 2 cents worth take care. Choo Choo Kenny

This is what I use on my layout, I believe it goes back to my Heathkit Days.

Klein Multi Tool, #1000 & Ideal Brand Terminal Connectors.

Gary - Cheers from The Detroit and Mackinac Railway.

Lots of advice and plenty of suggestions to think about i am going to send the TIU back to MTH to get tested and repaired... When i get it back i am going to redo the crimps. I did not crimp these wires it was already done about a year ago. my crimping procedure i use UN-insulated U thermals put a piece of heat shrink un-shrunk on the wire crimp my pre-tined wire after the crimp solder the whole thing again for good measure that is how i crimp my wires. Can any one find any issues with that? i know it is lots of work and steps but seems the safe way to go. now i do not like the MTH binding posts they feel cheep to me. I am a experienced in soldering does any one see any issue of me removing the binding posts and soldering my wires directly to the PCB? At this point i do not want this to happen again.

I do the same thing you do Kenny, and have for years. Never had a connection fail doing it this way.

Just to clarify my previous  comment about location, you want easy access to your TIU's in case there is a problem. I can picture some TIU's being buried under some large permanent layouts.

What GGG and Rich said.

At work, I have become a fan of Belleville spring washers to lock and maintain pressure. Turns out people who run busbar have been using Bellevilles for a while.

http://ecmweb.com/content/how-...le-washers-correctly

But I don't know if the banana post cover comes off.

No. I was talking to Robert Lopez, the person commenting on the TIU.  G

Ok i was pointed out by one of our members that the TIU did not burn up the output But the Input See photo at beginning...

Also our TIU is on a wall easily accessible 

Robert Lopez, a loose connection on the input would have the same effect as a loose connection on the output.  Current would be the same.

Every TIU I have opened up has had at least one nut on the binding post not tight enough. To fix this you need to get some M4-.70 nuts. Unscrew the nut on the binding post and remove the external washer and wire. Replace the nut and tighten. Then replace the wire. Next the external washer. Then the nut.

This is how  the Z-4000 binding posts are setup with 2 nuts per binding post. I'm not sure why the TIU are using only 1 instead of 2.  ???