Wires on variable TIU channel getting hot when changed to Fixed output

you could have a tiu tvs diode shorted disconnected tiu and check output with a digital dvm digital voltmeter on ohms if you see a dead short with tiu disconnect I'd suspect shorted tiu tvs diode needs to be replaced. I would not recommend powering up again can damage tiu beyond repair!

Alan

@Texchap posted:

I have a MTH TIU a with the 2 fixed and 2 variable outputs.  I have reprogrammed one of the Variable channels to run fixed (using the handset). I am running a PS3 E7 AA setup pulling passenger cars.  I’m using a Lionel power brick, I use the same power bricks at all other channels. The wire running to the track on the reprogrammed track is getting vary hot.  Hot enough to melt the plastic where the wire plugs in on the Lionel fast track. I am using the Lionel wires.  I am wondering if there is an issue in the TIU or are the wires too small and are heating up under load.  I do not have this issue on any other track.

The wires are most definitely too small, heating under load. You are on the output side of the TIU- already past the TVS.

If the TVS was failed, you would be melting the INPUT wires on that channel to the TIU.

This is why I solder my own 16 gauge wires to the tabs under fastrack rather than using crimp terminals and hoping they stay tight and make a good connection.

Also, catch22 being invoked here. You have multiple transformers right? You might also want to check phasing. I'm not saying that is the problem, but most definitely, could contribute.

@Texchap posted:

  I’m using a Lionel power brick, I use the same power bricks at all other channels.

The fact that the wires are getting hot almost certainly means you're drawing more current than you should be from the TIU channel.  I'd stop and find out what is happening before you kill that TIU!

This could also be a result of loose terminal nuts inside the TIU if your wire is of the proper size.

@H1000 posted:

This could also be a result of loose terminal nuts inside the TIU if your wire is of the proper size.

Not sure that's a possibility, the excessive current is being felt at the track, not at the TIU terminal.  If the terminal is loose, the TIU terminal gets hot and melts, I've seen plenty of those.  However, that's not what the OP says.

@Texchap posted:

The wire running to the track on the reprogrammed track is getting vary hot.  Hot enough to melt the plastic where the wire plugs in on the Lionel fast track. I am using the Lionel wires.

Top suspect to me is too much current draw, likely exacerbated by insufficient wire gauge.

This is why I always have an ammeter on the power supplies. The Z4000 has them built in and it's amazing what you can learn from them.  If your power supply doesn't have them it's easy to add them.  Otherwise you are running blind.

How many motors in the engines?

Is the smoke on or off?

How many passenger cars?

Are the cars lit with incandescent bulbs or LEDs?

The answers to these questions will give us a rough idea of how much current you are using .

BTW, if you are melting plastic insulation off the wires, that's WAAAAY TOO HOT! Don't run your train again until you figure this out! Definitely a fire hazard.

Also, do you have a variable voltage transformer available? If so, what is it?

Chris

LVHR

2 Proto 3 E9 A units, 4 motors, LED lights, 5 passenger cars standard lighting.  BTW I changed the wires to a heavier wire, so far so good.   I am going to change all the Lionel wires to a heavier gauge wire.

I always use the correct rated wire size for expected current draw or if borderline go up one wire size (smaller gauge size), I'd rather be safe than sorry! I will not use Lionel Fastrack Track wiring that come with their starter sets, IMO it's not heavy duty enough to use to power your layout from your Transformer to your Track.

12 Gauge wire, rated 20 amps

14 Gauge wire, rated 15 amps

16 Gauge wire, rated 10 amps

18 Gauge wire, rated 5 amps

Stranded is much better than Solid wire to use on your layout, make sure you are using Pure Copper Wire, not Copper Coated Aluminum (CCA) wire. That is junk and dangerous to use.

Since nothing else seems to be getting hot… my assumption is that because your engine is running OK, It might be a good idea to check the phasing of the transformers.  Take an 18v light bulb with two wires attached.  Set all of the channels, including variables, to 20vac.  Connect one end of the wire to the center track of the channel in trouble.  Connect the other end, sequentially, to each other track.  If the lamp glows dimly each time, that’s good.  If the lamp glows brightly it's likely the extra current is going between bricks.  Question..  Are the outside tracks all connected as common somewhere on the layout? Best of luck troubleshooting.