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Discussion Starter #1
Yesterday, one of my ZWs got so hot, I couldn’t put my hand on it for more than a few seconds. The only reason I felt it was because, an MTH RDC would not pull its 3 dummies up a 2 percent incline. No breakers (internal or external) tripped. Not sure if it contributed to the problem, but shortly before this happened, I had an engine lock up due to a gear jam, but I hit the REV button on my DCS remote within about 15 seconds.

Today, I tried the ZW with no load. With the handles at 6V or 20V, it stayed cool for a few hours. And it put out 19.9 volts on all terminals. I hooked it back up and ran two trains (on the A and D terminals). Also had C set at 14 for switch machines and B set at 12 for lights. It did get hot under load, but not so hot I could not hold my hand on it. My other ZW (also running two trains) stayed cool as a cucumber. After about 45 minutes the red light came on. When I reduced the C post to zero, it went off. And after about 30-60 seconds, I heard the breaker reset itself.

I got the transformer from Henning’s about 35 years ago and it still has the original Lionel cord so I doubt that it has ever been refurbished.

I’m thinking I will contact Harry Lutz to see if he will take it as a trade in on a refurbished ZW.
 

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First, switch the ZWs. If the problem follows the suspect ZW, then its the transformer. Conversely, If the other second ZW gets hot running the A,C & D scenario, then it's a track and/or accessory issues. And the switch the wiring right at the ZW posts. A quick, simple test may confirm the root issue.

If it is the ZW, trading with Harry is a smart play. I don't know him. I would have pointed to Tranz4mr. Seems to be top notch restoration and gent.
 

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Discussion Starter #3
I will put a Z in its place temporarily. Since the Z goes to 25 volts, I will put a piece of tape on each knob after I set the voltage. I don't think the the Z will act up, but if it does, I'll look for problems with what it is powering.
I just looked at the ZW cord and after 70 years it's starting to show cracks, so maybe this little problem is a good thing.
 

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Shorted coil is the most likely suspect. The rollers wear down and the arm starts wiping the coil, it will sort two windings and things get VERY hot. It's likely cooked the enamel on the wiring around the short.
Ah, the voice of experience. Can it be repaired?
 

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If the coil hasn't been scored too much, you can possibly repair it. If the enamel has been fried off the wire, that may be more problematic. I've heard of people dipping transformers to restore the enamel coating, but I doubt I'd go to all that trouble, you have to disassemble the transformer down to the core.

The #1 cause of the total demise of PW transformers is typically coil damage. The #1 cause of coil damage is worn out carbon rollers, they are consumables. Once the coil has been damaged beyond practical repair, the transformer is toast.
 

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Discussion Starter #7
I’m trying to phase the Z to the good ZW. Attached a wire to the A terminal on the Z, set both transformers to 15 volts and touched the wire to the A terminal on the ZW. No spark.
Reversed the Z plug to double check. Touched the wire from the Z to the A terminal on the ZW. No spark.
What am I missing?
 

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Discussion Starter #8
Doh! What I was missing was the connection between the U terminals. Got a nice spark once I did that.
 

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Discussion Starter #10
Another D’oh moment.

I hooked up the Z in place of the ZW, turned it on and after a few seconds a 10 amp fuse (for the C terminal) blew. That circuit only runs a few solenoids, but I was not looking forward to tracing the problem. Didn’t take long though. I had previously been changing some scenery, disconnected a K-Line crossing gate and thought I had left some air between the end of the wires. Apparently not. But that is on a momentary contact switch. Why would there be voltage to it when I’m not operating the crossing gate? So, I measured the voltage with switch OFF and got 1.6 volts. Enough to melt the insulation. I pulled that wire and turned the Z back on. No blown fuse.

I hooked the ZW back up and ran trains for an hour with no overheating.

Mike was right.

I will still replace the cord for the ZW. When I do that, I’ll take a look at the rollers and coils.

547475

547476
 

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I think we all did that or something like it at one point or another.
If not the wires touching it is a screwdriver in the back forty you forgot to pickup, or a piece of metal touching somewhere.
It was an easy fix, that is for sure. :D
 

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Discussion Starter #13
I'm surprised the 10 amp mini fuse didn't blow when I had it on the ZW. I must have had the voltage on the ZW set a little lower than I had it on the Z. I'll have to see if I can put something smaller in that slot and that won't blow when I energize the solenoids. I don't like to see melted wire insulation.
 

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I'm surprised the 10 amp mini fuse didn't blow when I had it on the ZW. I must have had the voltage on the ZW set a little lower than I had it on the Z. I'll have to see if I can put something smaller in that slot and that won't blow when I energize the solenoids. I don't like to see melted wire insulation.
You could use a lower rated "slow blow" fuse. It won't blow on the solenoid activation but will given longer term short. Ina conventional environment that should work well.
 

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Or you could use push-to-reset circuit breaker. They act similar to a slow-blow fuse. For example, a 3A circuit breaker will not trip at 3 amps or less. At 4.5 amps it would take an hour to trip. At 10 amps, it would take nominally 1 second to trip. Here's a link to a 3-amp Breaker. There are a myriad of similar breakers. Click the link to the data sheet (below the pic) to get detailed info.

Here's it's performance graph and table: Overload % versus time-to-trip.

547492
 
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