Electrical wars, Part 20: one more time

Sigh. You can tell from the series number of this post that I do have electrical issues from time to time on my layout. (Previous ones, if of interest, are most easily found by using “Electrical wars” as the search term in the search box at right.) I’ve called this installment “one more time” because it addresses a particular switch that I’ve replaced once and then rebuilt after that.

This is probably the most-used switch anywhere in my trackwork, or at least roughly tied for first. It’s both the switch off the Southern Pacific Coast Division main line, onto my modeled Santa Rosalia Branch, and is also the lead into the yard trackage for my town of Shumala. It is used many, many times in every operating session that includes Shumala.

Below is a photo of the switch in question. At left is my trusty multi-meter. I’ve written this comment many times, but will repeat once more: I have absolutely no idea how anyone can build and operate a layout without one of these in frequent use (but I do know of examples). The edge of the turntable pit is visible at top.

I have, in recent op sessions, begun to have one of the point rails in this switch (the one nearest the camera) become dead — intermittently, the worst kind. Partway through my most recent session, it stopped being intermittent and became continuously dead. This one I could diagnose provisionally, because the switch had been rebuilt for DCC and has a jumper wire from each stock rail to each point rail. Earlier, when I had the intermittent “dead-ness,” I re-soldered that jumper. Or thought I did. 

Very careful visual examination, and meter use, showed that it was now disconnected. Possibly the solder joint had not actually been re-soldered that previous time, but only pressed into contact, which would account for the intermittent dead behavior. I now very carefully cleaned the wire and rail, and re-soldered, being sure to check for mechanical connection. So that was fixed.

But there was still a problem. The Frog Juicer with which this switch is equipped did not consistently trip. This was complicated to trace, but eventually I concluded that it apparently was due to the styrene block in the gap at the front of the frog, sticking up and lifting locomotive wheels over the gap, thus not allowing said wheels to contact both sides of the gap at once. 

When a locomotive wheel does touch both rails at such a gap, and the rails are of opposite polarity, there is a short. The Juicer is triggered by that brief short, and reverses the frog polarity and removing the short, but if there is no short, the Juicer doesn’t trip. That offending gap is visible above — if you know where to look. Here’s the same photo with a helping arrow:

Carefully cutting the height of this styrene block down sort of damaged it, so I pulled it out entirely. I don’t know why it had gotten raised up, perhaps displaced by a derailment at some point, but no matter. I replaced it with a fresh little piece of styrene. Now it all works fine.

Let me hasten to say that this theory of the gap behavior, and the failure of the Frog Juicer to trip, is still just a theory. It seems to fit my problem, and is consistent with what appears to be the solution of the problem, but is nevertheless just a theory. I would appreciate comments from anyone who knows more about this technology that I do (likely most of you readers). 

Is there a moral to this story? Probably not, if you’re an “electrical ace” and rarely have such problems. But the gap-filling styrene problem and the Frog Juicer behavior is kinda subtle, and if all else fails in your next electrical misbehavior, it could be worth a look to see if you might have this kind of thing, too.

Tony Thompson