Strange VOM readings with Caboose Industries switch stand

Model Railroader General Discussion (Model Railroader)
1

I have a CI switch stand with the electrical switch to power the frog. The switch is a curved Shinohara #6 (I think) with both sides of the frog insulated. The middle electrical connection of the CI switch stand is connected to the isolated frog area.

The first indication that I had a problem was when my 0-6-0 stalled entering the switch from the diverging track. I checked the engine over, cleaned engine and tender wheels as wells as the electrical pickups. Oddly the loco runs perfectly through the switch on the “closed” side of the switch.

Anyways, I got out my VOM and measured AC voltage (Zephyr DCC): everything measures about 14.5 V. EXCEPT at the frog area only when the switch is thrown to the diverging side. There the voltage is between 6.0 and 5.5 V.! Yes, I do know that the Voltage I was measuring is not exactly correct. I have no idea how the voltage at the isolated part of the switch could be 2/3s of normal, and I’d like to hear theories as to how this might be so.

I replaced the CI switch stand with a new identical unit, and voltages measure around 14.5 V. everywhere. Before I removed the defective switch stand, I removed the little copper thingy and burnished it bright, as I did for the three-prong electrical connections. I checked all the electrical wiring with a continuity tester, including having someone pull on the wires while I was testing to see if one of them was loose. All were solidly connected.

2

Sounds like a bad contact somewhere–apparently inside the switch on the switchstand since that seemed to correct the problem when it was replaced. Your 2/3 voltage is not that unusual with a bad contact, though typically it goes to zero. Anyway, that’s what I think. Ed

3

Definitely in the contacts in the stand. I have had this happen too. I use the contacts in my tortoises now. Cleaning the contacts was a great first step. Did you also clean the contacts that the “little copper thingy” is supposed to touch? Are the wires soldered to the lower end? Something was either misaligned, dirty or simply prevented from touching fully. Could have been some plastic flash or even a cold solder joint. Small possibility of a broken wire inside the insulation that got moved when you replaced the stand.

If the frog measured half voltage with no engine on it then it likely would measure zero with an engine. This means a very high resistance contact.

The best way to test is to jumper the center lead to one end with a clip lead. If the voltage returns to full, then the contacts are not touching cleanly.

Karl