RailPro > RailPro Specific Help & Discussion

How-come dept

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Dean:
I have just got back to working on this problem.
The switch points are not making good contact with the rails. I believe the wheels running across the points move the points enough to cause a momentary loss of power or arcing. This was even happening with my Peco switches that are spring loaded. I proved this theory by spiking the points hard against the rails. Didn't have any problems. Since then I have been working on the switches to get the points to make solid contact with the rails.  [ on all my switches, the frog is powered by the points. ]
I also found that the Stewart F units are just the right size to be on the points and the frog at the same time. If the wheelbase was just a little longer, there probably wouldn't be a problem.
I guess installing 'stay alive' circuits would fix the problem too. $$$$
It's odd that the DCC decoders didn't have any problems. Or maybe they recovered faster.

Alan:
Glad to hear you found the problem.

Relying on point rail contact with stock rail as a conductor is fraught with risk for a mechanical reason beyond sufficient closing pressure. Electrical contactors (switches, relays, brushes, etc.) are all designed so as to incorporate a wiping motion as they close and open. The contacts don't simply come together. They ever so slightly slide across each other upon contact. The wiping action abrades away the microscopic layer of oxidation that forms on metal contacts. All common metals oxidize. The oxide layer is less conductive (higher resistance) than the base metal. If the oxidation layer is not continually removed eventually the contactor will fail to conduct when closed. A great example of this is found in audio equipment controls such as a volume knob. If you leave the knob in one position for a long time the control becomes scratchy when you do move it. Rotating the knob back and forth several times removes the scratchiness. By repeatedly rotating the knob you are wiping one contactor across the other which is abrading away the oxidation. DeOx sprays do the same oxidation removal except chemically instead of abrasion.

Point rails do not slide across stock rails when they close. They simply come together. With no wiping action you are bound to eventually get an oxidation layer that even applying more closing pressure won't cure. The moral of the story... regular cleaning maintenance will be needed on the rail contacting faces to keep your arrangement working reliably.

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