Monday 2 September 2019

SEEP point motor switch

I was pleased, and slightly surprised, to find the electrics all worked first time. However extensive playing testing revealed that one of the points had a dead "frog" - crossing vee and blade - when switched on one direction, this is despite the electrical feed being switched by the point motor.

The SEEP motors have an in-built switch consisting of contacts on the PCB base and a washer sprung against them moved by the solenoid armature. The problem can be the washer not reaching the contact because the motor is mounted off centre (though I am sure this one is central), or the armature travel is not far enough (it is borderline with 009 points, keeping the pin long helps). I have to say I have rarely come across this issue despite having used dozens of these motors, but with this old re-used motor I think the contacts may have worn away too, making things worse.


In an attempt to ensure good contact I cut a small piece of phosphor-bronze strip (seen bottom right of the photo above), which was twisted and bent, then soldered to the contact so the washer presses against it at the end of it's travel, as can just be seen below. I also cleaned the contacts as best I could, though it is hard to clean the washer.


It works, but I'll admit I don't know how robust it will be - the solenoid moves with some force. If it does fail the options are:

  • Clean the point blade and rely on that for contact - I don't want to do that!
  • Fit an external switch, such as a microswitch, which is easy in theory but fiddly in practice
  • Use the working contact to drive a change-over relay, perhaps the easiest solution if suitable relay power can be arranged to the layout
  • Replace the motor with a new one - which shouldn't be too difficult

For now I'll see how it goes.

1 comment:

Phil Parker said...

I'd replace it, but don't discount the microswitch option. Using a long arm version means you don't need to be too accurate as the arm can be bent for adjustment after the switch is screwed in place.