@Vernon Barry posted:Put another way, there is more a problem of control.
If the controller was momentary pushbutton and there was no possible way that a coil could be activated for more than say 2 seconds, and activated only when we wanted to change position, then the limit switches to disconnect the coils are added safety but not required.
But the problem is, the controller is a rocker switch, or most devices you might attach are relay based with normally open and normally closed contacts. They latch and hold that position until a state change. As such, with this type of control system, the switches to disconnect the coils at full throw go from optional safety to suddenly mandatory status.
The problems at hand in this discussion actually apply to nearly any twin coil device for example an Atlas track switch dual coil motor.
Again, while a PTC is a good idea, in the bigger picture, we need a freely working device that work so well there is very limited concern of it getting stuck in the middle of states and the coil cooking.
For example, you could use the same solution for switches- a capacitive discharge circuit that dumps a stored charge across the coil to slam it, but then doesn't allow full power to sit there and cook a coil.
To be clear, when the passengers stop halfway up or down there is NO solenoid sound. The switches have cut that off.
John
