The AM Forum

Ok, I'm looking to tap into the vast knowledge base here.

Isn't there a condition when a solenoid actuator pulls the rod in too far and it sticks in the full in position unless there is a positive force to pull it out again??   I ran into this at work, and I can not recall where I heard this, but the fix I remembered worked. (keep the solenoid rod from fully entering the coil core area) so it must be true, right??? 

Or am I just nuts?

I think you are right. Doesn't the field reverse when the coil is opened (DC solenoid)?

The reason for a damper diode in a PDM rig.

Sounds more like whatever the solenoid is hooked up to has "overcentered". I take it that the solenoid is hooked up to a spring-like load or has an internal spring? Ususally the internal spring will return it, unless an external force prevents it.   

You didn't mention what the solenoid if for but here at work we have loads of door security. The locks have solenoids in them and return springs. You have to have the reverse action or the solenoid plunger has no reason to go back to position A. Same action as a motor contactor.
Hope this helps.

Is the moving piece making metal-to-metal contact with the fixed piece, and getting stuck?  You can reduce the closed-state magnetic attraction greatly by inserting a layer of tape or something to prevent the metal pieces from making direct contact.  The electromagnetic force will still be enough to pull the thing in, but when the voltage is removed, the residual magnetism will be a little more distant than usual, and that will make it much weaker.

Sometimes old relays that operated on DC would get stuck in the activated state, and we poor service techs believed that it was because they had built up magnetization from being activated so many times.  One service technique was to reverse the solenoid connection and begin to reverse the process.

I'm not sure that it worked.  So many other things were wrong with the old sytems, and so many people noodled with them, that it was hard to tell if something really solved a problem.

My experiences with solenoids can be summarized as follows:

...when they start sticking, replace them.
...if they start stinkin, same deal.
...if the stinkin' solenoids are sticking, they might start stinkin' soon too!
...it gets sticky if they stickin' solenoid gets funky, then replaceing them can be a funky stinky business dealing with stinkin' solenoids.
...who designed this stinkin' thing anyway!!  ;)

             _-_-WBear2GCR