There are two methods of protecting linear actuators that I have seen. One is purely mechanical, where the motor keeps running but the actuator stops moving. The other has electrical limit switches, where the motor stops completely at the end of travel. That is the kind I have.

No damage occurs to either kind if you drive it past the maximum travel.

 

I think that none of the two is present in the thomson actuator.
Infact you keep applying power (and it hasn't a load), it keeps rotating freely.
The motor never stops if you keep applying power..

I think this could be the problem..

 

made some tests and the solution is to rotate the shaft back manually. It comes back within the scale...
They should put this issue in the datasheet!

 

I think that none of the two is present in the thomson actuator.
Infact you keep applying power (and it hasn't a load), it keeps rotating freely.
The motor never stops if you keep applying power..

I think this could be the problem..

I have an actuator here where the motor keeps running forever when it reaches its mechanical limits. However, if you reverse polarity to the motor, and turn it the other way, it instantly re-engages the lead screw mechanism and begins moving in the opposite direction.

You could determine that the motor reached either limit by measuring the motor running current, because it drops substantially when the motor free-wheels after the lead screw disengages...

I am sure that if the actuator had a built-in position-measuring potentiometer, the pot would be coupled to the lead-screw mechanism so that the pot stops moving when the push-rod stops moving even though the motor continues to spin...

 

I don't know how it works inside, I can't open it, but for sure if I leave it to rotate freely, the pot doesn't work anymore.
Unless I manually push it back in scale...

 

I don't know how it works inside, I can't open it, but for sure if I leave it to rotate freely, the pot doesn't work anymore.
Unless I manually push it back in scale...

Ok, it seems that your specific actuator is one I have not seen. I am guessing that your actuator is designed to be used with an external controller that relies on the feedback signal from the pot to stop the motor just short of where the gear train becomes disengaged (both ends of the travel).

If your pot has failed, then the controller will not know when to stop.

 

They should write in the datasheet: "DO NOT USE WITHOUT A LOAD!".
I tested it without the load, so it went all the way out and at the end the shaft rotated for about 2 seconds (mabye 10 turns..).
If you use it with a load, it never becomes disengaged. I don't know if it's a normal behavior for an actuator, but in my mind I thought that was not a problem to test it without load, just to see if it goes in and out..
It's my fault, but also the documentation is very poor..

 

They should write in the datasheet: "DO NOT USE WITHOUT A LOAD!".
I tested it without the load, so it went all the way out and at the end the shaft rotated for about 2 seconds (mabye 10 turns..).
If you use it with a load, it never becomes disengaged. I don't know if it's a normal behavior for an actuator, but in my mind I thought that was not a problem to test it without load, just to see if it goes in and out..
It's my fault, but also the documentation is very poor..

So your thesis is that running it to where the push rod disengaged damaged the pot?

 

not damaged but only out of scale. Or disconnected.
For sure if I didn't try to manually rotate it back, the potentiometers seemed to be broken. I don't know why they don't mention this on the documentation. Maybe it's a normal behavior for an actuator..

 

btw- I bought a new 10-turn 10K linear pot on flea-bay, and replaced the one inside my actuator. Works again...