Suppose a push-pull solenoid head is pushed against an obstacle. Is it harmful for it?
It depends. Solenoids are intended for intermittent operation. They pull quite a lot of current to operate them smartly, which for a short period is not an issue. If you leave them energised, obstructed or not, the coil will heat up and may burn out.
As an example, the kickdown solenoid on my car has two windings, a high current one and a low current one. They both come in together so that there is maximum torque, but then the high current one drops out 500mS later to protect itself. The low current winding is capable of holding it without burning out.
So there are no mechanical parts that can be broken from obstruction , unlike in servos?
There are no flimsy plastic gears to strip in a rod of metal inside an electromagnet, no.
This is a nice brief read covering solenoid terminology. Some solenoids are designed for constant duty for example a water valve solenoid which may be energized for hours at a time while others are designed for intermittent duty where a duty cycle is expressed.
With a plunger type solenoid would obstructing the plunger or armature cause the coil to get hotter prematurely? Yes, especially on a solenoid designed for intermittent use and having a low duty cycle. However, this also depends on if the coil is wound for AC or DC current. AC current coils exhibit an inrush current where a DC coil doesn't.
Much of what you are asking really depends on the solenoid.
Ron
Ron_Blain:
With a plunger type solenoid would obstructing the plunger or armature cause the coil to get hotter prematurely? Yes, especially on a solenoid designed for intermittent use and having a low duty cycle. However, this also depends on if the coil is wound for AC or DC current. AC current coils exhibit an inrush current where a DC coil doesn't.
A rather confused and confusing explanation.
A DC solenoid is completely unaffected by whether the armature is pulled in or not.
In an AC solenoid, the inductance depends on whether the armature is pulled in or not. If the armature is not pulled in, the inductance is much less so the AC current is much greater until it is pulled in, so if the armature can not be pulled in, it will continue to draw the much heavier current which is usually beyond its continuous rating and it will overheat - often badly.
This is not an "inrush current" as inductors actually oppose a current "inrush", it is a consequence of whether the armature is able to be pulled in or not.
Garfielder:
Suppose a push-pull solenoid head is pushed against an obstacle. Is it harmful for it?
A very strange question because all the solenoids I have have stops the keep the armature from flying away. Every time they are used, the armature either hits a limit of what it is pushing or it hits the internal stop.
Paul
Paul__B:
A rather confused and confusing explanation.A DC solenoid is completely unaffected by whether the armature is pulled in or not.
In an AC solenoid, the inductance depends on whether the armature is pulled in or not. If the armature is not pulled in, the inductance is much less so the AC current is much greater until it is pulled in, so if the armature can not be pulled in, it will continue to draw the much heavier current which is usually beyond its continuous rating and it will overheat - often badly.
This is not an "inrush current" as inductors actually oppose a current "inrush", it is a consequence of whether the armature is able to be pulled in or not.
Thinking about this no, it is not an inrush current. If we call the armature a slug and can move it in and out, at any given position the current is what it is. The only reason that when the solenoid is activated a higher current is drawn is exactly as you stated and "inrush" was a poor choice of words and I actually read that somewhere but no, it isn't inrush current since at any point the current is what it is.
Thanks
Ron
Thanks for the answers!
BTW what is the relationship between the wattage of the solenoid and its force?
e.g., data for 2 solenoids:
DC12V 2A -> 20N
DC24V 0.36A -> 60N (both 10mm stroke)
Is there a reason why the higher wattage unit is weaker?
Just two followup questions -
I have hooked up a DC6V 0.3A solenoid, when it's on it can hold the plunger if I push it in but it can't move by itself with no help. Also I can measure on the solenoid 10-35 milligauss when it's on. Any idea what can be the problem?
Is there any difference between hooking up a solenoid and a motor or, as long as they need up to 5A, 60V I can use for them the same TIP120+resistor+diode structure?
Garfielder:
BTW what is the relationship between the wattage of the solenoid and its force?
For a given solenoid, the wattage is proportional to the square of the force.
For two different solenoids, no relationship whatsoever.
Reason: the force is proportional to the current for any given construction, and the wattage is proportional to the square of the current.
How effective any solenoid is at generating a force for a given current and resistance, is entirely dependent on its construction.