Solenoid polarity

[tahir4awan]

Hello everyone,

Today I have to connect a solenoid in a machine. It was a 24VDC solenoid. But the problem was the wires have no marking. So I have checked it with a 24V transformer. Regardless of the polarity the solenoid functioned. Which seems confusing for me. Because when we reverse the polarity the magnetic field also reverses, so the plunger must move in the opposite direction.

I have asked my instructor, he told me that, may be this solenoid has bridge rectifier. But I have never seen solenoid with bridge rectifier. I mean normally they consist of just coil. I may be wrong. Has anyone any idea?


Thanks

 

[Audioguru]

A solenoid that has no magnet always pulls its armature inwards regardless of AC or DC or the polarity of the DC.
If it has a magnet and also has a bridge rectifier then it will always do the above.

 

[tahir4awan]

A solenoid that has no magnet always pulls its armature inwards regardless of AC or DC or the polarity of the DC.
If it has a magnet and also has a bridge rectifier then it will always do the above.

This is what makes it confusing. Of course when current flows in opposite direction, then why not the armature moves in the opposite direction? This is a simple electro magnetic principle.

 

[betwixt]

Take anything steel or iron and place a magnet near to it, the magnet will attract to the metal. Now turn the magnet around and try again, it will still attract.
You are confusing the armature with another magnet which will either attract or repel but if the armature holds no magnetism itself it will attract to both 'polarities'.

Brian.

 

[c_mitra]

It was a 24VDC solenoid. But the problem was the wires have no marking. So I have checked it with a 24V transformer. Regardless of the polarity the solenoid functioned. Which seems confusing for me. Because when we reverse the polarity the magnetic field also reverses, so the plunger must move in the opposite direction.

It has a coil and the coil produces a magnetic field. You are right that when the current in the solenoid moves in the opposite direction, the sense of the magnetic field also changes.

This magnetic field attracts the plunger (which is a magnetic material, say soft iron), just like a magnet attracts a piece of iron. It does not matter whether you point the north pole or the south pole towards the iron object (why???)

However, if the plunger has a permanent magnetic moment (you can join a permanent magnet to it) then you will find attraction and repulsion depending on the sense of the current in the solenoid.

But the plunger is not a permanent magnet and we use a spring to push the plunger out when the magnetic field is removed.

So your question is: why does a magnet always attracts a piece of iron, even when we stitch the magnet the other way? Think over it.