# A transformer question?

1. Sep 14, 2006

### the Physic freak

If a transformer has loose parts, then a hum is heard while there is current flowing through the primary coil. how do you explain this noise?

2. Sep 14, 2006

### chroot

Staff Emeritus
Sounds like a homework problem. What are your thoughts?

- Warren

3. Sep 14, 2006

### the Physic freak

could it be because the coil vibrates?

4. Sep 14, 2006

### chroot

Staff Emeritus
Well, the loose part -- whatever it is -- is pulled back and forth by the changing magnetic field, right?

- Warren

5. Sep 14, 2006

### the Physic freak

oh ic, thx alot ^^

6. Sep 14, 2006

### Averagesupernova

I envision the following inserted in the answer space of a homework question: The loose part -- whatever it is -- is pulled back and forth by the changing magnetic field.

7. Sep 14, 2006

### chroot

Staff Emeritus
Yeah, well, you can't win 'em all.

- Warren

8. Sep 14, 2006

### the Physic freak

what do you mean averagesupernova?

9. Jun 23, 2009

### fawk3s

whats the loose part? and how can you be sure its metal :P?

10. Jun 23, 2009

### vk6kro

11. Jun 24, 2009

### vk6kro

Just to wrap this one up a bit.....

The laminations in a transfromer all get the same magnetic polarity induced in them by the changing current in the coil, so they tend to repel each other. If they are not adequately clamped, they can tend to hum or even rattle a bit.

Likewise, the coil interacts with this changing magnetic field and it can experience forces, too. So you can get coil movement and corresponding sounds.

12. Jun 24, 2009

### Bob S

There are three possible sources of hum:
Loose lamination(s)
Loose coil or coil windings
Magnetostriction of iron

13. Jun 24, 2009

### negitron

Four, if you count loose mounting hardware as part of the transformer.

14. Jun 26, 2009

### b.shahvir

The hum is due to property of 'magnetostriction' exhibited by ferromagnetic materials. It is due to the elongation and contraction of the core laminations at 100 times/sec (for 50Hz supply) and causes noise due to vibrations. Go to wikipedia and search for 'magnetostriction', you will get the detailed theory for the same.

The hum is also due to the magnetic forces of attraction and repulsion between the primary and secondary windings as well as between identical windings when the transformer is considerably loaded.

Best regards,
Shahvir