What is, and what is the purpose of this part of a laptop power adapter?

March 16, 2008 2:25 PM

What is, and what is the purpose of this part of a laptop power adapter?

I took it apart and there was just some sort of metal or ceramic material wrapped around the cord. I though it was a magnet at first, but it didn't stick to the fridge...

Link

posted by jjbb to computers & internet (6 comments total)

Its a ferrite bead.
posted by jmnugent at 2:26 PM on March 16

A friend's dog chewed the cord to his adapter, and in cutting out the damaged section and splicing the wires back together I had to remove this ferrite bead. Is it risky to keep using this adapter? It works fine now.
posted by jjbb at 6:06 PM on March 16

This is a surge protector. The metal/ceramic material would be a capacitor, intended to absorb spikes in your electrical current, so that they don't reach the PC and blow the very expensive electronics in there. If you have a good surge protector between the wall socket and the power supply, you should be fine.
posted by sgmax at 6:33 PM on March 16

It's fine to keep using it.

The bead is a component that attenuates electro-magnetic interference.

You want to do this for two reasons... one is to reduce susceptibility of the thing you are powering to noise outside the thing; the other is to keep from radiating (or conducting) noise back into the common power distribution.

In practice, they do something, but the thing they do is usually pretty subtle, so missing a ferrite bead on a single wall wart is no big deal.
posted by FauxScot at 6:34 PM on March 16

It's not a surge protector, sgmax... it's a ferrite bead.

A surge progector would be like a tranzorb or metal oxide varistor. They are usually inside the power box and are for different purposes. Specifically, high voltage transients supression.
posted by FauxScot at 6:36 PM on March 16

Yup - I came back to say that I mixed up the frequencies. Fauxscot is quite correct in stating that this is a Ferrite bead, which will filter out high frequency signals (radio waves and TV frequency EMI). You probably will not notice its absence. If you do notice any odd behavior, you can buy these at places like Radio Shack, or specialty electronics component stores. They snap onto the cable, but you need to wrap the cable *around* the bead 1-2 times, before snapping it shut.
posted by sgmax at 7:16 PM on March 16