Why is my laptop's AC adapter chirping?
April 10, 2010 8:17 PM   Subscribe

Why is my laptop's AC adapter chirping?

I just noticed my laptop's running off its battery even though it's plugged in. When I picked up the adapter (the adapter is HP branded and only a few months old), the box was making an audible but faint chirping noise. When I pulled the plug, the chirping stopped. It's not at all hot.

Google says I need to replace it, but how and why is it making that noise?
posted by IndigoRain to Computers & Internet (8 answers total)
Some circuit has gone bad and it makes that noise for the same reason old flash cameras made "the charging noise".

It is one of the ways power supplies fail.
posted by gjc at 8:26 PM on April 10, 2010

Certain types of capacitors make high-pitched sounds when they are failing/have failed. Sounds like you'll need a new adapter.
posted by Hardcore Poser at 8:32 PM on April 10, 2010

Inductors can do that, too, when they are failing.
posted by Chocolate Pickle at 10:56 PM on April 10, 2010

Get a new adaptor pronto. Don't plug it back into your laptop - you don't want it to disasterously fail and fry your laptop.
posted by porpoise at 8:57 AM on April 11, 2010

2nding purpoise's advice -- change it ASAP. When a cap or inductor fails, it cannot "store" energy. This is critical in case there's a surge or a noisy power line; whereas before the cap or inductor would act like an electrical cushion, now it goes straight into the laptop's much more sensitive electronics.
posted by spiderskull at 4:08 PM on April 11, 2010

Response by poster: I didn't plug it back in, and the store replaced it since I still had the receipt.

I'm still curious *how* it made the chirping sound. Is it a side effect of electricity passing through it? Is there a built-in chirping speaker to let you know when it goes bad?
posted by IndigoRain at 8:19 PM on April 11, 2010

Best answer: Sadly, there is no such fail-warning speaker system. In the case of electrolytic capacitors it's the sound of the electrolyte venting out of tiny openings in the metal case. For inductors (wire-wound ones) the noise is because the coil is subject to resonant frequencies. Certain combinations of voltage and load will cause the coil to resonate and produce high-pitched sound.
posted by Hardcore Poser at 8:53 PM on April 11, 2010

Best answer: An alternating current in an inductor will cause a changing magnetic field, and thus changing force on the wires. Ordinarily the wires are glued in place, so they don't move. But if the glue is starting to fail, the wires will vibrate.

In switching supplies the frequency is usually pretty high (multiple kilohertz) so if the inductor is failing it manifests as a singing or chirping sound, not as a 60 Hz hum.
posted by Chocolate Pickle at 1:18 PM on April 12, 2010

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